Abstract
Attempts to restore Lake Lugano, Switzerland and Italy, from eutrophication have produced weak responses in the target variables (primary productivity and hypolimnetic oxygen concentrations), indicating shortcomings in the underlying eutrophication model. An analysis of monitoring data showed that the decrease in phosphorus concentration, although nearly compliant with restoration targets, produced only slight decreases in primary productivity and no change in hypolimnetic oxygen conditions. These target variables were equally or more sensitive to factors external to trophic state, including plankton structure, which influenced primary productivity, and the depth of mixing during turnovers, which influenced hypolimnetic oxygen. To improve the chance of success, the restoration approach should revise the phosphorus concentration target and explicitly account for the influence of external variation, especially mixing depth.
Highlights
In lakes, cultural eutrophication is the most widespread environmental problem (Smith & Schindler, 2009)
The hypothesised pathway (Fig. 1) probably overemphasises the links between these variables and falls short of identifying the controlling factors. Further assessments of this pathway are needed, because inadequate assumptions concerning the causal relationships between phosphorus, primary productivity and hypolimnetic oxygenation can hinder the success of restoration efforts
We examined in detail the response of lake phosphorus concentration ? primary productivity ? hypolimnetic oxygen pathway (Fig. 1) to investigate the effect of phosphorus reduction on hypolimnetic oxygen
Summary
Cultural eutrophication is the most widespread environmental problem (Smith & Schindler, 2009). Eutrophic lakes have undesirable traits, including algal blooms and the release of harmful gases from the sediments. Because these traits reduce the ability of lakes to provide ecosystem services, eutrophic lakes have long been a priority for ecological restoration (Edmondson, 1970). The hypothesised pathway (Fig. 1) probably overemphasises the links between these variables and falls short of identifying the controlling factors. Further assessments of this pathway are needed, because inadequate assumptions concerning the causal relationships between phosphorus, primary productivity and hypolimnetic oxygenation can hinder the success of restoration efforts
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