HESS Hydrology and Earth System Sciences HESS Hydrol. Earth Syst. Sci. 1607-7938 Copernicus Publications Göttingen, Germany 10.5194/hess-18-967-2014 Antecedent flow conditions and nitrate concentrations in the Mississippi River basin Murphy J. C. https://orcid.org/0000-0002-0881-0919 1 Hirsch R. M. 2 Sprague L. A. 3 Tennessee Water Science Center, US Geological Survey, Nashville, USA National Research Program, US Geological Survey, Reston, USA National Water-Quality Assessment Program, US Geological Survey, Boise, USA 10 03 2014 18 3 967 979 Copyright: © 2014 J. C. Murphy et al. 2014 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://hess.copernicus.org/articles/18/967/2014/hess-18-967-2014.html The full text article is available as a PDF file from https://hess.copernicus.org/articles/18/967/2014/hess-18-967-2014.pdf

The relationship between antecedent flow conditions and nitrate concentrations was explored at eight sites in the 2.9 million square kilometers (km<sup>2</sup>) Mississippi River basin, USA. Antecedent flow conditions were quantified as the ratio between the mean daily flow of the previous year and the mean daily flow from the period of record (Qratio), and the Qratio was statistically related to nitrate anomalies (the unexplained variability in nitrate concentration after filtering out season, long-term trend, and contemporaneous flow effects) at each site. Nitrate anomaly and Qratio were negatively related at three of the four major tributary sites and upstream in the Mississippi River, indicating that when mean daily streamflow during the previous year was lower than average, nitrate concentrations were higher than expected. The strength of these relationships increased when data were subdivided by contemporaneous flow conditions. Five of the eight sites had significant negative relationships (<i>p</i> ≤ 0.05) at high or moderately high contemporaneous flows, suggesting nitrate that accumulates in these basins during a drought is flushed during subsequent high flows. At half of the sites, when mean daily flow during the previous year was 50 percent lower than average, nitrate concentration can be from 9 to 27 percent higher than nitrate concentrations that follow a year with average mean daily flow. Conversely, nitrate concentration can be from 8 to 21 percent lower than expected when flow during the previous year was 50 percent higher than average. Previously documented for small, relatively homogenous basins, our results suggest that relationships between antecedent flows and nitrate concentrations are also observable at a regional scale. Relationships were not observed (using all contemporaneous flow data together) for basins larger than 1 million km<sup>2</sup>, suggesting that above this limit the overall size and diversity within these basins may necessitate the use of more complicated statistical approaches or that there may be no discernible basin-wide relationship with antecedent flow. The relationships between nitrate concentration and Qratio identified in this study serve as the basis for future studies that can better define specific hydrologic processes occurring during and after a drought (or high flow period) which influence nitrate concentration, such as the duration or magnitude of low flows, and the timing of low and high flows.

