Normandy Reservoir

Ecological health rating

Normandy Reservoir rated poor in 2010, consistent with poor ecological 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. Three indicators (dissolved oxygen, chlorophyll, and bottom life) exhibited 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 small area that comprises the forebay of Normandy Reservoir, the aeration system continues to have some influence on two (dissolved oxygen and chlorophyll) of these three indicators. Results are discussed below.

TVA monitors one location on Normandy Reservoir — the deep, still water near the dam — usually on a two-year cycle. (Monitoring was changed to an every-other-year rotation after 1996).

Normandy Reservoir Ecological Health Ratings, 1994-2010

Click chart for raw data.

The table below shows the ratings for individual ecological health indicators at Normandy in 2010. These ratings are briefly explained in the paragraphs that follow.

Ecological Health Indicators for
Normandy Reservoir, 2010

Monitoring location

Dissolved oxygen

Chlorophyll

Fish

Bottom life

Sediment

Forebay

Dissolved oxygen

As in previous years, dissolved oxygen rated poor due to low concentrations in the lower water column near Normandy Dam. However, the volume of water affected in 1998-2004 was smaller than in other years because the sampling site was in the immediate area of the diffusers. Since the site was moved upstream in 2006, the volume of low-oxygen water has increased but remains less than pre-1998 levels.

Chlorophyll

Good ratings for chlorophyll changed to poor in 1998-2010 due to a substantial increase in concentrations. It is plausible that the chlorophyll increase is due to an upwelling of nutrients from the lower water column caused by the aeration system.

Fish

The fish community rated good, as in all previous years.

Bottom life

Bottom life rated poor in 2010. Bottom life also rated poor each year from 1994 to 1996. The poor rating for bottom life changed to a low-fair in 1998-2006, probably because of the 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 again rated poor.

However, episodes of low dissolved oxygen have impacted the density and composition of organisms found on the reservoir bottom each year. The majority of the organisms collected have been species capable of tolerating poor water quality conditions. Higher ratings in 1998-2006 were the result of improvements in the number of tolerant organisms collected rather than an improvement in the variety of organisms.

Sediment

Sediment quality rated good during all monitoring periods except in 2002, when sediment samples contained low levels of chlordane, and arsenic concentrations were slightly higher than the expected background concentration. Chlordane is a pesticide previously used to control termites and crop pests.

See definitions of ecological health indicators and monitoring locations.

Fish consumption advisories

Normandy Reservoir - 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 Normandy Reservoir, visit the Water Quality Division of Tennessee Department of Environment & Conservation’s web page. http://www.tn.gov/environment/water.shtml