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Water Quality Data from Douglas Lake, Tennessee, US
Citation:
Beaulieu, J., J. Neeper, R. Pilla, N. Griffiths, T. Jett, M. Jones, AND N. Jones. Water Quality Data from Douglas Lake, Tennessee, US. U.S. Environmental Protection Agency, Washington, DC, 2026.
Impact/Purpose:
Douglas Reservoir is a warm, monomictic reservoir on the French Broad River in eastern Tennessee, USA, which was created in 1943 by the construction of Douglas Dam. The reservoir is managed by the Tennessee Valley Authority (TVA) for flood control, hydropower, and recreation and water quality is of interest to a broad array of stakeholders.
Description:
Douglas Reservoir is a warm, monomictic reservoir on the French Broad River in eastern Tennessee, USA, which was created in 1943 by the construction of Douglas Dam. Managed by the Tennessee Valley Authority (TVA) for flood control, hydropower, and recreation, the 115 km² reservoir experiences seasonal water level fluctuations of about 13.4 m, with the greatest drawdown occurring in winter (Mosher et al. 2015). We sampled 200 sites in Douglas Reservoir over five consecutive days in July 2024 when the reservoir was at full summer pool (each sample representing 0.58 km2 of reservoir). We used a generalized random tessellation stratified (GRTS) survey design (Olsen et al. 2012) to identify the 200 sampling sites, based on the NHDPlus High Resolution dataset’s shapefile of the reservoir (USGS 2022) and using the “spsurvey” package in R version 4.5.2 (Dumelle et al. 2023). The GRTS design was stratified by depth, with 100 sites ≤ 10 m deep, 50 sites between 10-20 m deep (“mid-depth”), and 50 sites > 20 m (Figure 1), using digitized bathymetry data. At each site we measured ebullitive and diffusive CH4 and CO2 fluxes (mg C m-2 d-1) following methods detailed in Beaulieu et al. (2026), US EPA (2019), and briefly described here. Diffusive fluxes were measured using a floating chamber attached to an onboard CO2/CH4 analyzer (Los Gatos Research Microportable Gas Analyzer, San Jose, California, USA) that recirculated gas through the chamber/analyzer system for a minimum of two minutes, while recording CH4 and CO2 partial pressure every one to five seconds. CH4 ebullition was measured using inverted funnel traps (0.251 m2 in area) deployed for 12-24 hours. CH4 in gas samples retrieved from the funnels was quantified via gas chromatography. At each site surface and bottom measurements of water temperature (°C), dissolved oxygen (DO; mg L-1), specific conductivity (µS cm-1), pH, and turbidity (FNU) using a data sonde following US EPA (2022a). Water for chlorophyll-a analysis was sampled at 0.1 m below the water surface, filtered immediately through a 0.7 µm pore size glass fiber filter, stored in a dark cooler until transferred to a freezer, and extracted with acetone and quantified on a Turner Designs 10-AU Fluorometer (San Jose, California, USA) following US EPA (2022b). The data set contains several missing values, reported as NA, due to equipment failure. In additions, 27 sites were unable to be sampled for CH4 ebullition due to time constraints, of which 23 were in the deep (> 20 m) strata with minimal expected ebullition. These are also reported as NA.