The ecological health of Normandy Reservoir rated “poor” in 2016, consistent with health ratings since 2000. Historically, the main issue has been low dissolved oxygen. In 1994, TVA installed aeration equipment in the reservoir to add oxygen to the deep water near the dam and to improve conditions in the Duck River downstream from the dam. A new, larger compressor and four new diffuser lines were added to the aeration system in 1997. Two of the new diffuser lines extended upstream of the sampling location and influenced the ecological health ratings, causing three indicators (dissolved oxygen, chlorophyll, and bottom life) to exhibit marked changes. In 2006, a new sampling site for dissolved oxygen, chlorophyll, and sediment quality was established just upstream of the diffuser lines. The sampling site for bottom life was moved upstream in 2008. However, because of the relatively small area that comprises the forebay of Normandy Reservoir, the aeration system continues to have some influence on at least two of the ecological indicators — dissolved oxygen and chlorophyll. Results are discussed below.
The ecological health of Normandy 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 one location on Normandy Reservoir — the deep, still water near the dam, called the forebay (Duck River Mile 251.3).
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>72 = Good
59-72 = Fair
<59 = Poor
As in previous years, dissolved oxygen rated “poor” in 2016 due to low concentrations in the lower water column during summer. It is notable that the volume of water affected from 1998 to 2004 was smaller than in other years because the sampling site was in the immediate area of the new diffusers lines, which were installed in 1997. Since the site was moved upstream in 2006, the volume of low-oxygen water has increased to levels generally similar to those observed prior to 1998.
Chlorophyll in 2016 rated “poor”, consistent with most ratings since 1998 when chlorophyll concentrations increased substantially. Chlorophyll rated “good” prior to 1998. It is plausible that the increase in chlorophyll concentrations is due to an upwelling of nutrients from the lower water column caused by the aeration system.
As in previous years, the fish community in 2016 rated “good”. Characteristics of the fish community (e.g., fish abundance, species richness and composition) were similar to long-term averages. A total of twenty-six species was observed in 2016, with composition being dominated by a few species such as bluegill, spotfin shiner, green sunfish, and gizzard shad. Fish health was assessed a “good” rating with low incidences of disease and parasites.
Bottom life rated “poor” in 2016. Bottom life rated “poor” each year from 1994 to 1996, then increased to the low end of the “fair” range from 1998 to 2006, probably due to improved dissolved oxygen conditions that resulted from the aeration system. The sample site was moved upstream of the diffuser lines in 2008, and bottom life has again rated “poor” each year since.
Sediment quality in 2016 rated “fair” because low levels of PCBs were detected in the sample. Sediment quality rated “good” all other years except 2002, when the sediment sample contained low levels of the pesticide chlordane and the concentration of arsenic was slightly higher than the suggested background concentration.
TVA maintains a program to examine contaminants in fillets of fish collected from TVA reservoirs and their major tributary streams on a rotational basis. The data collected from this program are 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 Normandy Reservoir, visit the Tennessee Wildlife Resource Agency.