User:Sophie Bazan/Lake Geneva

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Limnology and Research

Lake Geneva is the largest natural lake in Western Europe^[1] and sourced mainly by the Rhône River, along with multiple other smaller rivers. Most of the water the enters the lake comes from glacial meltwater from nearby mountains, and the lake was originally formed by a glacier as it withdrew, eroding away sediment^[2] during a period called the Würmian deglaciation^[3]. The Rhône glacier withdrew from the area about 12,000 years ago during the late Pleistocene period^[2], which gave the lake its signature crescent shape^[4]. As a result of the former glacial activity, Lake Geneva is incredibly deep, with an average depth of 154.4m, with the deepest point at about 310m^[5]. There has also been some tectonic folding and sedimentation that has occurred in the past which has helped to shape the lake into what we see today^[6]. In addition, there are two main tributaries, Dranse to the south and Venoge to the north. There are 20 native fish species inhabiting the lake, which include true fera, perch, pike, trout, arctic char, carp, and many more^[6]. There are another 10 species which have been introduced to the lake that have established themselves, including crayfish, which were released by accident in the 1980s and have inhabited the lake since then^[6].

Lake Geneva has recently undergone a shift from being in a eutrophic state to a mesotrophic state within the last 40 years. It is thought that these changes relate to increased restoration projects and efforts, which have reduced phosphorus concentrations in the lake. There have been observed seasonal changes in the phytoplankton community as a result, which likely explains the shift away from a eutrophic state. Because the lake supports an array of recreational activities, and supplies water to over 700,000 people^[7], it is important to maintain the water quality of the lake, which is why much of the research that takes place on the lake relates to water quality and bacterial levels^[1]. In addition, there are many questions relating to the effects climate change may have on the lake.

A case study was done on Lake Geneva relating to the phytoplankton, Plankothrix rubescens, and the changes these communities have seen as a result of the recent shift to a mesotrophic state. This species of cyanobacteria is of interest to researchers as it is potentially toxic to humans when there are large blooms. There are also questions about how P. rubescens may evolve in response to climate change in the future. The researchers were questioning whether climate change could potentially favor the development of P. rubescens, and more broadly cyanobacteria, to reverse the mesotrophic shift of the last 40 years and make Lake Geneva eutrophic again. It was found that this hypothesis was supported through their study, so long as phosphorus levels do not drop too low to support the growth and development of the species. It was also suggested that warmer temperatures during the spring may be the element that triggers an increase in cyanobacteria biomass in years when the temperatures are deemed "extremely hot" ^[1].

Pollution

One of the concerns about water quality comes from anthropogenic pollution. Pollutants such as antibiotics, heavy metals, organic compounds, and pesticides attach themselves to sediments in the water, where the contaminants may then either accumulate or be remobilized from the sediments^[7]. In addition, it is estimated that about 55 tons of plastic waste ends up in Lake Geneva annually, which is why the lake is estimated to be as polluted as most of the planet's oceans and the Mediterranean Sea^[8]. Like the chemical pollutants, plastic particles may also be deposited into sediments^[8].These plastics can be ingested by plankton, fish, or birds and disrupt their metabolism. Human pollution inputs to lakes in general are more localized than they are to the oceans, and usually have a higher percentage of floating pollutants and pollutants which reach the shore^[9].

One study examined the effects chemical pollutants such as antibiotics and heavy metals from wastewater may have on different bacterial communities, focusing on Vidy Bay. It was found that limnological conditions changed due to eutrophication in the 1970s because of an increase in nutrients supplied to Lake Geneva as a result of pollution from nearby towns and agriculture. In addition, poor mixing in the hypolimnion allowing bacterial activity to increase in deeper waters. It was also concluded that municipal wastewater treatment plants and the trophic state of the lake have substantial effects on fecal indicator bacteria abundance. If these fecal indicator bacteria are resuspended from the sediments, they may be detrimental to water quality and pose health risks to humans using the water for drinking or recreation, as well as to other organisms using the affected water for drinking or other necessary activities. There were also several markers found indicating that there are bacterial communities present that are developing or have already developed antibiotic resistance. The researchers from this study hope that these conclusions can be used as a reference point for future research on water polluted from wastewater^[7].

It has also been found that pollution may be a factor affecting community structure in microbes. Large groups of Betaproteobacteria, which are related to another group of bacteria called Dechloromonas, which are able to remove chlorine and break down certain contaminants in water, have been found on Vidy Bay, an area with high levels of contamination in its sediments^[10]. In addition, entrapment, confining pollutants to a bay, may allow pollutants to accumulate near the shores of the lake^[11]. Vidy Bay is of interest to several pollution studies occurring on Lake Geneva because it sits at a crucial point where the area receives wastewater and stormwater inputs from Lausanne. It also receives an input of water from the Chamberonne River, which often carries water contaminated by both urban and agricultural pollutants from nearby towns, cities, and farmland. This allows for the Vidy Bay to be studied extensively for the impact the anthropogenic input of chemicals has on water quality, and any changes that can be made in response to remedy any negative effects ^[5].

References