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Federal Register / Vol. 86, No. 167 / Wednesday, September 1, 2021 / Proposed Rules chemical spills in the Hiwassee and Ocoee watersheds.
One of the biggest factors still affecting the snail darter is the impoundment of large portions of the Tennessee River Valley. The TVA
operates 9 dams on the mainstem Tennessee River and 38 dams on tributaries to the Tennessee River. These impoundments create large areas of deep, still water that do not meet the habitat needs of the snail darter. Snail darters are limited in the depth they can occupy by the presence of food resources. Snails, the darters preferred prey, live only in water shallow enough for light to penetrate and allow algae to grow on the substrate, about 1520 ft 5
7 m in much of the Tennessee mainstem. Impoundment also reduces stream flow and allows fine sediments to settle out, which can cover the clean gravel habitats needed by snail darters.
Additionally, these dams were initially operated with a hydropeaking strategy, only releasing water when needed to generate electricity or maintain reservoir level or flood storage capacity. In addition, many of these releases came from the water levels within the reservoir that held cold, oxygendeficient water. Collectively, these factors created conditions in the tailwaters that negatively affected water quality, food availability, and fish diversity.
Given the long operational lifespan of dams >100 years, it is nearly certain that the TVA reservoirs will be in place for the foreseeable future. However, beginning in 1981, TVA began studies to improve conditions in the tailwaters of their dams. The cold, oxygen-deficient water released from the bottom of many of the dams created conditions that eliminated many fish and mussel species from these areas. Through the RRIP, TVA began implementing strategies to increase minimum flow, dissolved oxygen, and, in some cases, temperature, in the tailwaters of their dams beginning in 1991 Bednarek and Hart 2005, p. 997. In 2002, TVA
conducted a reservoir operation study to consider how to implement these changes across the basin to improve the health of the river TVA 2004, p. ES3.
The result was to manage the river based on minimum flows instead of reservoir level and improve tailwater conditions. These changes have resulted in significant improvements in biological and abiotic variables and increases in fish and invertebrate diversity in many TVA dam tailwaters Layzer and Scott 2006, entire; Bednarek and Hart 2005, entire; Scott et al. 1996, entire. These improvements have likely resulted in improved conditions for the
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snail darter and may have contributed to improvements to the species status within tailwaters since the 1990s, across more than 400 miles 640 km of the mainstem of the Tennessee River. Since the RRIP is based on ecologically meaningful parameters in the tailwaters, such as dissolved oxygen and temperature, this program may be able to provide some resiliency to a warming climate and precipitation variability in the future, especially if TVA adjusts the program to maintain the needed conditions in the tailwaters. The reservoir operation study is planned along an approximately 25-year timeline, extending to 2030 TVA 2004, p. ES4. However, given the presence of at least 10 other listed aquatic species in the tailwaters of the mainstem Tennessee River reservoirs and the complexities of changing the operations plan, it is very likely that TVA will continue RRIP as part of their compliance with the Act for these other species beyond the timeline of the environmental impact statement EIS
and biological opinion that were prepared under Section 7 of the Act before alterations were made to dam release management. For these same reasons, TVA will likely incorporate RRIP to protect federally listed mussels present when it revisits its EIS around 2030, and because the current EISs term is 25 years, it is reasonable to assume TVA will issue another 25-year EIS.
Therefore, we estimate these conditions benefiting the snail darter will continue through at least midcentury Baxter 2020, pers. comm.. Overall, the persistence and expansion of snail darter populations in the mainstem since the 1970s indicate greater resiliency in these habitats than was considered at the time of listing, particularly now with the implementation of TVAs RRIP.
Anthropogenic changes to the land can also negatively impact the snail darter and its habitats. Sedimentation is one of the biggest threats to water quality in the Tennessee River Valley, including in streams occupied by snail darters. Big Sewee Creek has been impacted by sedimentation from persistent farming in the watershed, reducing the amount and quality of gravel habitat in the stream. The predominant agricultural activities contributing to sedimentation in Big Sewee Creek livestock pasture and row crops are exempt from many State and Federal regulations designed to reduce sediment runoff, and these activities are likely to continue into the future.
Therefore, we do not expect this population to reestablish unless habitat
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conditions improve in the future.
Sedimentation from agriculture and development is also considered a concern in the lower Little Tennessee River, Sequatchie River, South Chickamauga Creek, and Paint Rock River watersheds. There have been watershed-level efforts to address sedimentation issues in some of the tributaries where snail darters have been found. The South Chickamauga Creek Land Treatment Watershed Project, an effort of the Natural Resources Conservation Service NRCS of the U.S.
Department of Agriculture USDA, began in 2001, to reduce the runoff of sediment and nutrients in the watershed by installing animal waste management systems see 65 FR 44519; July 18, 2000. Additionally, the Limestone Valley Resource Conservation and Development Council is working with a wide variety of partners to implement the South Chickamauga Creek Headwaters Management Plan, developed in 2012, to address water quality issues Smith and Huser 2012, pp. i3. In the Paint Rock River, The Nature Conservancy TNC has designated a landscape conservation area and worked to address sedimentation issues from agriculture throughout the watershed, resulting in improved conditions for aquatic fauna Throneberry 2019, unpublished data.
Many of these efforts include restoring natural stream channel characteristics where streams have been channelized.
These efforts have been undertaken outside of species-specific recovery efforts for the snail darter, and they are likely to continue regardless of the delisting of the species. Other smallscale efforts have been undertaken to reduce sedimentation in many of the other tributaries inhabited by snail darters. It is likely that sedimentation has resulted in the extirpation of snail darters from Big Sewee Creek, but there is some potential for recolonization by individuals from Chickamauga Reservoir if habitat conditions improve.
Urban and suburban development may impact the snail darter as well.
Increases in the amount of impervious surfaces associated with development increase runoff to streams, destabilize hydrology, and increase water temperature. Additionally, residential and commercial development are associated with increased runoff of lawn and automotive chemicals into the streams Matthaei and Lang 2016, p.
180; Walsh et al. 2005, p. 707. The snail darter tributaries currently most impacted by development and the chemical and sediment runoff associated with it are South
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