Study site
Field data were collected at Falling Creek Reservoir (FCR), a small (0.12 km2, maximum depth = 9.3 m), dimictic reservoir located in Vinton, Virginia, USA (Figure 1, Gerling et al. 2014). FCR was constructed in 1898 and is managed as a drinking water reservoir by the Western Virginia Water Authority (WVWA) in Roanoke, VA. The summer stratified period at FCR typically lasts from May to October. FCR is located in a forested catchment with one primary inflow and several smaller tributaries. Due to the underlying geology, which consists of Fe- and Mn-rich rocks of the Blue Ridge and Piedmont Provinces (Woodward, 1932), this region has elevated Fe and Mn concentrations in surface and groundwater (Chapman et al. 2013).
FCR contains a HOx system, which can be activated and deactivated to control DO concentrations in the hypolimnion without altering thermal stratification or water temperature (Figure 1, Gerling et al. 2014). The HOx system at FCR was activated from 29 June 2020 until 2 December 2020, when it was turned off for the winter period. It remained deactivated from 2 December 2020 until 11 June 2021, at which point it was turned back on and remained activated until the end of the study period on 21 June 2021.
FCR is equipped with sensors that continuously monitor the physical, chemical, and meteorological conditions at the reservoir’s deepest spot, which was the primary sampling location in this study (Figure 1). DO sensor data was collected using a YSI EXO2 (Yellow Springs, OH) deployed at 1.6m and two In-Situ RDO-PRO-X sensors (Fort Collins, CO) at 5m and 9m (Carey et al. 2022b). Ten-minute resolution temperature measurements were collected by in situ sensors deployed every meter from the surface to the reservoir sediments (Carey et al. 2022b). To quantify the intensity of reservoir thermal stratification during each deployment, we calculated Schmidt stability (J m-2, Idso 1973) using temperature measurements and bathymetric data from FCR (Carey et al. 2022c) as inputs to the R package rLakeAnalyzer (Winslow et al. 2019). Meteorological variables were measured by a research-grade Campbell Scientific meteorological station deployed on the dam of FCR (Carey et al. 2022a).