1. Groundwater modeling of pesticide
fluxes in the Faga`alu Watershed,
American Samoa
By Eric Welch, Global Environmental Science,
SOEST
Mentor: Dr. Henrietta Dulai
2. Introduction
Objective
Estimate inventories and fluxes of the herbicide
glyphosate in the Faga`alu watershed.
Why do this?
1. To determine if levels of concern are present by
direct sampling and measurement of surface and
groundwater.
2. To identify source regions by determining transport
pathways in aquifer’s groundwater by a hydrological
model and matching to land-use by GIS spatial
analysis.
3.
4. Introduction
Faga`alu Watershed
2.5 km2 watershed
Forested slopes
Densely populated alluvial plain
Faga`alu Stream drains to ocean
Mt. Matafao1
Faga`alu Quarry2
Agricultural LandFaga`alu Watershed on the inner Pago
5. Introduction
Drinking water and contamination
90% of American Samoa’s drinking water supply
comes from groundwater
Anthropogenic groundwater pollutants:
◦ Pesticides
◦ Pathogens
◦ Excess Nutrients
Inadequate agricultural
techniques can leach
contaminants into aquifer
Contaminant pathways into the
groundwater system. 3
6. Introduction
What is Glyphosate?
Glyphosate (aka “Roundup”)
Most Popular Herbicide Worldwide
Used on: Crops, Roadsides, Lawns,
Forests, Gardens
Various Roundup/
Glyphosate products
at Tutuila’s ACE
Hardware.
Fields being sprayed with herbicide to control weed
growth.4
7. Methods
Fieldwork in American Samoa
(August 2016)
•Collected Water Samples
for
Pesticide Concentration
•From the Faga`alu
watershed
sampled:
1 Well
2 Coastal Springs
2 Tributaries
7 Main Stream Locations
7 Base Flow
3 High Flow
3 Stream Bank Groundwater
Educating Samoan children as
they helped collect water samples.
Ditch portion of the lower Faga`alu
Stream.
8. Methods
Sample Analysis and Labwork at UH Manoa
•Also tested for:
•Nutrients, Ions, D&O, Salinity,
Conductivity, DO%, Radon
•Tested for concentrations of
herbicide glyphosate using
an
ELISA Method
Measuring Equipment used to analyze samples. 5, 6, 7
Dr. Dulai and myself running glyphosate tests in lab.
9. Methods
GIS and Groundwater Modeling
Used ArcGIS to:
•Spatial analysis of
glyphosate
concentrations
in watershed.
Used GMS to:
•Create hydrological
model
using USGS
MODFLOW
and MODPATH
modeling
programsWorking on ArcGIS, mapping glyphosate
distribution.
Modeling the Faga`alu Aquifer with GMS.
9
8
10. •Gaining stream reaches
had elevated 222Rn levels
and losing stream
reaches had lower levels,
confirming groundwater
input.
Results
Base flow and
Radon
1
10
100
1000
0 500 1000 1500
222RnConcentration(dpm/L)
Distance Upstream (m)
Faga`alu Radon Levels
1
2
3 4
5
6
7
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0 500 1000 1500
StreamFlow(m3/s)
Distance Upstream (m)
Faga`alu Base Flow
Gaining Losing
1
2
3 4
5
6 7
Base flow discharge values for Faga`alu
stream
Rn-222 Levels in Faga`alu Stream (yellow
stars represent streambank groundwater
samples)
The Faga`alu Watershed with
sampling locations marked.
Faga`alu
watershed
12. Results
Glyphosate
Concentrations 0
0.05
0.1
0.15
0.2
0.25
0.3
0 500 1000 1500
Concentration(ppb)
Distance Upstream (m)
Fagaalu Glyphosate Concentrations
Stream- Low Flow
Stream- High Flow
Stream- Tributaries
Groundwater Samples
Glyphosate concentrations from sampling locations in
Faga`alu by sample-type , mapped with land use data.
