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Mercury and Organic Carbon Dynamics in an Upland Landscape during Snowmelt. Jamie Shanley 1 Paul Schuster 2 Mike Reddy 2 Dave Roth 2 Howard Taylor 2 George Aiken 2 1 U.S. Geological Survey Montpelier, Vermont 2 U.S. Geological Survey, Boulder, Colorado. Objectives. - PowerPoint PPT Presentation
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Mercury and Organic Carbon Dynamics in an Upland Landscape during Snowmelt
Jamie Shanley1
Paul Schuster2
Mike Reddy2
Dave Roth2
Howard Taylor2
George Aiken2
1U.S. Geological Survey Montpelier, Vermont
2 U.S. Geological Survey, Boulder, Colorado
Objectives
Develop and test methodologies for intensive spatial and temporal event sampling of Hg
Investigate the dynamics of Hg transport during snowmelt across a gradient of land cover and watershed size
Evaluate linkages between dissolved and particulate Hg and dissolved and particulate carbon
Previous Hg research in Vermont Wet and dry deposition measurements in Underhill since 1993 - world’s longest
continuous record. High Hg in leaffall (Rae, 1998) corroborates high Hg in dry deposition (up to 5x wet)
(Scherbatskoy et al., 1998) Hg deposition retained (>90%) in terrestrial watershed; export episodic,
associated with POC (Scherbatskoy et al., 1998; Shanley et al,. 1999) High Hg in O-horizon soil solution, associated w/DOC (Donlon, 1999) Hg export in agricultural landscape similar to forest (Rinehart, 2000) Routine measurements by State since 1970s show high Hg in fish Current focused study of sediment, water and fish Hg in VT lakes (Kamman et al.,
1998; 2000)
Sleepers River Research Watershed USDA Agricultural Research Service 1957-1975
Established 17 stream gages, 13 meteorological stations National Weather Service 1968-1986
Snowmelt modeling - energy balance approach Cold Regions Lab (CRREL) 1979-present
Snowmelt modeling, sensor testing US Geological Survey 1991-present
Water, Energy, and Biogeochemical Budgets (WEBB)
Sleepers River Research WatershedBasin characteristics
Elevation: 200 to 690 m, slopes gentle to very steep Precipitation: 1100 mm per year, ~30% as snow Climate: Humid continental, Mean annual T: 6°C Gaged watersheds from 3.4 ha to 111 km2
Land cover - overall 2/3 forested, 1/3 open land Mixed / Northern hardwoods (Sugar maple, beech, ash, spruce/fir) Dairy farming (pasture, hayfields, corn fields)
Economics: Dairy farming, maple sugaring, logging
Sleepers River Research WatershedBasin characteristics
Bedrock: quartz-mica phyllite with beds of calcareous granulite Surficial: 1-3 m of dense basal till from local bedrock Soils: Inceptisols, spodosols, and histosols w/wetlands Stream chemistry: well-buffered calcium bicarbonate / sulfate
waters Hydrology: Flashy streams, snowmelt dominated
Study watersheds (with % of area forested)
W-5 11,125 ha (67%)
W-3 837 ha (80%) W-2 59 ha (27%) W-9 41 ha (100%) W-9A 17 ha (100%)
W-9B 13 ha (100%) W-9C 7 ha (100%) W-9BX 5.1 ha (100%) W-9BY 3.4 ha (100%) W-9BXA ~2 ha (100%)
.
W-9
W-2W-3
W-5
N
Stream gaging stationMeteorological and snow survey station Stream
Catchment boundary
St.Johnsbury
Danville
N. Danville
PassumpsicRiver
Sleepers River
FieldLaboratory
Montpelier
VERMONT
44°30'
44°25'
72°05'72°10'
2 4 6 8 Kilometers0
Burlington
450
600
Elevation contour (m)
300
W-9 watershed
.
100 m0
Contour interval 100 ft
Hg sampling siteWetland
W-9BXA
W-9
W-9BY
W-9C
W-9BX
W-9BW-9A
Field procedures Streamwater
Grab sample in teflon holding bottle for Hg - collected wearing particle-free gloves.
Grab sample in pre-baked amber glass bottle for C fractions. Grab sample in PE bottle for major ions Field sonde for Temp., pH, DO, Sp. Cond., ORP
Snow Lexan scoop into PE bag while wearing particle-free gloves; 7
profiles at peak snowpack
Groundwater and seeps Peristaltic pump with teflon tubing - 6 samples near peak melt
On-site sample processingField laboratory - within 4 hours - complete duplicate processing
of all samples Mercury
Dissolved:Vacuum filtered through 0.4-µm cellulose acetate membrane into acid- washed 125-mL glass bottle. Acidified with K2Cr2O7.
