INVESTIGATING HUMAN IMPACT ON THE JORDAN RIVER USING SEDIMENTARY AND STABLE ISOTOPIC RECORDS

Changes in sediment size over time can represent past river dynamics and changes in stable isotope concentrations with depth can highlight environmental changes in aquatic ecosystems. Together, sedimentary and isotope data from sediment cores can reveal potential delivery processes and probable sources of organic matter inputs, particularly those from human activities. In this study, a total of nine one meter-long sediment cores along three transects were taken in June 2013. We subsampled the cores at 5cm intervals for δ¹³C, δ¹⁵N, C, N and grain size analyses. We used the depth profiles of the data to characterize important changes due to invasive species, farming practices and river dynamics. Our principle objectives were to answer the following questions: (1) How has the overall ecosystem changed with respect to vegetation and river dynamics? (2) How have the abundances of carbon and nitrogen isotopes changed prior to and after European settlement, and what are the carbon and nitrogen sources to Jordan River? Preliminary data has shown that the grain size percentages (clay, silt, sand) in several cores exhibit large shifts, particularly in JR2b, which coarsens dramatically in the top 20 cm of the core. These changes indicate variations in flow between the past and present. The depth profiles of δ¹³C showed large variations at different depths of the cores, ranging from -33‰ to -24‰ (vs. V-PDB). The large fluctuations of δ¹³C of sediment organic matter indicated rapid organic matter source change in the system post-European settlement in 1840, likely in part due to the introduction of the invasive species Phragmites australis. The depth profiles of δ¹⁵N have showed higher δ¹⁵N values in the upper sediment layers of the cores, which were likely due to historical nutrient discharges into the river associated with farming and untreated sewage. These data contribute to a growing interdisciplinary dataset that provide insight into the Utah Lake/Jordan River history.