Abstract
Characterizing and modeling hydrochemical catchment dynamics is dealing with the challenge of upscaling point measurements to a regional, spatially distribution. Additionally regional spatial dynamics of nonpoint and point sources and their relation to catchment management have to be considdered regarding water qualtiy concerns. Theese two challenges can be met by applying the concept of Chemical Hydrological Response Units (CHRUs) and using GIS-analysis to delinate their spatial distribution. CHRUs can be defined as computational elements having similar hydrochemical dynamics depending on their landuse management and physiographic catchment characteristics. The concept was applied to the mesoscale Broel catchment in Germany (A=216 skm). The landuse pattern of the catchment was mapped in the field, digitized by the aid of a GIS-system and compared to remote sensed data. A project database included analysed water samples and atmospheric deposition samples for dissolv! ed solids, fertilzer application a nd landscape catchment characteristics. Solute chemical balancing within the watershed in relation to the CHRU-concept were than compared to the measured catchment output at the basin outlet. Results showed deviations associated with undetected point sources but also fits during periods with unique hydrological conditions. In summary the concept of CHRUs by using GIS is a powerful and practical method to evaluate the hydrochemical dynamics and the estimation of their environmental hydrochemical changes in a heterogenuous catchment. Therefor it can be used for longterm observation of water quality within rivers. Future research will combine the CHRU-method with a hydrological model like MMS/PRMS and coupling it with the AgNPS and CHRIS model.