AN INTERDISCIPLINARY STUDY OF STABLE AND RADIOGENIC ISOTOPES IN THE MIDDLE AND NORTH OCONEE RIVERS IN ATHENS, GEORGIA

River systems are of vital importance to the drinking water supply of Georgia. Monitoring of these valuable resources is therefore of high interest to ensure water quality as well as obtaining data on chemical, physical and biological water parameters for research purposes. Other natural systems alike, river systems are controlled by many processes of different nature, including geologic (e.g. weathering and erosion), hydrologic (e.g. precipitation and runoff) and biologic (e.g. metabolism) processes. Understanding these environmental processes and their interactions are a prerequisite for the assessment of potential impacts on river catchment areas caused by climate change.

This project investigates the changes in isotopic composition of Strontium, water oxygen and Dissolved Organic Carbon (DO¹³C) over one year in two major rivers in Georgia.

Sr is a biologically conservative trace element with its ⁸⁷Sr/⁸⁶Sr ratio being controlled by geologic processes such as selective weathering of minerals contained in the bedrock, types of lithologies eroded by the rivers etc. ⁸⁷Sr/⁸⁶Sr ratios provide the geologic baseline reflecting geochemical and geophysical processes in the river catchment area.

In contrast, dissolved organic carbon isotopes (DO¹³C) represent the largely biological component of this river monitoring project. DO¹³C can be affected by both terrestrial organic carbon supplies and subsequent in-stream processes (e.g. primary production and community respiration).

The ¹⁸O/¹⁶O isotope ratio of river water is largely driven by hydrological patterns, such as precipitation and temperature variation and could help indicate otherwise unnoticed environmental changes and trends against the Sr background.

The two rivers sampled for this study, the Middle and Oconee river, both flow through the city of Athens, where samples are taken monthly starting in March 2024. Sampling locations are adjacent to USGS hydrological gauging stations to assess the effect of river parameters such discharge and water height on isotope systems. A multimeter probe is used to determine water temperature, pressure, Dissolved Oxygen (DO), %DO, Specific Conductivity (SPC), conductivity (C), and pH at the time of sample extraction.

The goal of this project is to evaluate the combined use of different isotopic systems to investigate processes and their changes in river catchment areas.