Decades needed for ecosystem components to respond to a sharp and drastic phosphorus load reduction
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RESTORATION OF EUTROPHIC LAKES
Decades needed for ecosystem components to respond to a sharp and drastic phosphorus load reduction Ingrid Chorus . Antje Ko¨hler . Camilla Beulker . Jutta Fastner . Klaus van de Weyer . Tilo Hegewald . Michael Hupfer
Received: 21 September 2019 / Revised: 10 October 2020 / Accepted: 20 October 2020 Ó The Author(s) 2020
Abstract Lake Tegel is an extreme case of restoration: inflow treatment reduced its main external phosphorus (TP) load 40-fold, sharply focused in time, and low-P water flushed the lake volume & 4 times per year. We analysed 35 years of data for the time TP concentrations took to decline from & 700 to 20–30 lg/l, biota to respond and cyanobacteria to become negligible. The internal load proved of minor relevance. After 10 years, TP reached 35–40 lg/l, phytoplankton biomass abruptly declined by 50% and Guest editors: Tom Jilbert, Raoul-Marie Couture, Brian J. Huser & Kalevi Salonen / Restoration of eutrophic lakes: current practices and future challenges
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10750-020-04450-4) contains supplementary material, which is available to authorised users. I. Chorus (&) C. Beulker J. Fastner German Environment Agency, Schichauweg 58, 12307 Berlin, Germany e-mail: [email protected] A. Ko¨hler Berlin Senate Department for the Environment, Transport and Climate Protection, Am Ko¨llnischen Park 3, Berlin 10179, Germany C. Beulker Landeslabor Berlin Brandenburg; Presently Federal Environment Agency, Schichauweg 58, 12307 Berlin, Germany
cyanobacteria no longer dominated; yet 10 years later at TP \ 20–30 lg/l they were below quantifiable levels. 20–25 years after load reduction, the lake was stably mesotrophic, macrophytes had returned down to 6–8 m, and vivianite now forms, binding P insolubly in the sediment. Bottom-up control of phytoplankton through TP proved decisive. Five intermittent years with a higher external P load caused some ‘re-eutrophication’, delaying recovery by 5 years. While some restoration responses required undercutting thresholds, particularly that of phytoplankton biomass to TP, resilience and hysteresis proved irrelevant. Future research needs to focus on the littoral zone, and for predicting time spans for recovery more generally, meta-analyses should address P load reduction in combination with flushing rates.
K. van de Weyer Lanaplan, Lobbericher Str. 5, 41334 Nettetal, Germany T. Hegewald Department Water Quality, State Reservoir Administration of Saxony, Bahnhofstraße 14, 01796 Pirna, Germany M. Hupfer Department of Chemical Analytics and Biogeochemistry, Leibnitz Institute for Freshwater Ecology and Inland Fisheries, Mu¨ggelseedamm 301, 12587 Berlin, Germany
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Hydrobiologia
Keywords Restoration Phosphorus Sediment Plankton Macrophytes Cyanobacteria
Introduction Since Vollenweider (1976) first published the OECD study on eutrophication of inland waters, the basis for focusing eutrophica
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