Differences in the Quality of Seepage Water and Runoff Caused by Plant Community and Grazing at an Alpine Site in Hol, Southern Norway

Martinsen, Vegard; Grund, Franz; Kjeve, Marit Ness; de Wit, Heleen A.; Austrheim, Gunnar; Mysterud, Atle; Mulder, Jan

Differences in the Quality of Seepage Water and Runoff Caused by Plant Community and Grazing at an Alpine Site in Hol, Southern Norway

2013

Alpine ecosystems, representing a large proportion of the land area in Europe, are under pressure from changes in climate and land-use. This may also impact the quality of drainage waters. Here, we assess effects of plant communities (snowbed, dwarf shrub heath, and tall herb meadow) on concentrations of dissolved organic carbon and nitrogen (DOC and DON), ammonium (NH₄-N), nitrate (NO₃-N), and phosphorus (tot-P and PO₄-P) in locally derived seepage water in a non-fertilized sub-alpine area of southern Norway. In addition, we investigated effects of two density levels of sheep (no sheep and 80 sheep km⁻²) on infiltration capacity, pore size distribution and concentrations of nutrients and bacteria in surface runoff. Concentrations of NO₃-N (<0.02–0.03 mg l⁻¹) and NH₄-N (<0.02–0.03 mg l⁻¹) were low in seepage waters with no significant differences associated with plant community. Also, concentrations of DOC and DON were low, in particular in snowbeds, probably due to low productivity and small soil carbon pools. Infiltration rates, which were significantly smaller in snowbeds than in tall herb meadow, were further reduced by grazing. In turn, this caused increased runoff of coliform bacteria, whereas no effect of grazing on NH₄-N, NO₃-N and PO₄-P was observed. Grazing may significantly alter biological water quality but is not likely to affect the productivity of surface waters in non-fertilized alpine areas.

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