Fowler, S., W. Deutsch, A. E. Wilson, and E. Reutebuch. 2012. Tallapoosa River basin numerical nutrient criteria for wadeable streams. Final Report for the Alabama Department of Environmental Management, Agreement ADEM-C00594051.
Physical, chemical and biological data were collected by the Alabama Department of Environmental Management (ADEM) for this nutrient criteria study during the 2010 growing season at 34 sites in the Piedmont Ecoregion (Ecoregion 45) in east-central Alabama. These data were from stream, river and reservoir embayment sample sites, and were the basis of analyses to evaluate the effects of nutrient concentrations (nitrogen and phosphorus) on aquatic biota. Separate analyses were conducted for stream/river data and for reservoir embayment data.
Levels of nutrient enrichment of sampled waterbodies ranged from very low to high, based on phosphorus concentrations, with stream/river growing season mean phosphorus levels ranging from 0.011 mg/L to 0.468 mg/L, and embayment growing season mean phosphorus levels ranging from 0.009 mg/L to 0.053 mg/L. Twenty-fifth percentile values for the concentration of total phosphorus in the Tallapoosa Basin streams, river and reservoir embayments sampled in 2010 were 0.025 mg/L, 0.034 mg/L and 0.012 mg/L respectively. Comparing this reservoir embayment twenty-fifth percentile value (0.012 mg/L) to the value reported by EPA, 0.0225 mg/L for Ecoregion 45 (Piedmont), it appears that the Tallapoosa Basin reservoir sites are nutrient poor relative to phosphorus levels of the entire Piedmont (EPA 2000).
Results of Classification and Regression Tree (CART) analyses yielded significant breakpoints for both stream/river and reservoir embayment datasets. In most cases, total phosphorus was the nutrient driving changes in response variables for both reservoir embayments and streams/rivers.
Reservoir embayment CART breakpoints in photic zone depth, Secchi depth and chlorophyll a levels occurred at total phosphorus (TP) concentrations in the range of 20-29 µg/L. Relationships between TP and photic and Secchi depth were inverse, and between TP and chlorophyll a was direct – TP increased with higher measurements of chlorophyll a, as expected.
CART breakpoints for fish metrics from stream/river sampling occurred at TP concentrations in the range of 16-23 µg/L. Relationships between TP and fish metrics were inverse – increased TP was observed with decreases in fish species and Index of Biotic Integrity, as expected. Stream/river CART breakpoints for macroinvertebrate metrics were mixed. TP was the driver for some variables, and total nitrogen (TN) for others. All metrics were directly related to TP, except for percent nutrient tolerant individuals and percent tolerant individuals, which were related to TN. Relationships between nutrient levels and stream biota represented as macroinvertebrate communities for lotic environments sampled in this study were not well defined.