 References Alexander, R. B., Smith, R. A., Schwarz, G. E., Boyer, E. W., Nolan, J. V., and Brakebill, J. W.: Differences in Phosphorous and Nitrogen Delivery to The Gulf of Mexico from the Mississippi River Basin, Environ. Sci. Technol. 42, 822–830, 2008. Ashby, J. A., Bowden, W. B., and Murdoch, P. S.: Controls on denitrification in riparian soils in headwater catchments of a hardwood forest in the Catskill Mountains, USA, Soil Biol. Biochem., 30, 853–864, 1998. Aulakh, M. S. and Bijay-Singh: Nitrogen losses and fertilizer N use efficiency in irrigated porous soils, Nutrient Cy. Agroecosyst., 27, 197–212, 1997. Aulenbach, B. T., Buxton, H. T., Battaglin, W. A., and Coupe, R. H.: Flow and nutrient fluxes of the Mississippi-Atchafalaya River Basin and subbasins for the period of record through 2005, US Geological Survey Open-File Report 2007–1080, 2007. Bernal, S. and Sabater, F.: Changes in discharge and solute dynamics between hillslope and valley-bottom intermittent streams, Hydrol. Earth Syst. Sci., 16, 1595–1605, <a href="http://dx.doi.org/10.5194/hess-16-1595-2012">https://doi.org/10.5194/hess-16-1595-2012</a>, 2012. Biron, P. M., Roy, A. G., Courschesne, F., Hendershot, W. H., Cote, B., and Fyles, J.: The effect of antecedent moisture conditions on the relationship of hydrology to hydrochemistry in a small forested watershed, Hydrol. Process. 13, 1541–1555, 1999. Bowman, J. A. and Collins, M. A.: Impacts of irrigation and drought on Illinois ground-water resources, State of Illinois, Department of Energy and Natural Resources, Illinois state water survey, ISWS/RI-109/87, 31 pp., 1987. Brown, J. B., Sprague, L. A., and Dupree, J. A.: Nutrient sources and transport in the Missouri River basin, with emphasis on the effects of irrigation and reservoirs, J. Am. Water Resour. Assoc. 47, 1034–1060, 2011. Burkart, M. R. and Stoner, J. D.: Chapter 7. Nitrogen in groundwater associated with agricultural systems, in: Nitrogen in the Environment: Sources, Problems, and Management (2nd Edn.), Academic Press/Elsevier, Amsterdam, edited by: Hatfield, R. F. and Follett, J. L., 177–202, 2008. Burt, T. and Worrall, F.: Non- stationary in long time series: some curious reversals in the "memory" effect, Hydrol. Process. 21, 3529–3531, 2007. Burt, T. P. and Worrall, F.: Stream nitrate levels in a small catchment in south west England over a period of 35 years (1970–2005), Hydrol. Process. 23, 2056–2068, 2009. Burt, T. P., Arkell, B. P., Trudgill, S. T., and Walling, D. E.: Stream nitrate levels in a small catchment in south west England over a period of 15 years, Hydrol. Process. 2, 267–284, 1988. Cooper, R., Thoss, V., and Watson, H.: Factors influencing the release of dissolved organic carbon and dissolved forms of nitrogen from a small upland headwater during autumn runoff events, Hydrol. Process. 21, 622–633, 2007. Creed, I. F. and Band, L. E.: Export of nitrogen from catchments within a temperate forest: Evidence for a unifying mechanism regulated by variable source area dynamics, Water Resour. Res., 34, 3105–3120, 1998. de Klein, C. A. M. and van Logtestijn, R. S. P.: Denitrification in grassland soils in the Netherlands in relation to irrigation, N-application rate, soil water content and soil temperature, Soil Biol. Biochem., 28, 231–237, 1996. Detty, J. M. and McGuire, K. J.: Topographic controls on shallow groundwater dynamics: implications of hydrologic connectivity between hillslopes and riparian zones in a till mantled catchment, Hydrol. Process., 24, 2222–2236, 2010. Dinnes, D. L., Karlen, D. L., Jaynes, D. B., Kaspar, T. C., Hatfield, J. L., Colvin, T. S., and Cambardella, C. A.: Nitrogen management strategies to reduce nitrate leaching in tile-drained Midwestern soils, Agron. J., 94, 153–171, 2002. Donner, S. D. and Scavia, D.: How climate controls the flux of nitrogen by the Mississippi River and the development of hypoxia in the Gulf of Mexico, Limnol. Oceanogr., 52, 856–861, 2007. Emmerich, W. E. and Heitschmidt, R. K.: Drought and Grazing: II. Effects on runoff and water quality, J. Range Manage., 55, 229–234, 2002. Foster, I. D. L. and Walling, D. E.: The effects of the 1976 drought and autumn rainfall on stream solute levels, Earth Surf. Process. 