Impact of redox and transport processes in a riparian wetland on stream water quality in the Fichtelgebirge region, southern Germany

• Published in: Hydrological processes 2007-01, Vol.21 (1), p.123-132
• Main Authors: Lischeid, G., Kolb, A., Alewell, C., Paul, S.
• Format: Article
• Language: English
• Subjects: denitrification; Earth sciences; Earth, ocean, space; Exact sciences and technology; Freshwater; groundwater; Hydrology. Hydrogeology; mobile fraction; riparian zone; runoff generation; stream water; water quality
• ISSN: 0885-6087; 1099-1085
• DOI: 10.1002/hyp.6227

Biologically mediated redox processes in the riparian zone, like denitrification, can have substantially beneficial impacts on stream water quality. The extent of these effects, however, depends greatly on the hydrological boundary conditions. The impact of hydrological processes on a wetland's nitrogen sink capacity was investigated in a forested riparian fen which is drained by a first‐order perennial stream. Here, we analysed the frequency distributions and time‐series of pH and nitrogen, silica, organic carbon and oxygen concentrations in throughfall, soil solution, groundwater and stream water, and the groundwater levels and stream discharges from a 3‐year period. During baseflow conditions, the stream was fed by discharging shallow, anoxic groundwater and by deep, oxic groundwater. Whereas the latter delivered considerable amounts of nitrogen (∼0·37 mg l−1) to the stream, the former was almost entirely depleted of nitrogen. During stormflow, near‐surface runoff in the upper 30 cm soil layer bypassed the denitrifying zone and added significant amounts to the nitrogen load of the stream. Nitrate‐nitrogen was close to 100% of deep groundwater and stream‐water nitrogen concentration. Stream‐water baseflow concentrations of nitrate, dissolved carbon and silica were about 1·6 mg l−1, 4 mg l−1 and 7·5 mg l−1 respectively, and >3 mg l−1, >10 mg l−1 and