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Conservation potential of North American large rivers: the Wabash River compared with the Ohio and Illinois rivers

Conservation potential of North American large rivers: the Wabash River compared with the Ohio... Background: Large rivers are ecological treasures with high human value, but most have experienced decades of degradation from industrial and municipal sewage, row-crop agricultural practices, and hydrologic alteration. We reviewed published analyses of long-term fish diversity publications from three intensively managed large river ecosystems to demonstrate the conservation potential of large river ecosystems. Results: We show how the incorporation of recent advances in river concepts will allow a better understanding of river ecosystem functioning and conservation. Lastly, we focus on the Wabash River ecosystem based on high conservation value and provide a list of actions to maintain and support the ecosystem. In the Wabash River, there were originally 66 species of freshwater mussels, but now only 30 species with reproducing populations remain. Although there were multiple stressors over the last century, the largest change in Wabash River fish biodiversity was associated with rapid increases in municipal nutrient loading and invasive bigheaded carps. Conclusions: Like similarly neglected large river systems worldwide, the Wabash River has a surprising amount of ecological resilience and recovery. For instance, of the 151 native fish species found in the 1800s, only three species have experienced local extinctions, making the modern assemblage more intact than many comparable rivers in the Mississippi River basin. However, not all the changes are positive or support the idea of recovery. Primary production underpins the productivity of these ecosystems, and the Wabash River phytoplankton assemblages shifted from high-quality green algae in the 1970s to lower less nutritional blue-green algae as nutrient and invasive species have recently increased. Our recommendations for the Wabash River and other altered rivers include the restoration of natural hydrology for the mainstem and tributaries, nutrient reductions, mechanisms to restore historical hydrologic patterns, additional sediment controls, and improved local hydraulics. Keywords: River conservation, Freshwater fishes, Long-term Background and conserve these services and functions can be both Large river ecosystems have under-appreciated socio- expensive and conceptually difficult because of their size economic importance because they are key sources of and complexity (Erős et al. 2019). High species richness water for agriculture and society, are transportation and productivity of large rivers result from their geologic highways for large volumes of goods, and provide a myr- history, size, and connectivity of their complex lateral iad of ecosystem services including flood protection to and longitudinal habitat mosaic (Sparks 1995; Ward millions of people worldwide (Thorp et al. 2010; Ward et al. 1999). This is especially true of large rivers with et al. 1999; Sparks 1995). However, to monitor, manage, north-south orientations like the Wabash River in the US Midwest that retained biodiversity by acting as refu- * Correspondence: mpyron@bsu.edu gia during periods of glaciations (Jacquemin and Pyron Department of Biology, Ball State University, Muncie, IN 47306, USA 2011). Large rivers are also important for maintaining Full list of author information is available at the end of the article © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 2 of 14 productivity through their role as corridors for move- continued into the twenty-first century until the cumula- ment: migratory fishes like the iconic sturgeon utilize tive impact finally affected human health and livelihood them to connect critical but disjunct reproductive, nur- at a national scale after which society required change sery, and feeding resources (Pracheil et al. 2013). Large (Carson and Mitchell 1993). The subsequent ecological rivers also support high productivity through regular an- recovery due to federal policies including the U.S. Clean nual spring flood pulses that provide access to critical Water Act of 1972, which focused mainly on point nutrient sources, limited habitat, sediment sinks, and at- source pollutants, was a demonstration of the ability of tenuation of excess flood water (Thorp et al. 2010; many freshwater ecosystems in general and large river Bayley 1995). Large river ecosystems have additional ecosystems to recover following reductions in point simultaneous but seldom quantified values including nu- source pollution (Pyron et al. 2006, 2008, 2019; Gibson- trient and carbon sequestration and flood risk reduction. Reinemer et al. 2017). However, non-point source pollu- Yet, restoration of large river ecosystems is uncommon tion from agriculture and urbanization as well as other (Jacobson and Galat 2006). The same spatial and tem- non-chemical degradation like stream dewatering, and poral complexity that are key to large river ecological floodplain/wetland modifications remain significant im- and economic functions are major challenges to incorp- pediments to greater ecological recovery (Cosens and orate into policy, management, and engineering (Erős Stow 2014). The remaining challenge for the conserva- et al. 2019). Despite this portfolio of benefits, efforts to tion of large river systems is to clearly demonstrate their inform stakeholders and stimulate funding for large river potential for continued recovery while developing a tool- conservation and restoration have been limited (Palmer box of effective actions and policies for achieving that et al. 2005; Lamouroux et al. 2015). When these efforts conservation potential (Palmer et al. 2005). are successful, the focus tends to be on a narrow set of A large river conservation toolbox requires establish- economic benefits rather than ecological values and out- ing a timeline and expectations for the potential status comes (Jacobson and Galat 2006; Palmer et al. 2005) and the ecosystem could achieve. Many US rivers suffered often occurs at the local, site-specific spatial scale (Gore from similar problems as most of the tributaries of the and Shields Jr. 1995). We review research on three adja- Mississippi River basin: well-documented progression of cent large river watersheds with similar issues. Our final human activities from shifts in land-use and agricultural focus is to bring attention to the recovery potential for practices, point and non-point source nutrient loads, rehabilitation of the Wabash River as an example to hydrologic alterations from dam and reservoir construc- stimulate additional interest in the study and restoration tion, and the establishment of invasive species (Pyron of large rivers worldwide. et al. 2019; DeBoer et al. 2019). Ultimately, for the evalu- Prior to their development large rivers contained high ation of the links between stressors and expectations for biodiversity and productivity as well as other valuable potential policy and conservation responses—a timeline non-commercial services including recreation, drinking can be a first tool. In addition to a documented history water supply, and flood risk reduction (Johnson et al. of ecological response, the Wabash River also has attri- 1995). Following the rapid expansion of industrial agri- butes that improve the likelihood of successful restor- culture in the 1950s, a more limited set of non- ation and conservation efforts, especially recovery from ecological services including irrigation, sewage disposal, many anthropogenic pressures that long-term monitor- power generation, and navigation predominated in many ing has demonstrated. Our objectives are to (1) describe highly modified floodplain rivers like those of the US the history and ecology of the Wabash River fish ecosys- Midwest. The typical ecological response pattern to this tem, (2) compare ecological trends in two midwestern degradation is a corresponding decline in biodiversity, US rivers using published sources, and (3) suggest po- including in some cases reduced ecological functions tential steps for protecting and conserving the Wabash such as productivity (DeBoer et al. 2019). This is a River that could be applied to other large river worldwide-wide phenomenon: construction of dams for ecosystems. water development began in the US in the nineteenth century resulting in more than 79,000 dams that altered The Wabash River: history hydrologic regimes, natural interactions and functions, The Wabash River is the largest tributary of the Ohio and associated biota (Magilligan and Nislow 2005; River with a length of 764 km, a watershed area of 85, 2 3 Nilsson et al. 2005). Dams and inland navigation led to a 340 km and mean annual discharge of 1000 m /s cascade of developmental pressures, and over the first (Benke and Cushing 2005, Fig. 1). Although there are half of the twentieth century in midwestern large rivers; numerous reservoirs on its tributaries and one mainstem this included steadily increasing industrial and municipal reservoir at river 662 km, the lower two-thirds is still the point source pollution that degraded the diversity and longest undammed reach east of the Mississippi River. function of most aquatic ecosystems. This progression The Wabash River watershed was historically dominated Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 3 of 14 Fig. 1 Illinois River, Ohio River, and Wabash River map by beech-maple forest, prairies, and wetlands (Küchler green from a mixture of sediments and diatoms. Thus, 1966) that were converted prior to and during the twen- during the twentieth century, the setting of the Wabash tieth century to allow row-crop agriculture. European River shifted from a less impacted frontier basin to ex- immigrants also expanded large-scale agriculture periencing most of the ills associated with large rivers whereby they also altered runoff patterns by installing around the world. tile drains that connect to channelized ditches and streams. Together, this resulted in an estimated 62% of Hydrologic alterations to the Wabash River the watershed being converted into intensive row-crop One of the largest yet least understood changes in large agriculture, despite the basins poorly drained soils with rivers during the rapid expansion of Europeans in North high clay content (US Army Corps of Engineers 2011). America was the radical alteration of river hydrology for Although agriculture dominates the Wabash River land- navigation and water supply (Graf 1999). Hydrologic al- scape, industrial development was also extremely suc- terations occur with dams, dyke fields, and underground cessful in the state of Indiana during the twentieth tile drains that rapidly transport water off fields and into century, with many wastes piped directly into tributary stream channels. These engineering approaches to water streams. Further impacts on the ecosystem include dam management modified many aspects of annual hydro- construction throughout the watershed during the 1960s graphs, and especially the magnitude, duration, and fre- and 1970s, subsequently creating barriers to aquatic ani- quency of high and low water events (Poff et al. 1997). mal movements, altering river hydrology, connectivity, Fish and mussel life histories are finely tuned to hydrol- and changing sediment erosion, transport, and depos- ogy attributes. Although ecological responses to altered ition patterns. The earliest records of the biodiversity hydrology are chronic and cumulative and profoundly and ecology of the fishes of Wabash River are from the negative, they are not as obvious as acute exposure to more pristine period prior to significant development high profile agricultural and industrial chemicals (Poff (Jordan 1890). However, even before 1900, the Wabash et al. 1997). Further, the natures of these impacts are River became noticeably more turbid likely due to the el- idiosyncratic and can vary substantially with geography, evated sediments and nutrients generated by the rapid geomorphology, land-use, and engineering practices for expansion of agriculture in the watershed (Jordan 1890). each specific river. In the Wabash River example, 80 Currently, the river downstream from the single reser- USGS gaging stations measured altered hydrographs due voir is turbid, but the water color is brown or yellow- to dam construction (Pyron and Neumann 2008). Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 4 of 14 Resulting hydrographs in the Wabash River watershed high flows during Oct and Apr, compared to historic tend to have statistically significant increased minimum flows. Frequencies of large flood events for the Wabash flows, decreased maximum flows, increased fall rate, de- River were historically rare (four events from 1928- creased summer monthly flows, and decreased high 1985), however are more common in recent decades pulse counts, compared to historic flows (Fig. 2, Pyron (four events from 1985 to 2005) (Pyron et al. 2010). and Neumann 2008). Watersheds with row-crop agricul- Rahman and Bowling (2018) further found that reservoir ture land-use resulted in an increased number of zero management in the Wabash River basin resulted in flow days, increased low pulse counts, and decreased decreased annual maximum discharge and flashiness (rapid flow increases following rain events) and in- creased annual minimum discharge. Thus, in the Wabash River basin, early twentieth century develop- ment culminated in a more compressed hydrograph with, paradoxically, more variable and extreme condi- tions in low flow months. Wabash river water quality and the clean water act During the late twentieth and early twenty-first centur- ies, there was a steady reversal in some of the anthropo- genic stresses, especially the discharge of point-source pollutants to the river. Prior to the Clean Water Act of 1972, summer fish kills were frequent, occurring when dissolved oxygen concentrations were low, the water temperature was high, and river discharge was low (Gammon 1998). Those summer kill conditions were ul- timately driven by the increases in the amount of largely untreated municipal sewage at the same time as wet- lands were being converted to row-crop agriculture in the early to the late twentieth century. The combination of the Clean Water Act point-source controls through the National Pollution Discharge Elimination System along with the adoption of agricultural best management practices including no-tillage, filter strips, and winter cover crops that help reduce non-point source pollution led to water quality improvements, yet some problems remained. In particular, mineral phosphorus inputs and suspended sediment loads that result from agricultural practices have become a water quality issue (Muenich et al. 2016). Similar patterns of changing nutrient speci- ation were observed in other agricultural midwestern rivers and around the world (Powers et al. 2016). The re- sult has become, instead of fish kills, eutrophication and potential for reduced fish productivity with both in- creased phytoplankton abundance and a simultaneous rising dominance of lower quality pelagic blue-green, diatom, and euglenoid algae (Minder and Pyron 2017). Thus, the benefits of fewer summer fish kills were offset by a shift in the food base that led to a change from the historically warm water fish assemblage that favors rec- Fig. 2 3-day minimum flow by year calculated by Indicators of reational and commercial species like catfish and buffalo, Hydrologic Alteration software (Richter et al. 1996) for the Montezuma USGS gaging station on the Wabash River (top), fall rate to a modern assemblage dominated by planktivores in- by year for the Valley City USGS gaging station on the Illinois River cluding the rising threat of invasive bigheaded carps. (middle), and fall rate by year for the Louisville USGS gaging station Thus, instead of the conservation potential leading to a on the Ohio River (bottom) state resembling the clear-water conditions of the pre- Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 5 of 14 development nineteenth century, we are faced with an river discharge was low and the air temperature was ecosystem that appears to have shifted to a new and al- high (Gammon 1998). This was the period when ternate high-productivity but a turbid state. DePauw University faculty member James Gammon followed in the footsteps of David Starr Jordan with an- Changes in Wabash River biodiversity: fishes, nual fish collections in the Wabash River (Gammon mussels, and David Starr Jordan 1998). His collections and observations are summarized Early assessment of the biodiversity was begun in the in his textbook, The Wabash River Ecosystem (Gammon late nineteenth century by the pioneering ichthyologist 1998). The book includes a history of the Wabash River, in North America, David Starr Jordan in 1878. Despite descriptions of the dominant fish species, and general the initial impacts of altered hydrology and increased patterns of the fish assemblages during this time period pollution, Jordan found the Wabash River still contained following the Clean Water Act. Gammon’s goal was to high biodiversity with 151 native fish species, including use the fish community to assess water quality and iden- key regional species like sturgeon, Blue Catfish, and tify problem discharge locations. Gammon’s efforts were Redhorse suckers (Gammon 1998; Simon 2006). The at the forefront of utilizing the results of natural history hardiness of these species is evidenced by the relatively surveys to effectively communicate the links to pollution few local extinctions with the exception of Alligator Gar to agencies and society at large. Gammon (1998) in- (Atraclosteus spatula), Popeye Shiner (Notropis ariom- cluded an innovative fish-based tool, the Index of Well- mus), and Crystal Darter (Crystallaria asprella). At the Being (IWB) that incorporated fish biomass, abundance, height of the degradation in the 1970s through the and diversity to gauge the level of impairment, which 1980s fish assemblages were strongly impacted and proceeded with other indices developed in the region dominated by less desirable Gizzard Shad (Dorosoma like the influential Index of Biotic Integrity. The IWB cepedianum). The recent fish assemblage (1990-present) data collected during his 1970 to 1998 career and again is characterized by resurgent populations of native river beginning in 2001 by a new team from Ball State specialists like River Carpsucker (Carpiodes carpio) and University demonstrated continually improving fish as- Freshwater Drum (Aplodinotus grunniens) alongside de- semblages (Pyron and Lauer 2004). Standardization in clining invaders like Common Carp (Cyprinus carpio, collection and data analysis included collections at sites Fig. 3). Recent surveys showed increased species richness where Gammon made his collections, and boat and relative abundances of sensitive species such as Blue electrofishing at 500-m distances in a downstream direc- Sucker (Cycleptus elongatus), Redhorse suckers, and tion. Combining these early and recent collections was Shovelnose sturgeon (Scaphirhyncus platorhyncus) that key to building the long-term trends we present to were recorded by David Starr Jordan (Pyron et al. 2006). establish the status and conservation potential of the The twentieth century, especially the 1960s through Wabash River ecosystem (Broadway et al. 2015; Pyron 1980s, was a nadir for both environmental conditions et al. 2017). and biodiversity in the Wabash River. Effluent from mul- Freshwater mussels represent taxon another which, tiple industries, sewage treatment plants along the Wa- unfortunately, has not recovered. Mussel species rich- bash River, and row-crop agriculture throughout the ness decreased from a high of 66 species in the twentieth watershed contributed to pollution and increased nutri- century to only 30 species with reproducing populations ents. Evidence of the impact of these problems was eas- (Fisher 2006). Likely causes of mussel losses include ily observed with frequent large fish kill events when overharvesting by commercial shelling (Cummings et al. 1992), direct exposure to sewage and wastewater, local extinctions of their fish hosts (Unioinidae mussels re- quire a fish or other host for larvae.), and indirect effects of altered hydrology that degraded adult habitat includ- ing sedimentation, hypoxia, or lethal summer water tem- peratures (Box and Mossa 1999; Fisher 2006). The twenty-first century has brought improving environmen- tal conditions, increases in host species abundances, and greater interest in population enhancement and reintro- ductions (Indiana Department of Wildlife Resources 2017 Wildlife Science Report, indianawildlife.org). How- ever, despite losses of more than 50% of the species and on-going anthropogenic threats from agriculture and de- Fig. 3 Relative abundance CPUE of four common fish species by velopment, the mussel assemblage of the Wabash River collection year in the Wabash River. Data from Pyron et al. (2017) is still among the most intact large river mussel Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 6 of 14 assemblages remaining in the midwestern region (Page et al. 1997). Ecological stressors to aquatic ecosystems are evolving but tend to be chronic stresses whose impacts are felt decades after the stress was initiated. We suggest that to create conservation strategies for chronic problems like anthropogenic, demographic, or climate changes, we need to be able to test a range of hypothesized solutions. Long-term ecological research like the work carried out on the Wabash River since David Starr Jordan’s time produces relevant data for long-term hypothesis testing (Dodds et al. 2012; Strayer et al. 2014). Pyron et al. (2008) identified a temporal decrease in a multimetric score (Index of Biotic Integrity, IBI) from 1974 to 1998, and IBI scores increased with an upstream river location. For instance, long-term data resulted in the detection of a regime shift from planktivore-detritivores that domi- nated between 1960 and 1980, to benthic invertivores, that was attributed to reductions in pollution with the Clean Water Act (Broadway et al. 2015; Pyron et al. 2017; Fig. 3). More recent (1990–present) modifications to the fish assemblages included further reductions in gizzard shad, caused perhaps by nutrient loading modifi- cations (Muenich et al. 2016) and/or increased abun- Fig. 4 CPUE for sensitive fishes by collection year in the Wabash dances of invasive Silver Carp (Hypopthalmichthys River. Data from Pyron et al. (2017) molitrix, Pyron et al. 2017). However, Silver Carp abun- dances in the Wabash River did not approach extreme densities as in the Illinois River (McClelland et al. 2012). (Bacula et al. 2009). Abundances in the Wabash River Evidence that nutrients impacted the ecosystem includes were low during the 1970s and increased recently likely changes in the phytoplankton assemblages that were following water quality improvements (Gammon 1998). dominated by high-quality green algae in the 1970s and We found increased abundance as catch per unit effort recently are dominated by diatoms and lower nutrition- (CPUE) of blue sucker from 1974 to 2017 (Fig. 4). quality blue-green algae (Minder and Pyron 2017). How- Redhorse suckers (Moxostoma spp.) are an emblematic ever, a lack of continuous long-term nutrient monitoring large river species (Simon 2006) that were in low abun- data to examine with fish assemblage data prevents fur- dances in the Wabash by the 1970s (Fig. 4). Subse- ther conclusion. Despite the decades of ecological stress, quently, several Moxostoma increased in abundance, the fish assemblage of the Wabash River contains mul- likely following water quality improvements (Gammon tiple sensitive species that increased in abundance dur- 1998). Trautman (1981) stated that redhorse suckers are ing the past several decades (Pyron et al. 2006). intolerant to pollution and siltation, which are products Examples of sensitive but recovering fish include the of industrial point source pollution and agriculture in following: the Wabash River watershed. Catch per unit effort of Shovelnose Sturgeon (Scaphirhynchus platorynchus) Shorthead Redhorse (Moxostoma macrolepidotum) did have a strong Wabash River population (Fig. 4) that sup- not change significantly from 1974 to 2017 in the ports a commercial caviar harvest (Kennedy et al. 2007). Wabash River (Fig. 4). Although Thornton et al. (2018) found the shovelnose Smallmouth Buffalo (Ictiobus bubalus) and Freshwater sturgeon population was healthy, condition, weight of Drum (Aplodinotus grunniens) increased in abundance roe-per-fish, and size-at-maturity were decreasing from (Fig. 4) during this same time period. 2009 to 2016. Shovelnose sturgeon life history character- Although many large-river-adapted species have im- istics of high age of maturity and infrequent proved abundances, additional conservation problems reproduction result in susceptibility to over-harvest remain for the Wabash River. Sauger (Sander canaden- (Thornton et al. 2018). sis), Bowfin (Amia calva), and American Eel (Anguilla Blue Sucker (Cycleptus elongatus) is a large-river spe- rostrata) which all have large river linked life histories, cialist with decreased abundance during recent decades declined between 1974 and 2017, but are also still throughout its range in the Mississippi River basin present in the system (MP unpubl. data). Taken Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 7 of 14 together, the presence of robust populations of these The Ohio River historically supported high species sensitive fish species suggests that the ingredients of a richness of freshwater mussels and with species richness healthy large river assemblage are still present. This is a of individual pools up to 63 (Watters and Flaute 2010). primary reason that restoration and conservation efforts Mussel diversity decreased the past century with high in the Wabash River have a high likelihood of success. variation in losses among Ohio River pools. Watters and Flaute (2010) identified the causes of mussel extirpations Ohio River: hydrologic alterations, fish, and as water quality, existing dams, and invasive zebra mussel assemblages mussels. The Ohio River has a larger watershed than either the Wabash or Illinois rivers (Fig. 1). Unlike the watersheds Illinois River: a history of pollution and hydrologic of the Wabash and Illinois rivers, agricultural land use in alterations the Ohio River watershed has decreased while forest The Illinois River whose basin is immediate to the west cover has increased since the 1960s (Tayyebi et al. 2014; of the Wabash River has many similarities to its neigh- Pyron et al. 2019). Land-use in the Ohio River watershed bor such as the domination of their watersheds by row- was dominated by row-crop agriculture in the 1930s, but crop agriculture, a history of untreated industrial and conservation reserve programs