Phosphorus Export from an Agricultural Watershed
- Richard McDowell,
- Andrew Sharpley * and
- Gordon Folmar
Many source and transport factors control P loss from agricultural landscapes; however, little information is available on how these factors are linked at a watershed scale. Thus, we investigated mechanisms controlling P release from soil and stream sediments in relation to storm and baseflow P concentrations at four flumes and in the channel of an agricultural watershed. Baseflow dissolved reactive phosphorus (DRP) concentrations were greater at the watershed outflow (Flume 1; 0.042 mg L−1) than uppermost flume (Flume 4; 0.028 mg L−1). Conversely, DRP concentrations were greater at Flume 4 (0.304 mg L−1) than Flume 1 (0.128 mg L−1) during stormflow. Similar trends in total phosphorus (TP) concentration were also observed. During stormflow, stream P concentrations are controlled by overland flow–generated erosion from areas of the watershed coincident with high soil P. In-channel decreases in P concentration during stormflow were attributed to sediment deposition, resorption of P, and dilution. The increase in baseflow P concentrations downstream was controlled by channel sediments. Phosphorus sorption maximum of Flume 4 sediment (532 mg kg−1) was greater than at the outlet Flume 1 (227 mg kg−1). Indeed, the decrease in P desorption between Flumes 1 and 4 sediment (0.046 to 0.025 mg L−1) was similar to the difference in baseflow DRP between Flumes 1 and 4 (0.042 to 0.028 mg L−1). This study shows that erosion, soil P concentration, and channel sediment P sorption properties influence streamflow DRP and TP. A better understanding of the spatial and temporal distribution of these processes and their connectivity over the landscape will aid targeting remedial practices.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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