Particulate: Filter membrane placed in 60-mL glass bottle, filled with DI water, acidified with K2Cr2O7
Carbon DOC: Vacuum filtered through 0.7-µm GFF (glass fiber) filter into pre-baked amber bottles POC: I set of duplicate filter membranes wrapped in Al foil for solid C analysis; additional set
saved for LOI determination.
Major ions Cations: syringe-filtered through 0.4-µm cellulose acetate membrane into acid-washed 125-
mL PE bottle. Acidified to pH 2 with HNO3
Anions: syringe-filtered through 0.4-µm cellulose acetate membrane into clean 125-mL PE bottle. Kept chilled.
Laboratory AnalysisAll analyses except POC, PON at USGS, Boulder, CO Mercury
Dissolved:Cold vapor atomic fluorescence spectrometry (CVAFS) on filtered aliquot. Particulate: CVAFS on acidified solution containing filter membrane .
Carbon DOC (and TOC): Ultraviolet persulfate oxidation with infrared detection POC (and PON) at Chesapeake Biological Lab, University of Maryland Loss-on-ignition (LOI) to estimate organic C by combustion at 550 C.. SUVA - Absorbance at 254 µm
Major ions Cations: ICP Anions: Ion chromatography Alkalinity: Gran titration.
Concentrations, ng/L Duplicates median min max mean % diff.
Hg, dissolved 0.9 <0.3 4.1 5.8Hg, particulate 2.3 0.6 16.3 12
Hg concentration ranges and results of duplicate analyses
Based on 66 duplicate analyses
Hg vs. alkalinity, all sites, Sleepers River snowmelt 2000
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Hg,
dis
solv
ed, n
g/L
Alkalinity, meq/L
r2 = 0.43, p<.0001
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2
DO
C, m
g/L
Discharge, mm/hr
r2 = 0.41, p<.0001
DOC vs. discharge, all sites, Sleepers River snowmelt 2000
0
2
4
6
8
10
12
14
16
0 5 10 15 20 25 30
Hg,
par
ticul
ate,
ng/
L
POC, mg/L
r2 = 0.84, p<.0001
Particulate Hg vs. POC, all sites, Sleepers River snowmelt 2000
Hg vs. discharge, all sites, Sleepers River snowmelt 2000
0.0
0.5
1.0
1.5
2.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Hg,
dis
solv
ed, n
g/L
Discharge, mm/hr
r2 = 0.46, p<.0001
0.0
0.5
1.0
1.5
2.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Hg,
dis
solv
ed, n
g/L
DOC, mg/L
r2 = 0.50, p<.0001
Dissolved Hg vs. DOC, all sites, Sleepers River snowmelt 2000
Specific discharge and DOC at W-9B (forested, 13 ha)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
80 85 90 95 100 105 110 115
DO
C, m
g/L
Discharge, C
FS
Day of year, 2000
0.0
1.0
2.0
3.0
4.0
5.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
80 85 90 95 100 105 110 115
Hg,
ng/
L
Discharge, C
FS
Day of year, 2000
12.3
Particulate
Dissolved
Dissolved and particulate Hg at W-9B
0.0
1.0
2.0
3.0
4.0
5.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
80 85 90 95 100 105 110 115
Hg,
dis
solv
ed, n
g/L,
DO
C, m
g/L
or
Discharge, C
FS
Day of year, 2000
Dissolved Hg and DOC at W-9B
0.0
1.0
2.0
3.0
4.0
5.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
80 85 90 95 100 105 110 115
Hg,
dis
solv
ed, n
g/L,
DO
C, m
g/L
or
Discharge, C
FS
Day of year, 2000
Dissolved Hg and DOC at W-9B
0
1
2
3
4
5
6
7
60 70 80 90 100 110 120
DO
C/H
gD x
10
6
Day of year, 2000
W-9B
All other sites
DOC vs. Hg flushing, all sites
Conclusions We developed a methodology for accurate and reproducible
sampling of Hg at high temporal frequency using ultraclean sample handling protocols
Dissolved and particulate Hg concentrations closely tracked the respective dissolved and particulate C fractions, despite 6 order-of-magnitude difference in concentrations
Hg and C may be biogeochemically linked, or they simply have a common source -- shallow soil -- that is flushed during snowmelt. Needs further research.
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