Mesotrophy is not enough: Re-assessing phosphorus objectives for the restoration of a deep Alpine lake (Lake Lugano, Switzerland and Italy)

Lepori, Fabio and Lucchini, Bianca and Capelli, Camilla and Rotta, Federica (2022) Mesotrophy is not enough: Re-assessing phosphorus objectives for the restoration of a deep Alpine lake (Lake Lugano, Switzerland and Italy). Advances in Oceanography and Limnology, 13 (2). ISSN 1947-5721

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Abstract

The restoration of eutrophic lakes requires the identification of phosphorus objectives, i.e., the phosphorus reductions needed to achieve desired water quality goals. Due to inherent uncertainty, phosphorus objectives need periodic revision as the restoration progresses. We used monitoring data from a deep southern Alpine lake (Lake Lugano, Switzerland and Italy) to assess restoration progress and revise the current phosphorus objective of 30 mg m–3. Because one basin of the lake is meromictic (North basin) and the other is holomictic (South basin), restoration focussed on the mixolimnion for the North basin and the entire water column for the South basin. Time series analyses indicated that, thanks to restoration, phosphorus concentrations in the lake declined to values compliant with the objective (~20-30 mg m–3). In contrast, little progress was observed towards achieving the main water quality goals (chlorophyll a ≤4 mg m–3, primary production ≤150 g C m–2 year–1 and oxygen concentrations ≥4 mg L–1). Using predictive models, we estimated that achieving these goals requires a phosphorus objective of <10 mg m–3, which would bring the lake back to the original oligotrophic state. The concentration of <10 mg m–3 is lower than the objectives predicted for other (mainly northern) deep Alpine lakes. The apparent sensitivity of Lake Lugano, which we attribute to unfavorable hydrodynamic conditions common in lakes south of the Alps (weak mixing and long stratification), calls for particularly attentive phosphorus management.

Item Type:	Scientific journal article, Newspaper article or Magazine article
Subjects:	Biological Sciences > Biology > Applied biology Biological Sciences > Biology > Marine/Freshwater biology > Freshwater biology Biological Sciences > Biology > Ecology Biological Sciences > Biology > Ecology > Ecosystem ecology & land use Physical sciences > Chemistry > Environmental chemistry Physical sciences > Science of aquatic & terrestrial environments > Environmental sciences Physical sciences > Science of aquatic & terrestrial environments > Environmental sciences > Biogeochemical cycles Physical sciences > Science of aquatic & terrestrial environments > Science of aquatic & terrestrial environments not elsewhere classified
Department/unit:	Dipartimento ambiente costruzioni e design > Istituto scienze della Terra
Depositing User:	Fabio Lepori
Date Deposited:	05 Sep 2023 10:20
Last Modified:	05 Sep 2023 10:22
URI:	http://repository.supsi.ch/id/eprint/14597

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