Chemical composition of first-order forest streams in the upper Black Forest - Variability related to runoff dynamics and soil liming

In two small watersheds in the upper Black Forest (SW Germany) the temporal variation of water quality in relation to runoff dynamics was investigated during the period of 1989 through 1998. In 1990, one of the two watersheds was limed according to forest management practice (4t dolomite ha(-1)). Ep isodic acidification during high-flow conditions is primarily due to the mo bilization of nitrate. Acid buffering and cation composition were related t o the time-variable flow paths in the watershed. The effects of soil liming on water quality were relatively small. Nevertheless, the acid neutralizin g capacity during peak runoff events tended to be slightly improved. Even t hough microbial activity and nitrification were enhanced in the top-soils a s a result of liming, the nitrate concentrations in the stream increased on ly slightly With regard to recent changes in the atmospheric deposi tion pa ttern (distinct decline in S while N endures) in the middle to long term a better availability of N in forests can be expected. As a consequence, ther e is an increasing risk of NO3- leaching after liming. This development sho uld be taken into account when large-scale liming operations in forests are planned in the future.