The period between 1955 and 1988 was the time of reconstruction in the destroyed Federal Republic of Germany, marked by booming industrial development and - with some delay -by the rise and spread of ecological awareness and the idea of water conservation. This is the background against which the analysis of water quality and of pollution load trends should be seen.
The study of a long-term load trend presupposes the following requirements:
sufficiently large number of measured data;
reliable, reproducible analytical methods which produce comparable results over long time series; and
hydrological interpretation and evaluation of results.
The continuous efforts to improve analytical methods and the elimination of distorting substances and matrix effects led to the situation that long time series of data are not directly comparable. In some cases, summative analyses (aggregate parameters) have been replaced by newly developed substance-specific methods so that the continuity of records has been broken.
Furthermore, there is a general underestimation of the necessity to consider and evaluate analytical data in a space-time continuum.
However, on the whole, we are able to give a satisfying interpretation of trends for the classical parameters. In the case of the trace substances detected by modem methods, this is possible only for the past two decades and with some reservations.