COMPARISON OF LAND-USE AND HYDROLOGIC CHARACTERISTICS FOR TWO SOUTHEASTERN US DRINKING WATER RESERVOIRS

Water quality is of increasing importance for drinking water reservoirs in the US Southeast due to predicted population increase, changes in land-use, and climate uncertainty. Water quality is determined by an array of factors including dissolved oxygen levels, temperature, and nutrient concentrations. Nutrient concentrations are largely controlled by the hydrologic and land-use characteristics of a reservoir watershed, as well as internal loading of nutrients from reservoir sediments. As part of a longitudinal study on the impact of solar-powered mixers on reservoir water quality, this investigation compared the hydrologic characteristics and watershed land-uses between two drinking water reservoirs located in central Georgia: Lake Varner (LV) and Hard Labor Creek Reservoir (HLCR). LV was established in 1983 and utilizes solar-powered mixers, while HLCR was established in 2018 and does not utilize mixers. Both reservoirs are warm, monomictic lakes.

Geospatial analyses determined the reservoir and watershed sizes using USGS hydrologic and elevation datasets. Land-use was classified using USDA Cropscape data from 2019 and combined into eight major land classes. HLCR was found to have a surface area of approximately 4.9 km² and a watershed size of approximately 77.3 km². LV’s surface area was approximately 3.3 km² and had a watershed size of approximately 63.5 km². The watersheds of both reservoirs were dominated by forested land (52% of HLCR, 58% of LV), followed by pasture/grassland (29% of HLCR, 25% of LV), and developed land (10% of HLCR, 7% of LV).

LV and HLCR are hydrologically similar, with comparable surface and watershed areas. As land-use is also quite similar between the reservoir watersheds, the difference in external loading of nutrients can be expected to be minimal. In addition, previous findings suggest dissolved oxygen levels and thermal stratification patterns are similar between the two reservoirs but are less clear on nutrient patterns. The similarities in hydrological and land-use characteristics, as well as dissolved oxygen and temperature patterns, suggest that any differences in nutrient dynamics between LV and HLCR are likely due to differences in internal processes, such as the presence of solar-powered mixers or reservoir age.