WATER QUALITY CONDITIONS IN A NATIONAL CONTEXT

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Seven major water-quality characteristics were evaluated for stream sites in each NAWQA Study Unit. Summary scores for each characteristic were computed for all sites that had adequate data. Scores for each site in the Western Lake Michigan Drainages were compared with scores for all sites sampled in the 20 NAWQA Study Units during 1992-95. Results are summarized by percentiles; higher percentile values generally indicate poorer quality compared with other NAWQA sites. Water-quality conditions at each site also are compared to established criteria for protection of aquatic life. Applicable criteria are limited to nutrients and pesticides in water and semivolatile organic compounds, organochlorine pesticides, and PCBs in sediment. (Methods used to compute rankings and evaluate aquatic-life criteria are described by Gilliom and others, in press.)

EXPLANATION

Ranking relative to national conditions-- Darker colored circles generally indicate poorer quality. Bold outline of circle indicates one or more aquatic-life criteria were exceeded.

NUTRIENTS in water

Nutrient concentrations in the study area were principally related to land use of the drainage basin. Relative to other Study Units nationally, low, moderate, and high nutrient levels were found in forested, urban, and agricultural basins, respectively. One agricultural site exceeded drinking-water standards during periods of stormwater runoff. Fertilizer and manure application to croplands is the major anthropogenic source of nutrients; however, point sources and atmospheric deposition also contribute to nutrient loading.

ORGANOCHLORINE PESTICIDES and PCBs in bed sediment and biological tissue

Concentrations of PCBs and organochlorine compounds in three streams that drain urban areas were among the highest of all NAWQA Study Unit sites nationally. The three urban sites also exceeded aquatic-life criteria; PCB concentrations in fish have been high enough to prompt bans on fish consumption for the protection of human health. A metabolite of the persistent compound DDT (p,p'-DDE) is also commonly detected at urban sites. Concentrations at agricultural sites were moderately high, whereas those in forested basins were low compared to other national NAWQA sites.

PESTICIDES in water

Atrazine was detected at all nine fixed sites where samples were analyzed for pesticides. However, concentrations were generally low, especially at sites draining basins with a low percentage of agricultural land use. At the three sites where sufficient data exist for comparison, pesticide concentrations were at or below the median national NAWQA concentration.

TRACE ELEMENTS in bed sediment

Some of the highest trace-element concentrations at NAWQA sites nationally were from the lower Fox and Milwaukee Rivers, major rivers in urban settings. Concentrations of arsenic, selenium, and mercury in forested basins in the study area were near the median of all NAWQA sites nationwide. Sites dominated by agricultural land use typically had low levels of trace elements compared to other NAWQA sites nationwide.

SEMIVOLATILE ORGANIC COMPOUNDS in bed sediment

Rivers in urban settings had some of the highest concentrations of SVOCs of all NAWQA sites nationwide. Three urban sites, the lower Fox and Milwaukee Rivers and Lincoln Creek, had concentrations of SVOCs that exceeded aquatic-life criteria. Forested and agricultural sites had low to moderate concentrations of SVOCs compared to sites nationwide.

FISH COMMUNITY DEGRADATION

Assessment of fish community degradation was based on several factors, including presence of non-native and pollutant-tolerant species, and percentage of diseased fish. Most sites within the study area have relatively high quality fish communities compared to the NAWQA sites in the rest of the Nation. However, Lincoln Creek, an urban site, had highly degraded fish community quality compared to other NAWQA sites.

STREAM HABITAT DEGRADATION

Degradation of stream habitat was based on several factors such as bank erosion, stream modification, and the stability and density of bank vegetation. The degree of stream-habitat degradation within the Study Unit depended on stream size and land use. Sites on streams draining agricultural or urbanized landscapes were degraded compared to NAWQA sites nationwide.

CONCLUSIONS

• Nutrient and pesticide concentrations are elevated in agricultural basins.
• Sites draining urban areas have elevated concentrations of trace elements, SVOCs, and PCBs.
• Northern forested basins have relatively good surface-water quality; however, trace element concentrations are slightly elevated and fish community quality is moderate.