3, 393–406, 1978. Ferguson, R., Shapiro, C., Wortmann, C., Shaver, T., and Hergert, G.: University of Nebraska-Lincoln Extension, CropWatch, Nebraska crop production & pest management information, Checking for Residual nitrate this spring: <a href="http://cropwatch.unl.edu/web/cropwatch/archive?articleID=5121463">http://cropwatch.unl.edu/web/cropwatch/archive?articleID=5121463</a> (last access: 21 June 2013), 2013. Garrett, J.: Concentrations, loads and yields of select constituents from major tributaries of the Mississippi and Missouri Rivers in Iowa, Water Years 2004–2008, US Geological Survey Scientific Investigations Report 2012-5240, 72 pp., 2012. Gascuel-Odoux, C., Aurousseau, P., Durand, P., Ruiz, L., and Molenat, J.: The role of climate on inter-annual variation in stream nitrate fluxes and concentrations, Sci. Total Environ. 408, 5657–5666, 2010. Groves, S. J. and Bailey, R. J.: The influence of sub-optimal irrigation and drought on crop yield, N uptake and risk of N leaching from sugarbeet, Soil Use Manage., 13, 190–195, 1997. Helsel, D. R. and Hirsch, R. M.: Statistical methods in water resources, Techniques of water-resources investigations, Book 4, chapter A3, US Geological Survey, 522 pp., 2002. Hirsch, R. M., Moyer, D. L., and Archfield, S. A.: Weighted regressions on time, discharge, and season (WRTDS), with an application to Chesapeake Bay river inputs, J. Am. Water Resour. Assoc. 46, 857–880, 2010. Hornberger, G. M., Bencala, K. E., and McKnight, D. M.: Hydrological controls on dissolved organic carbon during snowmelt in the Snake River near Montezuma, Colorado, Biogeochemistry 25, 147–165, 1994. Hrachowitz, M., Savenije, H. H. G., Blöschl, G., McDonnell, J. J., Sivapalan, M., Pomeroy, J. W., Arheimer, B., Blume, T., Clark, M. P., Ehret, U., Fenicia, F., Freer J. E., Gelfan, A., Gupta, H. V., Hughes, D. A., Hut, R. W., Montanari, A., Pande, S., Tetzlaff, D., Troch, P.A., Uhlenbrook, S., Wagener, T., Winsemius, H. C., Woods, R. A., Zehe, E., and Cudennec, C.: A decade of Predictions in Ungauged Basins (PUB) – a review, Hydrol. Sci. J., 58, 1198–1255, 2013. Kalkhoff, S. J.: Occurrence and Transport of Nutrients in the Missouri River Basin, April through September 2011, U.S. Geological Survey Professional Paper 1798-G, 23 pp., 2013. Lange, J. and Haensler, A.: Runoff generation following a prolonged dry period, J. Hydrol., 464–465, 157–164, 2012. Lucey, K. J. and Goolsby, D. A.: Effects of Climatic Variations over 11 Years on Nitrate-Nitrogen Concentrations in the Raccoon River, Iowa, J. Environ. Qual., 22, 38–46, 1993. Macrae, M. L., English, M. C., Schiff, S. L., and Stone, M.: Influence of antecedent hydrologic conditions on patterns of hydrochemical export from a first-order agricultural watershed in Southern Ontario, Canada, J. Hydrol., 389, 101–110, 2010. National Oceanic and Atmospheric Administration, National Climatic Data Center, Climate Monitoring Group Palmer Hydrological Drought Index – May 2012 to April 2013, available at: <a href="http://www.ncdc.noaa.gov/oa/climate/research/prelim/drought/palmer.html">http://www.ncdc.noaa.gov/oa/climate/research/prelim/drought/palmer.html</a> (last access: 21 June 2013), 2013. Nolan, J. V., Brakebill, J. W., Alexander, R. B., and Schwarz, G. E., ERF1_2 – Enhanced River Reach File 2.0: <a href="http://water.usgs.gov/GIS/metadata/usgswrd/XML/erf1_2.xml">http://water.usgs.gov/GIS/metadata/usgswrd/XML/erf1_2.xml</a> (last access: 2 June, 2013), 2002. Pervez, M. S. and Brown, J. F.: Mapping irrigated lands at 250-m scale by merging MODIS data and national agricultural statistic, Remote Sens., 2, 2388–2414, 2010. Rabalais, N. N. and Turner, R. E.: Hypoxia in the northern Gulf of Mexico: description, causes and change, in: Coastal Hypoxia: Consequences for living resources and ecosystems, Coastal and Estuarine Studies, American Geophysical Union, 1–36, 2001. Randall, G. W., Vetsch, J. A., and Huffman, J. R.: Nitrate losses in subsurface