The Effects of Agrochemical Pesticide Applications on Target and Off-target Species in Aquatic Ecosystems

The increase in the global human population is driving agricultural expansion, which increases the likelihood and degree by which agrochemicals impact aquatic systems. It is projected that by 2100 the global human population will exceed 11 billion, and to feed the increased human population, the necessary increase in agricultural infrastructure is estimated to double irrigation, nearly triple fertilizer applications, and increase pesticide applications by tenfold. It stands to reason that wetlands impacts from agriculture are also likely to increase as the industry expands its operation to meet the globally growing demand for food. Wetlands are highly productive habitats that not only serve as essential habitat thousands of wildlife species globally, but also provide billions of dollars of ecosystem services annually. Together, these traits make wetlands one of the valuable biomes in the world. The agricultural industry typically impacts wetland habitats by altering the local hydrology, which changes the volume and speed at which water enters and leaves wetlands, and by exposing wetlands to agricultural runoff in form of nutrients or pesticides. Altering wetland hydrology can potentially cause a shift in wetland vegetative community composition, and can leave wetlands open to invasion by new species, which can, in turn, reduce community stability, decreased landscape heterogeneity, biodiversity, and economic value of impacted wetlands. And the introduction of pesticides into wetlands is known to cause reduction of primary productivity, instability in food webs, and lethal and sublethal effects to aquatic animals. This doctoral dissertation aims to address knowledge gaps with respect to how pesticide applications and agricultural runoff impact individual wetland animal species and the whole of the vegetative communities within subtropical floodplain marshes. The research presented here specifically examines how different herbicide applications impact the vegetative community of floodplain marshes with particular respect to invasive species, as well as assess the impact of various herbicide and insecticide applications on freshwater crustaceans, amphibians, and fishes. As the global human population and food demand increases, the accompanying conversion of natural habitat and the sharp increase in pesticide applications is likely to negatively impact wetland communities that are adjacent to existing and newly created agricultural sites. Chapter 1 introduces the links between the increasing applications of agrochemicals and their impacts to aquatic systems, including ecological effects to the biota and system stability, as well as the effects to the values of wetland ecosystem services, including potential impacts to human disease systems. Chapter 2 details an experiment to determine if an aerially applied herbicide treatment of either imazapyr or a combination of 2,4-D and triclopyr are able to remove invasive Carolina willows (Salix caroliniana) from floodplain marshes in the Upper St. Johns River Basin. Chapter 3 explores the potential toxicity of the herbicides 2,4-D, imazapyr, and triclopyr on Eastern mosquitofish (Gambusia holbrooki) and Cuban treefrog tadpoles (Osteopilus septentrionalis). Chapter 4 examines the potential toxicity of three organophosphate and three pyrethroid insecticides on the giant river prawn (Macrobrachium rosenbergii). And chapter 5 summarizes the conclusions of the previous three chapters and discusses future directions in which the research can be continued to further the ultimate goal of determining how to feed the growing global human population without unnecessarily impacting aquatic systems which provide essential ecosystem services. Together these research chapters provide insight into how aquatic and wetland flora and fauna are likely to respond to increased agrochemical exposure resulting from an expansion of global agricultural infrastructure and suggest future research objectives that still need to be explored