Shrnutí

Popis

Excessive sedimentation and nutrient enrichment are affecting the biology of the Cahaba Riverwatershed. Deleterious effects of sediment deposition on the fish and benthic macroinvertebratecommunities were evident in the mainstem Cahaba River below Trussville to below Helena and atseveral tributaries to the Cahaba unnamed tributary to Little Cahaba Creek, Little Cahaba River, and Buck Creek. Excessive nutrient inputs nitrogen and phosphorus to the Cahaba system from both point and nonpoint sources have allowed the excessive and widespread growths of filamentous algae. The filamentous green alga, Cladophora, often associated with nutrient enrichment and nuisance conditions, was predominant and widespread during the study. Total phosphorus and total nitrogen ranged from 12 to 960 gL and 230 to 21,094 gL, respectively. The upper reaches of the Cahaba were generally phosphorus limited, followed bynitrogen limitation in the middle segment, and then tending toward phosphorus limitation again in the lower reaches. Cahaba waters of 12 gL TP and 230 gL TN maintained as a monthly mean should restore the Cahaba system to maximum use by reducing nuisance excursions of over 40 periphyton cover and over 100 mgm2 chlorophyll a biomass. The mainstem Cahaba from below Trussville to Helena contains excessive amounts of sediments that have degraded the habitat and altered the benthic community structure and species diversity within this section of the river. Sediment characterization studies documented a shift from coarser substrates at the upper Cahaba River stations to finer substrates at the Cahaba River stations below Trussville and theheavily developed middle reach of the Cahaba. GIS land change analysis for the Cahaba River watershed documented dramatic increases in the disturbed land use class since 1990. Results of studies by EPA in 2001 and 2002 raise an issue concerning listing under the states 303d list 1998; 2000. The issue involves that section of the Cahaba River above US 280 to I59 which is now listed for siltation. An examination of a Permit Compliance System PCS retrieval file of the major discharges 1 mgd to the Cahaba River and associated tributaries revealed incidences of NPDES permit violations, for nutrient or nutrient related parameters, over the last several years.Permit Compliance System, Database retrieval, 10152002 Compliance issues within the Cahaba watershed need to be addressed.