Swiss lakes reveal secrets
Lakes are important ecosystems. Their secrets have been explored in Switzerland for over 100 years. Nevertheless, there are always surprises. For example, researchers encountered a fish species in Lake Constance that had already been declared extinct.
Lake research always offers new surprises. At an information day organized by Eawag, the Swiss Federal Institute of Aquatic Science and Technology, experts were informed about new findings and trends.
In the large-scale "Projet Lac", Eawag, together with the cantons, the Federal Office for the Environment, the University of Bern and the Natural History Museum of the Bernese Burgergemeinde, as well as other partners, investigated fish diversity in lakes near the Alps from 2010 to 2015.
More than 70 fish species could be detected. Whitefish predominate to the greatest depths, but only in the cleanest lakes. Perch and carp fish dominate the more nutrient-rich lakes today or in the past. Many species from greater water depths, especially whitefish and char, occur only in individual lakes where they have evolved, mostly since the last ice age, by adapting to the extreme habitats. In most of the lakes, however, the former deep-water fish species have been lost. For example, in Lake Zug, which is 197 meters deep, there are hardly any fish left below 30 meters.
Yet not extinct
The "Projet Lac" also brought good news: In Lake Constance, thanks to a targeted search, several specimens of the deep-water char (Salvelinus profundus), which is native only there, were rediscovered. This species, still frequently caught by Lake Constance fishermen until the 1960s, was declared extinct by the IUCN Nature Conservation Union in 2008. The deep-sea char was found at depths of around 80 meters and fed on strudel worms, small crustaceans and mussels. How large the population still is, from which the now found specimens originate, should be investigated in the future.
Overfertilization already 2000 years ago
It is well known that historical information is stored in lake sediments - from pile-dwellers to the occurrence of pollutants and the cesium fallout from Chernobyl. Now, using a 10-meter sediment core from Lake Murten, Eawag researchers have gone one step further. They have reconstructed the land-use history around the lake from the deposited information.
Around 100 BC, at the time when the Romans began to clear large areas of forest around the lake, a rapid change can be seen in the sediments: Within a short time, a lot of soil was washed into the lake and with it many nutrients. Thus, Lake Murten was already overfertilized at one time 2000 years ago. It was not until the fall of the Roman Empire and several periods of significantly colder climate at the beginning of the Middle Ages that the overfertilization subsided again. What effects this phase in Roman times had on the ecology of the lake still needs to be researched in more detail.
Antibiotic resistance more common in ARA discharges.
In sewage treatment plants (WWTPs), fecal germs encounter many other bacteria as well as a cocktail of antibiotic residues and pollutants in relatively warm water. Under these conditions, resistance genes can be transferred to previously antibiotic-sensitive species or to environmental bacteria. Resistant bacteria also enter the environment with the treated wastewater.
A study by Eawag has demonstrated in the sediment of Lake Geneva off Lausanne that resistance genes are clustered in the vicinity of a discharge point. The influence of wastewater can also be demonstrated for other waterbodies. The health risk from this pollution is very low. Nevertheless, the researchers involved advocate that, when expanding wastewater treatment plants with treatment stages against micropollutants, attention should also be paid at the same time to removing as much antibiotic resistance as possible before it enters the environment.
