Role of concentrated flow pathways on the movement of pesticides through agricultural fields and riparian buffer zones

Riparian buffers are an important component of watershed management strategies aimed at improving surface water quality. Under ideal conditions, they are well-documented to effectively mitigate nutrients and pesticides in agricultural runoff. However, previous studies have shown that the performance of vegetated buffers can be undermined by the development of concentrated flow pathways (CFPs) that bypass the vegetation, thereby limiting water quality benefits. To understand the occurrence and potential effects of CFPs on pesticide transport from agricultural fields to nearby streams, soil samples (0-2 cm depth) were collected along surface runoff pathways from the field to the stream for nine sites in a Long-Term Agroecosystem Research (LTAR) site in the ridge and valley physiographic region of Pennsylvania. At each site, samples were collected in areas where sheet flow was likely occurring and in CFPs to identify the potential for CFPs to act as sources or sinks of pesticides along the flow path. Samples were extracted for three pesticides of interest: atrazine, metolachlor, and imidacloprid. Two dominant patterns emerged, with concentrations found to be either mitigated or enhanced in CFPs based on pesticide application to surrounding land use. Sites in the first category were row-cropped fields that received inputs of all three pesticides. Concentrations were highest in the non-concentrated flow areas in the field, suggesting that as pesticides are transported across the row-cropped fields, they are mitigated prior to reaching the stream. In contrast, sites in the second category included hay fields that had not been treated with any of the pesticides of interest. Concentrations were highest in the CFPs, suggesting that CFPs were bringing pesticides into the hay fields from upgradient row-crop fields. The results of this study highlight the importance of the land management factors and hydrologic connectivity that cause CFPs to serve different functions (mitigation or enhancement) as runoff is conveyed from the field, to a buffer, and ultimately to an adjacent stream. Further, the results highlight the need for design and maintenance solutions addressing the erosion and sediment control issues that commonly undermine agricultural buffer effectiveness.