Effects of oligotrophication on primary production in peri‐alpine lakes

Abstract

[1] During the second half of the 20th 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 reoligotrophication in many freshwater lakes. To understand and assess the effects of reoligotrophication on primary productivity, we analyzed 28 years of 14 C 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 14 C 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.

Application of remote sensing for the optimization of in-situ sampling for monitoring of phytoplankton abundance in a large lake

“…In fact, although we have found an overall negative trend in phytoplankton concentration at the surface, Lake Geneva shows a positive CHL f development in depths below 10 m (Tadonléké et al, , data until 2005, due to a deepening of phytoplankton growth (Rimet, 2013). This occurs as a response to the modification of the vertical profile of phosphorus concentration and light attenuation during the course of reoligotrophication (Anneville and Leboulanger, 2001;Finger et al, 2013). Such dynamics can only be determined by in-situ measurements.…”

“…However, from an ecological point of view, the best results are obtained with a high sampling frequency. Finger et al (2013) state that model-based integration of measured monthly carbon assimilation provides significant and reliable annual production estimates. Chlorophyll peak detection, however, as shown in this study, seems to need a much narrower temporal sampling frequency.…”

A century of human‐driven changes in the carbon dioxide concentration of lakes

“…The concentration of TP was found to be the major factor controlling summer concentrations of CO 2aq in these lakes, over the last century. While valid in these P‐limited lakes [ Finger et al ., ] with long water residence time, it might not be true for lakes with shorter flushing rates, for which TP loads were shown to covary with DIC [ Maberly et al ., ] or DOC [ Kortelainen et al ., ] inputs from their watersheds. Consistently, the TP concentration in the Rhone river in 1975–2011, the main tributary of Lake Geneva, was not related to its concentration of CO 2 ( R 2 = 0.01; p = 0.25 on linear and R 2 = 0.06; p = 0.30 on cubic fit) nor DOC ( R 2 < 0.01; p = 0.27).…”

Warming and oligotrophication cause shifts in freshwater phytoplankton communities

“…This has, for example, been well studied in Lake Biwa, Japan, for which both biotic and abiotic variables have been tracked over 32 years, showing an increase in nutrient loading in the 1960s and 1970s, followed by a decline during the 1980s, when management practices showed effect (Hsieh et al, 2010;Tsai et al, 2014). High nutrient concentrations are often characterized by high biomass production by few dominant species (Borge et al, 2004), whereas re-oligotrophication increases species richness and community evenness (Pomati et al, 2012) coupled with a decrease in autotrophic productivity or standing stocks (Finger, Wuest, & Bossard, 2013;Verbeek et al, 2018).…”