History and prospect of catchment biogeochemistry: a european perspective based on acid rain

Hydrochemical monitoring of catchments provided a philosophical framework as well as hard data to understand and quantify the linked biological and abiotic processes that explain how atmospheric deposition of S and N changed soils and waters in nonagricultural areas across Europe. Initially, as a tool to collect relevant data in a representative and systematic way, hydrochemical monitoring provided evidence for widespread surface water acidification related to atmospheric pollution and long-range air transport. Recognizing the strong effect biota can have on their chemical environment, in the context of catchment biogeochemistry, these data provided new insights into individual processes of soil and water acidification and helped to quantify the relative importance of natural and anthropogenic sources of H+. Furthermore, combined with large-scale ecosystem manipulation and modeling, catchment biogeochemistry offered an effective tool to investigate risks of acidification and of nitrogen saturation of soils and water