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

Authors: CHANDLER, JOSEPH - Pennsylvania State University; PREISENDANZ, HEATHER - Pennsylvania State University; Veith, Tameria - Tamie; Elkin, Kyle; ELLIOTT, HERSCHEL - Pennsylvania State University; WATSON, JOHN - Pennsylvania State University; Kleinman, Peter

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2021
Publication Date: 2/25/2021
Citation: Chandler, J.W., Preisendanz, H.E., Veith, T.L., Elkin, K.R., Elliott, H.A., Watson, J.E., Kleinman, P.J. 2021. Role of concentrated flow pathways on the movement of pesticides through agricultural fields and riparian buffer zones. Transactions of the ASABE. 64(3):975-986. https://doi.org/10.13031/trans.14221.
DOI: https://doi.org/10.13031/trans.14221

Interpretive Summary: As surface runoff moves across a field, it can converge and form concentrated flow pathways that tend to increase erosion and accelerate transport of contaminants from the field to nearby streams. Riparian buffers intercept this runoff and generally mitigate the contaminants present in the runoff. However, the development of concentrated flow pathways in riparian buffers can reduce the functionality of the buffer, enabling the contaminants to bypass the buffer. We sought to understand the role that concentrated flow pathways have on the transport of three pesticides: atrazine, metolachlor, and imidacloprid as they are transported along flow paths from field to streams. At each field site (4 row-cropped fields, 2 pasture field, and 2 hay fields), soil samples were collected to a depth of 2 cm inside the concentrated flow pathway just before it entered the buffer or the stream. Samples in the areas of the field where sheet flow was expected (i.e., areas that were not CFPs) were sampled using a zig-zag pattern to collect a representative sample of the field. Samples were composited and labeled either as CPFs or areas that experienced overland flow (OLF) that was likely occurring as sheet flow. All three pesticides were used in row-cropped fields; however, none were applied in the pasture and hay fields. Pesticides in the row-cropped fields were highest in the areas of the field outside of the concentrated flow pathways and decreased along the flow pathway towards the stream. In the pasture and hay fields, pesticide concentrations were generally higher in the concentrated flow pathways compared to areas of the field that experienced sheet flow, suggesting that the concentrated flow pathways are facilitating transport of pesticides from upgradient fields. Additionally, the findings suggest that concentrated flow pathways may undermine the ability of buffers to reduce pesticides in surface runoff. Investigation of the factors that cause sheet flow to converge and cause concentrated flow pathways could inform adoption of land practices to reduce the likelihood that flow convergence occurs. Overall, this research found that concentrated flow pathways do affect the transport of pesticides in agricultural settings, but the specific roles that they play can be site specific and depend on both natural and human factors.

Technical Abstract: Riparian buffers are an important component of watershed management strategies. Under ideal conditions, riparian buffers effectively mitigate nutrients and pesticides in agricultural runoff. However, the performance of buffers can be undermined by the development of concentrated flow pathways (CFPs) that effectively bypass soils and vegetation. 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 to occur as well as in CFPs to differentiate between possible sources and sinks of pesticides along the flow path. Samples were extracted for three pesticides of interest: atrazine, metolachlor, and imidacloprid. Two dominant patterns emerged. Pesticide concentrations were either diminished or enhanced in CFPs based on likely sources of pesticides. Pesticide concentrations in CFP soil samples from row-cropped fields were lower than in areas of probable sheet flow. Elevated pesticide concentrations from non-concentrated flow areas suggest that as pesticides are transported across the row-cropped fields, they are mitigated prior to reaching the stream. In contrast, sites such as hay field had higher pesticide concentrations in CFPs. These sites likely had not been treated with any of the pesticides of interest, suggesting that CFPs were a conduit of pesticides through the hay fields from upgradient row-crop fields. This study highlights 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.