User:Marissarp/Lake Constance

Limnology
Lake Constance (Bodensee) is a well studied lake bordering Germany, Austria, and Switzerland. The study of Lake Constance dates back as far as the fifteenth and sixteenth centuries. It has served as the site for many limnological, ecological, and zoological studies. The major limnological finds of Lake Constance took place in the 1900s with the introduction of two notable limnological institutions on the Lake.

Thermal Stratification
Lake Constance undergoes stratification in the warm weather months. It is monomictic as the water column overturns completely in the winter. Warmer air temperatures in summer in spring result in an increase in temperatures in the epilimnion but not in the deeper waters of Lake Constance. Therefore, during extremely hot summers, Lake Constance undergoes much stronger stratification.

Effect of Global Warming on Thermal Stratification in Lake Constance
The effect of climate change on deep monomictic lakes with little to no ice cover during the winter. like Lake Constance have been studied immensely in the past few years. Heat uptake in the water is exacerbated by more intense vertical transport and results in a deeper thermocline. This results in a reduction of convective heat loss such as evaporation which in turn results in cooler surface temperatures driven by the downward transport of heat from more intense vertical mixing. This leads to more stored heat in lake waters and requires more heat to be released during the winter in order to remove thermal stratification, meaning the warming of the deep water would lag behind the warming of the epilimnion and atmospheric air temperatures. So henceforth, the effect of global warming would result in larger thermal stratification in deep monomictic lakes and it would be harder for the lake to completely mix in the winter.

Eutrophication
As a result of increased human activity and other anthropogenic factors beginning in the late 1950s, Lake Constance underwent massive eutrophication in the 1960s to 1970s. Industrial sewage and agricultural runoff, resulted in massive excess nutrient inputs into the lake. Runoff and waste water deposits caused levels of phosphorus in the lake to increase nearly eight times the initial amount by the end of the 1970s. The increased level of phosphorus in the lake led to severe algal blooms. This severe increase in phytoplankton resulted in a bottom up effect. The increased phytoplankton led an increase in zooplankton in the lake. As adult and juvenile whitefish have zooplankton utilize Daphnia as their main source of food, the increase in zooplankton led to the accelerated growth of whitefish in the 1970s during eutrophication and a decrease in growth post-1970s with the gradual reoligotrophication of the lake.

Oligotrophication
Starting in the 1980s, an effort to reduce the amount of runoff and wastewater was initiated in conjunction with the "Regulations on Maximum Concentration of Phosphorus in Detergents and Washing Agents Act" in Germany. Treatments of wastewater and sewage in were implemented along with the new law and ultimately lead to decreases in levels of phosphorus and other nutrients. The reduction of excess nutrients and phosphorus eventually lead to the re-oligotrophication of the lake. The depletion of phosphorus led to a decrease in phytoplankton biomass and variability. Oligotrophication is the process of nutrients being depleted in an aquatic system resulting in overall low levels of primary production.

Effect of Oligotrophication on Lake Vegetation
As a result of the re-oligotrophication of Lake Constance, light conditions in the lake have improved significantly. It was also discovered that species richness and abundance of submerged macrophytes was not only affected by changes in water transparency but was stringly correlated to nutrient levels in the water. Macrophytes were found to have rapid responses to changes in levels of phosphorus in Lake Constance. This has consequentially allowed vegetation to spread to deeper areas of the lake as opposed to previous years where vegetation was primarily limited to along the edges of the Lake and channels. The increase in vegetation has led to an increase in flow resistance allowing water levels to rise. Beginning in 2007-2008, a noticeable increase in water level differences between the upper lake basin (Obsersee) and the lower lake basin (Untersee) began which has led to changes in outflows into the Rhine River.

History of the Effects of Lake Productivity on Fish Growth
As Lake Constance has undergone eutrophication and re-oligotrophication, there were significant declines in many species of fish such as bream, burbot, chub, and ruffe. This was also met with significant increases in a few species of fish such as dace, loach, and perch as the lake shifted from mesotrophic to oligotrophic. significant influence on the growth of local whitefish populations. Whitefish growth accelerated in the 1960s, as the lake underwent massive eutrophication. As the fishing industries rely largely in size-selective fish harvesting techniques, there was a noticeable change in the fish being caught by gillnets. The whitefish's growth in body size resulted in the harvesting of large numbers of immature fish, which prompted lake management to increase the mesh sizing allowed for gillnets to promote the capture of mature whitefish. As new laws were put into action in the 1980s to reduce nutrient inputs into the lake, the lake began to undergo re-oiligotrophication and the reduction of nutrients in the lake resulted in a severe decline in whitefish growth. Since 2015, whitefish growth has been at a record low and many fishing industries have put stress on lake management to allow for smaller mesh sizes. This has brought some conflict between the fishing industry and lake management as the primary goal of lake management is to protect young immature fish from being harvested at too young of an age.

Limnological Institutions
Lake Constance is home to two major limnological institutions known as Anstalt fϋr Bodenseeforchung (Institute for Lake Constance Research) in Konstanz-Staad and the Institut fϋr Seenforschung und Seenbewirtsschaftung (Institute for Lake Research and Lake Management) in Langenargen. These two institutions celebrated their 100th anniversaries in 2019 and 2020. The founding of these institutions helped contribute largely to the study of Lake Constance and helped expand the field of limnology.