CN1

1. CN1 Effect of historic land management on groundwater nitrate in the Judith River Watershed Stephanie A. Ewing Christine Miller, Jack Brookshire, ClainJones, Adam Sigler Department of Land Resources & Environmental Sciences Montana State University Douglas Jackson-Smith Department of Sociology Utah State University Scott Wankel Woods Hole Oceanographic Institute Gary Weissmann University of New Mexico Nitrate in Montana Hydrologic Systems April 23, 2014

2. THE LARGER PROBLEM – elevated groundwater nitrate is common in agricultural regions Burow et al., 2010 Young groundwater, high inputs, and well-drained soils

3. High groundwater nitrate in the Judith River Watershed How has land use influenced groundwater nitrate in this region over time? How can we manage that effect sustainably given intimate association of land use with local communities? – dryland wheat production and livestock, common fallowing (3 y rotation) – shallow unconfined aquifers, well drained soils, high nitrate levels, little BMP adoption

4. Rising nitrate-N concentrations in a monitoring well near Moccasin Open symbols: Montana Department of Agriculture, Montana Groundwater Information Center (GWIC). Filled symbols: Montana State University Environmental Analysis Laboratory (mean of . We know this is a longer term issue. MDA (C. Schmidt and R. Mulder) 2010. Groundwater and Surface Water Monitoring for Pesticides and Nitrate in the Judith Basin, Central Montana.

5. Rising wheat yields and and associated N fertilizer use in Montana data: USDA National Agricultural Statistics Service; USDA Agricultural Census How have increasing N inputs influenced groundwater nitrate?

6. Participatory research to evaluate and address sources of nitrate in groundwater B: Moccasin C: Moore A: Stanford Testing effects of management changes on nitrate leaching from soils dryland farmed for wheat (A. John, C. Jones et al.): • Peas in place of fallow in three year rotation • Timing of fertilizer application Participatory approach to tackle the problem (D. Jackson-Smith et al.) Evaluating field and landscape scale hydrology as a driver of nitrate leaching from soils to groundwater (and surface water) (A. Sigler et al.) maps by A Sigler

7. C2E.01 Ap depth to gravel: 80 cm A Bk1: 26 cm 2Bk2 2Bk3 2CBk

8. Variation of annual nitrate balance with rotation component WHEAT FALLOW FIELD PEAS fertilizer yield fixation yield 80 60 80 40 20 20 kg N/ha Biomass Biomass SOM SOM 11000 SOM 50 50 120 mineralization NO3- NH4+ NO3- NH4+ NO3- NH4+ SOIL leaching (fraction) 30 (0.3) 10 (0.1) 40 (0.3) GROUNDWATER water & nitrate storage leaching susceptible long-term fertility loss low inputs to IN pool water & nitrate use limited leaching limited high inputs (fert + min)

9. Soil nitrate and water Both mineralization of SOM and fertilization make nitrate available for leaching In rotational sequences, storage of water and mineralization of soil organic N set the stage for nitrate leaching – this is enhanced in fallow Seasonal timing and amount of rainfall relative to root growth are critical to quantifying leaching for a given crop or fallow year, particularly in soils with shallow gravel contacts Is this nitrate really making it into groundwater?

10. Looking for larger scale controls: wells, springs and surface water on the Moccasin terrace - no mountain front stream recharge; dispersed recharge only - emergent streams fed by springs that drain the shallow aquifer dispersed recharge upscale to landform M-1 well Louse Cr. upper Louse Cr. lower Rock Cr. (Moore fan) groundwater flow Groundwater expected to accumulate nitrate at rates determined by nitrate supply and deep percolation (recharge), as well as groundwater flow and discharge rates.

