Temporal and Spatial Variability of Groundwater Nitrate in the Southern Willamette Valley, Oregon - PowerPoint PPT Presentation

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Temporal and Spatial Variability of Groundwater Nitrate in the Southern Willamette Valley, Oregon

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Title: Temporal and Spatial Variability of Groundwater Nitrate in the Southern Willamette Valley, Oregon


1
Temporal and Spatial Variability of Groundwater
Nitrate in the Southern Willamette Valley, Oregon
  • Glenn Mutti Roy Haggerty
  • Oregon State University
  • Department of Geosciences

2
Introduction
  • Overview of previous spatial and temporal studies
  • Sampling Network
  • Results and Implications
  • Modeling Nitrogen Dynamics
  • Conclusions

3
Spatial Distribution of Nitrate from Previous
Studies
4
Prior Documentation of Temporal Variability
(From Faega et al., 2004)
5
Hypothesis
  • Seasonal precipitation should impact shallow
    groundwater nitrate concentrations
  • Why should it matter?
  • Distinguish seasonal trends vs. actual trends in
    monitoring data
  • Determine optimal sampling periods

6
Monitoring Network
  • 19 wells sampled monthly for 15 months
  • 15 residential wells
  • 4 monitoring wells
  • Well log extant
  • Well Depth 50 ft
  • Screening Interval 15 ft
  • Pass Coliform bacteria test

7
Was there Seasonal Variability?
  • Yes, precipitation influences nitrate values
  • However, seasonal wetting patterns are critical!

8
Wetting Up Period Necessary to have NO3- Response
  • Used water levels to indicate when recharge
    occurred
  • Soil needs to wet up before recharge, then
    groundwater nitrate values respond to
    precipitation

9
When might policy managers want to sample?
10
Can we relate temporal variability to spatial
variability?
11
Sample Distributions Based on Geology and Soil
n 6
n 6
n 6
  • Qal Holocene Floodplain and Alluvial Deposits
  • Qs Pleistocene Alluvium and Flood Deposits
  • FSL Fine Sandy Loam
  • SCL Silty Clay Loam
  • SL Silt Loam

12
Part II What if we can model these Variabilities?
13
Modeling Goals
  • Calibrate SWAT so that reasonable outputs are
    obtained and validated
  • Examine different land management options and
    their impact on leached nitrate
  • Examine future scenarios and the impacts of
    nitrate Best Management Practices

14
SWAT GIS Inputs
15
Non-GIS Model Inputs
  • Climate Data
  • River flows originating from non-modeled areas
  • Land Management Practices

16
Modeled Area Pre-Calibration Results
17
Closing Points
  • Relationship between NO3- and precipitation may
    be biased by data set needs further analysis
  • Data uncertainties have yet to be analyzed
  • Small sample size could limit the significance of
    results

18
Conclusions
  • Nitrate concentrations in the Southern Willamette
    Valley are dynamically linked to precipitation
    during recharge months
  • The recharge month with the highest annual
    precipitation is likely to have the highest
    annual groundwater NO3- concentration (but also
    the highest variability!!)
  • Wells drilled in different geologic formations or
    soil classes are likely to exhibit different
    seasonal variabilities

19
Acknowledgements
  • Funding provided by USGS Small Grants Program,
    Award No. 01HQGR0145
  • SWAT Development USDA ARS and Blackland Research
    Center, Texas AM University
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