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Small-scale Watershed Monitoring
Matthew HelmersDean’s Professor, College of Ag. & Life Sciences
Professor, Dept. of Ag. and Biosystems Eng.Iowa State University
Department of Agricultural and Biosystems Engineering
NWRF Drainage
Gilmore City DRF
NERF Drainage
COBS
SERF Drainage
Replicated subsurface drainage plots to evaluate performanceof various in-field management practices
Department of Agricultural andBiosystems Engineering
Plot Sampling Layout
125 ft
50 ft
Perforated border tile -drains to remote outlet
Flow monitoring sump(three drain lines in each sump)
Treatment plot
125 ft
50 ft
Perforated border tile -drains to remote outlet
Flow monitoring sump(three drain lines in each sump)
Treatment plot
Flow and sampling set-up at Gilmore City site
Avera
ge
Corn-Soybean Rotation 150/160 lb-N/acre Application Rate
Variability in Drainage, Nitrate Concentrationand Nitrate Loss – Weather a Major Driver
Impact of Nitrogen Application Rate
Impacts of Cover Crops on Nitrate-N Load inDrainage Water – Gilmore City
36% Reduction
34% Reduction
Using PrairieStrips to ReduceSediment andNutrient Loss
prairiestrips.org
Watershed Experiment: NSNWR
Neal Smith PrairieLearning Center
Site 1
Site 2
Site 3
#S#S#S
#SSite 1
Site 2
Site 3
Site 0%U
Neal SmithPrairie Learning Center
0 2 4 6 8 10 12 Kilometers
N
EW
S
300 0 300 600 Meters
Walnut Creek Watershed boundary
Refuge boundary
What is unique?
Natural Flow Conditions
Surface RunoffMonitoringH-flumes monitor movement ofwater, sediment, and nutrients
Surface Runoff
Sediment Loss in Runoff (2007-2012)
>95% Reductionin sedimentexport fromwatersheds withprairie filter strips
Phosphorus Loss in Runoff (2007-2012)
Zhou et al., 2014
>90% Reductionin TP export fromwatersheds withprairie filter strips
Visual Examples (4 inch rain in June 2008)
100% Crop 100% Prairie10% Prairie90% Crop
Field scale reflects processes and practices but may notreflect actual delivery to streams
Slide from Dr. W. Crumpton - ISU
Field scale reflects processes and practices but may notreflect actual delivery to streams
Field to streamtransport
Slide from Dr. W. Crumpton - ISU
Larger scales reflect combination ofdelivery and in-stream processes
Field scale reflects processes and practices but may notreflect actual delivery to streams
Field to streamtransport
Slide from Dr. W. Crumpton - ISU
Larger scales reflect combination ofdelivery and in-stream processes
Field scale reflects processes and practices but may notreflect actual delivery to streams
Field to streamtransport
In-streamprocesses
Slide from Dr. W. Crumpton - ISU
Larger scales reflect combination ofdelivery and in-stream processes
This scale reflects nutrient load actuallydelivered to stream
Field scale reflects processes and practices but may notreflect actual delivery to streams
Field to streamtransport
In-streamprocesses
Slide from Dr. W. Crumpton - ISU
Monitoring sites instrumented forclose interval sampling and flow
measurement
Slide from Dr. W. Crumpton - ISU
Scale of Monitoring
Point at which load delivered tostream
Example Results from One WatershedMonitored as Part of EPA – TWG Project
The PAL3 and PAL5 watersheds
• Similar watersheds in theupper Des Moines lobe ofNorthcentral Iowa
• Similar watershed characteristics– Area (1128 ha and 1356 ha)– Elevation 400 m above sea
level– Slope 0-2% with 0.5% avg– Soils lowland Canisteo and
Clarion-Nicollet-Webster– Almost exclusively agricultural
land use– Heavily tile drained
throughout -Stars indicate watershed outlets
Model Validation Watershed– PAL 5
Corn
Soybean
1 km
Targeted Wetland Restoration
DD Tile
W.G. Crumpton, Iowa State University
Iowa Conservation Reserve Enhancement Program (CREP)Iowa Conservation Reserve Enhancement Program (CREP)
0
5
10
15
20
25
30
Nit
rate
-N(m
gL
-1)
0
40000
80000
120000
Infl
ow(m
3d-1
)
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
GF Wetland2015
Observed nitrate-N inflow (mg/L)
Observed nitrate-N outflow (mg/L)
Model expected outflow nitrate range
Inflow
Wetland Performance – Examplefrom CREP Monitoring
Slide from Dr. W. Crumpton - ISU
Summary
• Small plots or small watersheds allowexamination of specific managementpractices
• Depending on transport pathways smallplots may or may not directly reflect streamdelivery
• Monitoring at scale at which water,sediment, and nutrients are delivered to thestream is critical for assessing impacts ofpractices at scale of implementation
Contact
• Twitter: @ISUAgWaterMgmt
• Website: http://agwatermgmt.ae.iastate.edu/
