Effects of winter weather and mixing regime on the restoration of a deep perialpine lake (Lake Lugano, Switzerland and Italy)

Lepori, Fabio and Bartosiewicz, Maciej and Simona, Marco and Veronesi, Mauro (2018) Effects of winter weather and mixing regime on the restoration of a deep perialpine lake (Lake Lugano, Switzerland and Italy). UNSPECIFIED. Hydrobiologia, 824 (1). pp. 229-242. ISSN 0018-8158

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Abstract

Long-term (1987–2015) monitoring data from Lake Lugano (Switzerland/Italy) were used to examine the effects of winter weather, solar radiation and mixing regime on the recovery of the trophic state of a lake undergoing nutrient management. Main hypotheses were that (H1) trends in trophic state were influenced not only by nutrient management, but also by winter weather and solar radiation, and (H2) the effects of management were more pronounced in the holomictic South basin than in the meromictic North basin of the lake. External loadings of phosphorus were strongly reduced during the study period, but key indicators of trophic state, including phosphorous concentration, primary production, chlorophyll a and deep-water oxygenation, showed inconsistent responses. Supporting H1, winter weather (parameterized using an index of the East Atlantic pattern) influenced temporal variation in phosphorus concentration and primary production in the North basin. Supporting H2, the effects of management on trophic state were clearer in the South basin, where most trophic-state indicators declined. Meromixis affected the restoration of the North basin lake by transmitting effects of climatic variation on trophic state. The added variability obscured the effects of restoration and caused sudden deteriorations in water quality, indicating that the restoration of meromictic lakes presents unique challenges.

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