Distribution and Availability of Trace Metal(loid)s Within the
Plant-Soil-Water Nexus at the St. Jones Salt Marsh
Kristy Northrup, Dr. Angelia L. Seyfferth
Department of Plant and Soil Sciences
Abstract
St. Jones Boardwalk
The presence of toxic metals and metalloids such as copper,
chromium, and arsenic in soils may pose toxicological risks to biota even
at trace concentrations. In preliminary analyses, the Seyfferth Research
Group has observed elevated levels of arsenic in pore waters (0.4 – 27 ug
L-1) and sediments (up to 47mg/kg) at the St. Jones Reserve that may
impact its ecosystem service as a nutrient buffer between the terrestrial
and oceanic environments. We hypothesize that the elevated
concentrations are due to the use of pressure treated lumber for
boardwalk materials. Trace metal(loid) concentrations and partitioning
among the soil, pore water, and vegetation pools were monitored to
assess the potential chronic toxicity to salt marsh biota as well as the
source and fate of arsenic. Expanding water inundation from projected
sea level rise will influence the redox chemistry and therefore the
mobility of trace metal(loid) contaminants. This study aims to determine
whether the influence of redox potential or salinity is the dominant
control over the availability of trace metal(loid)s in the St. Jones salt
marsh.
Preliminary Pore Water Results
Arsenic Concentration (uM)
0
0.15
0.2
0.25
0.3
0
Depth (cm)
-20
Average Conductivity
-40
Average Arsenic
-60
-80
-100
0
1000
2000
3000
4000
5000
6000
7000
Conductivity (uS/cm)
Figure 4: Pore water arsenic and conductivity for near boardwalk peepers
Figure 1: Aerial View of St. Jones Salt Marsh and Sampling Points
Preliminary Soil Results
Arsenic Concentration (uM)
0
0.1
0.15
0.2
0.25
0.3
0
-20
Depth (cm)
40.00
Arsenic Concentration (mg/kg soil)
0.05
20
50.00
CCA-Treated Wood
• Wood treated with chromated copper arsenate (CCA) leaches
metal(loid)s into nearby soil and interstitial water
• Leaching rate decreases during the first year after installation,
but surface rejuvenation causes leaching to continue years later
• Older piers with low water flow interaction have highest
metal(loid) enrichment within 1 meter radius
• St. Jones boardwalk installed cir. 1996, with several renovations
Arsenic Availability and Toxicity
• EPA Heavy Metal Standards for Chronic Exposure in Salt Water:
0.48 uM As, 0.96 uM Cr (VI), and 0.049 uM Cu
• Low redox potential reduces iron (oxyhydr)oxides, releasing As
• Salinity has unclear influence on As availability
Research Question 1: What is the source of elevated arsenic in the
soils at St. Jones Reserve?
Research Question 2: What factors are controlling the cycling and
bioavailability of arsenic and how does it change with shifting
biogeochemical regimes?
30.00
Average Eh
-40
Average Arsenic
-60
20.00
-80
10.00
-100
-25
25
75
125
175
225
275
325
375
Redox Potential (mV)
Figure 5: Pore water arsenic and redox potential for near boardwalk peepers
0.00
Interior Marsh 1
Interior Marsh 2
Interior Marsh 3
Near Boardwalk 1
Near Boardwalk 2
Near Channel
Near Boardwalk
Sampling Location
Figure 2: Total soil arsenic concentration for sampling sites at St. Jones
Preliminary Pore Water Results
• Future soil incubation will test arsenic release over salinity gradient and
controlled redox potential
20
0
0
Depth (cm)
Preliminary Conclusions/Future Directions
• Chromium and arsenic in pore water samples were on average lower than
EPA heavy metal standards. Pore water copper was below detection
1
2
3
4
5
6
7
8
• Sequential Extraction Procedure (Wenzel et al. 2001)
9
• Adding more pore water sampling sites: near boardwalk, away from channel
-20
Near Boardwalk
-40
Acknowledgements
Interior Marsh
-60
• Monthly to bimonthly collection of soil, plant, and pore water samples
• Processed and digested soil and plant samples (EPA Method 3050b)
• Measured redox potential, pH, and conductivity of pore water with standard electrodes;
acidified pore water with 2% nitric acid
• Pore water and plant digests analyzed by ICP-MS at UD Advanced Materials
Characterization Lab; Soil digests analyzed by ICP-OES at UD Soil Testing Lab
0.1
20
Introduction
Methods of Analysis
0.05
-80
-100
Ratio of As:Cr
Figure 3: Ratio of As:Cr in different pore water sampling locations at St. Jones
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•
•
•
Seyfferth Research Group, University of Delaware
Caroline Golt, Advanced Materials Characterization Laboratory, University of Delaware
Karen Gartley, Soil Testing Laboratory, University of Delaware
Kari St. Laurent, Department of Natural Resources and Environmental Control &
Delaware National Estuarine Research Reserve