In recent decades, the water quality in Switzerland has increased thanks to scientific knowledge and political action. However, it is too early to rest on our laurels: micropollutants are increasing, biodiversity is decreasing and climate change is already having an influence on the aquatic environment.
Less than 30 years ago, swimming in the Rhine was not recommended due to the presence of chemical impurities such as phosphorous and nitrate originating from urban, industrial and agricultural areas. Thanks to the expansion of wastewater treatment since 1980, the ban on phosphate in laundry detergents in 1985 and the greening of agriculture since 1990, the nutrient load is slowly but steadily decreasing (see Figure). As a result, the quality of Swiss waters has risen, especially in lakes that were once heavily contaminated. Depending on population, livestock density and the residence time of water in a lake, phosphorous and nitrate concentrations evolve differently. Today, phosphorous is mainly leached out of soils and washed into lakes and rivers by precipitation. It will take decades until this store of phosphorous is depleted. The presence of phosphorous and nitrate in water leads to over-fertilization of the aquatic environment, or eutrophication. This occurs because algae (phytoplankton) have the nutrients they need for practically unlimited growth. However, growth requires oxygen; as the algae grow, the oxygen content of the water decreases until fish and other aquatic life “suffocate”. A study shows that nearly 40% of the native whitefish species in Switzerland have disappeared due to the eutrophication of lakes (Vonlanthen et al. 2012). These species are now found only in deep, less affected mountain lakes such as Lake Thun, Lake Brienz and Lake Lucerne.
The recent increase in micropollutants from drugs and pesticides is worrying. These include hormones and nanoparticles, the fate and behavior of which we know very little about. Also a cause for concern is the elevated nitrate levels in groundwater from the Central Plateau resulting from agricultural practices.
Climate change represents a new, dual challenge for the ecology of aquatic environments (FOEN 2012). In addition to changing flow patterns, both air and water temperatures rose by 0.1 to 1.2 degrees Celsius between 1970 and 2010, depending on the flow regime. In glaciated catchments, the increase and fluctuation range (variability) of the temperature changes are less pronounced (see Figure). However, experts expect an increase in air temperature of three to four degrees by the year 2085. This warming will be especially felt in the summer, when the seasonal redistribution of runoff will result in lower summer runoff in the Central Plateau, Jura and south of the Alps. Together, generally warmer water and lower water levels in the summer will cause local water bodies to warm even more, with consequences for aquatic life and water users. Current warming has already led trout populations to retreat to elevations 100 to 200 meters higher than their traditional ranges (Hari et al. 2006). Lower, warmer discharge flows also reduce the oxygen concentration in lakes and rivers and strongly influence the spread of fish diseases such as proliferative kidney disease (PKD).
Urban expansion and the intensification of agriculture and flood protection measures strongly increase the pressure on rivers. A quarter of Switzerland’s watercourses are either channeled or diverted through culverts, as shown in the Figure. Human intervention has reduced the ecological structural diversity of watercourses, thereby also reducing biodiversity (Ewald and Klaus, 2010). By “structural diversity”, experts refer to a varied stream- or riverbed with gravel and sand bars, places of both fast and slow flowing water, zones with different water depths, fallen trees and networks of banks and floodplains. These different habitats in and around the water are important for a high level of biodiversity. Structural diversity is found especially in flat areas where rivers can meander freely and naturally.
The federal government has reconsidered the channeling of rivers, especially after the floods of 1999, 2005 and 2007. To avoid similar incidents in the future (the flood of 2005 was the most financially damaging incident in the last 100 years), a new strategy is needed. Thanks to restoration, rivers get more space, which helps slow floodwaters and prevent rivers from breaching their banks. At the same time, flow spaces are ecologically enhanced and become more attractive as recreational areas, as is the case for the Thur, Birs, Linth and Brenno rivers.