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NUTRIENT AND CHLOROPHYLL RELATIONS IN SELECTED STREAMS OF THE NEW ENGLAND COASTAL BASIN: POTENTIAL METHODS FOR ESTABLISHING NUTRIENT CRITERIA
27th Annual Meeting of the New England Association of Environmental Biologists (NEAEB), 2003
Jeffrey R. Deacon1, Matthew L. Liebman2, Melissa L. Riskin1, and Keith W. Robinson1
1 U.S. Geological Survey, 361 Commerce Way, Pembroke, NH 03275
Nutrient and chlorophyll samples were collected from 13 wadeable streams in the New England Coastal Basin during June-September 2001. The study was designed to evaluate the response of periphyton chlorophyll a to nutrients and light and to compare previously considered nutrient thresholds to ambient nutrient concentrations in those streams. The stream sites represented three classes of water-quality impairment (reference, moderately impaired, impaired )- based on previously assessed phosphorus, nitrogen, and dissolved oxygen data. Open- and closed-canopy sites were sampled in six streams to assess the effect of light on periphyton biomass under similar nutrient conditions. Median total phosphorus (TP) and total nitrogen (TN) concentrations differed significantly (p < 0.05) between reference and impaired sites and between moderate and impaired sites. Concentrations of chlorophyll a were positively correlated with concentrations of total phosphorus and total nitrogen. Correlation coefficients were higher at open-canopy sites (p < 0.05, rho = 0.64 for TP and 0.71 for TN) than at closed-canopy sites (p < 0.05, rho = 0.36 for TP and 0.40 for TN). Concentrations of periphyton chlorophyll a were significantly (p < 0.05) larger at open- than at closed-canopy sites.
Nutrient concentrations were plotted against chlorophyll a concentrations and a regression line was drawn and used to estimate the total phosphorus and total nitrogen concentrations that corresponded to various chlorophyll a thresholds. Using this relation, a median literature value for mesotrophic streams of 21 milligrams per square meter of chlorophyll a , corresponded to estimated concentrations of 0.12 milligrams per liter for total phosphorus and 1.3 milligrams per liter for total nitrogen. Results from this study suggest that nutrient-response relations, and appropriate periphyton chlorophyll a thresholds for impairment, may be useful in setting criteria to prevent nutrient enrichment in wadeable streams.
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