2017 SWCS Annual Conference July 30-August 2, 2017 Monona Terrace Convention Center

1. Field Evaluation of a Passive Sampler for Soluble
Nitrogen and Phosphorous: Performance
Comparison to Grab and Continuous Sampling
Niroj Aryal, Ph.D.
ORISE Post-Doctoral Fellow
USDA-ARS, Delta Water Management Research Unit
Michele L. Reba, Ph.D., PE (PI/Mentor)
Research Hydrologist
USDA-ARS, Delta Water Management Research Unit
Philip A. Moore, Ph.D.
Soil Scientist
USDA-ARS, Poultry Production and Products Safety
Research
Submission ID 74

2. Overview
• Introduction
• Non-point source from agriculture
• Nutrient monitoring
• Current methods
• Passive sampling technology
• Objectives
• Methods
• Watersheds location
• Deployment and sample collection
• Sample preparation
• Laboratory analysis
• Preliminary Results
• Ongoing studies

3. Introduction: Non-Point Source from Agriculture
• Agriculture in MR Basin
• 31 states and 2 Canadian provinces
• 92% of country’s agricultural exports
• $105 billion worth GDP
• 200 million jobs directly and indirectly
• Water quality in MR Basin
• Source of drinking water to 18 million people
• 180 fish species unique to the Mississippi river
• Aesthetics, tourism and economic value of water
• Hypoxia in the Gulf of Mexico and agriculture
• 22,000 km2 areal cover in 2002 (26,131 km2 predicted for 2017)
• Gulf of Hypoxia Action Plan 2008
• Decrease of N and P loading by 20%
• Decrease of hypoxia to less than 5,000 km2 by 2035
• Monitoring of tributaries-largest source of nutrients-
identified as necessary Source: Gulf Hypoxia Action Plan 2008
Source: Dr. Bill Dennison http://ian.umces.edu/blog/2014/04/24/lower-
mississippi-river-environmental-literacy/

4. • Concentration, loads and yields from a watershed
• Daily, seasonal, or event locally or regionally
• Effectiveness of mitigation measures
eg. conservation practices
• Compliance of regulatory standards
• Total maximum daily load
• Water treatment methods
• Recreational use of water body
Introduction: Nutrient Monitoring

5. • Grab/Manual/Bottle sampling
• Quick, simple, accurate (at the time of sampling), inexpensive
• Not indicative of the temporal variability
• Passive sampling
• Continuous sampling/monitoring
• Most accurate, labor intensive, expensive
• Requires specialized instruments for sampling (autosamplers)
and for in-situ measurement/analysis
• Requires frequent calibration and maintenance
• Requires power, perhaps cooling/heating also
Introduction: Current Methods of Nutrient
Monitoring
Source: Deltares

6. Introduction: A Passive Sampler-Sorbi Cell
The concentration of N or P
The volume of flow
Flow
entrance
Filter
Sorbent
Tracer salt
Luer lock tip
Permeable frit
Flow entrance

7. Introduction: Passive Sampling Technology
• No power requirement
• In-situ sampling over time
• Flow proportional sampling (represents flow conditions)
• Flexible time period (weeks to months)
• Comparable cost to grab sampling or cheaper
Source: Deltares

8. Introduction: Prior Application
Rozemeijer et al. 2010. Application and Evaluation of a New Passive Sampler
for Measuring Average Solute Concentrations in a Catchment Scale Water
Quality Monitoring Study. Environment Science and Technology.

9. 1. Measure nitrate and phosphate concentrations in the agricultural drainage ditches at two watersheds in
Northeast Arkansas using a passive sampler (Sorbi cell)
2. Compare the phosphate concentrations from passive sampler to phosphate concentration from grab
sampling
3. Compare the nitrate concentrations from passive sampler to nitrate concentration from grab sampling
and from continuous measurement using sondes
4. Evaluate and contrast the cost and management requirements for three methods of sampling
Objectives

10. Methods: Watersheds
Lower St. Francis Basin (LSFB)
• Approximately 5769 acres (23.4 km2)
• >90% area in row crops, rice and soybean
• Mostly Sharkey clay soils (>97.4% group D)
• Ditch no. 1-St. Francis River
Little River Ditches Basin (LRDB)
• Approximately 13,200 acres (53.4 km2)
• >87% in row crops, cotton and soybean
• Mostly silty loam soil (>64.5% group C/D)
• Ditch no. 14-Buffalo Creek Ditch