from 1970 to the present municipal sewage pollution, and dramatic alteration resulted in shifts from agriculture to the forest (Tayyebi from pre-European hydrologic baselines. However, there et al. 2014). Percent urban use more than doubled dur- are also important differences that may explain the di- ing the same time period (Tayyebi et al. 2014). Although vergence in the conservation history of the two rivers— increased forest cover in the watershed likely contributes sewage originated from a much larger urban-industrial to improvements in water quality, geochemical signa- center (Chicago) in the headwaters of the Illinois River tures from past land-uses remain (Harding et al. 1998). (Delong 2005). Prior to the twentieth century, hypoxia Like many rivers of the developed basins of the US and acute toxicity were common more than 100-km Midwest, historic hydrology patterns in the Ohio River downstream. The subsequent construction of the watershed were significantly altered by a system of 20 Chicago Sanitary and Ship Canal diluted the polluted low-head navigation dams (Thomas et al. 2005). Hydro- river with water diverted from Lake Michigan while also logical alterations included 10 variables encompassing expanding commercial navigation. While this success- ecologically important attributes of discharge magnitude, fully lowered lethal hypoxia events and pollutant con- duration, high- and low-pulse frequencies, fall rate, and centrations, this effort ultimately swung the pendulum rise rate (Fig. 2, Pyron et al. 2019). in the other direction when the oligotrophic lake water As across North America, invasive species such as began to account for between 10 and 25% of the dis- Common Carp and Bigheaded carps and zebra mussels charge in the upper third of the river after the canal are a significant problem in the Ohio River (Angradi opened (Delong 2005). Additionally, commercial naviga- et al. 2011). Zebra mussels are in the Wabash River and tion expanded dramatically on the Illinois River: the ori- are a potential threat to native mussels (Schneider et al. ginal low-head wicket dams that were constructed in the 1998) but are currently at low abundances (MP pers. late 1800s were upgraded in the 1930s to create a deeper obs.). However, despite their influence, Thomas et al. navigation channel year-round (Gibson-Reinemer et al. (2005) identified improvements in fish assemblage met- 2017). This meant greater minimum flows, fewer high rics over the last 50 years, especially noticeable since the flow pulses, a less well-defined flood season, and a highly implementation of the 1972 Clean Water Act. Like the variable rate of rise/fall during any flood event than the post-CWA era in the Illinois and Wabash rivers, there pre-1930s river hydrograph (Lian et al. 2012). Analysis were increases in fish abundance, a tripling of species of historical discharge records showed that since the richness, and increased trophic diversity of the fish fauna 1930s, there are at least 11 key hydrologic variables that with time in the Ohio River, with the trend accelerat- are still significantly altered (Table 1) including fall rate ing with each year (Pyron et al. 2019). Pyron et al. (Fig. 2). There were dramatic rises in the suspended (2019) further hypothesized that the shift in the early sediment load and subsequent sedimentation rates, espe- 1900s from benthic to pelagic fish dominance ob- cially in the once diverse and productive floodplain served throughout the Ohio River coincided with de- backwaters (Bhowmik and Demissie 1989). These com- clines in water clarity and quality as urban, bined factors significantly limit native fish diversity re- agricultural, and industrial inputs became significant. covery from point-source pollution-related stresses. The accompanying declines in diversity and secondary production of benthic invertebrates then cascaded up Fish assemblages of the Illinois River to declines in the invertivore and piscivore fishes ob- The fish assemblage in the upper Illinois River reached served by Bowes (2016). its environmental low point in the 1950s with low Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 8 of 14 Table 1 Hydrology variables that were significantly altered (P < zebra and quagga mussels. These invaders expanded 0.05) from Indicators of Hydrologic Alteration analysis (Richter downstream into the Illinois River from the Great Lakes et al. 1996) using daily discharge from the Valley City, Illinois, in the 1980s and, arguably a bigger threat, the bigheaded USGS gaging station on the lower Illinois River. We used carps moved upriver from the lower Mississippi River in discharge data from 1939 to 2015 to create hydrology variables, the 1990s (Stoeckel et al. 1997; Sass et al. 2010). There is which were then regressed with year to detect significantly a sad irony that the decades of improvements in water altered variables quality from the CWA that helped recover native species IHA group CorrelationrP value may now also benefit these recent invasive species. Group 1: monthly magnitude December 0.27 0.025 Similarities and differences among large June 0.28 0.025 midwestern US rivers Similarities in the influences shaping fish assemblages of September 0.25 0.025 the Wabash, Illinois, and Ohio rivers include a large pro- Group 2: magnitude duration of annual extremes portion of the watershed in row-crop agriculture, con- 3-day minimum 0.28 0.025 centrated urbanization, and alteration of hydrology from 7-day minimum 0.30 0.01 damming (Table 2). However, despite the similarities 30-day minimum 0.26 0.025 among the drivers, the response patterns and trends in 30-day maximum 0.25 0.025 fish assemblages do not mirror each other. These rivers had varied responses to the staggered arrival of invasive 90-day maximum 0.28 0.025 bigheaded carps. Fish assemblages in the upper third of Group 4: frequency and duration of high and low pulses the Illinois River closest to the headwaters had not re- High pulse duration 0.41 0.001 covered as much as the lower river before the bigheaded Group 5: rate and frequency of change in conditions carp invasion (Gibson-Reinemer et al. 2017). In contrast, Rise rate 0.37 0.001 the fish assemblages of the Wabash River recovered Fall rate − 0.44 0.001 from the pre-1970s pollution due to the CWA prior to invasive bigheaded carp establishment (Pyron et al. abundances of generalist species (common carp and 2019). However, in the Wabash River, invasive big- goldfish, Carassius auratus). However, following the im- headed carps never successfully established, with no plementation of the Clean Water Act, there was a doub- measurable impact during the same period bigheaded ling in native species richness, increase abundances of carps negatively influenced the Illinois River fish assem- commercially harvested species by more than 25%, while blage (Broadway et al. 2015; DeBoer et al. 2018). the relative abundance of the pollution-tolerant common Bigheaded carp populations are higher in abundance carp fell to a mere 2% of the community (Gibson-Reine- in the Illinois River ecosystem than in the Wabash River, mer et al. 2017). The recovery of the Illinois River in the while the body condition and abundance of the native decade after the CWA is celebrated as a victory for con- competitors Gizzard Shad and Bigmouth Buffalo, and servation and restoration. In addition to demonstrating even Silver Carp simultaneously decreased (Solomon the power of national policy to have profound local ben- et al. 2016; Pendleton et al. 2017). In contrast, Wabash efits, this also demonstrated that even the most stressed River Silver Carp abundance is lower and body condition ecosystems may be capable of recovery. However, by the is higher. Several authors attributed lower abundances of twenty-first century, a new type of pollution emerged— the bigheaded carp in the Wabash River to less altered Table 2 Three rivers compared by history of modifications Modification Wabash River Illinois River Ohio River Recent land- Agriculture Agriculture Mixed agriculture and forest use Hydrologic Monthly magnitude, high- and Monthly magnitude, 3-day, 7-day, and 30-day minimum dur- Monthly magnitude, duration, alterations low-pulse frequencies, minimum ation; 30-day and 90-day maximum duration; high-pulse dur- high- and low-pulse frequencies, flows, fall rate ation, rise rate, fall rate fall rate, rise rate Invasive Minor: bigheaded carps Major: bigheaded carps Minor: bigheaded carps species effects Native fish Strong Strong ? recovery since CWA Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 9 of 14 hydrology which may suppress carp diet and including catchment disturbance, pollution, and water reproduction, while fostering a more intact assemblage resource development (Counihan et al. 2018). Despite of native predators and competitors (Stuck et al. 2015; their widely divergent environments, socio-economic Coulter et al. 2018). Love et al. (2017) reinforced the settings, and ecological responses, the main stressors for idea that strong competitive interactions can constrain all the large rivers studied were consistently dams and bigheaded carp by showing a rapid rebound in Gizzard land-use modifications. Counihan et al. (2018) noted Shad body condition in Illinois River after the targeted that while improvements in water quality associated with harvest of Silver Carp began. In the Wabash River, the the post-CWA (Clean Water Act) era affected all the gizzard shad population crashed between 1974 and systems, they varied in the initiation and the magnitude 2008, prior to the arrival of the bigheaded carps, mean- of improvement. ing that despite the lower plankton productivity of the Wabash, there was still less competition during their es- Placing large river conservation into a theoretical tablishment (Pyron et al. 2017). Thus, although invasive context bigheaded carp are present in both the Illinois River and The theory has firmly established hydrology, geomorph- the Wabash River, the difference in invasion trajectory ology, and human development as key drivers of river suggests that the ecological constraints of the invader structure and function (Poff et al. 1997; Thorp et al. are very different. 2010; Gibson-Reinemer et al. 2017). However, the lack The Ohio River watershed apparently benefitted from of a flexible, adaptable framework for use in divergent the twentieth century increases in forest cover, likely systems has been one practical limitation to conservation contributing to the recovery of the fish assemblages in in large rivers. Two recent advances in theory can pro- conjunction with the Clean Water Act (Pyron et al. vide an example solution: Riverscapes (Fausch et al. 2019) especially since no measurable impact of big- 2002) and Macrosystems (McCluney et al. 2014). The headed carps was yet detected in this large river. The riverscape perspective integrates ecological processes CWA also benefitted the Wabash River fish assemblages and spatial complexity by increasing the spatial and tem- as shown by a similar increase in species richness and poral scale of research (Fausch et al. 2002). Fausch et al. recovery of sensitive taxa (Gammon 1998; Pyron et al. (2002) recommended sampling designs that allow testing 2006). While the Wabash River did not entirely escape at multiple spatial scales and time intervals appropriate the added stresses of dams and navigation, the amount to the life history attributes of target fishes or other or- of infrastructure and traffic is substantially less than ei- ganisms. For example, long-term analyses of Wabash ther the Illinois or Ohio river experiences. The only River fish assemblages that included variation in traits mainstem dam and reservoir on the Wabash River was (Beugly and Pyron 2010) and body size variation designed for flood retention and control rather than pro- (Broadway et al. 2015) provided new information about moting navigation. Its major impact is the combined re- ecosystem effects. Fish assemblages of the Wabash River duction of discharge during spring high-flow periods Beugly and Pyron 2010) and in addition to embracing and discharge variation in the stable, low-flow summer the Riverscape scales, expanding to larger spatial and months, along with allowing a more rapid rate of fall temporal scales, allows river ecology to incorporate a and rise of flood pulses (Table 1, Fig. 2). Despite the macrosystem view (McCluney et al. 2014). The macro- similarity with the Illinois River, the Wabash River is still system view of river ecosystems is of watershed-scale less severely impacted than the more variable and sea- networks containing distinct patches that are connected sonally unstable flow regime of the Illinois River. While and interacting. The River Ecosystem Synthesis model the biota of all three of these rivers benefitted from im- (Thorp et al. 2006) predicts that river geomorphology proving water quality, the altered hydrology of the and hydrology result in unique reaches or functional Illinois and Ohio rivers have replaced poor water quality process zones, which have unique ecosystem characteris- as major limiting factors. This is another attribute of the tics and can repeat with river distance. Thorp et al. Wabash River situation that increases its potential con- (2010) further concluded that river ecosystem function- servation value. Thus, we can conclude that one of the ing is primarily caused by its hydrologic pattern (Poff attributes of the Wabash River that make it a good re- et al. 1997), and understanding can come from