LITTORAL-ZONE - GIS OF LAKE-CONSTANCE - A USEFUL TOOL IN LAKE MONITORING AND AUTECOLOGICAL STUDIES WITH SUBMERSED MACROPHYTES

In 1993, the submersed vegetation of the whole littoral zone of Lake C onstance was mapped by boat on the basis of aerial photographs. The su rvey was the third of its kind after 1967 and 1978, including a period of fast eutrophication in the 1960s and 1970s (mainly caused by incre asing phosphate concentrations) and a subsequent period of decreasing trophy, due to the international efforts of the countries and states i n the catchment area in eliminating phosphate from waste water. The ch ange in distribution of most aquatic macrophytes shows a high relation to the changes in trophic status of the lake. The oligotraphentic spe cies Cham contraria Kutzing decreased in the 1960s and 1970s and incre ased in the 1980s and 1990s, the eutraphentic species Zannichellia pal ustris L., a very rare species before the 1970s, increased to one of t he most dominant species until the late 1970s, but decreased in the 19 80s and was rarely found in 1993. The use of GIS for data storage and analyses enabled to plot geographically referenced maps of single spec ies distribution areas, to analyse changes of distribution area of spe cies based on data from the whole littoral zone of the lake and to cal culate summarising indices like a macrophyte index of nutrient load in the littoral zone. GIS-based analyses of whole lake above ground biom ass and depth niches of selected species for the mappings of 1978 and 1993 show, that the difference in aboveground biomass of Potamogeton p ectinatus L. is small, but distribution area and depth distribution ar e wider, whereas density of stands is lower in 1993. Potamogeton perfo liatus L. in 1993 has a higher aboveground biomass, a wider distributi on area and depth distribution and a deeper depth optimum than in 1978 . (C) 1997 Elsevier Science B.V.