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(1999)
A Procedure to Estimate the Response of Aquatic Systems
W. Zevenboom, L.R. Mur (1980)
Hypertrophic Ecosystems
K. Sand‐Jensen, M. Søndergaard (1981)
Phytoplankton and Epiphyte Development and Their Shading Effect on Submerged Macrophytes in Lakes of Different Nutrient StatusInternational Review of Hydrobiology, 66
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European Framework Directive 2000/60/EC
K. Sand-Jensen, M. Søndergaard (1981)
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Population dynamics of duckweed cover in polder ditchesArchiv für Hydrobiologie
L. Liere, J. Janse, M. Jeuken, P. Puijenbroek, O. Schoumans, R. Hendriks, J. Roelsma, D. Jonkers (2002)
Effect of nutrient loading on surface waters in polder Bergambacht, The Netherlands
(2000)
Natural Biocoenosis of Dutch Inland Fresh Waters
Critical nutrient loads to prevent duckweed dominance loads in polder ditches were assessed using the eutrophication model PCDitch. In this article the ecological target was set at 50% duckweed coverage. This may be very high for ditches with a nature function, but is not unreasonable for ditches in agricultural areas, with upwelling nutrient rich groundwater, run-off and drainage. Since the change from a ditch with submersed vegetation to duckweed coverage is often a sudden shift, the choice of the amount of duckweed coverage does not influence the calculated loading very much. The main topic of this paper is to present a method to calculate critical loads of nutrients when ecological targets have been set. Sediment type, residence time and water depth influenced the critical loading rates. The calculated critical phosphorus load ranged from 1.8 to 10.2 g P m−2 year−1, while the calculated critical nitrogen load stretched from 12.1 to 43.8 g N m−2 year−1. The concentration ranges that were derived from the loading rate were 0.19–0.42 mg P l−1 and 1.3–3.3 mg N l−1. Since PCDitch does not distinguish between Lemna spp. and Azolla spp., no definite conclusions were drawn concerning the effects of nitrogen reduction. In a model situation a pristine ditch was loaded with phosphorus, which resulted into complete duckweed coverage during summer within a few years. When reducing the phosphorus load, it took 10 years before the original situation was reached again. Dredging would accelerate the process of recovery significantly, because the water depth would increase and the phosphorus release from the sediments in summer would decrease.
Aquatic Ecology – Springer Journals
Published: Sep 15, 2006
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