linking gional candidate for conservation is that it receives all hydrogeomorphology of a river with its biocomplexity the benefits of improving land-use practices and envir- and ecosystem services (Williams et al. 2013). Defining onmental legislation while, unlike the Illinois and Ohio river ecosystems by hydrogeomorphological gradients is rivers, it has not been as severely degraded by invasive an advance over the river continuum concept, which in- species like the bigheaded carps. cludes only river distance attributes (Vannote et al. Several large U.S. rivers resulted in significant tem- 1980). Defining distinctive geomorphologic reaches or poral and spatial trends, all with multiple stressor effects functional process zones (FPZ) for the Wabash River Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 10 of 14 can provide a start to diagnosing potential conservation 3) Partnerships and policies like the proposed National issues and opportunities (Fig. 4). A quantitative method Fish Habitat Conservation Through Partnerships to define functional process zones using GIS data is cur- Act which engage the public and politicians to rently available. For instance, Robbins and Pyron (in re- arrest on-going degradation and promote important view) used a quantitative approach (Williams et al. 2013) habitat restoration (Crawford et al. 2016). to identify three distinct functional process zones (FPZ) 4) Reframing of our perception of habitat in river for the Wabash River (Fig. 5); FPZ A has a narrow chan- basins—especially the recognition that the nel width and wide floodplain, FPZ B has a wide channel distribution of habitats are often determined by and wider floodplain, and FPZ C has a wide channel reach scale hydrogeomorphological attributes like width and constrained, narrow floodplain. Robbins and functional process zones rather than simply by local Pyron (in review) then demonstrated that Wabash River site conditions. fish assemblages varied by FPZ (Fig. 5). This approach is 5) Develop detailed fluvial hydrogeomorphology especially useful for large river assessment because it studies of the mainstem Wabash River to identify clearly demonstrates strong links between species com- high-quality habitat remnants or to guide rehabilita- position and FPZ characteristics (DeBoer et al. 2019). tion. This might include the characterization of The take-home message for conservation is that theoret- sediment distribution and flux, erosion, and sedi- ical models can be tailored to the specific limitations or mentation patterns, linked to local hydrology vari- opportunities of a river (e.g., flow modifications in ero- ation (Baranya et al. 2018). sional zones below dams versus habitat enhancement in 6) Map geomorphological variation and identify depositional areas of the lower river), thus increasing the locations that are most appropriate for an action success and efficiency of the effort and funds expended (e.g., cover crop incentives, instream habitat across the basin. construction) and policy (e.g., conservation easements) where flood frequency is changing and Recommendations for moving from theory to increasing impacts are expected to human practice in the Wabash River structures or land-use. James Gammon (1998) began a long-term record of fish 7) Restore floodplains by allowing natural seasonal abundances for the Wabash River in the 1970s. Continu- flooding. ation of this long-term effort requires permanent fund- 8) Build a watershed partnership with representation ing and supplemental data collection similar to other from resource users, agriculture interests, and long-term monitoring programs. Examples of programs management agencies whose goal is to identify and are the Long-Term Resource Monitoring program on promote potential conservation, land-use modifica- the Upper Mississippi River (Gibson-Reinemer et al. tions, policy, and mitigation that will protect or im- 2017) and the Ohio River Valley Sanitation Commission prove watersheds in all rivers (Garvey et al. 2010). (ORSANCO). To maximize the insights and benefits, a An example of a watershed partnership for a large monitoring program should include the key drivers iden- river is the Upper Mississippi River Conservation tified by theory, water quality, nutrient flux, hydrology, Committee (https://www.umrcc.org/umrcc-history). and sediment transport, and plankton monitoring. The roadmap to restoration and conservation of Wabash Outcomes: the future of the Wabash River River biodiversity would be a case study for aquatic con- ecosystem servation in general and large river conservation in par- Several successful examples of conservation improve- ticular. Specific examples for inclusion in the effort ment in river-floodplain habitats exist. For example, The would include: Nature Conservancy’s Emiquon Preserve adjacent to the Illinois River (Lemke et al. 2017). While the primary goal 1) Experimental modification of the release regime at Emiquon has always been to improve the river basins from upstream flood-control reservoirs in to diversity and productivity by connecting a high-quality mimic the natural flow regime with concurrent source habitat, the project embraces the presence of monitoring of ecological and sediment responses agricultural levees by the installation of gated structure (Konrad et al. 2011). that permits export of material and fishes to the river 2) Incentives for modification of cover crops in while preventing extreme flooding, excessive backwater agricultural subwatersheds to reduce peak flow sedimentation, and limiting invasive species in the flood- runoff and subsequent nutrient spikes (Babbar- plain. In addition, the local society benefits through in- Sebens et al. 2013) with monitoring of resulting creased recreational hunting and fishing, tourism, and changes in both sediment and nutrient exports, and the potential for flood risk reduction. Modifying this ap- primary producers. proach to the opportunities available in Wabash River Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 11 of 14 Fig. 5 Three functional process zones for the Wabash River, defined by geomorphology. FPZ A has a narrow channel width and wide floodplain, FPZ B has wide channel and wider floodplain, and FPZ C has wide channel width and constrained, narrow floodplain (Robbins and Pyron in review) could include a combination of reduced nitrogen and stage ditch constructions (Mahl et al. 2015) that are phosphorus fertilizer application rates that consider leg- effective with targeted approaches. Reduced nutrient acy soil nutrients, application methods that maintain nu- loading to the Wabash River is predicted to result in trients in the soil, and improved application timing modifications of the ecosystem including the fish assem- (such as considering the potential for rain near-future), blages. Potential changes to fish assemblages with de- creation of wetlands to enhance nutrient uptake, restor- creased primary productivity include reduced abilities ation of riparian zones, and modification of flood control for bigheaded carps to forage on phytoplankton, the abil- management to allow natural flooding into wetlands and ity for gizzard shad to switch from planktivory to detri- backwaters (Mitsch et al. 2001). Additional nutrient re- tivory, and modifications of food webs. Increased water duction approaches include best management practices clarity may result in increased benthic primary product- that reduce the loss of sediments and nutrients and two- ivity and subsequent secondary benthic productivity and Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 12 of 14 increased abundances of benthic invertivore fishes. riparian vegetation and has led to an increase in bank Impacts on mussels are unknown with decreased phyto- slumping. Many of the tributaries are supplying a signifi- plankton in the water column. However, these modifica- cant and increasing amount of sediments to both the tions are costly and politically difficult to implement at local channel habitats as well as to downstream back- sufficient levels. Local activism to educate politicians water and channel habitats (Odgaard 1987; Magner and and citizens may provide impetus to invest resources in Steffen 2000; Sekely et al. 2002) resulting in habitat sim- conservation. plification or loss of appropriate habitat for fishes and The early twentieth century agricultural and industrial macroinvertebrates (Blann et al. 2009). In addition, pre- development of river basins often focused on optimizing cipitation is increasing in the Wabash River watershed one or two aspects of management (e.g., irrigation sup- (Pyron and Neumann 2008) and further climate change ply, rapid field drainage) while, for ease or economics, may contribute by increasing the magnitude while de- discounting other potential ecological or cultural uses. creasing the predictability of discharge patterns and their However, more recently, water and land management nutrient and sediment loads in both the mainstem and and planning as a discipline is moving towards recogni- tributaries (Knox 2000, 2006). tion of the value of a portfolio of these resource uses in Restoring river hydrology to approach a “naturalized” conservation to broaden the appeal and thus support of flow regime is possible and includes restoration of chan- projects and goals (Horne et al. 2017). Flow experiments nel geomorphology with appropriate sediment transport provided evidence that small inexpensive modification of and habitat creation (Newson and Large 2006). Nilsson hydrology to mimic natural flow regimes can improve et al. (2018) recommended ecological restoration to at- ecosystems (Olden et al. 2014). Flood control dams are tenuate floods by increasing channel roughness, increas- designed to capture water during high-flow situations ing in-stream habitat complexity with large boulders or and subsequently release it gradually. The resulting al- large woody debris, or increasing wetland construction. tered hydrology has loss of peak flows, elimination of Restoration of natural hydrology in tributaries contrib- small floods, and artificially elevated flows (Richter and utes to the successful restoration of the mainstem hy- Thomas 2007). Dam release modifications for environ- drology. These approaches function to improve stream mental flows are relatively simple. Richter et al. (2003) habitats by increasing water retention capacity. Success- used the Green River, Kentucky, as a case study. A reser- ful conservation for the Wabash River is possible and voir was constructed in 1963 by the US Army Corps of begins with nutrient reductions, mechanisms to restore Engineers for flood control and recreation. Dam releases historical hydrologic patterns, additional sediment con- were modified to allow steady low flows in the fall sea- trols, and improved local hydraulics. We recommend son and avoid large releases in short periods. A similar similar approaches for other impacted large river modification of the flow regime of the Wabash River ecosystems. might be initiated with designed ecological releases from Acknowledgements the upstream flood control dams. If this is implemented We are grateful to multiple students and scientists who collected fishes or as an experiment with before and after components, it collaborated with us for data. Thanks to Kristen Bouska for editorial suggestions on an earlier draft. could be a robust test of ecological flow effects (Olden et al. 2014). Authors’ contributions Human impacts that contribute to hydrologic alter- All authors designed the study and drafted the manuscript. The authors read and approved the final manuscript. ations include deforestation, channel-bed reconfigur- ation, floodplain development, drainage, agricultural Funding intensification, and urbanization (Wheater and Evans Funding for earlier collections was from Eli Lilly and Company, Duke Energy, and U.S. Fish and Wildlife Service. 2009). All of these impacts are present and even expand- ing in the Wabash River watershed. In addition, activities Availability of data and materials that promote channelization and alterations designed to Not applicable. move water downstream more rapidly appear to be Ethics approval and consent to participate expanding (Nilsson et al. 2018). Nilsson et al. (2018) de- Not applicable scribed lowland agricultural rivers that are similar to the Wabash River as rivers where extreme flooding has haz- Consent for publication Not applicable ardous consequences to human populations. The flood- ing frequency of the lower Wabash River is less altered Competing interests from historical flows (Pyron and Neumann 2008), likely The authors declare that they have no competing interests. because the river is mainly free-flowing. However, row- Author details crop agriculture impacts caused altered flows that re- 1 2 Department of Biology, Ball State University, Muncie, IN 47306, USA. School sulted in incised channels where the loss of permanent of Sustainable Engineering and the Built Environment, Arizona State Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 13 of 14 University, Tempe, AZ 85281, USA. Illinois River Biological Station, Illinois Fausch KD, Torgerson CE, Baxter CV, Li HW. 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J Hydrol Eng. published maps and institutional affiliations. 2018;24:05018034. Richter B, Thomas GA. Restoring environmental flows by modifying dam operations. Ecol Soc. 2007;12:12. http://www.ecologyandsociety.org/vol12/iss1/art12/. Richter BD, Baumgartner JV, Powell J, Braun DP. A method for assessing hydrologic alteration within ecosystems. Conserv Biol. 1996;10:1163–74. Richter BD, Mathews R, Harrison DL, Wigington R. Ecologically sustainable water management: managing river flows for ecological integrity. Ecol Appl. 2003; 13:206–24. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Fisheries and Aquatic Sciences Springer Journals

