The overall ecological condition of Pickwick Reservoir rated “fair” in 2018. Ecological health ratings for Pickwick have fluctuated between “good” and “fair”, but scores have been lower, overall, since 2008. Weather conditions, particularly the timing and amount of rainfall, and the related changes in runoff have proven to be major factors in the variation of ecological health scores for Pickwick and many other reservoirs.
Dissolved oxygen and chlorophyll, the ecological indicators most responsive to changes in weather conditions, tend to rate lower during dry, low flow conditions, especially if periodic rain events wash nutrients and organic material into the reservoir. In turn, dissolved oxygen conditions along the reservoir bottom affect bottom life. Additional information about each indicator is provided in the paragraphs that follow.
The ecological health of Pickwick Reservoir has been assessed using the same methodology since 1994. Ecological health evaluations focus on five indicators: dissolved oxygen, chlorophyll, sediment quality, benthic macroinvertebrate community (bottom life), and the fish assemblage. TVA monitors four locations on Pickwick Reservoir — the deep, still water near the dam, called the forebay (Tennessee River Mile (TRM) 207.3); the middle part of the reservoir (TRM 230.0); the Bear Creek embayment (Bear Creek Mile 8.4); and the riverlike area at the upper end of the reservoir called the inflow (TRM 253-259). Only bottom life and the fish assemblage are assessed at the inflow monitoring location.
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>72 = Good
59-72 = Fair
<59 = Poor
|Bear Creek embayment||Fair||Poor||Good||Fair||Good|
|Inflow (near Wilson Dam)||–||–||Good||Good||–|
Dissolved oxygen in 2018 rated “good” at the forebay and mid-reservoir and “fair” at the Bear Creek embayment monitoring location. The “fair” rating was the result of low dissolved oxygen concentrations (<2 mg/L) in the lower water column during some sample periods. This indicator usually rates “good” at the mid-reservoir, and ratings typically have varied between “good” and “fair” at the forebay and embayment locations, generally in response to reservoir flow conditions. The only “poor” rating for this indicator occurred at the forebay in 2016, which was one of the driest summers on record. Dry, low flow conditions can allow water to sit long enough that oxygen in the deeper waters becomes depleted as it is used in the natural process of decomposition.
Chlorophyll in 2018 rated “fair” at the forebay and “poor” at the mid-reservoir and embayment monitoring locations. Chlorophyll typically rates “poor” at the embayment location, “fair” or “poor” at the forebay, and varies between “good”, “fair” and “poor” at the mid-reservoir. As with dissolved oxygen, reservoir flows have played a part in the year-to-year fluctuations as low-flow conditions tend to allow more time for algal populations to become established. Additionally, ratings at the mid-reservoir have been more variable because this portion of the reservoir is influenced more by changes in river flows due to its smaller cross-sectional area (i.e., greater variations in flow velocities) relative to more downstream portions of the reservoir.
The fish community in 2018 was assessed a “fair” rating at the forebay and the mid-reservoir and a “good” rating at the inflow and embayment. Historically, ratings at the forebay and mid-reservoir have fluctuated between “good” and “fair”, while the fish communities at the inflow and embayment have rated “good”.
In 2018, the number and variety of fish observed at each location were consistent with previous years. A total of fifty species was observed reservoir wide. Fish health was assessed a “good” rating with low incidences of disease and parasites
Monitoring results for bottom life in 2018 were generally similar to previous years. Bottom life rated “good” at the mid-reservoir and inflow locations and “fair” at the forebay and Elk River Embayment.
Ratings have varied between low “fair” and “poor” at the Elk River embayment, while ratings for the three monitoring locations on the main channel of the Tennessee River typically have varied between “good” and “fair” due to greater abundance and diversity, which includes a better representation of sensitive and long-lived species such as mayflies and snails. As with dissolved oxygen, the only “poor” rating for bottom life among the Tennessee River locations occurred at the forebay in 2016.
Sediment quality in 2018 rated “good” at the mid-reservoir and embayment monitoring locations, and “fair” at the forebay. No PCBs or pesticides were detected in the sediment samples, but the concentration of arsenic in the sample collected at the forebay was slightly above the suggested background concentration, resulting in a “fair” rating.
Sediment quality usually rates “good” in Pickwick Reservoir, but the detection of low levels of pesticides (i.e., DDT/DDD and chlordane) or PCBs have resulted in lower sediment quality ratings (i.e., “fair”) in some previous years. These are man-made compounds and do not occur naturally. The pesticides were banned from use in the 1970s and 1980s. PCBs were banned from commercial production in 1979, though they may be present in products and materials produced before the ban. These compounds continue to be detected sporadically in sediments because of their persistence in the environment.
Arsenic naturally occurs in soils but can also originate from many sources. The concentrations of arsenic in sediments deposited in the reservoir are usually slightly below the suggested background concentration.
TVA maintains a program to examine contaminants in fish fillets from TVA reservoirs and their major tributary streams on a rotational basis. The data collected from this program is distributed to the state officials who are responsible for placing or removing fish tissue consumption advisories on those bodies of water. For information on advisories currently in effect for Pickwick Reservoir, visit the Tennessee Wildlife Resource Agency and the Epidemiology Division of the Alabama Department of Public Health.