Browsing by Subject "Herbicide"
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Item Biochar as a sorbent for naturally occurring and synthetic agricultural chemicals(2018-06) Hall, KathleenThe idea of adding biochar to soil to sequester carbon and improve fertility has soared in popularity over the past few decades; however, a strong scientific understanding of this material and its environmental effects is still lacking. This body of work explores biochar's interactions with chemicals, both naturally occurring (i.e., allelochemicals) and anthropogenically applied (i.e., herbicides), and sheds light on the mechanisms involved and our ability to predict and optimize its sorptive behavior. The first chapter investigates how the feedstock material from which a biochar is produced impacts its sorptive behavior toward allelochemicals. Mixing different feedstocks, such as pine chips and poultry litter, is thought to be a way to create “designer biochars” that combine the beneficial properties of each feedstock. However, results from this study revealed that mixing feedstock materials did not have predictable effects on organic compound sorption. The second chapter begins to evaluate biochar-chemical interactions in soil to better understand realistic applications of biochar as a sorbent. Here, the leaching potentials of six different herbicides were assessed in vulnerable Hawaiian soils, and biochar was tested as a tool to reduce the transport of the most mobile herbicide, aminocyclopyrachlor. It was found that none of the four biochar amendments tested significantly altered the leaching potential of aminocyclopyrachlor in these soils based on fate and transport models. In the third chapter, the focus shifts more towards understanding the mechanisms of biochar-herbicide interactions. Here we specifically looked at glyphosate, the world’s most widely used herbicide, and found that biochar macroporosity and specific surface functionality influenced glyphosate sorption. Additionally, pre-pyrolysis addition of Fe and Cu had no significant effect on sorption. Results from this work also demonstrated the reversibility of glyphosate sorption on biochar in the presence of phosphate, suggesting similar binding mechanisms and potential interferences from phosphate fertilizers. The fourth chapter continues to investigate the sorption mechanisms responsible for the observed biochar-herbicide interactions and simultaneously assesses our ability to optimize biochars for sorption through activation treatments. It was found that activation of a low-temperature biochar by hydrogen peroxide can improve the removal of organic acid herbicides from aqueous solution, but was of little value in optimizing the removal of non-ionizable herbicides. The improved removal efficiency was attributed to pH effects and charge-based interactions with biochar. Collectively, the research presented in this dissertation highlights the variability of biochar's sorptive behavior and illustrates the challenges in predicting this behavior, particularly when feedstocks are combined. While the sorptive applications in soil initially appear limited, there is potential to improve the sorption capacity of these materials through activation, and more targeted improvements will be possible once sorption mechanisms are better understood.Item Evaluation of lake-wide, early-season herbicide treatments for controlling invasive curlyleaf pondweed (Potamogeton crispus) in Minnesota Lakes.(2010-05) Johnson, James AaronSubmersed aquatic plants play an important role in freshwater systems, affecting nutrient dynamics, trophic interactions, biological assemblages, and fish productivity. However, waters infested with non-native invasive aquatic plants often experience severe impairment of ecological and recreational quality due to excessive plant growth. Curlyleaf pondweed (Potamogeton crispus L.), one such exotic submersed aquatic plant, has become a widespread nuisance in temperate regions of North America. Curlyleaf’s early-season growth, propensity to form dense surface mats, and ability to out-compete native aquatic plants allow it to degrade the ecological and recreational quality of lakes. Consequently, there has been a great deal of interest in adopting lake-wide management strategies that can reduce the negative impacts of curlyleaf and provide some degree of long-term control. We collaborated with the Minnesota Department of Natural Resources in 2006, 2007, and 2008 to evaluate lake-wide, early-season herbicide treatments for curlyleaf management. Six curlyleaf-infested lakes were treated with herbicide (endothall or fluridone) for at least three consecutive years. Three additional lakes with established curlyleaf infestations were selected to serve as untreated reference lakes during the same period. For all study lakes, we annually assessed the frequency and biomass of curlyleaf in May and June, documented the production of new curlyleaf turions (reproductive buds) on standing plants, and tracked changes in the abundance and viability of turions in lake sediments. Previous studies have shown that biomass is a key metric for evaluating aquatic plant management projects. We used a boat-based rake method for collecting biomass samples rather than the standard diver (SCUBA) quadrat method because it allowed us to collect a greater number of samples in each lake and provided a higher degree of safety than the diver quadrat method. However, this boat-based rake method had not been thoroughly evaluated to determine whether it produced biomass estimates that were comparable to the diver quadrat method. Consequently, we conducted a separate study to compare the vertical rake sampling method to the diver quadrat method. Results of this study showed that biomass estimates from rake samples were comparable to diver quadrat samples for most individual plant taxa. However, the rake method produced substantially higher estimates than the quadrat method when sampling in dense stands of aquatic plants, particularly in areas dominated by coontail (Ceratophyllum demersum L.). Although rake estimates of plant biomass were significantly less precise than quadrat estimates, we determined that the rake method allowed us to collect a sufficiently greater number of samples to offset the method’s lower precision. Consequently, we concluded that the biomass data we collected were precise enough to make meaningful relative comparisons in our study lakes. After three to four consecutive years of herbicide treatment, curlyleaf frequency, biomass, turion production, and sediment turion abundance were all reduced and were all significantly lower in treated lakes than in untreated reference lakes. However, viable turions remained in lake sediments after three consecutive years of treatment. These results suggest that serial lake-wide, early-season herbicide treatments can effectively decrease the negative impacts of curlyleaf infestation and reduce the abundance of curlyleaf turions in lake sediments, but ongoing management will likely be required to maintain long-term control of curlyleaf in infested lakes.