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Nutrient-related Water Quality Indicators and Risk Factors for Estuaries of the Texas Coast

Charles R. Smith 1 and James D. Simons 2

1 Texas Parks and Wildlife Department, Science and Policy Branch, Austin, Texas
2 Texas Parks and Wildlife Department, Science and Policy Branch, Corpus Christi, Texas

Nutrient-related water quality data collected over five years along the Texas coast for the federal National Coastal Assessment program were analyzed for evidence of human impact on the local estuarine resource. Dissolved nitrogen and phosphorus, chlorophyll a, and total suspended solids comprised the water properties related to local anthropogenic resource utilization as represented by the 2004 human population and water usage reported for municipalities, manufacturing, mining, power generation, irrigation, and livestock. Summed ammonium, nitrate, and nitrite concentrations represented a measure of dissolved nitrogen. For each major water body segment, the summed populations or annual water usage of adjacent counties were divided by the area of the local estuarine habitat to serve as measures of resource utilization and potential environmental stress.

A correlational analysis showed that population density, municipal use, manufacturing and mining related most closely with patterns in local bay water quality. Principal component analysis showed strong positive relationships between all water quality parameters on the first component, but the dissolved nutrients separated out from chlorophyll a and dissolved solids on the second axis. Nitrite levels showed the strongest relationships with anthropogenic factors and corresponded most closely with population density or municipal use. Other nitrogen measures appeared to be indicative of nitrogen from irrigation sources. Orthophosphate and chlorophyll a occurred at highest levels in areas with mining, manufacturing, and power generation. Quantification of the relationships between pertinent water quality parameters and anthropogenic inputs to the estuaries could lead to a risk management approach for protecting the resource.

Keywords: estuary, bay, water quality, nutrient, nitrogen, phosphorus, chlorophyll a, total suspended solids, water use, indicator

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