drainage from a corn-soybean rotation as affected by time of nitrogen application and use of Nitrapyrin, J. Environ. Qual., 32, 1764–1772, 2003. Rehm, G., Schmitt, M., and Eliason, R., University of Minnesota-Extension, Using soil nitrate test in Minnesota, WW-07310: available at: <a href="http://www.extension.umn.edu/distribution/cropsystems/DC7310.html">http://www.extension.umn.edu/distribution/cropsystems/DC7310.html</a> (last access: 21 June 2013), 2009. Rozemeijer, J. C., van der Velde, Y., van Geer, F. C., Bierkens, M. F. P., and Broers, H. P.: Direct measurements of the tile drain and groundwater flow route contributions to surface water contamination: From field-scale concentration patterns in groundwater to catchment-scale surface water quality, Environ. Pollut., 158, 3571–3579, 2010. Sanford, W. E. and Pope, J. P.: Quantifying Groundwater's Role in Delaying Improvements to Chesapeake Bay Water Quality, Environ. Sci. Technol., 47, 13330–13338, 2013. Sawyer, J.: Iowa State University-Extension, Soil profile nitrate in corn fields following the 2012 drought, available at: <a href="http://www.extension.iastate.edu/CropNews/2013/0221sawyer.htm">http://www.extension.iastate.edu/CropNews/2013/0221sawyer.htm</a> (last access: 21 June 2013), 2013. Scavia, D., Rabalais, N. N., Turner, R. E., Justic, D., and Wiseman, W. J.: Predicting the response of Gulf of Mexico hypoxia to variation in Mississippi River nitrogen load, Limnol. Oceanogr., 48, 951–956, 2003. Shaman, J., Steiglitz, M., and Burns, D.: Are big basins just the sum of small catchments?, Hydrol. Process., 18, 3195–3206, 2004. Sidle, R. C.: Field observations and process understanding in hydrology: essential components in scaling, Hydrol. Process., 20, 1439–1445, 2006. Sivapalan, M.: Process complexity at hillslope scale, process simplicity at the watershed scale: is there a connection?, Hydrol. Process., 17, 1037–1041, 2003. Soulsby, C., Petry, J., Brewer, M. J., Dunn, S. M., Ott, B., and Malcolm, I. A.: Identifying and assessing uncertainty in hydrological pathways: a novel approach to end member mixing in a Scottish agricultural catchment, J. Hydrol., 274, 109–128, 2003. Soulsby, C., Tetzlaff, D., Dunn, S. M., and Waldron, S.: Scaling up and out in runoff process understanding: insights from nested experimental catchment studies, Hydrol. Process., 20, 2461–2465, 2006. Sprague, L. A., Hirsch, R. M., and Aulenbach, B. T.: Nitrate in the Mississippi River and its tributaries, 1980 to 2008: Are we making progress?, Environ. Sci. Technol., 45, 7209–7216, 2011. Stites, W. and Kraft, G. J.: Nitrate and chloride loading to groundwater from an irrigated north-central US sand-plain vegetable field, J. Environ. Qual., 30, 1176–1184, 2001. Turner, R. E., Rabalais, N. N., and Justic, D.: Predicting summer hypoxia in the northern Gulf of Mexico: Riverine N, P, and Si loading, Mar. Pollut. Bull., 52, 139–148, 2006. Vecchia, A.: Relation between climate variability and stream water quality in the continental United States, Hydrol. Sci. Technol., 19, 77–98, 2003. Vecchia, A. V., Martin, J. D., and Gilliom, R. J.: Modeling variability and trends in pesticide concentrations in streams, J. Am. Water Resour. Assoc., 44, 1308–1324, 2008. Walling, D. E. and Foster, I. D. L.: Variations in the natural chemical concentration of river water during flood flows, and the lag effect: some further comments, J. Hydrol., 26, 237–244, 1975. Webb, B. W. and Walling, D. E.: Stream solute behavior in the River Exe basin, Devon, UK, Dissolved loads of rivers and surface water quantity/quality relationships, Proceedings of the Hamburg Symposium, August 1983, IAHS Publ no. 141, 153–169, 1984. Welsch, D. L., Kroll, C. N., McDonnell, J. J., and Burns, D. A.: Topographic controls on the chemistry of subsurface stormflow, Hydrol. Process., 15, 1925–1938, 2001.