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United States Department of Agriculture

Agricultural Research Service

Title: Influence of a Riparian Wetland on Nitrate and Herbicides Exported from a Field Applied with Agrochemicals

Authors
item Angier, Jonathan
item McCarty, Gregory
item Rice, Clifford
item Bialek Kalinski, Krystyna

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 11, 2001
Publication Date: N/A

Interpretive Summary: Nutrient and pesticide export from agricultural fields is linked to oxygen depletion in rivers, lakes, and coastal oceans, leading to large-scale destruction of aquatic life, outbreaks of water-borne bacteria (such as Pfisteria piscida), and contamination of drinking water supplies. A need for practical and economical solutions to the problem of excess agrochemicals currently exists. Riparian zones (vegetated stream corridors) are considered natural sites for mitigation of these substances. This study is part of a broader project that includes assessing the overall function of a riparian zone. The contaminant-removing capabilities of the system are highly variable, and local differences are largely related to groundwater delivery patterns. The overall mitigative capacity of a riparian system appears to be more closely related to groundwater and surface water behavior than to total riparian zone width, which is the currently accepted regulatory standard. Results from this study should ai in designing regulations to enhance the mitigation potential of riparian corridors.

Technical Abstract: Agrochemicals are a major source of non-point pollution. Forested corridors along stream channels (riparian zones) are thought to be potential sites for removal of agricultural contaminants from ground and surface waters. First-order riparian wetlands are reputed to be especially effective at groundwater remediation. The study site is a fairly typical (for eastern Maryland) small, 1st-order stream in an agricultural watershed. Preferential flow supplies most of the stream water within the riparian headwater wetland. This upstream area also contains the highest average stream N and pesticide loads in the entire 1st-order riparian system. Zones of active groundwater emergence onto the surface display high concentrations of nitrate throughout the soil profile and in the exfiltrating water, while inactive areas (where there is no visible upwelling) show rapid attenuation of nitrate with decreasing depths. Atrazine degradation products appear to penetrate more readily through the most active upwelling zones, and there is a correlation between zones of high nitrate and high atrazine metabolite levels. Deethylatrazine/atrazine ratios suggest that stream flow is dominated by groundwater, and that much of the groundwater may have reached the stream via preferential flow. Remediative processes appear to be very complex, heterogeneous, and variable in these systems. Additional research is needed before effective formulation and application of riparian zone initiatives and guidelines can be accomplished.

Last Modified: 11/27/2014
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