Tims Ford Reservoir rated “poor” in 2016, similar to previous years. Low dissolved oxygen concentrations in the lower water column and “poor” ratings for bottom life continue to be issues in Tims Ford. “Fair” ratings for chlorophyll and sediment quality have also reduced the overall ecological health score in some years.
The ecological health of Tims Ford Reservoir has been monitored 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 two locations on Tims Ford Reservoir — the deep, still water near the dam, called the forebay (Elk River Mile 135.0), and the middle part of the reservoir (Elk River Mile 150.0).
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>72 = Good
59-72 = Fair
<59 = Poor
As in previous years, dissolved oxygen rated “poor” at both monitoring locations. Oxygen concentrations were below two milligrams per liter in portions of the lower water column during summer and autumn at both monitoring locations, including extended periods of time when an area of water was completely devoid of oxygen. TVA has installed equipment to add oxygen to the water as it is flows through Tims Ford Dam.
In 2016, chlorophyll rated “good” at the forebay and “fair” at the mid-reservoir. At the forebay, chlorophyll has rated “good” or high “fair” each year monitored, but ratings at the mid-reservoir have fluctuated more, varying between “good”, “fair”, and “poor”. Chlorophyll concentrations have varied in response to the timing and amount of rainfall. Because of the mid-reservoir’s proximity to the Elk River inflow, chlorophyll concentrations at this location are more influenced by the nutrients flowing into the reservoir.
The fish community rated “good” at both monitoring locations. Historically, the fish community has been assessed “good” or high “fair” ratings. In 2016, a total of thirty-one fish species was observed, including “good” numbers of sunfish, intolerant species (species known to require good water quality conditions), and top carnivores (e.g., black bass, walleye, and white bass). Fish health also was assessed a “good” rating with low incidences of disease and parasites.
As in previous years, bottom life rated “poor” at both monitoring locations because few benthic invertebrates were collected and all were species capable of tolerating a wide variety of environmental conditions. Low dissolved oxygen concentrations and cold water temperatures in the lower water column are contributing factors.
Sediment quality rated “fair” for both monitoring locations in 2016. Low levels of PCBs were detected in the samples from both locations. Nickel also exceeded suggested background levels in the forebay sample. Sediment quality typically rates “fair” at the forebay and “good” or “fair” at the mid-reservoir location. Nickel has exceeded suggested background levels at the forebay location in all previous years of monitoring. Arsenic also exceeded suggested background levels at the forebay during three monitoring years and at the mid-reservoir only in 2008. Low levels of the pesticide chlordane have been detected at the mid-reservoir location in the past (1996, 1998, and 2002).
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 Tims Ford Reservoir, visit the Tennessee Wildlife Resource Agency.