https://hdl.handle.net/10388/13440

Wade, Andrea (2021) Role of Vegetated Buffer Zones for Mitigating Wetland Pesticide Contamination and Protecting Aquatic Invertebrate Communities in Northern Prairie Wetlands, USASK Harvest - Theses and Dissertations, https://hdl.handle.net/10388/13440

Prairie Pothole Region (PPR) wetlands are unique resources that provide a number of ecosystem services. However, the majority of these wetlands have been drained or otherwise degraded due to agricultural activities. Wetlands in the PPR are frequently contaminated by agrochemicals from surrounding agriculture, which has been previously demonstrated to have negative impacts on wetland ecology. Vegetation buffers have been proven to be effective in mitigating pesticide and nutrient contamination of water bodies, but have yet to be fully researched in their efficacy in protecting PPR wetlands. Here I examined how multiple agricultural stressors impact PPR wetland health, and whether natural wetland vegetation or producer-implemented perennial plantings are effective buffers, able to mitigate some of the negative effects of agriculture to wetlands. Measurements of pesticides, nutrients, other water quality parameters, in addition to aquatic invertebrate community endpoints were used to comprehensively evaluate the health of PPR wetlands. Pesticide contamination was widespread, with 59 of the 60 wetlands sampled in 2018 and 2019 containing one or more pesticides in a single growing season. Natural wetland vegetation and the degree of its disturbance from agricultural activities did not have a significant effect on pesticide concentrations in wetlands, although this disturbance did influence the aquatic invertebrate community. Wider and less disturbed wetland vegetation zones were associated with greater macroinvertebrate richness (p = 0.031) and greater abundance of Odonata (p = 0.001). Aspects of water quality were significant predictors of multiple aquatic invertebrate community indices. The occurrence of cyanobacteria blooms as well as increased total nitrogen (TN) were associated with declines in Shannon’s diversity (Cyanobacteria: p = 0.001 and TN: p = 0.016) and Shannon’s Evenness (Cyanobacteria: p = 0.002 and TN: p = 0.001) as well as increases in Berger-Parker Dominance (Cyanobacteria: p = 0.004 and TN: p = 0.001). The Pesticide Toxicity Index (PTIs) calculated for each wetland was associated with changes to the aquatic invertebrate community including a decline in total and relative insect abundance (p = 0.016 and p < 0.001) and an increase in relative snail abundance (p = 0.005). Higher PTIs were also associated with a shift in relative abundance of different functional feeding groups (p = 0.017). This PTI associated shift in taxa and functional feeding groups likely has greater implications for ecosystem function including the many wildlife species that depend on aquatic insects for food. Perennial buffers are considered an important management tool to reduce the negative impacts of agriculture on surface waters. Perennial vegetated buffers recently planted under conservation incentive programs were evaluated for their efficacy in mitigating pesticide and nutrient runoff and protecting wetland health. Wetlands that were fully surrounded by perennial buffers and/or other natural vegetation contained significantly lower concentrations of pesticides (p = 0.001), lower PTIs (p < 0.001), and total phosphorus (p = 0.005). However, the presence of perennial buffers alone did not have a significant effect on pesticide or nutrient detections, and even those wetlands that were fully surrounded by perennial buffers or additional natural vegetation all contained some detectable pesticide contamination. The presence of perennial buffers was significantly associated with greater abundances of macroinvertebrates (p = 0.001), zooplankton (p = 0.005 ), and insects (p = 0.039) which may benefit the many wildlife species that depend on wetland invertebrate productivity for food. This study establishes a framework for using wetland invertebrate communities as an integrative biomonitoring tool for assessing effects of complex agricultural stressors to PPR wetlands. The results from this study demonstrate negative effects of multiple agricultural stressors on wetland health, as measured by changes in the aquatic invertebrate community. Findings here suggest that leaving or planting wetland vegetation around PPR wetlands could increase community richness and abundance of beneficial insects, but is not sufficient for protecting wetlands from pesticide contamination. However, surrounding wetlands with perennial vegetation plantings in addition to other natural vegetation could be an effective method for reducing pesticide and nutrient contamination of wetlands and increasing the abundance and diversity of aquatic invertebrates, which are an important food source for many wildlife species. These findings may help guide producers and land managers motivated to improve wetland health and ecosystem services in prairie agricultural landscapes.

https://harvest.usask.ca/bitstreams/46ee632e-735c-43a5-8765-75d675d6e6f3/download