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).