This document summarizes research on monitoring surface water quality in the lower Mississippi River basin. The research aims to quantify the impacts of agricultural conservation practices on nutrient and sediment runoff. Edge-of-field monitoring has found no significant differences between fields with cover crops and conventional fields. In-stream water quality is also monitored continuously and through grab samples to validate models of nutrient and sediment transport. The long-term goal is to inform strategies to reduce excess nutrients entering waterways from agricultural lands in the region.

1. 12/9/2015
1
Field scale, edge-of-field
monitoring of surface
water quality in the
lower mississippi river
basin
Michele L. Reba, PhD, PE
USDA-Agricultural Research Service
Delta Water Management Research Unit
michele.reba@ars.usda.gov
Outline
• Motivation
• MRBI Edge-of-field monitoring
• Related research studies
4.804 M ac
8.297 M ac
7.862 M ac
4.489 M ac
2012 Census
4.461 M ac
5.010 M ac
8.559 M ac
8.016 M ac
2007 Census
Arkansas
Texas
California
Nebraska
Alluvial Aquifer
• 2012 (Mgal/d)
• Pumped: 8,036
• Sustainable Yield: 3,374
• Unmet Demand: 4,462
• Agriculture 98%
Source: Arkansas Natural Resources Commission 2015
Clark et al. (2011)

2. 12/9/2015
2
Water Quality
• Excess Nutrients
• Nitrogen
• Phosphorus
• Hypoxia
• < 2 ppm DO
• Sparrow model
• (Rebich et al., 2011)
• 32% N
• 50% P
Figure source: www.usepa.gov
Motivation
• Irrigation is key to
reducing production
variability
• Irrigate smarter
• Reduce inputs
• Improve profit
• Reduce excess nutrients
• Challenge
• Agro-economic
• Environmental
Mississippi River Basin Healthy
watersheds Initiative (MRBI)
• 13 states
• Facilitate implementation of
conservation practices
• Avoid, control & trap
nutrient runoff
• Maintain productivity
• Programs
• Cooperative Conservation
Partnership Initiative (CCPI)
• Wetlands Reserve
Enhancement Program
(WREP)
• Arkansas
• Conservation Practices
Conservation
Practices
• Monitoring
• Nutrient management
• Water management
• Irrigation management
• Cover crops
• Conservation tillage
• Grassed ways
• Riparian buffer
• Surface water storage
• Shallow water
development for wildlife
Collaborators Statewide Network

3. 12/9/2015
3
Study Sites Edge-of-Field
Data Collection
• Velocity
• Depth
• Turbidity
• Water sample
• Sediment
• Nutrients
• Event trigger
• Remote upload
Nutrient Analysis
• Sediment
• TSS (APHA 2005 method 2540 D)
• Suspended sediment cnc. (ASTM Method D3977-97)
• Nitrate
• APHA (2005) method 4500-NO3-E
• Cd reduction & analyzed as NO2 colorimetric reaction
• MDL: 0.02 mg N/L, Range: 0.2 – 5 mg N/L
• Orthophosphate
• APHA (2005) method 4500-P E
• Ascorbic acid method
• MDL: 0.01 mg/L, Range: 0.05 – 1.0 mg P/L
Little River Ditches MRBI
Caraway, AR
• Cotton
• One pair
• Two 75-acre
• Sandy Loam
Cover crop
Case study
• 2011/2012 and 2012/2013 fallow
season
• P & K Fall application (Oct)
• Plant cover crop wheat (Nov)
• Terminate cover crop
• (3-4 weeks before planting, ~early
April)
• Plant cotton (early May)
• Nitrogen: liquid knife 120 units N
per acre (early June)
• Harvest (October)
Photo Credit: Dr. Tina Gray Teague
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
11/17/11 11/22/11 12/5/11 11/12/12 1/30/13 2/19/13 2/22/13 2/26/13
DissolvedPO4(mg/L)
Event Date
Conservation
Conventional
Dissolved PO4

