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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

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