Glyphosate levels at low-flow and high-flow
stream conditions, and tributary and
groundwater samples.
13. Results Hydrological Model
Groundwater flow paths to
wells, coastal springs, and
stream bank groundwater
locations were modeled.
Computed vs. Observed water table values
for calibrated hydrological model.
Water table levels were
calibrated using base
flow discharge data
along with well and
spring levels in the
Faga`alu watershed.
Water
Level
14. Discussion / Conclusion
Glyphosate concentrations in Faga`alu watershed
are low, however transport through groundwater is
evident.
Elevated pesticide levels correlate with shorter flow
paths, suggesting that relative proximity to
glyphosate sources may be an important factor in
contamination.
The hydrological model points to sources of
contamination that originate under developed urban
areas. I am looking for a better ‘land use’ map that
has all agricultural lands present in the watershed.
15. Acknowledgements
I would like to give big thanks to:
UROP for the funding and supporting me
Dr. Henrietta Dulai and Dr. Aly El-Kadi for their
guidance and mentorship through this project
Christopher Shuler for his help in my fieldwork in
Samoa and advice and direction this past year
Dr. Michael Guidry (GES Chair) always great
guidance
Others who helped along the way: Olkeba Tolessa
Leta, my Samoa Crew (Daniel Amato, Veronica
Gibson, Nalani Olguin), employees from ASPA,
AS-EPA, ASCC, and NASDA in American Samoa,
Dr. Thomas Shea for the GIS skills, UH Manoa GG
Department, all my SOEST professors &
classmates for their encouragement
16. References
Dulaiova, Henrietta, R. Camilli, P. B. Henderson, and M. A. Charette. "Coupled Radon,
Methane and Nitrate Sensors for Large-scale Assessment of Groundwater Discharge
and Non-point Source Pollution to Coastal Waters.“ Journal of Environmental
Radioactivity 101.7 (2010): 553-63.
Glyphosate ELISA Microtiter Plate: Instruction Manual. Abraxis Inc. Warminster, PA. E-
mail: info@abraxiskits.com.
Izuka, Scot K., J.A. Perrault, and T. K. Presley. "Areas Contributing Recharge to Wells in
the Tafuna-Leone Plain, Tutuila, American Samoa." USGS Scientific Investigations
Report 2007-5167 (2007).
Messina, A.M., and T.W. Biggs. "Contributions of Human Activities to Suspended Sediment
Yield during Storm Events from a Small, Steep, Tropical Watershed.“ Journal of
Hydrology 538 (2016): 726-42.
Paul, Vijay, and R. Pandey. "Is the Herbicide Glyphosate Really Safe?" Current Science
112.1 (2017): p. 11-13.
Shuler, Christopher K. (2016). “Source partitioning of anthropogenic groundwater nitrogen
in a mixed-use landscape, Tutuila, American Samoa” (Masters diss.). University of
Hawai`i at Manoa.
Pictures from:
1- http://www.terragalleria.com/pacific/american-samoa/pago-pago/picture.samo3890.html
2- http://www.ecosailingcharters.com/2012/12/lbj-waterfall-hike-american-samoa.html
3- https://pubs.usgs.gov/fs/2005/3087/
4- https://www.thermofisher.com/blog/proteomics/pesticides-in-ambient-air-a-novel-lc-hrms-
protocol/
5- https://www.ysi.com/6920-v2-2
6- http://www.durridge.co.uk/products_rad_h2o.shtml
7- http://www.abraxiskits.com/products/readers/
8- http://www.esri.com/arcgis/about-arcgis
9- http://www.aquaveo.com/software/gms-groundwater-modeling-system-introduction
Introduce: My name is Eric Welch
Title of my Project is ‘Groundwater Modeling in pesticide fluxes of Faga`alu Stream, American Samoa’
My mentor is Dr. Henrietta Dulai
Thanks to UROP for funding this project and letting me be here today!
