科研之友
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摘要
In agricultural landscapes, pesticides can be transported by surface or tile-drained waters to aquatic ecosystems. In such situations, artificial wetlands can be placed to receive tile drainage discharge, and be effective pesticide pollution remediation tools. Artificial wetland implementation and design largely depend on land availability and suitability, which is particularly critical in Europe where land is scarce. Wetlands can be configured to either divert and treat a portion of stream discharge (i.e., parallel configuration), or placed to capture all stream discharge (i.e., series configuration) generated by a catchment. A field experiment was conducted at the outlets of two subsurface drained catchments in France to compare the pesticide retention efficiency of these two types of artificial wetlands. The two agricultural catchments were cultivated for similar crops (winter wheat, barley, rapeseed, and sugar beet) on poorly drained tile-drained soils. The Aulnoy artificial wetland was situated in-stream, at the outlet of a 36-ha watershed. It included a deep wetland with a 9000-m(3) water storage capacity. Its volume and surface area to watershed area ratios were 300 m(3) per upstream drained hectare (equivalent to 30 mm runoff storage capacity) and 1.2%, respectively. The Bray wetland was constructed off-stream, in parallel to the main agricultural ditch and associated with an open/close strategy managed by the farmer according to his pesticide applications. This artificial wetland consisted of three vegetated cells in a series with shallow water for a total volume of 330 m(3) corresponding to 7 m(3) ha(-1) (0.7 mm runoff storage capacity) and 0.5% of a 46-ha catchment. Inlet and outlet discharges and pesticide concentrations were continuously monitored to characterize the seasonality of pesticide export and the removal efficiency of the artificial wetlands. Both artificial wetlands showed positive impacts on water quality (54 and 45% reduction for in- and off-stream configurations, respectively), attributable to distinct retention processes. Significant dilution occurred at Aulnoy where pesticide concentrations were frequently below detection levels, making it difficult to discern whether significant degradation or retention took place in the wetland. Conversely, the Bray shallow artificial wetland showed significant pesticide adsorption, desorption and degradation. However, these processes were limited in the Bray wetland due to insufficient retention time. The off-stream constructed wetland appears to be a promising technical solution for reducing land use impact.
- 出版日期2013-7
