Spatio-temporal distribution of organic and inorganic pollutants from Lake Geneva (Switzerland) reveals strong interacting effects of sewage treatment plant and eutrophication on microbial abundance

Abstract

a b s t r a c tVariation with depth and time of organic matter (carbon, nitrogen, phosphorus), inorganic pollutant (mercury), as well as bacterial abundance and activity, were investigated for the first time in sediment profiles of different parts of Lake Geneva (Switzerland) over the last decades. The highest organic contents (about 32%), mercury concentration (27 mg kg À1 ), bacterial abundance (in order of 9 Â 10 9 cell g À1 dry sediment), and bacterial activity (1299 Relative Light Units (RLU)) were found in the highly polluted sediments contaminated by the waste water treatment plant (WWTP) discharge, which deposited during the period of cultural eutrophication. Such data, which contrast with the other sampled sites from deeper and more remote parts of the lake, prove that the organic matter and nutrients released from the municipal WWTP have considerable effects on bacterial abundance and activities in freshwater sediments. In fact, the relatively unpolluted deepwater sites and the coastal polluted site show large synchronous increases in bacterial densities linked to the anoxic conditions in the 1970s (lake eutrophication caused by external nutrient input) that subsequently increased the nutrient loading fluxes. These results show that the microbial activities response to natural or human-induced changing limnological conditions (e.g., nutrient supply, oxygen availability, redox conditions) constitutes a threat to the security of water resources, which in turn poses concerns for the world's freshwater resources in the context of global warming and the degradation of water quality (oxygen depletion in the bottom water due to reduced deep waters mixing). Moreover, the accumulation of inorganic pollutants such as high mercury (methyl-mercury) concentration may represent a significant source of toxicity for sediment dwelling organisms.

Characterization of fecal indicator bacteria in sediments cores from the largest freshwater lake of Western Europe (Lake Geneva, Switzerland)

“…Several studies have been performed to assess the presence and distribution of organic and inorganic pollutants in the sediments of Vidy Bay (Poté et al, 2008;Thevenon et al, 2011b), as well as the distribution, persistence and activities of bacteria in the bay (Haller et al, 2009 a, b;Thevenon et al, 2011a). The former results confirmed the effects of WWTP effluent water on the contamination of sediment of the bay and the effects of eutrophication on the bacteria distribution and activities.…”

“…2), which may be explained by the high organic matter preservation in the sediments at that time. It has been further demonstrated that the vertical distribution of bacterial abundance in the sediments of Lake Geneva highly increased following the eutrophication that affected Lake Geneva in the 1970s and early 1980s (Thevenon et al, 2011a). The accumulation and persistence of FIB in the upper part of core V4 may be explained by the continuous contamination of the sediments by the WWTP effluent water that is highly enriched in organic compounds.…”

“…The inferred age of the sediment samples allows to assess the effect of WWPT effluent water on time distribution of E. coli and ENT in proximity points and also to identify the processes (such as accumulation of organic matter and lake eutrophication) that influenced the spatiotemporal variability of FIB in lake sediments (Thevenon et al, 2011a).…”

“…synchronously with the abrupt rise in nutrient content (Fig. 2) that highly favored bacterial activity in Lake Geneva sediments (Thevenon et al, 2011a) and the dissemination of antibiotic resistant bacteria/genes in the Vidy Bay (Thevenon et al, in press). …”

Local to regional scale industrial heavy metal pollution recorded in sediments of large freshwater lakes in central Europe (lakes Geneva and Lucerne) over the last centuries

“…This site was previously investigated to evaluate the impact of the discharge of municipal and industrial waste sediments from the WWTP. High concentrations of heavy metals (Monna et al, 1999;Loizeau et al, 2004), high microbial activities (Poté et al, 2008;Thevenon et al, 2011a), and the spreading of pharmaceutical and hormonal micropollutants (Perazzolo et al, 2010) occurred in the sediment.…”