INFLUENCE OF CATCHMENT QUALITY AND ALTITUDE ON THE WATER AND SEDIMENTCOMPOSITION OF 68 SMALL LAKES IN CENTRAL-EUROPE

68 lakes (63 Swiss, 2 French and 3 Italian) located in an altitudinal range between 334 and 2339 m spanning a wide range of land-use have be en investigated. The aim of the study was to discuss influences of geo graphic location, vegetation and land-use in the catchment area on the water and sediment chemistry of small lakes. Detailed quantitative de scription of land-use, vegetation, and climate in the watershed of all lakes was established. Surface and bottom water samples collected fro m each lake were analyzed for major ions and nutrients. Correlations w ere interpreted using linear regression analysis. Chemical parameters of water and sediment reflect the characteristics of the catchment are as. All lakes were alkaline since they were situated on calcareous bed rock. Concentrations of nitrogen and phosphorus strongly increase with increasing agricultural land-use. Na and K, however, are positively c orrelated with the amount of urbanization within the catchment area. T hese elements as well as dissolved organic carbon (DOC), Mg, Ca, and a lkalinity, increase when the catchment is urbanized or used for agricu lture. Total nitrogen and organic carbon in the sediments decrease dis tinctly if large parts of the catchment consist of bare land. No corre lations between sediment composition and maximum water depth or altitu de of the lakes were found. Striking differences in the water composit ions of lakes above and below approximately 700 m of altitude were obs erved. Concentrations of total nitrogen and nitrate, total phosphorus, DOG, Na, K, Mg, Ca, and alkalinity are distinctly higher in most fake s below 700 m than above, and the pH of the bottom waters of these lak es is generally lower. Estimates of total nitrogen concentrations, eve n in remote areas, indicate that precipitation is responsible for incr eased background concentrations. At lower altitudes nitrogen concentra tions in lakes is explained by the nitrogen loaded rain from urban are as deposited on the catchment, and with high percentages of agricultur al land-use in the watershed.