4. 12/9/2015
4
0
10
20
30
40
50
60
70
11/17/11 11/22/11 12/5/11 11/12/12 1/30/13 2/19/13 2/22/13 2/26/13
SuspendedSedimentConcentation(g/L)
Event Date
Conservation
Conventional
Suspended Sediment CNC
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
P04 Dis Total P N03 Dis N02 Dis Total N
mg/L
Conservation
Conventional
0.0
5.0
10.0
15.0
20.0
25.0
30.0
P04 Dis Total P N03 Dis N02 Dis Total N Sediment
Conservation
Conventional
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
Conservation P04 Conventional P04 Conservation N03 Conventional N03 Conservation N02 Conventional N02
mg/L
Nutrients
Caraway 2012 & 2013 Winter
0
10
20
30
40
50
60
70
Conservation Sediment Conventional Sediment
g/L
Sediment
Caraway 2012 & 2013 Winter
• No statistical difference in any comparisons by t-test and Wilcoxon Rank-Sum test
• Reduction in variability at conservation field
Cotton Study Sites
2014
• Sandy Loam
• Variable
• 38 acre field split
• Year 1 of 2 years of baseline
• 2012/2013 winter cover crops
• Practices
• Oat cover crop (Nov)
• Oat terminated (April)
• Tillage-do all
• Liquid N 35 lb/ac, Broadcast N
110 lb/ac, KO2 41 lb/ac (June 19)
• Harvest (Oct 22)
• Terra Till
• Winter wheat cover crop (Nov)
• Sharkey Clay
• 3 field pair (40-acre)
• Year 1 of 2 years of baseline
• Rice/soybean rotation
• Practices
• Pre-plant N 30 lb/ac
• Tandom disk till
• Pre-flood N 86 lb/ac
• Harvest 190 lb/ac (XL 753)
• Burn stubble
Rice Study Sites
2014
Nutrients 2014
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700
DISSOLVED PO4
(lb/ac)
TOTAL P (lb/ac) DISSOLVED NO3
(lb/ac)
DISSOLVED NO2
(lb/ac)
TOTAL N (lb/ac)
Load(lb/ac)
COTTON-CONTROL COTTON-TREATMENT RICE-CONTROL
RICE-TREATMENT 1 RICE-TREATMENT 2
• No statistical difference in any comparisons for paired events by t-test and
Wilcoxon Rank-Sum test
• Sum of total N: 2 & 4.5% of applied N in rice (25 and 29 samples)

5. 12/9/2015
5
Ghg reduction
irrigation mngmt
Site
• 4 new MRBI sites
• Rice/soybean
• NE Arkansas
Alternate Wetting &
Drying
• GHG benefit
• Reduce water use
• Sustain yield & milling quality
CEAP Watershed
In-stream Water
Quality Study
• Monitor nutrients and sediments year round in-stream
(drainage ditches).
• Validate model simulations of nutrients and sediment
transport in irrigated agricultural land in the Little River
Ditches (080202040804) and Lower St. Francis
(080202031301) basin using both EOF and in-stream
monitoring (ISM) data.
• Develop an improved understanding of nutrient and
sediment transport, transformations and the hydrology in an
irrigated landscape.
In-stream Water
Quality Study
Little River Drainage Basin HUC
080202040804
Approximately 10,000 acres (4047 Ha)
Ditch no. 14-Buffalo Creek Ditch
Little River Ditches Basin
W1
W9W5
W7
W3
Inlet ditch
In-stream stations
EOF stations
In-stream Water
Quality Study
Lower St. Francis Basin HUC
080202031301
Approximately 5,000 acres (2023 Ha)
Ditch no. 1-St. Francis River

6. 12/9/2015
6
M2 M8
M10
M6
Inlet ditch
In-stream stations
EOF stations
M4
Lower St. Francis Basin Instrumentation
Per watershed
• 3 Isco autosamplers
• 3 area-velocity sensors and modules
• 2 trolls (water depth sensors)
• 3 to 5 DS5X sondes
• 2 OBS 500 sensors
× 2
Edge-of field
(5)
Nutrients
Grab,event
Lab
NO3, NO2,
TN, TP, SP
Sediments
Grab, event
Lab
SSC, TDS,
TSS
Continuous
OBS300
Turbidity
Flow
Continuous
ISCO
Rainfall,
H, V, Q
In-stream (10)
Nutrients
Grab, weekly
Lab
NO3, NO2,
TN, TP, SP
Continuous
Sonde
pH, NO3,
NH4, DO, T
Sediments
Grab, weekly
Lab
SSC, TDS,
TSS
Continuous
Sonde
TDS,
Turbidity
Flow
Continuous
Isco
H, V, Q
Modeling
APEX, AnnAGNPS
Autosampler Area-velocity
sensor
Sonde
deployed
in ditch
Laboratory
calibration of
sonde
monitoring Select Data: Turbidity and
nitrate
LowerSt.FrancisBasin
0
10
20
30
4/6 5/6 6/5 7/5 8/4 9/3 10/3
Nitrate,mgN
/l
Date
Downstrea
m
Upstream
Select Data: Nitrate (grab)
and nitrate (15 min)
Grab samples
Sonde
measurement
LowerSt.FrancisBasin
0
1
2
3
4
4/6 5/6 6/5 7/5 8/4 9/3 10/3
Nitrate,mgN
/L
Date
Downstream
Midstream
Upstream
Ceap effort
• Nearly 1 full year of data
• Modeling
• AnnAGNPS
• APEX
• Sampling strategies
• Grab
• Passive
• Continuous
• Biological analysis

7. 12/9/2015
7
summary
• Edge-of-field measurements
• Cover crops
• No statistical difference
• Baseline Year 1
• No statistical difference
• Off season spikes
• Additional analysis
• Long-term view
• State-wide network
• Future effort
• Inform in-stream impacts
• Co-benefits of management
Thank you
• Collaborators/Contributors
• Nadine Straitt (funded through CIG-Daniels)
• Dr. Niroj Aryal (funded through CEAP watersheds)
• Delta Water Management Research Unit
• Arkansas State University
• Dr. Tina Gray Teague
• Ecotoxicology Res. Lab
• Conservation Districts
• Producers
Michele L. Reba, PhD, PE
Research Hydrologist
USDA-ARS
Delta Water Management Research Unit
michele.reba@ars.usda.gov