Solute concentrations of overland flow water in a cultivated field: spatial variations, intra- and inter-storm trends
✍ Scribed by Patrick Durand; Sylvie Cros-Cayot; Chantal Gascuel-Odoux; Djilali Heddadj
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 229 KB
- Volume
- 13
- Category
- Article
- ISSN
- 0885-6087
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✦ Synopsis
Major solute concentrations in overland ¯ow water (OFW) were measured in an agricultural ®eld of Brittany (western France). Two storm events were monitored in detail to examine the short time-scale processes. During one year, samples were taken at dierent positions on the slope after each storm event to describe the spatial and seasonal variations of OFW chemistry. Although the total dissolved load in OFW is not much higher than in rain water, distinctive features are observed. K , Ca 2 , NH 4 , Cl À and SO 2À 4 are the major solutes. The main origin of the elements (sea salts, exchangeable soil complex or fertilizers) determined most of the variations observed. Spatial variations along the slope are mainly seen for exchangeable cations, while seasonal variations are predominant for sea salts. Rainfall intensity and suspended sediment load induce strong dierences between the two storm events studied in detail. However, the within-storm variations and the seasonal monitoring show that this relationship is complex. Within-storm variations suggest that, in addition to desorption processes, mixing with pre-event water may occur. The lack of a relationship between sediment load and dissolved load is attributed to the high rate of the exchange processes, which has been checked by a simple experiment in vitro. It is concluded that the conditions of the transit of water on the ®eld (velocity, length, status of the surface, crusted or not) may well play a major role in the chemical changes between rain water and OFW. The results suggest that vegetated buer strips designed to reduce the sediment load only, and not the amount of overland ¯ow, will have little eect on the transfer of dissolved pollutants to the watercourses.