1. CN1 Effect of historic land management on groundwater nitrate in the Judith River Watershed Nitrate in Montana Hydrologic Systems April 23, 2014 Stephanie A. Ewing Christine Miller, Jack Brookshire, Clain Jones, 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

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

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. 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. Rising nitrate-N concentrations in a monitoring well near Moccasin MDA (C. Schmidt and R. Mulder) 2010. Groundwater and Surface Water Monitoring for Pesticides and Nitrate in the Judith Basin, Central Montana.

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

6. 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.) Participatory research to evaluate and address sources of nitrate in groundwater C: Moore A: Stanford B: Moccasin maps by A Sigler

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

8. 80 kg N/ha Variation of annual nitrate balance with rotation component 30 (0.3) NH 4 + NO 3 - 40 (0.3) 120 SOM FALLOW FIELD PEAS NH 4 + NO 3 - 40 60 10 (0.1) 50 SOM Biomass yield fixation WHEAT NH 4 + SOM NO 3 - GROUNDWATER SOIL Biomass fertilizer yield leaching (fraction) 50 mineralization 11000 high inputs (fert + min) water & nitrate storage leaching susceptible long-term fertility loss low inputs to IN pool water & nitrate use limited leaching limited 20

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. M-1 well 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 Groundwater expected to accumulate nitrate at rates determined by nitrate supply and deep percolation (recharge), as well as groundwater flow and discharge rates. Rock Cr. (Moore fan) dispersed recharge Louse Cr. upper Louse Cr. lower upscale to landform

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. GROUNDWATER Nitrate (NO 3 - ) 21 ppm nitrate-N ~6x10 6 kg N (260 kg N/ha) 2-6x10 8 m 3 water Fertilizer NH 4 + SOM NO 3 - Biomass SOIL Yield Volatilization ~25-50 kg nitrate-N ha -1 y -1 SURFACE WATER 10 ppm nitrate-N 1.5x10 5 kg N (6 kg N/ha)/y 1-3x10 7 m 3 water/y Landform scale nitrate balance – Moccasin terrace 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? 50-200 mm water/y 1-3x10 7 m 3 water/y Do we observe losses due to denitrification that influence nitrate fluxes to groundwater?

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

14. How do apparent soil losses influence groundwater nitrate-N? Exploratory simulation for Moccasin terrace – annual timestep, 1920-2100 k L Sn leaching= recharge groundwater discharge Gn k D Gn 10-year lag in vadose change from 2-y to 3-y rotation in 1985 k L (y -1 ) =0.3 (fallow), 0.4 (wheat), 0.1 (peas) k D (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. 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 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 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. Clain Jones, MSU Dr. Douglas Jackson-Smith, USU Dr. Jack Brookshire, MSU Dr. Rob Payn, MSU Dr. Gary Weissmann, UNM MSU Environmental Analysis Lab Dr. Jane Klassen, Research Chemist Hailey Buberl, MS student Aaron Klingborg, MS student Erik Anderson, undergraduate assistant

17. LATE SUMMER 2012: fallow stores mineralized ON as nitrate ~40-80 kg nitrate-N/ha in fallowNitrate “bulges” at gravel contact 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

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

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