Development of environmental thresholds for nitrogen and phosphorus in streams.

Inputs of nutrients (P and N) to freshwaters can cause excessive aquatic plant growth, depletion of oxygen, and deleterious changes in diversity of aquatic fauna. As part of a "National Agri-Environmental Standards Initiative," the Government of Canada committed to developing environmental thresholds for nutrients to protect ecological condition of agricultural streams. Analysis of data from >200 long-term monitoring stations across Canada and detailed ecological study at ~70 sites showed that agricultural land cover was associated with increased nutrient concentrations in streams and this, in turn, was associated with increased sestonic and benthic algal abundance, loss of sensitive benthic macroinvertebrate taxa, and an increase in benthic diatom taxa indicative of eutrophication.

SHIFT FROM CHLOROPHYTES TO CYANOBACTERIA IN BENTHIC MACROALGAE ALONG A GRADIENT OF NITRATE DEPLETION(1).

A survey of the spatial distribution of benthic macroalgae in a fluvial lake of the St. Lawrence River (Lake Saint-Pierre, Quebec, Canada) revealed a shift in composition from chlorophytes to cyanobacteria along the flow path of nutrient-rich waters originating from tributaries draining farmlands. The link between this shift and changes in water quality characteristics was investigated by sampling at 10 sites along a 15 km transect.