1. Nitrogen Budgets for the Mississippi River Basin using the linked EPIC-CMAQ-NEWS Models Michelle McCrackin, Ellen Cooter, Robin Dennis, Jana Compton, John Harrison September 23, 2014 1

2. Project objectives Demonstrate capability of linking models for air (CMAQ), agriculture (EPIC), and river export (NEWS) to understand nitrogen pollution Estimate monthly nitrogen loading in the Mississippi River Basin (MRB) to the Gulf of Mexico (GoM) for different scenarios – Shift to bio-fuel crops – Effect of CAA on atmospheric deposition 2

3. Linking models CMAQ (Community Multi-scale Air Quality Model) – Bi-directional (land-air) fluxes of reduced and oxidized N EPIC (Environmental Policy Integrated Climate) – Agriculture N fluxes Nutrient Export from WaterSheds (NEWS) – River transport of N 3

4. NEWS Overview Land- based N inputs Land-to- river transfers Riverine N sinks DIN to river mouth Fertilizer Manure Atmospheric deposition Biological N- fixation Sewage Denitrification Reservoir retention Consumptive water use Runoff Tile drainage Temperature Sewage treatment Yield (kg N km -2 mo -1 ) Load (Mg N km -2 mo -1 )

5. Down-scaling NEWS Previously, NEWS has been applied to the entire MRB on annual and seasonal scales For this project, we developed NEWS MRB, a spatially and temporally down-scaled version – Major MRB sub-basins and whole basin – Monthly estimates of dissolved inorganic N export – Base year 2002 and 2022 bio-fuels crops scenario 5

6. Spatial downscaling: MRB Sub-basins 6 Missouri (MO) Arkansas-Red (AR-Red) Ohio- Tennessee (OH-TN) Upper MRB (UMRB) Lower MRB (LMRB)

7. Temporal downscaling Developed monthly N budgets for sub-basins and TMRB Calibrated land-to-river transfers using monthly monitoring data from USGS 7

8. Monthly Budgets 8

9. 9 More detail to follow for items in red box

10. Land use change in response to increased corn stover demand are provided to EPIC, which predicts new levels of fertilizer application and crop BNF EPIC Increase in fertilizer Decrease in crop BNF Net result is 3% increase in agricultural N inputs to MRB EPIC Scenario for 2022 Increase in corn cover nationally Decrease in soybean cover in MRB Shift in wheat cover

11. EPIC scenario for year 2022 2022 reflects shift from soy to corn production Results in 3% increase in agricultural inputs and 2% increase in annual total N inputs for MRB 11 Total Agricultural N inputs (Fertilizer, Manure, & BNF)

12. CMAQ scenario for year 2022 CMAQ output for year 2022 reflects – Change cropping practices per EPIC – CAA point and mobile NO X regulations as of 2012 Results in 6% decrease in N deposition and a 1% decrease in annual total N inputs for MRB 12 Total Inorganic N deposition

13. Comparison of all N inputs Combined changes in EPIC and CMAQ result in 1% increase in total N inputs to MRB between 2002 and 2022 Fertilizer & Manure (EPIC) Crop BNF (EPIC) Non-agriculture BNF Sewage Atmospheric deposition (CMAQ) 13

14. Monthly Calibration Data Monthly DIN load and discharge was obtained from USGS for 1993- 2002 Average monthly values were used for calibration LMRB was not modeled because of negative 10 y average flux – Per USGS, negative value is possible because LMRB is not measured, but estimated as: TMRB minus sum of AR-Red, MO, OH-TN & UMRB 14

15. New model features Previous versions of NEWS do not account for tile drainage or wetland N-retention Modified NEWS structure for MRB – Treats N on tile-drained lands similar to point sources – Includes wetlands N-removal term 15

16. Tile drainage Estimated annual fraction of net agricultural inputs applied to tile-drained land Distributed by month in proportion to runoff Treated like point source – no retention on land, just in river network (e.g. denitrification, reservoirs, consumptive withdrawals 16 Tile drain data: WRI

17. Wetlands N Removal Term Green areas represent locations of wetlands 17 Used woody and emergent wetland cover from 2006 NLDC – Total wetlands only ~4% of MRB basin area Estimated sub-basin average wetland retention with N removal factors as: Wetland area % x Wetland N retention, where (per Jordan 2011): 63% N removal for woody wetlands 49% N removal for emergent wetlands

18. Model performance 18 NSE = 0.94 Performance evaluated using Nash-Sutcliffe Efficiency – Measure of fit to 1:1 line – Values of -∞ to 1 – NSE = 1 means perfect fit to 1:1 line NEWS MRB performed well with NSE = 0.94

19. 19 Similar contribution by sub-basins for modeled and measured loads USGS (1993-2002 avg) Modeled 2002 Dissolved inorganic N UMRB OH-TN MO AR-Red LMRB

20. 20 NEWS MRB not strictly comparable to SPARROW USGS (1993-2002 avg) Modeled 2002 Dissolved inorganic N UMRB OH-TN MO AR-Red LMRB Total N LMRB SPARROW estimates total N, NEWS MRB estimates DIN SPARROW 2002

21. 21 Total Mississippi River Basin Box and whisker plots are for 1993-2002 USGS monitoring data NEWS MRB estimates falls within ranges of natural variability 2002 and 2022 export to GoM is nearly identical – 1% net increase in land-based inputs not visible in export to GoM because of retention on land – EPIC year 2022 scenario increases GoM export by 1% – CMAQ year 2022 scenario decreases GoM export by 0.8% NEWS MRB suggests that tile drainage contributes 6% of annual DIN export to GoM

22. 22 Arkansas-Red River Basin Box and whisker plots are for 1993-2002 USGS monitoring data NEWS MRB estimates falls within ranges of natural variability Spring and fall export increases between 2002 and 2022 due to changes in cropping – Total annual export increases 15% for year 2022 over 2002 – No significant effect on GoM export because of small contribution by AR-Red basin

23. 23 Missouri River Basin Box and whisker plots are for 1993-2002 USGS monitoring data NEWS MRB estimates falls within ranges of natural variability Spring and fall export increases, summer decreases between 2002 and 2022 due to changes in cropping – Total annual export increases 5% for year 2022 over 2002

24. 24 Ohio-Tennesse River Basin Box and whisker plots are for 1993-2002 USGS monitoring data NEWS MRB estimates falls within ranges of natural variability Spring export decreases slightly between 2002 and 2022 primarily because of N deposition – Total annual export decreases 2% for year 2022 over 2002

25. 25 Upper Mississippi River Basin Box and whisker plots are for 1993-2002 USGS monitoring data NEWS MRB estimates falls within ranges of natural variability For most months, export decreases slightly between 2002 and 2022 primarily because of cropping practices – Total annual export decreases 2% for year 2022 over 2002

26. Summary of Results 26 Linking EPIC-CMAQ-NEWS can enable scenario analysis for N from agriculture and atmospheric deposition NEWS MRB shows capability of temporally and spatially downscaled NEWS model

27. 27 Research opportunities and next steps Further couple NEWS and other models. e.g. VIC (hydrology) and GoM circulation and GEM and GoMDOM hypoxia models – Changes in hydrology have strong influence on river export to GoM Enhance representation of tile drainage Analyze historic trends in linkages between nutrient inputs and effects Model other nutrients, e.g. phosphorus Explore effects of climate change, such as changes in hydrology and temperature Model effects of population growth and sewage treatment practices