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Bioavailability of Dissolved Organic Nitrogen Originating from Natural Sources and Wastewater Effluent in the Truckee River N. Bertrando*, R. G. Qualls*, M. Brisbin**, M. *Univ. of Nevada, **City of Sparks, In processing the wastewater generated by the Reno-Sparks metropolitan area, the Truckee Meadows Water Reclamation Facility (TMWRF) uses an advanced Tertiary treatment system which employs bacteria to convert inorganic N and P to less available Organic forms (i.e DON and DOP) such that most of the N discharged into the river is DON. However, the current regulations only consider the Total Maximum Daily Load (TMDL) of all types on N combined. Objective In order to assess the affects that TMWRF effluent will have on the N balance of the Truckee River, our study examines the spatial and seasonal variations in bioavailability of Dissolved Organic Nitrogen originating from natural sources and wastewater effluent. This effort will help us to understand the nutrient loads in the Truckee River and how the urban corridor of the Reno-Sparks metropolitan area influences these loads. In particular, we have monitored in-stream nutrient limitation of periphyton growth and microbial mineralization of natural and effluent DON. Chl a (ug/sq cm) Spring 2008 Periphyton Growth Control 9.00 Nitrogen 8.00 Phosphorous 7.00 Nitro + Phos Amino Acids 6.00 5.00 4.00 3.00 2.00 1.00 1 Castano* Of Nevada Undergraduate Researchers Methods DON Biodegradation Summer 2007 Bioassays: 1000.00 Since the variety of constituents in DON have not been thoroughly identified and may vary based on source, the primary method for determining bioavailability is through bioassays. These bioassays provide an estimate of the fraction of DON that is biologically available. Samples of water were collected from above and below the Reno-Sparks metropolitan area, from an urban runoff site (the North Truckee Drain), and from the TMWRF effluent spout. These samples were then inoculated with a mixture of local soil microbes and exposed to a solar simulator UV light for 4 hours per day. Samples taken on days 0, 3, 7, 14, and 67 were analyzed for Total N (TN), Total Dissolved N (TDN), (NO3+NO2)-N, and NH4-N. From these measurements, the DON was calculated: Upstream 900.00 Downstream 800.00 Effluent 700.00 [DON] ug/L Nitrogen is an element of concern to the quality of water in the Truckee River. The supplies of either nitrogen (N) or phosphorus (P) are the elements that are most likely to limit the production of algae in freshwater streams, rivers, and lakes. High concentrations of available nitrogen or phosphorus can stimulate excessive algal growth, which in turn can lead to die off, decay, and anaerobic conditions. While inorganic forms of N (NO3, NH4) are considered 100% bioavailable, Dissolved Organic Nitrogen (DON) has many components varying degrees of bioavailability. These DON compounds range from small compounds such as urea and amino acids to large humic acid compounds, with the specific makeup DON in a water sample being dependent upon its specific source. K.L. Dean*, & L. Urban Runoff 600.00 y = 806.64e -0.0067x R2 = 0.874 500.00 400.00 y = 482.48e -0.0053x R2 = 0.9013 300.00 y = 289.43e -0.0069x R2 = 0.8939 200.00 100.00 y = 158.31e -0.0074x R2 = 0.8339 0.00 0 10 20 30 40 50 60 70 80 Time (days) DON = TDN – ((NO3+NO2)-N + NH4-N) DON Biodegradation Fall 2007 These tests were repeated seasonally for two consecutive years. 900.00 Upstream Nutrient Limitation Studies: 800.00 Since the affects of N inputs to the river are dependent upon the needs of the organisms which live there, we tested the nutrient limitation of periphyton growth in the river using Nutrient Diffusing Substrates (NDS) to create locally enriched zones of N, P, N+P, and Amino Acids. These NDS were places in riffle zones of the river for 11 days then collected and analyzed for chlorophyll a as a measure of biomass. The sampling locations were the same sites where we collected water samples with one addition at the E. McCarran Bridge just upstream from TMWRF and the North Truckee Drain. 700.00 Downstream Effluent Urban Outfall [DON] ug/L Introduction 1Univ. 1 Springer* , 600.00 y = 723.72e -0.0031x R2 = 0.7704 500.00 400.00 300.00 200.00 100.00 0.00 0 10 20 30 40 50 60 70 80 Time (days) Results and Discussion The results of the bioassays varied between season and between samples. A significant fraction (23-48%) of the wastewater effluent DON was mineralized in every trial while DON from the upstream sample was mineralized during the summer sampling (43%) but not during other seasons (<5%). The DON mineralization was most variable in the urban runoff sample (370%). It is also important to note the magnitude of [DON] was consistent at each site throughout the year, with the wastewater effluent being much higher than any other sample (~ 800 ug/L-N vs. <500 ug/L). For all samples where DON was degraded, the fate was primarily NH4 (ammonia) with some becoming particulate N. Figure 2. Biodegradation of DON in water sampled from three locations on the Truckee River and from TMWRF effluent. Confluence of North Truckee Drain and the Truckee River. TMWRF in background. Upstream of the RenoSparks metropolitan area, near Mogul 0.00 Upstream McCarran Bridge Urban Outfall Downstream Site Summer 2008 Periphyton Growth Control 12.00 Nitrogen Phosphorous Chl a (ug/sq. cm) 10.00 Nitro + Phos 8.00 The nutrient limitation studies demonstrated both seasonal and spatial variability as well. All locations on the Truckee River were consistently N+P limited, but the urban runoff did not exhibit nutrient limitation. Limitation by N alone was apparent only at the McCarran Bridge and showed a borderline effect downstream from the TMWRF discharge point. Downstream of TMWRF, Train Bridge near Lockwood, Truckee River Katie Dean installing stakes for securing NDS assemblies in the river. Amino Acids 6.00 4.00 2.00 0.00 Upstream McCarran Bridge Urban Outfall Downstream Site Figure 1. Tests of nutrient limitation to periphyton growth, measured as chlorophyll a (ug/cm2), on NDS at four locations in the Truckee River system. These results suggest that wastewater DON has a higher bioavailability than naturally derived DON and that bioavailability of natural DON may experience a seasonal cycle with increased DON bioavailability during the summer months (the growing season). However, no more than 50% of the wastewater DON was mineralized in any trial. Since the site downstream from the TMWRF experienced borderline N limitation during the spring and summer, the bioavailability of wastewater DON may play an important role in the nutrient dynamics in the Truckee River. Acknowledgements: Field work and lab analyses were assisted by Greg Wilson and the TMWRF Staff.