Agriculture is an essential land use which supports human life via the production of food, fuel, and fiber. However, agriculture exerts pressures on watercourses due to nutrient loss from fertilizers, biocide drift, water extraction, and hydromorphologic changes. This chapter provides an overview of pressures exerted upon watercourses draining agricultural landscapes. Nutrients contribute to eutrophication from both the misapplication of fertilizers and from natural inefficiencies within the plant-soil system. Nutrient loss is understood using a transfer continuum, including source, mobilization, transport, and delivery stages. Sediment presents a multi-faceted pressure to watercourses as it disturbs streambed habitats, has an interactive effect with other stressors on macroinvertebrates, and may carry attenuated phosphorus which is susceptible to later mobilization. Emerging contaminants from agriculture exert acute pressures on freshwater ecology. These contaminants include veterinary medications, disinfectants, herbicides, and insecticides. Artificial drainage may not itself be a pressure but rather accelerates the transport of potential contaminants from their source to receptors. Drainage is a hallmark of agricultural landscapes and has been essential to improving productivity for centuries. For each of the pressures discussed in this chapter, there are trade-offs between productivity and environmental impacts which must be considered.
Encyclopedia of Inland Waters, Second Edition, Volume 4, 2022, Pages 47-57,