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This article in JEQ

  1. Vol. 27 No. 3, p. 515-522
     
    Received: May 22, 1997


    * Corresponding author(s): stamm@ito.umnw.ethz.ch
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doi:10.2134/jeq1998.00472425002700030006x

Preferential Transport of Phosphorus in Drained Grassland Soils

  1. C. Stamm *,
  2. H. Flühler,
  3. R. Gächter,
  4. J. Leuenberger and
  5. H. Wunderli
  1. Institute of Terrestrial Ecology, Soil Physics, Grabenstr. 3, 8952 Schlieren, ETHZ, Switzerland;
    Swiss Federal Institute for Environmental Sciences and Technology (EAWAG), Limnological Research Centre, 6047 Kastanienbaum, Switzerland.

Abstract

Abstract

Phosphorus is the limiting factor for primary production in most freshwater ecosystems. In many areas, diffuse P losses from intensively cultivated land cause severe eutrophication of surface waters. We investigated the P export from two drainage systems under intensively used grassland in a catchment of the Swiss Plateau. Flow rate and nutrient concentrations were measured with a high temporal resolution during discharge events. During most flow peaks, P concentrations strongly increased with increasing flow rates. Concentrations of soluble-reactive P (SRP) reached up to 155 µmol L−1. Phosphorus was mainly transported as soluble-reactive and particulate P. Organic P compounds, as well as P associated with colloids between 0.05 and 0.45 µm in effective diameter, were of minor importance. Estimated P loads from the drainage systems were 227 g SRP ha−1 within a period of 2.5 mo at site I and 1290 g ha−1 during 6 mo at site II. Estimation uncertainty was large (±21 and ±36% for the two sites, respectively) due to the weak correlation between discharge and concentration for all data from a given site. Water-extractable P in the soil was concentrated in the uppermost layer of the profiles or, for short periods after spreading of manure, deposited on the vegetation. The discharge-concentration relationship indicated that P was transported through preferential flow paths extending from close to the surface to the drains. Sprinkling experiments with a blue dye confirmed this conclusion. At one site, we observed preferential flow in a downhill direction within the saturated zone.

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