"inputs of nutrients (phosphorus, P, and nitrogen, N) to fresh waters can cause excessive aquatic plant growth, depletion of oxygen, and deleterious changes in abundance and diversity of aquatic invertebrates and fish. As part of a National Agri-Environmental Standards Initiative, the Government of Canada committed to development of non-regulatory environmental ecological condition of agricultural streams. Analysis of data from long-term provincial monitoring programs and experimental studies in networks of 1 -15 streams showed that agricultural land use increased sestonic and benthic algal abundance, loss of sensitive benthic macroinvertebrate taxa, and an increase in benthic diatom taxa indicative of eutrophication. Calculation of provisional standards for total P or total N using three empirical methods followed by cross-calibration of these chemical standards with information on biological condition resulted in recommendations for total P and total N standards for agricultural streams in southern Ontario. These recommended standards should result in good ecological condition with respect to benthic algal abundance, benthic diatom composition and benthic macroinvertebrate composition. Research is continuing to determine whether these standards are protective of downstream receiving waters and to evaluate interactions of nutrients with other stressors (e.g., suspended sediments, pesticides), specifically their combined effects on aquatic food webs. Note: this project is part of a larger national study to determine the impacts of agricultural activities on streams across Canada and to define nutrient concentrations to protect aquatic life".
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