Submitted to: American Water Resources Association Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/15/2004
Publication Date: 6/28/2004
Citation: Angier, J., McCarty, G., Rice, C., Bialek, K. 2004. Improving riparian zone function by identifying critical areas with limited mitigation capacity. Proceedings of the Riparian Ecosystems and Buffers: Multi-scale Structure, Function and Management, American Water Resources Association, June 28-30, 2004, Olympic Valley, California. p. 1-6. 2004 CDROM. Interpretive Summary: Nutrient and pesticide export from agricultural fields has been implicated in 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 potential pollutants. 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 remediation 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 aid in designing regulations to enhance the mitigation potential of riparian corridors.
Technical Abstract: First-order riparian buffers are often considered the best line of defense in mitigating agricultural pollution, but the capacity for contaminant remediation can vary spatially and temporally within a single ecosystem. Research conducted at a small watershed in the mid-Atlantic coastal plain of Maryland indicated that certain areas in the riparian zone consistently contributed disproportionately to total exported stream contaminant loads. Source areas of groundwater-contributed agrochemicals were relatively small, focused, and stable. One area of the riparian floodplain, a zone of enhanced groundwater exfiltration to the surface, accounted for ~35% of total annual exported stream nitrate but comprised 0.06% of the riparian zone. Pesticide metabolites that were transported through groundwater also tended to surface in these foci of groundwater exfiltration. Areas such as these ("critical areas") limit the mitigation capacity of the entire ecosystem. Preferential subsurface flow appeared to be responsible for determining where these areas occurred. Identifying critical areas is necessary to assess the impact of agrochemicals on the environment. Current regulations and design specifications that assume uniform mitigation capacity within a riparian zone are not optimal; reevaluating riparian buffers in terms of critical and non-critical areas should allow more resources to be allocated for limiting the contamination potential from critical areas and thus improve overall riparian zone mitigation capability.