scholarly journals Antecedent flow conditions and nitrate concentrations in the Mississippi River basin

2014 ◽  
Vol 18 (3) ◽  
pp. 967-979 ◽  
Author(s):  
J. C. Murphy ◽  
R. M. Hirsch ◽  
L. A. Sprague
Keyword(s):  
River Basin ◽  
Mississippi River ◽  
Nitrate Concentration ◽  
Regional Scale ◽  
Mississippi River Basin ◽  
Flow Conditions ◽  
Daily Streamflow ◽  
Nitrate Concentrations ◽  
High Flows ◽  
The Mean

Abstract. The relationship between antecedent flow conditions and nitrate concentrations was explored at eight sites in the 2.9 million square kilometers (km2) 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 (p ≤ 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 km2, 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.

scholarly journals Antecedent flow conditions and nitrate concentrations in the Mississippi River Basin

2013 ◽  
Vol 10 (9) ◽  
pp. 11451-11484 ◽  
Author(s):  
J. C. Murphy ◽  
R. M. Hirsch ◽  
L. A. Sprague
Keyword(s):  
River Basin ◽  
Mississippi River ◽  
Nitrate Concentration ◽  
Mississippi River Basin ◽  
Storm Events ◽  
Flow Conditions ◽  
Continental Scale ◽  
Antecedent Moisture ◽  
Nitrate Concentrations ◽  
The Mean

Abstract. The influence of antecedent flow conditions on nitrate concentrations was explored at eight sites in the Mississippi River Basin, USA. Antecedent moisture conditions have been shown to influence nutrient export from small, relatively homogenous basins, but this influence has not been observed at a regional or continental scale. 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 (Q ratio), and the Q ratio 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 Q ratio were negatively related at three of the four major tributary sites and upstream in the Mississippi River, indicating that when the previous year was drier than average, at these sites, 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 (p ≤ 0.05) at high or moderately high contemporaneous flows, suggesting nitrate that accumulates in these basins during a drought is flushed during subsequent storm events. At half of the sites, when flow during the previous year was 50% drier than average, nitrate concentration can be from 9 and 27% higher than nitrate concentrations that follow a year with average daily flow. Conversely, nitrate concentration can be from 8 and 21% lower than expected when the previous year was 50% wetter than average. These relationships between nitrate concentration and Q ratio serve as the basis for future studies that can better define specific hydrologic processes occurring during and after a drought, which influence nitrate concentration, such as the duration or magnitude of low flows, and the timing of low and high flows.

scholarly journals Multi-scale measurements and modeling of denitrification in streams with varying flow and nitrate concentration in the upper Mississippi River basin, USA

2009 ◽  
Vol 93 (1-2) ◽  
pp. 117-141 ◽  
Author(s):  
John Karl Böhlke ◽  
Ronald C. Antweiler ◽  
Judson W. Harvey ◽  
Andrew E. Laursen ◽  
Lesley K. Smith ◽  
...  
Keyword(s):  
River Basin ◽  
Mississippi River ◽  
Nitrate Concentration ◽  
Mississippi River Basin ◽  
Upper Mississippi River ◽  
Multi Scale ◽  
Upper Mississippi River Basin

Subsurface reactivity dominates regional patterns of riverine nitrate concentration variability

2020 ◽  
Author(s):  
Andreas Musolff ◽  
Pia Ebeling ◽  
Jan H. Fleckenstein ◽  
Rohini Kumar ◽  
Rémi Dupas
Keyword(s):  
Large Scale ◽  
Nitrate Concentration ◽  
Low Flow ◽  
Flow Conditions ◽  
Regional Patterns ◽  
Low Concentration ◽  
Concentration Variance ◽  
Wide Range ◽  
Nitrate Concentrations ◽  
The Mean

<p>The mean surface water concentration and the concentration variance of nutrients are major water quality characteristics of catchments that directly relates to exported nutrient loads and ecosystems functioning. The mean concentration reflects nutrient input, discharge (Q) and retention within different compartments of the catchment. The concentration variability defines the export regime of a certain solute and can be characterized by the ratio of CV<sub>C</sub> and CV<sub>Q</sub> and the slope <em>b </em>of the logC-logQ relationship. Recent explorative modelling studies argue that the export regime is shaped by spatial variance of the solute source in the catchment and by the subsurface reactivity (Musolff et al. 2017, Zhi et al. 2019). Here, we seek large scale evidence of this hypothesis by analyzing nitrate concentration and discharge (C-Q) time series in more than 1400 catchments across France and Germany. We found a consistent relationship between mean nitrate concentrations and the fraction of cultivated area within the catchments pointing to agriculture as the dominant nitrate source. The upper boundary of this relationship follows an exponential function with catchments showing mean nitrate concentrations around this envelope function being characterized by chemostatic export regimes with low concentration variance and slope <em>b</em> near zero. In contrast, catchments deviating from this relationship i.e. with lower than expected mean nitrate concentrations are characterized by higher concentration variance and steep, positive logC-logQ slopes. We argue, that subsurface retention is the major control of this behavior: i.e., effective denitrification decreases groundwater nitrate concentration. This was mainly observed in catchments with sedimentary aquifers and low topographic slopes. Here, old water components in the catchment storage that dominate discharge under low flow conditions are low in nitrate. Under high flow conditions, young water components high in nitrate concentrations are activated. Catchments without effective nitrate retention are characterized by a low concentration gradient between younger and older water components. The observed relationship between the fraction of cultivated areas, mean nitrate concentration and export regime was found to be surprisingly consistent across the wide range of hydroclimatic conditions, geology and topography. In consequence, steeply positive logC-logQ slopes can be used as indicators of effective subsurface reactivity. Future work will further elucidate the catchment characteristics that favor effective denitrification.</p><p>References</p><p>Musolff, A., Fleckenstein, J.H., Rao, P.S.C., Jawitz, J.W., 2017. Emergent archetype patterns of coupled hydrologic and biogeochemical responses in catchments. Geophys Res Lett, 44(9): 4143-4151. DOI:10.1002/2017GL072630</p><p>Zhi, W., Li, L. Dong, W.M., Brown, W., Kaye, J., Steefel, C., Williams, K.H., 2019. Distinct Source Water Chemistry Shapes Contrasting Concentration-Discharge Patterns. Water Resour Res, 55(5): 4233-4251. DOI:10.1029/2018wr024257</p>

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