Conservation potential of North American large rivers: the Wabash River compared with the Ohio and Illinois rivers

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Abstract

Background: Large rivers are ecological treasures with high human value, but most have experienced decades of degradation from industrial and municipal sewage, row-crop agricultural practices, and hydrologic alteration. We reviewed published analyses of long-term fish diversity publications from three intensively managed large river ecosystems to demonstrate the conservation potential of large river ecosystems. Results: We show how the incorporation of recent advances in river concepts will allow a better understanding of river ecosystem functioning and conservation. Lastly, we focus on the Wabash River ecosystem based on high conservation value and provide a list of actions to maintain and support the ecosystem. In the Wabash River, there were originally 66 species of freshwater mussels, but now only 30 species with reproducing populations remain. Although there were multiple stressors over the last century, the largest change in Wabash River fish biodiversity was associated with rapid increases in municipal nutrient loading and invasive bigheaded carps. Conclusions: Like similarly neglected large river systems worldwide, the Wabash River has a surprising amount of ecological resilience and recovery. For instance, of the 151 native fish species found in the 1800s, only three species have experienced local extinctions, making the modern assemblage more intact than many comparable rivers in the Mississippi River basin. However, not all the changes are positive or support the idea of recovery. Primary production underpins the productivity of these ecosystems, and the Wabash River phytoplankton assemblages shifted from high-quality green algae in the 1970s to lower less nutritional blue-green algae as nutrient and invasive species have recently increased. Our recommendations for the Wabash River and other altered rivers include the restoration of natural hydrology for the mainstem and tributaries, nutrient reductions, mechanisms to restore historical hydrologic patterns, additional sediment controls, and improved local hydraulics. Keywords: River conservation, Freshwater fishes, Long-term Background and conserve these services and functions can be both Large river ecosystems have under-appreciated socio- expensive and conceptually difficult because of their size economic importance because they are key sources of and complexity (Erős et al. 2019). High species richness water for agriculture and society, are transportation and productivity of large rivers result from their geologic highways for large volumes of goods, and provide a myr- history, size, and connectivity of their complex lateral iad of ecosystem services including flood protection to and longitudinal habitat mosaic (Sparks 1995; Ward millions of people worldwide (Thorp et al. 2010; Ward et al. 1999). This is especially true of large rivers with et al. 1999; Sparks 1995). However, to monitor, manage, north-south orientations like the Wabash River in the US Midwest that retained biodiversity by acting as refu- * Correspondence: mpyron@bsu.edu gia during periods of glaciations (Jacquemin and Pyron Department of Biology, Ball State University, Muncie, IN 47306, USA 2011). Large rivers are also important for maintaining Full list of author information is available at the end of the article © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 2 of 14 productivity through their role as corridors for move- continued into the twenty-first century until the cumula- ment: migratory fishes like the iconic sturgeon utilize tive impact finally affected human health and livelihood them to connect critical but disjunct reproductive, nur- at a national scale after which society required change sery, and feeding resources (Pracheil et al. 2013). Large (Carson and Mitchell 1993). The subsequent ecological rivers also support high productivity through regular an- recovery due to federal policies including the U.S. Clean nual spring flood pulses that provide access to critical Water Act of 1972, which focused mainly on point nutrient sources, limited habitat, sediment sinks, and at- source pollutants, was a demonstration of the ability of tenuation of excess flood water (Thorp et al. 2010; many freshwater ecosystems in general and large river Bayley 1995). Large river ecosystems have additional ecosystems to recover following reductions in point simultaneous but seldom quantified values including nu- source pollution (Pyron et al. 2006, 2008, 2019; Gibson- trient and carbon sequestration and flood risk reduction. Reinemer et al. 2017). However, non-point source pollu- Yet, restoration of large river ecosystems is uncommon tion from agriculture and urbanization as well as other (Jacobson and Galat 2006). The same spatial and tem- non-chemical degradation like stream dewatering, and poral complexity that are key to large river ecological floodplain/wetland modifications remain significant im- and economic functions are major challenges to incorp- pediments to greater ecological recovery (Cosens and orate into policy, management, and engineering (Erős Stow 2014). The remaining challenge for the conserva- et al. 2019). Despite this portfolio of benefits, efforts to tion of large river systems is to clearly demonstrate their inform stakeholders and stimulate funding for large river potential for continued recovery while developing a tool- conservation and restoration have been limited (Palmer box of effective actions and policies for achieving that et al. 2005; Lamouroux et al. 2015). When these efforts conservation potential (Palmer et al. 2005). are successful, the focus tends to be on a narrow set of A large river conservation toolbox requires establish- economic benefits rather than ecological values and out- ing a timeline and expectations for the potential status comes (Jacobson and Galat 2006; Palmer et al. 2005) and the ecosystem could achieve. Many US rivers suffered often occurs at the local, site-specific spatial scale (Gore from similar problems as most of the tributaries of the and Shields Jr. 1995). We review research on three adja- Mississippi River basin: well-documented progression of cent large river watersheds with similar issues. Our final human activities from shifts in land-use and agricultural focus is to bring attention to the recovery potential for practices, point and non-point source nutrient loads, rehabilitation of the Wabash River as an example to hydrologic alterations from dam and reservoir construc- stimulate additional interest in the study and restoration tion, and the establishment of invasive species (Pyron of large rivers worldwide. et al. 2019; DeBoer et al. 2019). Ultimately, for the evalu- Prior to their development large rivers contained high ation of the links between stressors and expectations for biodiversity and productivity as well as other valuable potential policy and conservation responses—a timeline non-commercial services including recreation, drinking can be a first tool. In addition to a documented history water supply, and flood risk reduction (Johnson et al. of ecological response, the Wabash River also has attri- 1995). Following the rapid expansion of industrial agri- butes that improve the likelihood of successful restor- culture in the 1950s, a more limited set of non- ation and conservation efforts, especially recovery from ecological services including irrigation, sewage disposal, many anthropogenic pressures that long-term monitor- power generation, and navigation predominated in many ing has demonstrated. Our objectives are to (1) describe highly modified floodplain rivers like those of the US the history and ecology of the Wabash River fish ecosys- Midwest. The typical ecological response pattern to this tem, (2) compare ecological trends in two midwestern degradation is a corresponding decline in biodiversity, US rivers using published sources, and (3) suggest po- including in some cases reduced ecological functions tential steps for protecting and conserving the Wabash such as productivity (DeBoer et al. 2019). This is a River that could be applied to other large river worldwide-wide phenomenon: construction of dams for ecosystems. water development began in the US in the nineteenth century resulting in more than 79,000 dams that altered The Wabash River: history hydrologic regimes, natural interactions and functions, The Wabash River is the largest tributary of the Ohio and associated biota (Magilligan and Nislow 2005; River with a length of 764 km, a watershed area of 85, 2 3 Nilsson et al. 2005). Dams and inland navigation led to a 340 km and mean annual discharge of 1000 m /s cascade of developmental pressures, and over the first (Benke and Cushing 2005, Fig. 1). Although there are half of the twentieth century in midwestern large rivers; numerous reservoirs on its tributaries and one mainstem this included steadily increasing industrial and municipal reservoir at river 662 km, the lower two-thirds is still the point source pollution that degraded the diversity and longest undammed reach east of the Mississippi River. function of most aquatic ecosystems. This progression The Wabash River watershed was historically dominated Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 3 of 14 Fig. 1 Illinois River, Ohio River, and Wabash River map by beech-maple forest, prairies, and wetlands (Küchler green from a mixture of sediments and diatoms. Thus, 1966) that were converted prior to and during the twen- during the twentieth century, the setting of the Wabash tieth century to allow row-crop agriculture. European River shifted from a less impacted frontier basin to ex- immigrants also expanded large-scale agriculture periencing most of the ills associated with large rivers whereby they also altered runoff patterns by installing around the world. tile drains that connect to channelized ditches and streams. Together, this resulted in an estimated 62% of Hydrologic alterations to the Wabash River the watershed being converted into intensive row-crop One of the largest yet least understood changes in large agriculture, despite the basins poorly drained soils with rivers during the rapid expansion of Europeans in North high clay content (US Army Corps of Engineers 2011). America was the radical alteration of river hydrology for Although agriculture dominates the Wabash River land- navigation and water supply (Graf 1999). Hydrologic al- scape, industrial development was also extremely suc- terations occur with dams, dyke fields, and underground cessful in the state of Indiana during the twentieth tile drains that rapidly transport water off fields and into century, with many wastes piped directly into tributary stream channels. These engineering approaches to water streams. Further impacts on the ecosystem include dam management modified many aspects of annual hydro- construction throughout the watershed during the 1960s graphs, and especially the magnitude, duration, and fre- and 1970s, subsequently creating barriers to aquatic ani- quency of high and low water events (Poff et al. 1997). mal movements, altering river hydrology, connectivity, Fish and mussel life histories are finely tuned to hydrol- and changing sediment erosion, transport, and depos- ogy attributes. Although ecological responses to altered ition patterns. The earliest records of the biodiversity hydrology are chronic and cumulative and profoundly and ecology of the fishes of Wabash River are from the negative, they are not as obvious as acute exposure to more pristine period prior to significant development high profile agricultural and industrial chemicals (Poff (Jordan 1890). However, even before 1900, the Wabash et al. 1997). Further, the natures of these impacts are River became noticeably more turbid likely due to the el- idiosyncratic and can vary substantially with geography, evated sediments and nutrients generated by the rapid geomorphology, land-use, and engineering practices for expansion of agriculture in the watershed (Jordan 1890). each specific river. In the Wabash River example, 80 Currently, the river downstream from the single reser- USGS gaging stations measured altered hydrographs due voir is turbid, but the water color is brown or yellow- to dam construction (Pyron and Neumann 2008). Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 4 of 14 Resulting hydrographs in the Wabash River watershed high flows during Oct and Apr, compared to historic tend to have statistically significant increased minimum flows. Frequencies of large flood events for the Wabash flows, decreased maximum flows, increased fall rate, de- River were historically rare (four events from 1928- creased summer monthly flows, and decreased high 1985), however are more common in recent decades pulse counts, compared to historic flows (Fig. 2, Pyron (four events from 1985 to 2005) (Pyron et al. 2010). and Neumann 2008). Watersheds with row-crop agricul- Rahman and Bowling (2018) further found that reservoir ture land-use resulted in an increased number of zero management in the Wabash River basin resulted in flow days, increased low pulse counts, and decreased decreased annual maximum discharge and flashiness (rapid flow increases following rain events) and in- creased annual minimum discharge. Thus, in the Wabash River basin, early twentieth century develop- ment culminated in a more compressed hydrograph with, paradoxically, more variable and extreme condi- tions in low flow months. Wabash river water quality and the clean water act During the late twentieth and early twenty-first centur- ies, there was a steady reversal in some of the anthropo- genic stresses, especially the discharge of point-source pollutants to the river. Prior to the Clean Water Act of 1972, summer fish kills were frequent, occurring when dissolved oxygen concentrations were low, the water temperature was high, and river discharge was low (Gammon 1998). Those summer kill conditions were ul- timately driven by the increases in the amount of largely untreated municipal sewage at the same time as wet- lands were being converted to row-crop agriculture in the early to the late twentieth century. The combination of the Clean Water Act point-source controls through the National Pollution Discharge Elimination System along with the adoption of agricultural best management practices including no-tillage, filter strips, and winter cover crops that help reduce non-point source pollution led to water quality improvements, yet some problems remained. In particular, mineral phosphorus inputs and suspended sediment loads that result from agricultural practices have become a water quality issue (Muenich et al. 2016). Similar patterns of changing nutrient speci- ation were observed in other agricultural midwestern rivers and around the world (Powers et al. 2016). The re- sult has become, instead of fish kills, eutrophication and potential for reduced fish productivity with both in- creased phytoplankton abundance and a simultaneous rising dominance of lower quality pelagic blue-green, diatom, and euglenoid algae (Minder and Pyron 2017). Thus, the benefits of fewer summer fish kills were offset by a shift in the food base that led to a change from the historically warm water fish assemblage that favors rec- Fig. 2 3-day minimum flow by year calculated by Indicators of reational and commercial species like catfish and buffalo, Hydrologic Alteration software (Richter et al. 1996) for the Montezuma USGS gaging station on the Wabash River (top), fall rate to a modern assemblage dominated by planktivores in- by year for the Valley City USGS gaging station on the Illinois River cluding the rising threat of invasive bigheaded carps. (middle), and fall rate by year for the Louisville USGS gaging station Thus, instead of the conservation potential leading to a on the Ohio River (bottom) state resembling the clear-water conditions of the pre- Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 5 of 14 development nineteenth century, we are faced with an river discharge was low and the air temperature was ecosystem that appears to have shifted to a new and al- high (Gammon 1998). This was the period when ternate high-productivity but a turbid state. DePauw University faculty member James Gammon followed in the footsteps of David Starr Jordan with an- Changes in Wabash River biodiversity: fishes, nual fish collections in the Wabash River (Gammon mussels, and David Starr Jordan 1998). His collections and observations are summarized Early assessment of the biodiversity was begun in the in his textbook, The Wabash River Ecosystem (Gammon late nineteenth century by the pioneering ichthyologist 1998). The book includes a history of the Wabash River, in North America, David Starr Jordan in 1878. Despite descriptions of the dominant fish species, and general the initial impacts of altered hydrology and increased patterns of the fish assemblages during this time period pollution, Jordan found the Wabash River still contained following the Clean Water Act. Gammon’s goal was to high biodiversity with 151 native fish species, including use the fish community to assess water quality and iden- key regional species like sturgeon, Blue Catfish, and tify problem discharge locations. Gammon’s efforts were Redhorse suckers (Gammon 1998; Simon 2006). The at the forefront of utilizing the results of natural history hardiness of these species is evidenced by the relatively surveys to effectively communicate the links to pollution few local extinctions with the exception of Alligator Gar to agencies and society at large. Gammon (1998) in- (Atraclosteus spatula), Popeye Shiner (Notropis ariom- cluded an innovative fish-based tool, the Index of Well- mus), and Crystal Darter (Crystallaria asprella). At the Being (IWB) that incorporated fish biomass, abundance, height of the degradation in the 1970s through the and diversity to gauge the level of impairment, which 1980s fish assemblages were strongly impacted and proceeded with other indices developed in the region dominated by less desirable Gizzard Shad (Dorosoma like the influential Index of Biotic Integrity. The IWB cepedianum). The recent fish assemblage (1990-present) data collected during his 1970 to 1998 career and again is characterized by resurgent populations of native river beginning in 2001 by a new team from Ball State specialists like River Carpsucker (Carpiodes carpio) and University demonstrated continually improving fish as- Freshwater Drum (Aplodinotus grunniens) alongside de- semblages (Pyron and Lauer 2004). Standardization in clining invaders like Common Carp (Cyprinus carpio, collection and data analysis included collections at sites Fig. 3). Recent surveys showed increased species richness where Gammon made his collections, and boat and relative abundances of sensitive species such as Blue electrofishing at 500-m distances in a downstream direc- Sucker (Cycleptus elongatus), Redhorse suckers, and tion. Combining these early and recent collections was Shovelnose sturgeon (Scaphirhyncus platorhyncus) that key to building the long-term trends we present to were recorded by David Starr Jordan (Pyron et al. 2006). establish the status and conservation potential of the The twentieth century, especially the 1960s through Wabash River ecosystem (Broadway et al. 2015; Pyron 1980s, was a nadir for both environmental conditions et al. 2017). and biodiversity in the Wabash River. Effluent from mul- Freshwater mussels represent taxon another which, tiple industries, sewage treatment plants along the Wa- unfortunately, has not recovered. Mussel species rich- bash River, and row-crop agriculture throughout the ness decreased from a high of 66 species in the twentieth watershed contributed to pollution and increased nutri- century to only 30 species with reproducing populations ents. Evidence of the impact of these problems was eas- (Fisher 2006). Likely causes of mussel losses include ily observed with frequent large fish kill events when overharvesting by commercial shelling (Cummings et al. 1992), direct exposure to sewage and wastewater, local extinctions of their fish hosts (Unioinidae mussels re- quire a fish or other host for larvae.), and indirect effects of altered hydrology that degraded adult habitat includ- ing sedimentation, hypoxia, or lethal summer water tem- peratures (Box and Mossa 1999; Fisher 2006). The twenty-first century has brought improving environmen- tal conditions, increases in host species abundances, and greater interest in population enhancement and reintro- ductions (Indiana Department of Wildlife Resources 2017 Wildlife Science Report, indianawildlife.org). How- ever, despite losses of more than 50% of the species and on-going anthropogenic threats from agriculture and de- Fig. 3 Relative abundance CPUE of four common fish species by velopment, the mussel assemblage of the Wabash River collection year in the Wabash River. Data from Pyron et al. (2017) is still among the most intact large river mussel Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 6 of 14 assemblages remaining in the midwestern region (Page et al. 1997). Ecological stressors to aquatic ecosystems are evolving but tend to be chronic stresses whose impacts are felt decades after the stress was initiated. We suggest that to create conservation strategies for chronic problems like anthropogenic, demographic, or climate changes, we need to be able to test a range of hypothesized solutions. Long-term ecological research like the work carried out on the Wabash River since David Starr Jordan’s time produces relevant data for long-term hypothesis testing (Dodds et al. 2012; Strayer et al. 2014). Pyron et al. (2008) identified a temporal decrease in a multimetric score (Index of Biotic Integrity, IBI) from 1974 to 1998, and IBI scores increased with an upstream river location. For instance, long-term data resulted in the detection of a regime shift from planktivore-detritivores that domi- nated between 1960 and 1980, to benthic invertivores, that was attributed to reductions in pollution with the Clean Water Act (Broadway et al. 2015; Pyron et al. 2017; Fig. 3). More recent (1990–present) modifications to the fish assemblages included further reductions in gizzard shad, caused perhaps by nutrient loading modifi- cations (Muenich et al. 2016) and/or increased abun- Fig. 4 CPUE for sensitive fishes by collection year in the Wabash dances of invasive Silver Carp (Hypopthalmichthys River. Data from Pyron et al. (2017) molitrix, Pyron et al. 2017). However, Silver Carp abun- dances in the Wabash River did not approach extreme densities as in the Illinois River (McClelland et al. 2012). (Bacula et al. 2009). Abundances in the Wabash River Evidence that nutrients impacted the ecosystem includes were low during the 1970s and increased recently likely changes in the phytoplankton assemblages that were following water quality improvements (Gammon 1998). dominated by high-quality green algae in the 1970s and We found increased abundance as catch per unit effort recently are dominated by diatoms and lower nutrition- (CPUE) of blue sucker from 1974 to 2017 (Fig. 4). quality blue-green algae (Minder and Pyron 2017). How- Redhorse suckers (Moxostoma spp.) are an emblematic ever, a lack of continuous long-term nutrient monitoring large river species (Simon 2006) that were in low abun- data to examine with fish assemblage data prevents fur- dances in the Wabash by the 1970s (Fig. 4). Subse- ther conclusion. Despite the decades of ecological stress, quently, several Moxostoma increased in abundance, the fish assemblage of the Wabash River contains mul- likely following water quality improvements (Gammon tiple sensitive species that increased in abundance dur- 1998). Trautman (1981) stated that redhorse suckers are ing the past several decades (Pyron et al. 2006). intolerant to pollution and siltation, which are products Examples of sensitive but recovering fish include the of industrial point source pollution and agriculture in following: the Wabash River watershed. Catch per unit effort of Shovelnose Sturgeon (Scaphirhynchus platorynchus) Shorthead Redhorse (Moxostoma macrolepidotum) did have a strong Wabash River population (Fig. 4) that sup- not change significantly from 1974 to 2017 in the ports a commercial caviar harvest (Kennedy et al. 2007). Wabash River (Fig. 4). Although Thornton et al. (2018) found the shovelnose Smallmouth Buffalo (Ictiobus bubalus) and Freshwater sturgeon population was healthy, condition, weight of Drum (Aplodinotus grunniens) increased in abundance roe-per-fish, and size-at-maturity were decreasing from (Fig. 4) during this same time period. 