Phosphorus fractions in sediments and their relevance for historical lake eutrophication in the Ponte Tresa basin (Lake Lugano, Switzerland) since 1959

Tu, Luyao; Jarosch, Klaus; Schneider, Tobias; Grosjean, Martin (2019). Phosphorus fractions in sediments and their relevance for historical lake eutrophication in the Ponte Tresa basin (Lake Lugano, Switzerland) since 1959. Science of the total environment, 685, pp. 806-817. Elsevier 10.1016/j.scitotenv.2019.06.243

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Lake Lugano is one of several deep lakes in Switzerland that have not yet recovered from eutrophication after large reductions of external phosphorus (P) loadings. Persistent eutrophication has been attributed mainly to internal P loadings from sediments. To achieve the restoration goals, it is critically important to evaluate the sediment P availability and release risk in this lake. In this study, we combined sequential P extraction (four fractions) with enzyme hydrolysis to assess distribution characteristics of P forms and potential bioavailability of organic P in an anoxic sediment profile from the Ponte Tresa basin of Lake Lugano, southern Switzerland. Labile P forms, i.e. mostly redox-sensitive iron bound P and metal oxides bound P (Al/Fe-P), comprised ~70% of total P in the sediment profile (1959–2017 CE), suggesting a high potential for P release from the anoxic sediment. Potentially bioavailable organic P forms (determined by addition of substrate specific enzymes) were considerably higher in the surface sediments (top 5 cm), which is very likely to release P in the near future with early diagenesis. The net burial rates (NBR) of redox sensitive Fe-P fraction and total P in sediments both showed significant decreasing trends from 1959 to 2017 CE, when trophic levels of the lake increased from mesotrophic to hypertrophic status. We suggest that, in the Ponte Tresa basin, higher eutrophication conditions led to enhanced sediment P release (mainly from redox sensitive Fe-P fraction), thus reducing P-NBR in sediments. This study highlights the concern that in deep monomictic lakes, eutrophication restoration might be hindered by extensive internal P cycling and reduced capacity of sediment P-trapping.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geography
08 Faculty of Science > Institute of Geography > Physical Geography > Unit Paleolimnology
10 Strategic Research Centers > Oeschger Centre for Climate Change Research (OCCR)
08 Faculty of Science > Institute of Geography > Physical Geography

Graduate School:

Graduate School of Climate Sciences

UniBE Contributor:

Tu, Luyao; Jarosch, Klaus; Schneider, Tobias and Grosjean, Martin

Subjects:

900 History > 910 Geography & travel
500 Science > 540 Chemistry
500 Science > 550 Earth sciences & geology

ISSN:

0048-9697

Publisher:

Elsevier

Language:

English

Submitter:

Giulia Luise Wienhues

Date Deposited:

31 Jul 2019 10:52

Last Modified:

31 Jul 2019 10:52

Publisher DOI:

10.1016/j.scitotenv.2019.06.243

Uncontrolled Keywords:

Lake sediments, Deep lakes, Organic phosphorus, Labile phosphorus, Internal phosphorus loading

BORIS DOI:

10.7892/boris.131712

URI:

https://boris.unibe.ch/id/eprint/131712

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