H057-0009
Identifying Hot Moments of Iron and Manganese Cycling in a Drinking-Water Reservoir Using a High-Frequency Water Quality Sensor

Wednesday, 9 December 2020
Poster
Nicholas Hammond1, Madeline Eve Schreiber1, Bethany J. Bookout2, Rachel Simone Corrigan3, Francois Birgand4 and Cayelan Carey2, (1)Virginia Polytechnic Institute and State University, Geosciences, Blacksburg, VA, United States, (2)Virginia Polytechnic Institute and State University, Biological Sciences, Blacksburg, VA, United States, (3)Virginia Polytechnic Institute and State University, Forest Resources and Environmental Conservation, Blacksburg, VA, United States, (4)North Carolina State University, Biological and Agricultural Engineering, Raleigh, NC, United States
Abstract:
The biogeochemical cycles of iron (Fe) and manganese (Mn) in freshwater lakes and reservoirs have impacts on water quality, primary productivity, as well as organic carbon sequestration and mineralization. Dissolved oxygen (DO) has a strong influence on Fe and Mn cycling, as changes in redox state largely control the transformations of both metals. The relationship between seasonal anoxia in lakes and reservoirs and metals cycling has been well established, but less is known about the effects of short-term fluctuations in DO on Fe and Mn cycling.

We developed and applied a novel high-frequency monitoring system to assess the dynamics of metals chemistry in response to rapid changes in DO concentration in a seasonally-stratified drinking water reservoir located in Vinton, VA, USA. The reservoir contains a hypolimnetic oxygenation (HOx) system, which is designed to increase the hypolimnetic DO concentration. Water chemistry data are collected using an in-situ spectrophotometer connected to a multiplexor pump that can retrieve samples from multiple depths in the water column. The spectrophotometer measures UV-visible absorbance spectra for 216 wavelengths at a 10-minute resolution, and then partial least-squares regression (PLSR) models, calibrated on weekly water chemistry sampling data, are used to predict total and soluble Fe and Mn concentrations from absorbances. Preliminary results suggest that rapid increases in hypolimnetic DO facilitate higher rates of Fe and Mn oxidation in the water column, and rapid decreases in hypolimnetic DO quickly stimulate Fe and Mn release from the sediments. During summer 2020, this monitoring system is being used to measure Fe and Mn concentrations over the course of a reservoir-scale oxygenation experiment using the HOx system to induce shifts from anoxic to oxygenated conditions in the hypolimnion, and vice versa. By comparing the fluxes of metals observed during rapid shifts in DO concentration to those observed during periods of relatively static DO concentrations, we will elucidate the timing and magnitude of potential biogeochemical hot moments. Results from this study will aid drinking water managers in mitigating water quality issues, as well as improve our fundamental understanding of metals biogeochemistry in freshwater lakes and reservoirs.

<< Previous Abstract | Next Abstract >>