Estimate inventories and fluxes of the herbicide glyphosate in the Faga`alu watershed:
1. Determine if levels of concern are present.
2. Whether surface or groundwater flow transport pathways are important for its distribution.
Goal: Assess spatial distribution of glyphosate in stream and groundwater samples across watershed
Use GIS and geological tracers to study glyphosate distribution and fluxes in collected samples
Construct a hydrological model to map groundwater flow paths to explain spatial distribution and elucidate sources in watershed
Objectives - go from big picture to specifics. In the first bullet let your listeners know how your research helps answering some important environmental\management problem.
Then within that you had a 3-prong approach:
1) measurement of glyphosate
2) studying its distribution in stream, wells and mapping in GIS and
3)constructing a hydrological model that shows groundwater flow paths.
This is the island of Tutuila in American Samoa (2597 miles / 4179 km) (~2600mi/~4180km) from Oahu, HI.
137 km2 island
American Territory with capital city Pago Pago on the island (small population of 3600+ people)
Tutuila has 55,000+ people total
74 distinct villages
Notes:
Faga`alu
Mt. Matafao- Tutuila’s highest pt. (2142 ft.)
Faga`alu Quarry- farthest human-disturbed location up the valley from the ocean
LBJ Tropical Medical Center- island’s main hospital, large impervious surface area
Fagaalu characterized by steep forested slopes in upper watershed
Very little agriculture
Small urbanized alluvial plain at bottom of valley, with the large Lyndon B. Johnson Hospital contributing to impervious surface
Covers a ~2.5 km2 area from Mt. Matafao to the Bay, with the Faga`alu Stream traversing entirety
Little agricultural use aside from small taro and banana plantations
Piggeries and Septic Systems may contribute excess nutrients
5-acre quarry upstream from urban area
Izuka, Shuler info.
https://debiwood.wordpress.com/2014/03/ ----LBJ Pic
http://www.ecosailingcharters.com/2012/12/lbj-waterfall-hike-american-samoa.html ---Quarry Pic
http://www.terragalleria.com/pacific/american-samoa/pago-pago/picture.samo3890.html ---Matafao Pic
Notes:
High Annual Rainfall = Productive Aquifers
Rapid transport of contaminants through groundwater
Tutuila’s rainfall averaging 3,000 to 6,000 mm/year (~120-240 in/yr)
Excess Nutrients from Piggeries and OSDS (On-site disposal systems/Cesspools)
Pesticides (get from list in yellow book later)
Shuler Master’s Thesis citation for info
Picture- https://pubs.usgs.gov/fs/2005/3087/
Notes: Most Popular Herbicide Worldwide, (largest selling agrochemical)
Introduced 1974, under dozens of trade names by diff. manufacturers
Glyphosate-tolerant crops later introduced by Monsanto (‘Round Up Ready’ crops) really sparked its major use ---farmers able to control weeds easy w/out harming their crops
This leads to increased volume and freq. of applications or combination w/ other herbicides due to weed resistance
Used on Crops, Roadsides, in Gardens, Forests, Lawns
Very effective and non-selective
Used to control annual/perennial plants (broad leaf weeds, grasses, woody plants, aquatic weeds)
Inhibition of EPSPS enzyme (important in amino acid pathway in most plants, can affect many physiological processes)
Residue on many plants we eat, but well within MRL limit (0.1 to 20.0 mg/kg)
Rapidly excreted, but increased chronic and acute kidney, pancreas, and other disorders, as well as cancers have been observed more recently in exposed humans and animals
Some studies show links to non-Hodgkin’s Lymphoma in humans as well
Glyphosate adsorbs to soil, water soluble (not as bad as fat soluble), surface and groundwater contamination thru runoff, erosion, leaching
CURRENT SCIENCE, VOL. 112, NO. 1, 10 JANUARY 2017 VIJAY PAUL* RAKESH PANDEY
https://www.thermofisher.com/blog/proteomics/pesticides-in-ambient-air-a-novel-lc-hrms-protocol/ --Pest-spray-pic