2009 to 2016. Shovelnose sturgeon life history character- Although many large-river-adapted species have im- istics of high age of maturity and infrequent proved abundances, additional conservation problems reproduction result in susceptibility to over-harvest remain for the Wabash River. Sauger (Sander canaden- (Thornton et al. 2018). sis), Bowfin (Amia calva), and American Eel (Anguilla Blue Sucker (Cycleptus elongatus) is a large-river spe- rostrata) which all have large river linked life histories, cialist with decreased abundance during recent decades declined between 1974 and 2017, but are also still throughout its range in the Mississippi River basin present in the system (MP unpubl. data). Taken Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 7 of 14 together, the presence of robust populations of these The Ohio River historically supported high species sensitive fish species suggests that the ingredients of a richness of freshwater mussels and with species richness healthy large river assemblage are still present. This is a of individual pools up to 63 (Watters and Flaute 2010). primary reason that restoration and conservation efforts Mussel diversity decreased the past century with high in the Wabash River have a high likelihood of success. variation in losses among Ohio River pools. Watters and Flaute (2010) identified the causes of mussel extirpations Ohio River: hydrologic alterations, fish, and as water quality, existing dams, and invasive zebra mussel assemblages mussels. The Ohio River has a larger watershed than either the Wabash or Illinois rivers (Fig. 1). Unlike the watersheds Illinois River: a history of pollution and hydrologic of the Wabash and Illinois rivers, agricultural land use in alterations the Ohio River watershed has decreased while forest The Illinois River whose basin is immediate to the west cover has increased since the 1960s (Tayyebi et al. 2014; of the Wabash River has many similarities to its neigh- Pyron et al. 2019). Land-use in the Ohio River watershed bor such as the domination of their watersheds by row- was dominated by row-crop agriculture in the 1930s, but crop agriculture, a history of untreated industrial and conservation reserve programs from 1970 to the present municipal sewage pollution, and dramatic alteration resulted in shifts from agriculture to the forest (Tayyebi from pre-European hydrologic baselines. However, there et al. 2014). Percent urban use more than doubled dur- are also important differences that may explain the di- ing the same time period (Tayyebi et al. 2014). Although vergence in the conservation history of the two rivers— increased forest cover in the watershed likely contributes sewage originated from a much larger urban-industrial to improvements in water quality, geochemical signa- center (Chicago) in the headwaters of the Illinois River tures from past land-uses remain (Harding et al. 1998). (Delong 2005). Prior to the twentieth century, hypoxia Like many rivers of the developed basins of the US and acute toxicity were common more than 100-km Midwest, historic hydrology patterns in the Ohio River downstream. The subsequent construction of the watershed were significantly altered by a system of 20 Chicago Sanitary and Ship Canal diluted the polluted low-head navigation dams (Thomas et al. 2005). Hydro- river with water diverted from Lake Michigan while also logical alterations included 10 variables encompassing expanding commercial navigation. While this success- ecologically important attributes of discharge magnitude, fully lowered lethal hypoxia events and pollutant con- duration, high- and low-pulse frequencies, fall rate, and centrations, this effort ultimately swung the pendulum rise rate (Fig. 2, Pyron et al. 2019). in the other direction when the oligotrophic lake water As across North America, invasive species such as began to account for between 10 and 25% of the dis- Common Carp and Bigheaded carps and zebra mussels charge in the upper third of the river after the canal are a significant problem in the Ohio River (Angradi opened (Delong 2005). Additionally, commercial naviga- et al. 2011). Zebra mussels are in the Wabash River and tion expanded dramatically on the Illinois River: the ori- are a potential threat to native mussels (Schneider et al. ginal low-head wicket dams that were constructed in the 1998) but are currently at low abundances (MP pers. late 1800s were upgraded in the 1930s to create a deeper obs.). However, despite their influence, Thomas et al. navigation channel year-round (Gibson-Reinemer et al. (2005) identified improvements in fish assemblage met- 2017). This meant greater minimum flows, fewer high rics over the last 50 years, especially noticeable since the flow pulses, a less well-defined flood season, and a highly implementation of the 1972 Clean Water Act. Like the variable rate of rise/fall during any flood event than the post-CWA era in the Illinois and Wabash rivers, there pre-1930s river hydrograph (Lian et al. 2012). Analysis were increases in fish abundance, a tripling of species of historical discharge records showed that since the richness, and increased trophic diversity of the fish fauna 1930s, there are at least 11 key hydrologic variables that with time in the Ohio River, with the trend accelerat- are still significantly altered (Table 1) including fall rate ing with each year (Pyron et al. 2019). Pyron et al. (Fig. 2). There were dramatic rises in the suspended (2019) further hypothesized that the shift in the early sediment load and subsequent sedimentation rates, espe- 1900s from benthic to pelagic fish dominance ob- cially in the once diverse and productive floodplain served throughout the Ohio River coincided with de- backwaters (Bhowmik and Demissie 1989). These com- clines in water clarity and quality as urban, bined factors significantly limit native fish diversity re- agricultural, and industrial inputs became significant. covery from point-source pollution-related stresses. The accompanying declines in diversity and secondary production of benthic invertebrates then cascaded up Fish assemblages of the Illinois River to declines in the invertivore and piscivore fishes ob- The fish assemblage in the upper Illinois River reached served by Bowes (2016). its environmental low point in the 1950s with low Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 8 of 14 Table 1 Hydrology variables that were significantly altered (P < zebra and quagga mussels. These invaders expanded 0.05) from Indicators of Hydrologic Alteration analysis (Richter downstream into the Illinois River from the Great Lakes et al. 1996) using daily discharge from the Valley City, Illinois, in the 1980s and, arguably a bigger threat, the bigheaded USGS gaging station on the lower Illinois River. We used carps moved upriver from the lower Mississippi River in discharge data from 1939 to 2015 to create hydrology variables, the 1990s (Stoeckel et al. 1997; Sass et al. 2010). There is which were then regressed with year to detect significantly a sad irony that the decades of improvements in water altered variables quality from the CWA that helped recover native species IHA group CorrelationrP value may now also benefit these recent invasive species. Group 1: monthly magnitude December 0.27 0.025 Similarities and differences among large June 0.28 0.025 midwestern US rivers Similarities in the influences shaping fish assemblages of September 0.25 0.025 the Wabash, Illinois, and Ohio rivers include a large pro- Group 2: magnitude duration of annual extremes portion of the watershed in row-crop agriculture, con- 3-day minimum 0.28 0.025 centrated urbanization, and alteration of hydrology from 7-day minimum 0.30 0.01 damming (Table 2). However, despite the similarities 30-day minimum 0.26 0.025 among the drivers, the response patterns and trends in 30-day maximum 0.25 0.025 fish assemblages do not mirror each other. These rivers had varied responses to the staggered arrival of invasive 90-day maximum 0.28 0.025 bigheaded carps. Fish assemblages in the upper third of Group 4: frequency and duration of high and low pulses the Illinois River closest to the headwaters had not re- High pulse duration 0.41 0.001 covered as much as the lower river before the bigheaded Group 5: rate and frequency of change in conditions carp invasion (Gibson-Reinemer et al. 2017). In contrast, Rise rate 0.37 0.001 the fish assemblages of the Wabash River recovered Fall rate − 0.44 0.001 from the pre-1970s pollution due to the CWA prior to invasive bigheaded carp establishment (Pyron et al. abundances of generalist species (common carp and 2019). However, in the Wabash River, invasive big- goldfish, Carassius auratus). However, following the im- headed carps never successfully established, with no plementation of the Clean Water Act, there was a doub- measurable impact during the same period bigheaded ling in native species richness, increase abundances of carps negatively influenced the Illinois River fish assem- commercially harvested species by more than 25%, while blage (Broadway et al. 2015; DeBoer et al. 2018). the relative abundance of the pollution-tolerant common Bigheaded carp populations are higher in abundance carp fell to a mere 2% of the community (Gibson-Reine- in the Illinois River ecosystem than in the Wabash River, mer et al. 2017). The recovery of the Illinois River in the while the body condition and abundance of the native decade after the CWA is celebrated as a victory for con- competitors Gizzard Shad and Bigmouth Buffalo, and servation and restoration. In addition to demonstrating even Silver Carp simultaneously decreased (Solomon the power of national policy to have profound local ben- et al. 2016; Pendleton et al. 2017). In contrast, Wabash efits, this also demonstrated that even the most stressed River Silver Carp abundance is lower and body condition ecosystems may be capable of recovery. However, by the is higher. Several authors attributed lower abundances of twenty-first century, a new type of pollution emerged— the bigheaded carp in the Wabash River to less altered Table 2 Three rivers compared by history of modifications Modification Wabash River Illinois River Ohio River Recent land- Agriculture Agriculture Mixed agriculture and forest use Hydrologic Monthly magnitude, high- and Monthly magnitude, 3-day, 7-day, and 30-day minimum dur- Monthly magnitude, duration, alterations low-pulse frequencies, minimum ation; 30-day and 90-day maximum duration; high-pulse dur- high- and low-pulse frequencies, flows, fall rate ation, rise rate, fall rate fall rate, rise rate Invasive Minor: bigheaded carps Major: bigheaded carps Minor: bigheaded carps species effects Native fish Strong Strong ? recovery since CWA Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 9 of 14 hydrology which may suppress carp diet and including catchment disturbance, pollution, and water reproduction, while fostering a more intact assemblage resource development (Counihan et al. 2018). Despite of native predators and competitors (Stuck et al. 2015; their widely divergent environments, socio-economic Coulter et al. 2018). Love et al. (2017) reinforced the settings, and ecological responses, the main stressors for idea that strong competitive interactions can constrain all the large rivers studied were consistently dams and bigheaded carp by showing a rapid rebound in Gizzard land-use modifications. Counihan et al. (2018) noted Shad body condition in Illinois River after the targeted that while improvements in water quality associated with harvest of Silver Carp began. In the Wabash River, the the post-CWA (Clean Water Act) era affected all the gizzard shad population crashed between 1974 and systems, they varied in the initiation and the magnitude 2008, prior to the arrival of the bigheaded carps, mean- of improvement. ing that despite the lower plankton productivity of the Wabash, there was still less competition during their es- Placing large river conservation into a theoretical tablishment (Pyron et al. 2017). Thus, although invasive context bigheaded carp are present in both the Illinois River and The theory has firmly established hydrology, geomorph- the Wabash River, the difference in invasion trajectory ology, and human development as key drivers of river suggests that the ecological constraints of the invader structure and function (Poff et al. 1997; Thorp et al. are very different. 2010; Gibson-Reinemer et al. 2017). However, the lack The Ohio River watershed apparently benefitted from of a flexible, adaptable framework for use in divergent the twentieth century increases in forest cover, likely systems has been one practical limitation to conservation contributing to the recovery of the fish assemblages in in large rivers. Two recent advances in theory can pro- conjunction with the Clean Water Act (Pyron et al. vide an example solution: Riverscapes (Fausch et al. 2019) especially since no measurable impact of big- 2002) and Macrosystems (McCluney et al. 2014). The headed carps was yet detected in this large river. The riverscape perspective integrates ecological processes CWA also benefitted the Wabash River fish assemblages and spatial complexity by increasing the spatial and tem- as shown by a similar increase in species richness and poral scale of research (Fausch et al. 2002). Fausch et al. recovery of sensitive taxa (Gammon 1998; Pyron et al. (2002) recommended sampling designs that allow testing 2006). While the Wabash River did not entirely escape at multiple spatial scales and time intervals appropriate the added stresses of dams and navigation, the amount to the life history attributes of target fishes or other or- of infrastructure and traffic is substantially less than ei- ganisms. For example, long-term analyses of Wabash ther the Illinois or Ohio river experiences. The only River fish assemblages that included variation in traits mainstem dam and reservoir on the Wabash River was (Beugly and Pyron 2010) and body size variation designed for flood retention and control rather than pro- (Broadway et al. 2015) provided new information about moting navigation. Its major impact is the combined re- ecosystem effects. Fish assemblages of the Wabash River duction of discharge during spring high-flow periods Beugly and Pyron 2010) and in addition to embracing and discharge variation in the stable, low-flow summer the Riverscape scales, expanding to larger spatial and months, along with allowing a more rapid rate of fall temporal scales, allows river ecology to incorporate a and rise of flood pulses (Table 1, Fig. 2). Despite the macrosystem view (McCluney et al. 2014). The macro- similarity with the Illinois River, the Wabash River is still system view of river ecosystems is of watershed-scale less severely impacted than the more variable and sea- networks containing distinct patches that are connected sonally unstable flow regime of the Illinois River. While and interacting. The River Ecosystem Synthesis model the biota of all three of these rivers benefitted from im- (Thorp et al. 2006) predicts that river geomorphology proving water quality, the altered hydrology of the and hydrology result in unique reaches or functional Illinois and Ohio rivers have replaced poor water quality process zones, which have unique ecosystem characteris- as major limiting factors. This is another attribute of the tics and can repeat with river distance. Thorp et al. Wabash River situation that increases its potential