IMPACT OF CONCENTRATED FLOW PATHWAYS ON THE MOVEMENT OF PESTICIDES THROUGH AGRICULTURAL FIELDS
Open Access
- Author:
- Chandler, Joseph
- Graduate Program:
- Biorenewable Systems
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 09, 2019
- Committee Members:
- Heather Gall, Thesis Advisor/Co-Advisor
Peter J A Kleinman, Committee Member
Herschel Adams Elliott, Committee Member - Keywords:
- Pesticides
Concentrated Flow Pathways
Metolachlor
Soil Residues
Quechers
Atrazine
Imdacloprid
Riparian Buffers
Erosion Rills - Abstract:
- Riparian buffers are an important component of watershed management strategies aimed at improving water quality. These buffers are installed as best management practices (BMPs) to reduce runoff pollution from agricultural fields by diffusing surface runoff and allowing the water to percolate through the soil. They are well-documented to effectively mitigate nutrients and pesticides in agricultural runoff under ideal conditions. 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, limiting water quality benefits. To better understand the occurrence and potential effects of the presence of CFPs on the transport of pesticides from agricultural fields to nearby streams, soil samples were collected within CFPs and in adjacent areas outside of the CFPs in agricultural fields in Klingerstown, Pennsylvania. A total of nine sites representing various agricultural land uses, with two hay fields, two pasture fields and five cropland were studied. Soil samples were collected at a 0-2 cm depth to characterize pesticide concentrations in each of four categories of transport: CFPs within the field; non concentrated areas within the field; non concentrated areas in the associated riparian buffer zone (if present at the site); and, CFPs within the buffer. Samples were extracted using the QuEChERS (Quick, Easy, Cheap, Safe, Effective, Rugged, and Safe) solid phase extraction method for three pesticides of interest: atrazine, metolachlor, and imidacloprid, then analyzed using LC-MS. Concentrations of each of the analytes of interest in soil were compared within each site to understand differences within and outside of CFPs. This analysis showed that soils with highest concentrations of pesticides varied as a function of land use. Overall, the highest concentrations of atrazine, metolachlor, and imidacloprid in soil were found in one cropped study site: 3.4 ug/kg, 127 ug/kg, and 2085 ug/kg respectively. The lowest concentrations were found in the pasture and hay fields and were present in the samples below analytical method detection limits. The results of this study provided insights into the potential effects that CFPs may have on field-scale pesticide fate and transport, with two patterns emerging as dominant. Concentrations were found to either be mitigated or enhanced in CFPs of the field relative to the upslope non-concentrated flow areas of the field, with concentrations either decreasing or increasing along flow paths from the field to the stream. The sites that generally fell within the first pattern were cropland fields that have historically received all three pesticides as inputs. For those fields, the highest concentrations of each pesticide were generally found in the non-concentrated flow areas in the field itself, with concentrations lower in the CFPs in the field and lowest in the non-concentrated flow areas in te buffer. These results suggest that as the pesticides are transported across the field, they are mitigated prior to reaching the stream. In contrast, for the pasture and hay field sites, concentrations were generally were higher in the samples collected from the CFPs of the field locations than the non-concentrated flow areas of the field locations. This shift in trends demonstrated the impact of pesticide usage in upgradient cropland fields. Overall, the pesticide concentrations were consistently higher in the row cropland than the pasture and hay fields, and the patterns were generally consistent with land management (i.e., pesticide application history). For example, imidacloprid is often introduced to agricultural fields as a coating on corn and soybean seeds. It is not directly introduced into pasture and hay fields unless an imidacloprid-containing pesticide is applied by the farmer. The results of this study found that imidacloprid was nearly always absent from non-concentrated flow areas of the field samples collected in the pasture and hay fields, but that it was present in some of the CFPs of the fields. In these cases, the CFPs of the field were a result of CFPs starting in the upgradient cropland that contained imidacloprid. Therefore, the concentrations increased rather than decreased in the CFPs, suggesting that the presence of CFPs in these cases facilitates the transport of imidacloprid to the nearby streams. The results of this study highlight the importance of the underlying factors that caused the CFP to develop in determining which of the roles the CFP will play in pesticide transport (i.e., mitigation or enhancement). The majority of the CFPs identified in the study area appeared to be either erosional or groundwater driven. Erosional channels were likely caused from different factors, including biological (e.g., cattle crossings), anthropogenic (e.g., tractor usage) and topographical (e.g., swales). Many of the CFPs documented as part of this study appeared to have developed due to the presence of springs, with frequent movement of groundwater that originated from upgradient locations through the CFPs. In these cases, CFPs likely facilitated transport of pesticides that had not been applied in the adjacent field, but rather had been applied at upgradient fields and had leached into groundwater. For CFPs that were driven by biological and anthropogenic factors, pesticide concentrations decreased along the flow pathway, suggesting that pesticide concentrations were mitigated along the flow path as runoff traveled to a nearby stream. Overall, this study demonstrated that the role of CFPs in off-site pesticide loss is associated with a variety of factors, including: land use and land management practices, natural landscape factors, and pesticide physiochemical properties. The understanding of how these CFPs affect the transport of pesticides can help guide efforts to minimize pesticide loadings to local waterways. Specifically, CFPs appear to be important to pesticide transport in an agricultural setting and should be mitigated. Additionally, promoting awareness of the persistence of pesticides in agricultural soils could lead to farmers improving land management practices and local environmentalists modifying and utilizing different BMPs to reduce water-borne pesticide transport and improve soil health.