Discipline: Ecology Environmental and Earth Sciences
Kelsey Bicknell - University of New Mexico
Co-Author(s): Ricardo Gonzalez-Pinzon, University of New Mexico, NM
Understanding how rivers and river-dependent systems such as irrigation networks process nutrient loads from Wastewater Treatment Plants (WWTPs) will be key to developing effective nutrient management strategies. Paring stable isotope analysis with nutrient budgets of rivers can provide valuable insight to the specific processes influencing nutrient concentrations in the network. The nutrient budget of an ~300km stretch of arid river was studied over a three-year period (2005-2008) using a mass balance approach to determine source sink behavior of nitrate (NO3- ), ammonium (NH4+), and soluble reactive phosphorus (SRP). We hypothesized the irrigation network would be integral to the nutrient budget due to its higher residence times and increased biologic activity. Our study found the Albuquerque WWTP (ABQWWTP) was responsible for 83% of NO3-N, 92% of SRP, and 73% of NH4-N loads to the river. During the growing season (Mar-Oct), the agriculture network was calculated to retain approximately 77% of NO3-N and 85% of SRP inputs, the majority of which are supplied by the ABQWWTP. In the non-growing season (Nov-Feb), the irrigation network serves as a source of nutrients to the river, exporting approximately 131 kg/day of NO3-N and approximately 71 kg/day of SRP. This data indicates the irrigation network is key to managing downstream nutrient concentrations in the river because the network serves as a nutrient sink during biologically productive times. Applying full amounts of fertilizer to the crops in the reach may be redundant if the crop is using nutrients already available in the water, but answering this question requires further research. We intend to explore WWTP NO3- use by analyzing the δ15N and δ18O of NO¬3- and the δ15N of macrophyte foliage. Preliminary analysis suggests the ABQWWTP effluent outputs NO3- with an isotope signature distinct from the background signal of the river upstream the ABQWWTP input, allowing us to use the NO3- isotope signal from the ABQWWTP as an integrator of NO3- processing through the system. References: Mortensen, J. G., González-Pinzón, N, R., Dahm, C. N., Wang, J., Zeglin, L. H., & Van Horn, D. J. (2016). Advancing the Food-Energy-Water Nexus: Closing Nutrient Loops in Arid River Corridors. Environmental Science and Technology, 50(16), 8485–8496. Burns, D. A., Boyer, E. W., Elliott, E. M., & Kendall, C. (2009). Sources and transformations of nitrate from streams draining varying land uses: evidence from dual isotope analysis. Journal of Environmental Quality, 38(3), 1149–59. Robinson, D. (2001). δ 15 N as an integrator of the nitrogen cycle. Trends in Ecology & Evolution, 16(3), 153–162.ERN_abstract.docx
Funder Acknowledgement(s): Thank you to Dr. David Van Horn and his students for doing the field work to collect the data used in this project and for sharing the data with us. Big thanks to Jacob Mortenson and Dr. Ricardo González-Pinzón for their work on the first nutrient budget. Thank you to Dr. Seth Newsome for helping me decipher the initial isotope results. Funding provided by the Center for Water and the Environment (HRD-1345169).
Faculty Advisor: Ricardo Gonzalez-Pinzon, firstname.lastname@example.org
Role: My contribution is the stable isotope analysis and the mass balances of the river, drain, and delivery network.