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Phosphorus concentrations of brook runoff in a Swiss agricultural catchment: longitudinal variability and subsurface drainage impact

RAINER WEISSHAIDINGER1, BERND HEBEL2, PETRA OGERMANN1, PHILIPP SCHNEIDER1, CHRISTIAN KATTERFELD1 & RANDY KOCH1

1 University of Basel, Chair of Physical Geography and Landscape Ecology, Klingelbergstrasse 27,
CH-4056 Basel, Switzerland

rainer.weisshaidinger@unibas.ch

2 Swiss Federal Institute of Technology Zurich, Chair of Forest Engineering, ETH Zentrum HG G21.1,
Rämistrasse 101, CH-8092 Zurich, Switzerland

Abstract Hydrological characteristics and water quality of anthropogenic subsurface drainage and brook runoff were observed in a small agricultural catchment near Basel (NW Switzerland). A two year monitoring programme provided concentration data for soluble Molybdate Reactive Phosphorus (MRP = Dissolved Reactive Phosphorus) for both base flow and storm events. Recurrence frequency and correlation analyses were conducted to evaluate the samples with regard to time–space variability as well as observance of eutrophication limits. Results suggest substantial MRP input into the brook system via subsurface drains, partly originating from private wastewater treatment facilities. Runoff, particularly in upstream brook sections, clearly exceeds eutrophication limits already at MRP concentrations (CMRP) of low recurrence frequency. During non-event periods a decrease in CMRP is obvious from upstream brook sections towards the catchment outlet as a result of dilution as well as hydrobiological and chemical processes.

Key words anthropogenic subsurface drainage; molybdate reactive phosphorus; point and nonpoint sources; recurrence probability; water quality