Switzerland’s lakes are not only diverse ecosystems, but also recreation sites, fishing grounds and energy sources. At this year’s Info Day, the tensions between these competing interests were explored. It was concluded that sustainable management calls for an understanding of the complex interactions occurring in lakes – which in turn requires scientific data and appropriate methods of observation. By Andres Jordi
Today, Swiss lakes are subject to a wide variety of demands with regard to resource use and conservation. A scientific approach to lake management should take these diverse needs into account, rather than favouring any particular interests or stakeholders. The prime goal, however, according to Eawag researcher Bernhard Wehrli, must be to ensure that the ecological functioning of lakes – and their status as near-natural habitats – is preserved or restored. Wehrli was one of the speakers at this year’s Eawag Info Day, which – to mark the centenary of the Kastanienbaum hydrobiology laboratory – was held at the Transport Museum in Lucerne. The event, attended by around 250 scientists, water professionals, administration officials and policymakers, focused on new insights and trends in lake research, and their implications for practice (Fig. 1).
Scientific data vital for decision-making
The variety of demands referred to by Wehrli was reflected by the thematic diversity of the presentations: lake ecosystems were considered from a range of perspectives including biodiversity protection, energy production, fishery use and water quality. The presentations highlighted the importance of systematic data collection. Data on the physical, chemical and biological condition of a lake – and how this may change in response to external factors – is indispensable for sustainable management. In the absence of data, decisions cannot be made on a sound scientific basis.
Until recently, as evolutionary biologist Ole Seehausen pointed out, no quantitative data on fish communities, collected by standardized methods, was available for large, deep prealpine waterbodies such as Lake Thun or Lake Walen. Seehausen said: “If biodiversity and habitats are to be preserved or enhanced in a targeted manner, a comprehensive inventory of species is required.” For this reason, in 2010, Eawag –in collaboration with the Federal Office for the Environment and Bern University – launched “Projet Lac”, to collect data for as many lakes as possible. The aim was to document fish diversity, the situation of endemic and threatened species, and important trends for fish stock management.
Projet Lac showed that human activities have had a major impact on prealpine lakes. These ecosystems are now characterized by changes in nutrient levels and oxygen supplies, the loss of endemic species and the spread of exotic species. Altogether, the surveys revealed the presence of more than 70 fish species (Fig. 2): whitefish predominate down to the greatest depths, but only in the cleanest lakes. Perch and carp are the dominant species in lakes which are currently or were formerly eutrophic. Most of the lakes affected by eutrophication in the past have lost their deep-water species. In Lake Zug, for example, which is 197 metres deep, hardly any fish are found below a depth of 30 metres. At the same time, these lakes appear to be particularly rich in exotic shallow and warm-water species. Seehausen concludes: “Biodiversity and ecosystems are thus undergoing a process of homogenization in Swiss lakes.” But Projet Lac also offered some good news: the biologists discovered several specimens of the deep-water char (Salvelinus profundus), endemic to Lake Constance, which had previously been declared extinct.