Oconee River Isotope Project (ORIP)

Co-PIs: Alex Heri, Mike Marshall, Katie Reinberger

Water quality and environmental monitoring programs in rivers typically involve only one or two scientific disciplines to assess changes through time. However, rivers represent the integration many processes occurring in basins including geologic (e.g. weathering), hydrologic (e.g. precipitation) and biologic (e.g. metabolism). We recently initiated a project using an integrated approach to monitoring river systems that incorporates indicators of multiple disciplines through water-associated stable isotopes, including Strontium, water-Oxygen and Dissolved Organic Carbon.

Strontium: As a largely biologically conservative tracer in freshwater systems, strontium isotope ratio (87Sr/86Sr) will provide the geologic baseline of the monitoring reflecting the mostly physical and geochemical processes that occur in river basins.

Oxygen: Water oxygen isotopes (18O/16O) are largely driven by hydrological patterns and temperature variation and could help indicate otherwise unnoticed environmental changes and trends against the Sr backdrop.

Carbon: Dissolved organic carbon isotopes (DO13C) represent the largely biological component of the monitoring. DO13C can be affected by both terrestrial organic carbon supplies and subsequent in-stream processes (e.g. primary production and community respiration).

Project Status – 5/9/2024

We have completed 3 monthly sampling trips to 2 Athens-area rivers, North Oconee River (NOR) at MLK & Ruth and Middle Oconee River (MOR) at Atlanta Highway. Both sites are directly adjacent to USGS hydrologic monitoring stations (02217770 & 02217500) that continuously document river discharge and other useful variables. We have secured access to MOR via Big Dogs on The River and regular use of a multimeter probe from UGA’s River Basin Center to measure common hydrological covariates.

Multimeter Data Summary

Data collected using a multiprobe included water temperature, pressure, %DO, DO, SPC (Specific Conductivity), conductivity, and pH. This data was supplemented by USGS data on gauge height and discharge. The NOR and MOR had similar temperatures with the temperature increasing on average 2.9 degrees Celsius per month. Pressure across both sites were similar with an average increase of 2.8 mm Hg per month. The MOR had a slightly higher %DO compared to the NOR. There was a slight decrease of –0.8 per month in [DO] (mg/L) across both sites. MOR had a higher SPC (us/cm) and C (us/cm) compared to NOR which could suggest a higher amount of dissolved material at the MOR. The average pH was the same for both MOR and NOR at 7.2. NOR had a higher gauge height according to USGS data. The average discharge (ft3/s) was higher at MOR versus NOR.

Isotopic Analysis Status

Water samples have all been refrigerated or acidified as appropriate for each analysis. Aliquots have been freeze-dried and acidified to remove inorganic carbon in preparation for the dissolved organic carbon isotope analysis within the next week. The new TCEA-IRMS system is fully plumbed and initial testing and tuning is underway for the water-oxygen isotope analysis. Samples are also in the queue for strontium isotope analysis with initial results anticipated in time for the next status report in September.