Segments of the Clinch River in Virginia have experienced declining freshwater mussel populations during the past 40 years, while other segments of the river continue to support some of the richest mussel communities in the country. The close proximity of these contrasting reaches provides a study area where differences in climate, hydrology, and historic mussel distribution are minimal. The USGS conducted a study between 2009 and 2011 to evaluate possible causes of the mussel declines. Evaluation of mussel habitat showed no differences in physical habitat quality, leaving water and sediment quality as possible causes for declines. Three years of continuous water‐quality data showed higher turbidity and specific conductance in the reaches with low‐quality mussel assemblages compared to reaches with high‐quality mussel assemblages. Discrete water‐quality samples showed higher major ions and metals concentrations in the low‐quality reach. Base‐flow samples contained high major ion and metal concentrations coincident to low‐quality mussel populations. These results support a conceptual model of dilution and augmentation where increased concentrations of major ions and other dissolved constituents from mined tributaries result in reaches with declining mussel populations. Tributaries from unmined basins provide water with low concentrations of dissolved constituents, diluting reaches of the Clinch River where high‐quality mussel populations occur.
Reuse
of municipal and industrial wastewater treatment plant (WWTP)
effluent is used to augment freshwater supplies globally. The
Shenandoah River Watershed (U.S.A.) was selected to conduct on-site
exposure experiments to assess endocrine disrupting characteristics
of different source waters. This investigation integrates WWTP wastewater
reuse modeling, hydrological and chemical characterization, and in
vivo endocrine disruption bioassessment to assess contaminant sources,
exposure pathways, and biological effects. The percentage of accumulated
WWTP effluent in each river reach (ACCWW%) was used to predict environmental
concentrations for consumer product chemicals (boron), pharmaceutical
compounds (carbamazepine), and steroidal estrogens (estrone, 17-β-estradiol,
estriol, and 17-α-ethinylestradiol). Fish endocrine disruption
was evaluated using vitellogenin induction in adult male or larval
fathead minnows. Water samples were analyzed for >500 inorganic
and
organic constituents to characterize the complex contaminant mixtures.
Municipal ACCWW% at drinking water treatment plant surface water intakes
ranged from <0.01 to 2.0% under mean-annual streamflow and up to
4.5% under mean-August streamflow. Measured and predicted environmental
concentrations resulted in 17-β-estradiol equivalency quotients
ranging from 0.002 to 5.0 ng L–1 indicating low-to-moderate
risk of fish endocrine disruption. Results from the fish exposure
experiments showed low (0.5- to 3.2-fold) vitellogenin induction in
adult males.
A11. Time of travel for tracer studies conducted on the Clinch River in Virginia and Tennessee, September 9-17, 2009. A12. Cumulative tracer travel times for tracer studies conducted on the Clinch River in Virginia and Tennessee, September 9-17, 2009. A13. Data collected along each transect evaluating channel morphology, bank and riparian zone, fish habitat, and substrate for the habitat assessment of the Clinch River, 2009-2011.
River
waters contain complex chemical mixtures derived from natural
and anthropogenic sources. Aquatic organisms are exposed to the entire
chemical composition of the water, resulting in potential effects
at the organismal through ecosystem level. This study applied a holistic
approach to assess landscape, hydrological, chemical, and biological
variables. On-site mobile laboratory experiments were conducted to
evaluate biological effects of exposure to chemical mixtures in the
Shenandoah River Watershed. A suite of 534 inorganic and organic constituents
were analyzed, of which 273 were detected. A watershed-scale accumulated
wastewater model was developed to predict environmental concentrations
of chemicals derived from wastewater treatment plants (WWTPs) to assess
potential aquatic organism exposure for all stream reaches in the
watershed. Measured and modeled concentrations generally were within
a factor of 2. Ecotoxicological effects from exposure to individual
components of the chemical mixture were evaluated using risk quotients
(RQs) based on measured or predicted environmental concentrations
and no effect concentrations or chronic toxicity threshold values.
Seventy-two percent of the compounds had RQ values <0.1, indicating
limited risk from individual chemicals. However, when individual RQs
were aggregated into a risk index, most stream reaches receiving WWTP
effluent posed potential risk to aquatic organisms from exposure to
complex chemical mixtures.
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