The National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey (USGS) recently issued a report assessing the ecological health of U.S. streams.  Following a 2010 report assessing nutrient occurrence and distribution as a measure of stream and groundwater quality, USGS has expanded its water quality assessment to include an assessment of biological communities, providing a more comprehensive perspective on stream health.

USGS sampled biological communities of fish, macroinvertebrates, and algae at 51 major river basins across the country over a twelve-year period to ascertain stream health in agricultural, urban, and mixed land-use watersheds and to investigate how land and water use influence a stream’s chemical and physical factors, and ultimately impact stream health.

The assessment found that in 79% of the agricultural watershed sites, at least one biological community (algae, macroinvertebrates, or fish) was “altered,” meaning that the numbers and types of organisms present differed substantially from what the river would be expected to support.  Across all watersheds – urban, agricultural, and mixed – unaltered communities were present in only 17% of surveyed watersheds.  According to the report, the presence of these unaltered communities “suggests that it is possible to maintain stream health in the midst of substantial human influence.”

The report emphasizes that “[e]fforts to understand the causes of reduced stream health should consider the possible effects of nutrients and pesticides . . . particularly in agricultural and urban settings” and notes that, in addition to USGS, “other Federal and State agencies have also reported that excess nutrients were among the leading factors associated with reduced stream health throughout the Nation.”   Nitrogen concentrations in streams across the nation are by far greatest in agricultural streams, and are highest in the regions with most intensive use of fertilizer and manure — the Northeast, Midwest, and Northwest.

Importantly, the report highlighted the well-known benefits of riparian buffer zones to mitigate land use impacts on stream health.  In a Pennsylvania agricultural site sample site, “[g]reater amounts of natural vegetation in the riparian zone correspond to less altered biological condition and lower nutrient concentrations.”

The full report is available here.