11. Water vs. solute dynamics at the M-1 well and lower Louse Creek - spring recharge and mixing Adam Sigler • Nitrate leaching from soils is relatively rapid but also buffered in shallow aquifer

12. Landform scale nitrate balance – Moccasin terrace Volatilization Fertilizer Yield Biomass NH4+ • Do we observe losses due to denitrification that influence nitrate fluxes to groundwater? SOM SOIL ~25-50 kg nitrate-N ha-1 y-1 NO3- 50-200 mm water/y 1-3x107m3 water/y 10 ppm nitrate-N 1.5x105 kg N (6 kg N/ha)/y 1-3x107 m3 water/y 21 ppm nitrate-N ~6x106 kg N (260 kg N/ha) 2-6x108 m3 water Nitrate (NO3-) SURFACE WATER GROUNDWATER • Groundwater mean residence time determines nitrate balance (~10-60 y) • Ask not only what practices will reduce leaching, but how long will we need to undertake them?

13. Nitrate isotopes (2012) – source and loss downstream surface waters groundwater headwater stream deep soil denitrification Denitrification in soils and surface water – apparently limited within groundwater

14. How do apparent soil losses influence groundwater nitrate-N? Exploratory simulation for Moccasin terrace – annual timestep, 1920-2100 leaching= recharge kLSn groundwater Gn discharge kDGn 10-year lag in vadose change from 2-y to 3-y rotation in 1985 kL(y-1) =0.3 (fallow), 0.4 (wheat), 0.1 (peas) kD(y-1)=0.05 (20-y RT) denitrification = 50% constant mineralization = 40 kg/ha

15. C2E.01 • Conclusions • Nitrate supply to groundwater is a function of crop rotation/fallow and mineralization of soil organic matter, in addition to N fertilization practices. • Native soil fertility probably continues to supply N for crops, as it has since cultivation was initiated. • Nitrate losses to denitrification in soils and surface water are outpaced by increasing N inputs. • Nitrate in shallow aquifers is a legacy of land use over the last century; a comparable timeframe may be required to detect effects of management changes. • Changing rainfall patterns are likely to complicate efforts to address this issue.

16. Funding USDA/NIFA National Integrated Water Quality Program Montana State University College of Agriculture/MAES Montana State University Office of the Vice President for Research MSU Extension/Water Quality Program Montana Institute on Ecosystems/NSF EPSCoR Montana Wheat and Barley Committee Co-authors Christine Miller, MSU/GCWQCD Adam Sigler, MSU Dr. ClainJones, MSU Dr. Douglas Jackson-Smith, USU Dr. Jack Brookshire, MSU Dr. Rob Payn, MSU Dr. Gary Weissmann, UNM Key Collaborators Judith Project Advisory Council Judith Project Producer Research Advisory Group Andrew John (Jones MS student, MSU) Ann Armstrong, USU PhD student Dr. Paul Stoy, MSU Dr. Perry Miller, MSU Michael Bestwick, MSU MS student Kyle Mehrens, MSU/City of Bozeman Simon Fordyce, MSU undergraduate MSU Environmental Analysis Lab Dr. Jane Klassen, Research Chemist Hailey Buberl, MS student Aaron Klingborg, MS student Erik Anderson, undergraduate assistant Acknowledgements Judith Project Advisory Council Judith Project Producer Research Advisory Group Christine Miller (MS student, MSU) Ann Armstrong (PhD student, USU) Funding USDA/NIFA NIWQP Montana State University College of Agriculture/MAES Montana Institute on Ecosystems/NSF EPSCoR

17. LATE SUMMER 2012: fallow stores mineralized ON as nitrate nitrate-N; gravel depth 46 kg N/ha; 82 cm 69 kg N/ha; 94 cm 72 kg N/ha; 73 cm 78 kg N/ha; 92 cm 62 kg N/ha; 100 cm ~40-80 kg nitrate-N/ha in fallow Nitrate “bulges” at gravel contact

18. EFFECT OF CROP: shallow rooted peas draw down nitrate in the upper 50 cm Nitrate “bulges” at gravel contact Peas draw down shallower nitrate ~ 30 and ~60 kg nitrate-N/ha

19. EFFECT OF CROP: barley draws down soil nitrate to greater depth 75 60 45 30 15 0 Nitrate “bulges” at gravel contact Peas draw down shallower nitrate; cereals deep ~ 15 kg nitrate-N/ha