Biological and Water Quality Studies
March/April, July and September, 2002
with 2006 Addendum
US-EPA, Region 4, SESD, Athens, Georgia
Summary [ Full Report and 2006 Addendum ]
In order to characterize the present biology and water quality, the U.S. EPA Region 4, Water Management Division (WMD) requested staff of the Science and Ecosystem Support Division (SESD) to conduct studies of the Cahaba River and associated tributaries during the spring and summer of 2002. Studies were conducted in March /April, July and September of 2002 and focused on the causes of impairment in the Cahaba River. The objective of these studies was and is to provide supporting information for determination of an appropriate target for the development of a Total Maximum Daily Load (TMDL) for the §303(d) listed segments of the Cahaba River.
SUMMARY OF FINDINGS
- Excessive sedimentation and nutrient enrichment are affecting the
biology of the Cahaba River watershed. Deleterious effects of sediment
deposition on the fish and benthic macroinvertebrate communities were
evident in the mainstem Cahaba River below Trussville to below Helena
and at several 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 non-point sources have allowed the excessive and widespread growths
of filamentous algae.
- Past studies of the Cahaba River watershed (Onorata et al. 2000) in
the Birmingham area have documented the decline in pollution-intolerant
fish species with a concomitant increase in pollution-tolerant fish
species. Data from an ichthological survey conducted under contract
for the 2002 EPA studies (O'Neil 2002) reveals this same pattern. Endangered
species such as the gold-line darter and the Cahaba shiner have been
adversely affected. O'Neil (2002) suggests possible causes for disruptions
to the fish community from nutrient loading (point and non-point sources),
possible nitrogen deposition originating from the high automobile density
in the immediate airshed, sediment bedload and perhaps runoff of toxics
and other associated non-point sources.
- The filamentous green alga, Cladophora, often associated with nutrient
enrichment and nuisance conditions, was predominant and widespread during
- Total phosphorus and total nitrogen ranged from 12 to 960 ug/L and
230 to 21,094 ug/L, respectively. The upper reaches of the Cahaba were
generally phosphorus limited, followed by nitrogen limitation in the
middle segment, and then tending toward phosphorus limitation again
in the lower reaches.
- Cahaba waters of 12 ug/L TP and 230 ug/L 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 mg/m2 chlorophyll
- 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 the heavily developed
middle reach of the Cahaba. The literature documents that the preferred
substrates of pollution-sensitive benthic macroinvertebrates, such as
the Ephemeroptera, Plecoptera, and Trichoptera, are the coarser substrates
(gravels, pebbles, cobbles) whereas fine particle substrates (sand,
silt) are preferred by pollution-tolerant benthic macroinvertebrates
(chironomids and other burrowing forms). EPT fauna, common in the coarser
substrates, are more readily available as forage for fish than the benthic
macroinvertebrates common to the finer substrates.
- GIS land change analysis for the Cahaba River watershed documented
dramatic increases in the "disturbed" land use class since 1990. As
of 1998, over 38% of the watershed falls into the "disturbed' land use
class; this is up from 8.8% in 1990. Land use analysis of Buck Creek,
a major tributary to the Cahaba River, indicates that over 63% of that
watershed falls into the "disturbed" land use class. With the large
amount of both impervious and disturbed lands in the watershed, storm-generated
runoff, laden with sediments and/or nutrients, represents potential
impacts to both water quality and biology of the Cahaba system.
- Results of studies by EPA in 2001 and 2002 raise an issue concerning
listing under the state's §303(d) list (1998; 2000). The issue involves
that section of the Cahaba River above US 280 to I-59 which is now listed
for siltation. It is apparent, based on current EPA studies, that the
§303(d) listing of this section of the mainstem Cahaba River should
be reevaluated to possibly include nutrients.
- 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. Compliance issues within the Cahaba watershed need to be addressed.
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| Cahaba River: Biological
and Water Quality Studies
March/April, July and September, 2002
|211 pages||4 MegaBytes||Cahaba River Report|
|5 pages||28 KiloBytes||2006 Addendum|