Schadstoff-Untersuchungen an datierten Sedimentkernen aus dem Bodensee / Pollution Research on Dated Sediment Cores from Lake Constance

Abstract

The vertical distribution of nitrogen and phosphorus in dated sediments of four sedimentary profiles from the central part of Lake Constance was examined. From about 1900 until now a steady increase of N and P is to be observed. Nitrogen is enriched by a factor of about 5, phosphorus by a factor of about only 2. The N/P-ratio shows a continuous increase since 1900. The explanation for this development is the steady increase of phosphates delivered into the lake since about 1900. Thus, p.ex. the total amount of phosphorus increased between 1930 and 1974 from 274 to 1929 tons per year. Most of the sedimentary nitrogen is incorporated into the organic material, the production of which is clearly bound to the availability of phosphorus in the lake water. Phosphorus is mostly found in an adsorbed position on clay minerals. Between N and P on one hand and certain heavy metals (Cd, Zn) and polycyclic aromatic hydrocarbons on the other hand a positive correlation only can be found as long as the curves for phosphate delivery (responsible for N-and P-concentrations) and coal consumption (responsible for certain heavy metals and polycyclic aromatic hydrocarbons) have a parallel development. The decrease in coal consumption in connection with a very strong increase of phosphate delivery during the past 15 years has ceased the parallel evolution of the different groups of pollutants in the sediments, and also demonstrates, that a causal relationship N and P - heavy metals and polycyclic aromatic hydrocarbons does not exist.