Development of Environmental Thresholds for Nitrogen and Phosphorus in Streams

Abstract

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. Chemical thresholds for N and P were defined by applying five approaches, employing either a predetermined percentile to a water chemistry data set or a relationship between water chemistry and land cover, to identify boundaries between minimally disturbed and impaired conditions. Comparison of these chemical thresholds with biological thresholds (derived from stressor-response relationships) produced an approach for rationalizing these two types of thresholds and deriving nutrient criteria. The resulting criteria were 0.01 to 0.03 mg L(-1) total P and 0.87-1.2 mg L(-1) total N for the Atlantic Maritime, 0.02 mg L(-1) total P and 0.21 mg L(-1) total N for the Montane Cordillera, ~0.03 mg L(-1) total P and ~1.1 mg L(-1) total N for the Mixedwood Plains, and ~0.10 mg L(-1) total P and 0.39-0.98 mg L(-1) total N for the interior prairies of Canada. Adoption of these criteria should result in greater likelihood of good ecological condition with respect to benthic algal abundance, diatom composition, and macroinvertebrate composition.

Establishment of reference or baseline conditions of chemical indicators in New Zealand streams and rivers relative to present conditions

“…However, according to Unwin et al (2010), land use as characterised by the percentage of heavy pasture (renamed in the present study as intensive agriculture as it amalgamated cropland, vineyards, orchards and high-producing exotic grassland) was the single factor that explained most variation in water quality variables and hence is treated as a continuous variable. Although most other studies have emphasised either the percentage of cropland (Dodds and Oakes 2004) or the total percentage of agriculture (Chambers et al 2012), the focus on percentage of intensive agriculture (viz. heavy pasture), as a surrogate for anthropogenic activity, reflects the domination of New Zealand agriculture by the pastoral sector.…”

Agriculture and Eutrophication: Where Do We Go from Here?

“…500 mm), it has been estimated that about 50% of the arable land area would need to be taken out of production to achieve the statutory limit of nitrate in drinking water of 11.3 mg·N·L −1 required by the EU Nitrates Directive [114]. Even greater areas of agricultural land would need to be taken out of production to achieve the target concentrations of 1-2 mg·N·L −1 considered necessary to avoid deterioration in lake macrophyte communities [16,31], or reduce benthic and sestonic algae in rivers [115,116]. These levels of intervention would clearly cause major socio-economic issues for rural communities and regional agricultural output.…”

Avaliação integrada da qualidade de águas superficiais: grau de trofia e proteção da vida aquática nos rios Anil e Bacanga, São Luís (MA)

“…Integrando o estudo da qualidade das águas dos corpos aquáticos encontram-se os índices de qualidade, instrumentos de comunicação com a sociedade de temas científicos complexos e importantes para avaliação da qualidade do estado de degradação dos recursos hídri-cos (LANDWEHR & DEININGER, 1976;HOUSE & ELLIS, 1987;FLORES, 2002;PESCE & WUNDERLIN, 2000CETESB, 2004SILVA & JARDIM, 2006;BAKAN et al, 2010;CHAMBERS et al, 2012 O IET é útil para classificar os corpos aquáticos com relação ao seu grau de trofia, isto é, o seu grau de enriquecimento com nutrientes e os respectivos efeitos, como a produção excessiva de algas e de macrófitas.…”