Effects of oligotrophication on primary production in peri‐alpine lakes

During the second half of the 20^th century untreated sewage released from housing and industry into natural waters led to a degradation of many freshwater lakes and reservoirs worldwide. In order to mitigate eutrophication, wastewater treatment plants - including Fe-induced phosphorus precipitation - were implemented throughout the industrialized world, leading to re-oligotrophication in many freshwater lakes. To understand and assess the effects of re-oligotrophication on primary productivity, we analysed 28 years of ¹⁴C assimilation rates, as well as other biotic and abiotic parameters, such as global radiation, nutrient concentrations and plankton densities in peri-alpine Lake Lucerne, Switzerland. Using a simple productivity-light relationship, we estimated continuous primary production and discussed the relation between productivity and observed limnological parameters. Furthermore, we assessed the uncertainty of our modeling approach based on monthly ¹⁴C assimilation measurements using Monte Carlo simulations. Results confirm that monthly sampling of productivity is sufficient for identifying long-term trends in productivity and that conservation management has successfully improved water quality during the past three decades via reducing nutrients and primary production in the lake. However, even though nutrient concentrations have remained constant in recent years, annual primary production varies significantly from year to year. Despite the fact that nutrient concentrations have decreased by more than an order of magnitude, primary production has decreased only slightly. These results suggest that primary production correlates well to nutrients availability but meteorological conditions lead to interannual variability regardless of the trophic status of the lake. Accordingly, in oligotrophic freshwaters meteorological forcing may reduce productivity impacting on the entire food chain of the ecosystem.

16 November 2013

We presented the study at the Swiss Geoscience meeting in Lausanne

http://www.geoscience-meeting.scnatweb.ch/sgm2013/

17 September 2013

Swiss federal councillor Doris Leuthard congratulates us and expresses her gratitude for this work.

5 August 2013

The study is published in WRR:

http://onlinelibrary.wiley.com/doi/10.1002/wrcr.20355/abstract

27 June 2012

We presented the study at the SIL-Austria meeting:

http://www.kis.ktn.gv.at/259124_DE-SIL_SILMAS-Conference_Contributions