An ecohydrological framework for water yield changes of forested catchments due to forest decline and soil acidification

Abstract

The effect of forest decline on water resources is not well described, for there have been no long‐term measurements on catchments with declining forests. The precipitation/runoff relationship of the declining forests of the Eyach catchment in the Northern Black Forest/Federal Republic of Germany is analyzed. The uninhabited catchment is subdivided into four subcatchments (7, 10, 30, 52 km2) and is totally covered with coniferous forest, mostly Norway spruce. Long‐term monitoring from 1973 to 1986 indicates a significant increase in water yield and the runoff coefficient for the growing season, although there has been no extensive cutting in the catchment. An “ecohydrological systems model” was developed by the incorporation of field data and plant physiological processes to describe the increase in water yield. Field data include hydrological, hydrogeological, geological, soil‐physical, soil‐chemical, water‐chemical, air‐chemical, pollutant deposition, forest inventory, and forest decline field measurements from the Eyach catchment and comparable neighboring regions. The model indicates that the observed increase in water yield is likely to be caused by a reduction of forest transpiration. This change in water yield is linked to forest decline and soil acidification caused by anthropogenic sources of air pollution.