ISOTOPIC ANALYSIS OF THE JORDAN RIVER NITROGEN CYCLE

The Jordan River is a 58 mile, 4 th order system that begins in Utah Lake and flows north to the Great Salt Lake. An overabundance of nutrients and organic matter has led to depleted oxygen levels in the river which threaten in-stream ecosystems as well as wetland ecosystems of the Great Salt Lake directly downstream. Nitrogen (N) is one of the key nutrients contributing to the eutrophication problem. The Jordan River has a multitude of sources contributing to its N load, including three water reclamation facilities (WRF) which discharge effluent into the river system. In order to quantify the spatial variability in N forms and loads, we sampled the Jordan River system in 25 locations during May, August, and October of 2016. Samples were taken above and below each WRF, within each facility outfall, and along an intensively sampled reach (every ~2km). Water samples were analyzed for nitrate (NO 3 - ), ammonium (NH 4 + ), dissolved organic nitrogen (DON) and chloride (Cl - ).  Isotopic signatures of in-stream NO 3 - were obtained for I´ 15 N NO3 (‰) and I´ 18 O NO3 (‰). Discharge measurements were made at each sampling location. Through these measurements we intend to quantify the contributions of each WRF to the Jordan River's N load as well as characterize the dominate in-stream N processes. We hypothesized that high NO 3 - concentrations and low dissolved oxygen (DO) concentrations in the river would facilitate in-stream denitrification, potentially reducing the N load with distance downstream. Preliminary results show the Jordan River's N load is predominately sourced from wastewater, with some WRFs contributing a daily N load greater than the N load found in the river directly upstream of the facility. While characterizing the N transformation trends and microbial activities present in the Jordan River will require further analysis, results from May 2016 suggest the effects of in-stream denitrification are not significant enough to substantially reduce the river's N load.