Defining nutrient concentrations to prevent eutrophication of streams in agriculturally-dominated watersheds

Inputs of nutrients (P and 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 performance standards that establish nutrient concentrations to protect ecological condition of agricultural streams.  Analysis of data from long-term provincial monitoring programs and experimental studies in networks of 8-15 streams showed that agricultural land use increased nutrient concentrations in streams, resulting in increased sestonic and benthic algal abundance, loss of sensitive benthic macroinvertebrate taxa, and an increase in benthic diatom taxa indicative of eutrophication.  Calculation of 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 six agricultural regions of Canada.  These recommended standards should result in good ecological condition with respect to benthic algal abundance, benthic diatom composition and benthic macroinvertebrate composition.