11. • Grab samples
• Every week for 20 weeks May-Sep
• Nitrate+nitrite using Skalar auto-analyzer (EPA 353.2)
• Phosphate using Skalar auto-analyzer (EPA 365.1)
• Continuous measurement of nitrate
• Hach Hydromet DS5X Sonde
• Measurement every 15 min, May-Sep
• Calibration every 2 weeks
• Passive sampling
• Sorbi cells
• Every week sampling, May-Sep
Methods

12. Methods: Sorbi Deployment and Sample Collection

13. Methods: Sample Preparation
Samples from field
Tools required A cartridge
ready for
extraction
Wash filter
at the top
Cut the
cartridge
using
sharp
Stanley
knife
Wash
the silica

14. Methods: Sample Preparation (2)
Remove top filter, wash
sorbent
Push with
piston
towards the
opposite
direction of
flow
Add 50 mL of 2M HCL to
sorbent and 50 mL of 0.4 M
HCl to salt solution; sonicate
Recovered
salt and
sorbent
Washout
salt

15. • Analyzed in USDA lab at Fayetteville, AR
• Calcium by Varian Vista Pro ICP-OES
• Volume of flow calculated by
• Nitrate+nitrite using Skalar auto-analyzer (EPA 353.2)
• Concentration of nitrate or phosphorous calculated using
Methods: Laboratory Analysis

16. Results: Phosphorous
0.33±0.16 (sorbi) vs. 0.16±0.04 (grab) 0.33±0.22 (sorbi) vs. 0.16±0.04 (grab)
0
1
2
3
4
5
6
7
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
4/6 5/26 7/15 9/3 10/23
Discharge,m3/s
Phosphate-Pconcentration,mg/L
Grab
Sorbi
Discharge
LSFB
0
1
2
3
4
5
6
7
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
4/6 5/26 7/15 9/3 10/23
Discharge,m3/s
Phosphate-Pconcentration,mg/L
Grab
Sorbi
Discharge
LRDB

17. Results: Nitrate
0
1
2
3
4
50
1
2
3
4
5
6
7
8
9
10
5/12 7/1 8/20
Discharge,m3/s
Nitrate,Nmg/L
LSFB
Discharge-daily
Sonde_15 min
Grab_weekly
Sorbi_weekly
0
1
2
3
4
50
1
2
3
4
5
6
7
8
9
10
5/12 7/1 8/20
Discharge,m3/s
Nitrate,Nmg/L
LSFB
Discharge-daily
Grab_weekly
Sorbi_weekly

18. Results: Nitrate (2)
0
1
2
3
4
5
6
70
5
10
15
20
25
5/12 7/1 8/20
Discharge,m3/s
Nitrate,mgN/L
LRDB
Discharge_daily
Sonde_15 min
Grab_weekly
Sorbi_weekly
0
1
2
3
4
5
6
70.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
5/12 7/1 8/20
Discharge,m3/s
Nitrate,mgN/L
LRDB
Discharge_daily
Grab_weekly
Sorbi_weekly

19. Published literature
Bringhurst and Jordan 2015.
The impact on nutrient cycles
from tropical forest to pasture
conversion in Costa Rica.
Sustainable Water Resources
Management.

20. • Waiting for the laboratory analysis results from experiment in 2016/17
• 2-week sampling interval
• Identify the reason for low concentration of nitrate
• Non-retention of nitrate in the sorbent section?
• Injection of standard samples of nitrate showed 39-43% error
• Less than detectable nitrate-N concentration in the water?
• Continuous measurement and grab sampling consistently measure concentration >0.2 mg/L
• Possible interference from other ions?
• Inject stream/ditch water manually
• Beyond the limit of detection of sorbi?
• Inject stream/ditch water spiked with nitrate in increasing concentrations
• Skalar auto-analyzer or analysis issues?
• Used spectrophotometer
• Plan to use analysis method that is suitable for sea water
Ongoing Studies

21. Acknowledgement
Delta Water Management Research Unit
USDA-ARS Lab at
Fayetteville, AR
SorbiSense A/S, sorbi cells manufacturer
CEAP (Conservation
Effect Assessment
Project