Glyphosate ELISA Microtiter Plate Abraxis Manual
(add pic of someone spraying grass)
Notes:
Fieldwork in August 2016 for two- weeks
August 12th (?) Faga`alu stream study baseflow sampling of 7 Stream locations (3 w/ peizometers)
2 Tributaries
Later sampled 3 High Flow stations
2 Coastal Springs
1 Well
Also sampled:
Wells (all, 40+), Streams (~20), & Coastal Springs (~10) from around the island, 2 other stream study sites too (not as in-detail)
Notes:
Glyphosate measured using Abraxis Equipment (Microtiter Plate Reader):
-using an ELISA Method (the plate kit), ELISA-based recognition of glyphosate by polyclonal antibodies
-immunoassay for quantitative and sensitive screening of Glyphosate in H2O samples
-Stored in refrigerator (20-25degC) before use
-samples are derivitized, added to microtiter wells, coated w/ goat anti-rabbit antibodies
-incubated for 30min
-enzyme conjugate added, competitive reaction occurs w/ glyphosate (if present), allowed to occur for 60 mins
-color signal generated
-blue color intensity inversely proportional to glyphosate present in sample (meaning less color=more glyph, more color=less glyph.)
-color evaluated using ELISA reader (Abraxis machine)
-concentr. of samples determined by interpolating w/ standard curve for each run
Other measurements we took:
YSI – dissolved oxygen, conductivity, salinity, temperature
RAD7- Radon levels (RADH2O setup) using bubbling technique to get radon hits per sample.
Others: D&O(Deuterium and Oxygen, Nutrients (DIC, TOC, TN), Ions (Mg, Ca, Na, Cl, Si, P, S, etc.)
Borrowed pics from:
https://www.ysi.com/6920-v2-2
http://www.durridge.co.uk/products_rad_h2o.shtml
http://www.abraxiskits.com/products/readers/
NOTES: GMS is a graphical interface to run models like Modflow, Modpath, Seawat, MS3DMS, etc.
MODFLOW is program to form 3D saturated flow models of watershed (hydrological models)
Arc GIS (Geographic Information System) is graphic program - creating and using maps; compiling geographic data; analyzing mapped information
http://www.esri.com/arcgis/about-arcgis
http://www.aquaveo.com/software/gms-groundwater-modeling-system-introduction
Notes:
Radon is an indicator of ground-water discharge into a stream. (specifically Rn-222) half-life 3.8 days
Baseflow is the stream’s discharge rate when there has not been rain for a long period of time
-it should be solely fed by groundwater since there shouldn’t be any precipitation runoff available
As can be seen in my data, the Rn-levels precisely follow the base flow at every station, verifying groundwater input to the stream.
The peizometer locations as expected contain higher levels of Rn, being sampled from underneath the ground, also correlating.
‘Coupled radon, methane and nitrate sensors for large-scale assessment of
groundwater discharge and non-point source pollution to coastal waters’ (by Dulaiova et al)
Obtained readable glyphosate concentrations in 59% of sampling locations across island
Although our highest concentration found at .301ppb is nowhere near the MCL level of 700ppb, still shows presence and transport
Highest concentrated areas seem to be Faga`alu, Pago Pago, and certain areas of the Tafuna plain
1st picture: Baseflow Stream measurements, Well and Coastal Springs
2nd picture: Peizos, Tributaries, High Flow Stream
Graph: Shows all stream Glyphosate Levels based on Distance upstream (excludes well and coastal springs)
Can’t get exact matching symbols through Excel and Arc…
-MODFLOW Hydrological Model shows low relatively level head values in alluvial plain, with higher values in head rising with surface elevation (although staying below ground obviously)
Some effect of stream on head values, showing connection of stream to aquifer (especially in lower watershed)
-Not perfect, but computed vs. observed graph is not too bad.
-Model still needs work.