con- (2010) further concluded that river ecosystem function- servation value. Thus, we can conclude that one of the ing is primarily caused by its hydrologic pattern (Poff attributes of the Wabash River that make it a good re- et al. 1997), and understanding can come from linking gional candidate for conservation is that it receives all hydrogeomorphology of a river with its biocomplexity the benefits of improving land-use practices and envir- and ecosystem services (Williams et al. 2013). Defining onmental legislation while, unlike the Illinois and Ohio river ecosystems by hydrogeomorphological gradients is rivers, it has not been as severely degraded by invasive an advance over the river continuum concept, which in- species like the bigheaded carps. cludes only river distance attributes (Vannote et al. Several large U.S. rivers resulted in significant tem- 1980). Defining distinctive geomorphologic reaches or poral and spatial trends, all with multiple stressor effects functional process zones (FPZ) for the Wabash River Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 10 of 14 can provide a start to diagnosing potential conservation 3) Partnerships and policies like the proposed National issues and opportunities (Fig. 4). A quantitative method Fish Habitat Conservation Through Partnerships to define functional process zones using GIS data is cur- Act which engage the public and politicians to rently available. For instance, Robbins and Pyron (in re- arrest on-going degradation and promote important view) used a quantitative approach (Williams et al. 2013) habitat restoration (Crawford et al. 2016). to identify three distinct functional process zones (FPZ) 4) Reframing of our perception of habitat in river for the Wabash River (Fig. 5); FPZ A has a narrow chan- basins—especially the recognition that the nel width and wide floodplain, FPZ B has a wide channel distribution of habitats are often determined by and wider floodplain, and FPZ C has a wide channel reach scale hydrogeomorphological attributes like width and constrained, narrow floodplain. Robbins and functional process zones rather than simply by local Pyron (in review) then demonstrated that Wabash River site conditions. fish assemblages varied by FPZ (Fig. 5). This approach is 5) Develop detailed fluvial hydrogeomorphology especially useful for large river assessment because it studies of the mainstem Wabash River to identify clearly demonstrates strong links between species com- high-quality habitat remnants or to guide rehabilita- position and FPZ characteristics (DeBoer et al. 2019). tion. This might include the characterization of The take-home message for conservation is that theoret- sediment distribution and flux, erosion, and sedi- ical models can be tailored to the specific limitations or mentation patterns, linked to local hydrology vari- opportunities of a river (e.g., flow modifications in ero- ation (Baranya et al. 2018). sional zones below dams versus habitat enhancement in 6) Map geomorphological variation and identify depositional areas of the lower river), thus increasing the locations that are most appropriate for an action success and efficiency of the effort and funds expended (e.g., cover crop incentives, instream habitat across the basin. construction) and policy (e.g., conservation easements) where flood frequency is changing and Recommendations for moving from theory to increasing impacts are expected to human practice in the Wabash River structures or land-use. James Gammon (1998) began a long-term record of fish 7) Restore floodplains by allowing natural seasonal abundances for the Wabash River in the 1970s. Continu- flooding. ation of this long-term effort requires permanent fund- 8) Build a watershed partnership with representation ing and supplemental data collection similar to other from resource users, agriculture interests, and long-term monitoring programs. Examples of programs management agencies whose goal is to identify and are the Long-Term Resource Monitoring program on promote potential conservation, land-use modifica- the Upper Mississippi River (Gibson-Reinemer et al. tions, policy, and mitigation that will protect or im- 2017) and the Ohio River Valley Sanitation Commission prove watersheds in all rivers (Garvey et al. 2010). (ORSANCO). To maximize the insights and benefits, a An example of a watershed partnership for a large monitoring program should include the key drivers iden- river is the Upper Mississippi River Conservation tified by theory, water quality, nutrient flux, hydrology, Committee (https://www.umrcc.org/umrcc-history). and sediment transport, and plankton monitoring. The roadmap to restoration and conservation of Wabash Outcomes: the future of the Wabash River River biodiversity would be a case study for aquatic con- ecosystem servation in general and large river conservation in par- Several successful examples of conservation improve- ticular. Specific examples for inclusion in the effort ment in river-floodplain habitats exist. For example, The would include: Nature Conservancy’s Emiquon Preserve adjacent to the Illinois River (Lemke et al. 2017). While the primary goal 1) Experimental modification of the release regime at Emiquon has always been to improve the river basins from upstream flood-control reservoirs in to diversity and productivity by connecting a high-quality mimic the natural flow regime with concurrent source habitat, the project embraces the presence of monitoring of ecological and sediment responses agricultural levees by the installation of gated structure (Konrad et al. 2011). that permits export of material and fishes to the river 2) Incentives for modification of cover crops in while preventing extreme flooding, excessive backwater agricultural subwatersheds to reduce peak flow sedimentation, and limiting invasive species in the flood- runoff and subsequent nutrient spikes (Babbar- plain. In addition, the local society benefits through in- Sebens et al. 2013) with monitoring of resulting creased recreational hunting and fishing, tourism, and changes in both sediment and nutrient exports, and the potential for flood risk reduction. Modifying this ap- primary producers. proach to the opportunities available in Wabash River Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 11 of 14 Fig. 5 Three functional process zones for the Wabash River, defined by geomorphology. FPZ A has a narrow channel width and wide floodplain, FPZ B has wide channel and wider floodplain, and FPZ C has wide channel width and constrained, narrow floodplain (Robbins and Pyron in review) could include a combination of reduced nitrogen and stage ditch constructions (Mahl et al. 2015) that are phosphorus fertilizer application rates that consider leg- effective with targeted approaches. Reduced nutrient acy soil nutrients, application methods that maintain nu- loading to the Wabash River is predicted to result in trients in the soil, and improved application timing modifications of the ecosystem including the fish assem- (such as considering the potential for rain near-future), blages. Potential changes to fish assemblages with de- creation of wetlands to enhance nutrient uptake, restor- creased primary productivity include reduced abilities ation of riparian zones, and modification of flood control for bigheaded carps to forage on phytoplankton, the abil- management to allow natural flooding into wetlands and ity for gizzard shad to switch from planktivory to detri- backwaters (Mitsch et al. 2001). Additional nutrient re- tivory, and modifications of food webs. Increased water duction approaches include best management practices clarity may result in increased benthic primary product- that reduce the loss of sediments and nutrients and two- ivity and subsequent secondary benthic productivity and Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 12 of 14 increased abundances of benthic invertivore fishes. riparian vegetation and has led to an increase in bank Impacts on mussels are unknown with decreased phyto- slumping. Many of the tributaries are supplying a signifi- plankton in the water column. However, these modifica- cant and increasing amount of sediments to both the tions are costly and politically difficult to implement at local channel habitats as well as to downstream back- sufficient levels. Local activism to educate politicians water and channel habitats (Odgaard 1987; Magner and and citizens may provide impetus to invest resources in Steffen 2000; Sekely et al. 2002) resulting in habitat sim- conservation. plification or loss of appropriate habitat for fishes and The early twentieth century agricultural and industrial macroinvertebrates (Blann et al. 2009). In addition, pre- development of river basins often focused on optimizing cipitation is increasing in the Wabash River watershed one or two aspects of management (e.g., irrigation sup- (Pyron and Neumann 2008) and further climate change ply, rapid field drainage) while, for ease or economics, may contribute by increasing the magnitude while de- discounting other potential ecological or cultural uses. creasing the predictability of discharge patterns and their However, more recently, water and land management nutrient and sediment loads in both the mainstem and and planning as a discipline is moving towards recogni- tributaries (Knox 2000, 2006). tion of the value of a portfolio of these resource uses in Restoring river hydrology to approach a “naturalized” conservation to broaden the appeal and thus support of flow regime is possible and includes restoration of chan- projects and goals (Horne et al. 2017). Flow experiments nel geomorphology with appropriate sediment transport provided evidence that small inexpensive modification of and habitat creation (Newson and Large 2006). Nilsson hydrology to mimic natural flow regimes can improve et al. (2018) recommended ecological restoration to at- ecosystems (Olden et al. 2014). Flood control dams are tenuate floods by increasing channel roughness, increas- designed to capture water during high-flow situations ing in-stream habitat complexity with large boulders or and subsequently release it gradually. The resulting al- large woody debris, or increasing wetland construction. tered hydrology has loss of peak flows, elimination of Restoration of natural hydrology in tributaries contrib- small floods, and artificially elevated flows (Richter and utes to the successful restoration of the mainstem hy- Thomas 2007). Dam release modifications for environ- drology. These approaches function to improve stream mental flows are relatively simple. Richter et al. (2003) habitats by increasing water retention capacity. Success- used the Green River, Kentucky, as a case study. A reser- ful conservation for the Wabash River is possible and voir was constructed in 1963 by the US Army Corps of begins with nutrient reductions, mechanisms to restore Engineers for flood control and recreation. Dam releases historical hydrologic patterns, additional sediment con- were modified to allow steady low flows in the fall sea- trols, and improved local hydraulics. We recommend son and avoid large releases in short periods. A similar similar approaches for other impacted large river modification of the flow regime of the Wabash River ecosystems. might be initiated with designed ecological releases from Acknowledgements the upstream flood control dams. If this is implemented We are grateful to multiple students and scientists who collected fishes or as an experiment with before and after components, it collaborated with us for data. Thanks to Kristen Bouska for editorial suggestions on an earlier draft. could be a robust test of ecological flow effects (Olden et al. 2014). Authors’ contributions Human impacts that contribute to hydrologic alter- All authors designed the study and drafted the manuscript. The authors read and approved the final manuscript. ations include deforestation, channel-bed reconfigur- ation, floodplain development, drainage, agricultural Funding intensification, and urbanization (Wheater and Evans Funding for earlier collections was from Eli Lilly and Company, Duke Energy, and U.S. Fish and Wildlife Service. 2009). All of these impacts are present and even expand- ing in the Wabash River watershed. In addition, activities Availability of data and materials that promote channelization and alterations designed to Not applicable. move water downstream more rapidly appear to be Ethics approval and consent to participate expanding (Nilsson et al. 2018). Nilsson et al. (2018) de- Not applicable scribed lowland agricultural rivers that are similar to the Wabash River as rivers where extreme flooding has haz- Consent for publication Not applicable ardous consequences to human populations. The flood- ing frequency of the lower Wabash River is less altered Competing interests from historical flows (Pyron and Neumann 2008), likely The authors declare that they have no competing interests. because the river is mainly free-flowing. However, row- Author details crop agriculture impacts caused altered flows that re- 1 2 Department of Biology, Ball State University, Muncie, IN 47306, USA. School sulted in incised channels where the loss of permanent of Sustainable Engineering and the Built Environment, Arizona State Pyron et al. Fisheries and Aquatic Sciences (2020) 23:15 Page 13 of 14 University, Tempe, AZ 85281, USA. Illinois River Biological Station, Illinois Fausch KD, Torgerson CE, Baxter CV, Li HW. 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