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CN1. Effect of historic land management on groundwater nitrate in the Judith River Watershed. Stephanie A. Ewing Christine Miller, Jack Brookshire, Clain Jones, Adam Sigler Department of Land Resources & Environmental Sciences Montana State University. Douglas Jackson-Smith - PowerPoint PPT Presentation
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CN1
Effect of historic land management on groundwater nitrate in the Judith River Watershed
Nitrate in Montana Hydrologic SystemsApril 23, 2014
Stephanie A. Ewing
Christine Miller, Jack Brookshire, Clain Jones, Adam SiglerDepartment of Land Resources & Environmental Sciences
Montana State University
Douglas Jackson-SmithDepartment of Sociology
Utah State University
Scott WankelWoods Hole
Oceanographic Institute
Gary WeissmannUniversity of New Mexico
Young groundwater, high inputs, and well-drained soils
THE LARGER PROBLEM – elevated groundwater nitrate is common in agricultural regions
Burow et al., 2010
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
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.
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?
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
C2E.01
depth to gravel: 80 cm
Ap
A
Bk1: 26 cm
2Bk3
2CBk
2Bk2
8080
kg N/ha
Variation of annual nitrate balance with rotation component
30 (0.3)
NH4+NO3
-
40 (0.3)
120SOM
FALLOW FIELD PEAS
NH4+NO3
-
4060
10 (0.1)
50SOM
Biomass
yield fixation
WHEAT
NH4+
SOM
NO3-
GROUNDWATER
SOIL
Biomass
fertilizeryield
leaching(fraction)
50mineralization
11000
high inputs (fert + min)
water & nitrate storageleaching susceptible
long-term fertility loss
low inputs to IN poolwater & nitrate use limited
leaching limited
20 20
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?
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 flow
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
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
GROUNDWATERNitrate (NO3
-)21 ppm nitrate-N~6x106 kg N (260 kg N/ha)2-6x108 m3 water
Fertilizer
NH4+
SOM
NO3-
Biomass
SOIL
Yield
Volatilization
~25-50 kg nitrate-N ha-1 y-1
SURFACE WATER
10 ppm nitrate-N1.5x105 kg N (6 kg N/ha)/y1-3x107 m3 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/y1-3x107 m3 water/y
Do we observe losses due to denitrification that influence nitrate fluxes to groundwater?
Nitrate isotopes (2012) – source and loss
Denitrification in soils and surface water – apparently limited within groundwater
denitrification
deep soil
downstream
headwaterstream
groundwater
surfacewaters
How do apparent soil losses influence groundwater nitrate-N? Exploratory simulation for Moccasin terrace – annual timestep, 1920-2100
kLSnleaching=recharge
groundwater
discharge
Gn
kDGn10-year lag in vadosechange from 2-y to 3-y rotation in 1985kL (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
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.
Key CollaboratorsJudith Project Advisory CouncilJudith Project Producer Research Advisory Group
Andrew John (Jones MS student, MSU)Ann Armstrong, USU PhD student
Dr. Paul Stoy, MSUDr. Perry Miller, MSU
Michael Bestwick, MSU MS studentKyle Mehrens, MSU/City of BozemanSimon Fordyce, MSU undergraduate
FundingUSDA/NIFA National Integrated Water Quality ProgramMontana State University College of Agriculture/MAESMontana State University Office of the Vice President for ResearchMSU Extension/Water Quality ProgramMontana Institute on Ecosystems/NSF EPSCoRMontana Wheat and Barley Committee
Co-authorsChristine Miller, MSU/GCWQCDAdam Sigler, MSUDr. Clain Jones, MSUDr. Douglas Jackson-Smith, USUDr. Jack Brookshire, MSUDr. Rob Payn, MSUDr. Gary Weissmann, UNM
MSU Environmental Analysis LabDr. Jane Klassen, Research ChemistHailey Buberl, MS studentAaron Klingborg, MS studentErik Anderson, undergraduate assistant
LATE SUMMER 2012: fallow stores mineralized ON as nitrate
~40-80 kg nitrate-N/ha in fallow Nitrate “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
EFFECT OF CROP: shallow rooted peas draw down nitrate in the upper 50 cm
~ 30 and ~60 kg nitrate-N/haNitrate “bulges” at gravel contactPeas draw down shallower nitrate
EFFECT OF CROP: barley draws down soil nitrate to greater depth
~ 15 kg nitrate-N/ha Nitrate “bulges” at gravel contactPeas draw down shallower nitrate; cereals deep
75
60
45
30
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