Using Chemistry to Determine Sediment Source in
White Clay Creek
Dr. Diana L. Karwan
University of Delaware Department of Geological Sciences
Stroud Water Research Center
White Clay Wild and Scenic Watershed Summit
September 25, 2012
Research Questions
(www.udel.edu/czo)
Christina River Basin CZO:
What is the net carbon source or sink provided by the Christina River
Watershed?
My Research:
1. What is the composition and source of suspended material in White Clay
Creek?
2. Does eroded mineral material stabilize and transport organic carbon in the
Photo: Marissa Morton
fluvial network?
3. (How) does the fluvial transport of suspended material differ based on its
composition on seasonal and storm time scales?
Research Questions
What is the composition and source of suspended material in White Clay
Creek?
Photo: Marissa Morton
Approach
Sediment Fingerprinting – possible sources
Rill Erosion
Road Dust
(high Zn)
Photo: Marissa Morton
Overland Flow
(surface soil: high 7Be, C&N
reflect plant community)
Channel Banks
Trail Crossing
(legacy sediments + buried
soil horizons, higher Fe)
(animal evidence???)
Study Area
Christina River Basin:
•Total area: 1440 km2
•3 main tributaries – Brandywine River, Red
Clay Creek, White Clay Creek
•Urban, agriculture, and forest land use
•Sediment TMDL
White Clay Creek:
Photo: Marissa Morton
•
Total area: 277 km2
•
Wild and Scenic River for entire watershed
•
Urban, agriculture, and forest land use
•
Drinking water supply in areas of PA and
DE
Approach
Sediment Fingerprinting
1. Field collection of suspended materials, landscape materials, precipitation
2. Analyze for several chemical signatures
3. Use data in a statistical model to determine fraction of stream material from various sources
Particulate Analyses:
•
•
•
•
•
•
Photo: Marissa Morton
•
•
Fallout radionuclides (7Be, 137Cs, 210Pb)
C, N, stable isotopes
Mineral surface area
Grain size
Mineral content (elemental and composition)
Microbial community characterization (16S,
rRNA, PCR, ITS-DGGE, sequencing)
FTIR
Separate colloids quantification
Streamwater Chemistry:
•
•
•
•
TSS
DOC
Anions + Cations
Others?
Approach
Field Collection
Precipitation for Radioisotopes
7Be
7Be
Photo: Marissa Morton
Radionuclide Fingerprints
•Precipitation delivered
•Strong particle surface affinity
•All radioactive, so primary method of
‘disappearance’ is decay.
•Plant interception not well known
(recent source < 30%)
•Erosion tracers:
Beryllium-7 (54 days)
Lead-210 (22 years)
Cesium-137 (30 years)
Beryllium-10 (1.3 million years)
Approach
Field Collection of Precipitation
Photo: Marissa Morton
Open Precipitation
Stemflow
Canopy Throughfall
Approach
Field Collection!
Challenge: collecting enough solid material for all analyses during baseflow
and storms
55 gallon barrel and
cell-phone-triggered
submersible pump for
suspended sediment
ISCO automatic
sampler for 1 L
streamwater
samples
Photo: Marissa Morton
Photo: Marissa Morton
Pressure
transducer for
water height
Approach
Field Collection!
The “Dial-a-Pump”
float switch
turns off pump
open source
electronics
(Arduino)
55 gal.
barrel
submersible
pump
Cell phone
12V marine
battery
Approach
Field Collection!
The “Dial-a-Pump”
Scaled Up: 3 barrels
Photo: Marissa Morton
Approach
Sediment fingerprinting at nested sites in White Clay Creek
Field Collection – Locations
1st order – Avondale PA
3rd order – Avondale PA
Photo: Marissa Morton
5th order – Newark DE
Results - Rainfall
Trees
Leaves
•
No Trees
Summer
No Trees
Winter
Trees
No Leaves
No significant difference in concentration per event with canopy when examining a year of data
Results – Shallow Soil
White Clay Creek Shallow Soils - 137Cs
White Clay Creek Shallow Soils - 7Be
0
20
7Be40(mBq/g) 60
0
2
2
Cumulative Mass (g/cm2)
0
4
Cumulative Mass (g/cm2)
6
8
10
137Cs (mBq/g)
20
30
40
4
6
8
10
10
12
12
14
14
16
16
18
18
20
Open / Agriculture
•
•
•
0
80
Forest Canopy
Forest Canopy
Open / Agriculture
Similar 7Be (short lived!) profile in open and forested area
Longer-lived 137Cs shows mixture that occurs in ‘plow layer’
Signatures of these isotopes in the stream might help tell us about the depth from which
erosion and sediment delivery occur
50
Preliminary Results – Source /Suspended Variations
Preliminary Results
Suspended Material – Storm Collections
Storm collections began 9/30/2010
• 1 large sediment sample per storm
• Target peak
• For example: 25 February 2011
Photo: Marissa Morton
Preliminary Results
Suspended Material – Storm Collections
Differences noted along storm hydrograph, beginning in April 2011
Photo: Marissa Morton
Preliminary Results
Suspended Material – Storm Collections
August 25 – September 12, 2011
Hurricane
Irene
66 metric tons
sediment export
Tropical
Storm
Lee
135 metric tons
sediment export
Photo: Marissa Morton
54 metric tons
In peak event
Preliminary Results
Suspended Material – Storm Collections
Preliminary Results – Radioisotope Fingerprinting
•
7Be
•
One year of rainfall data does not show significant differences across
seasons or in the presence or absence of a tree canopy.
•
Does this mean the differences seen in stream material are from
differences in erosion and delivery??????
on stream sediment varies between seasons, with higher values in
the spring and summer, and within single storms, with higher values
generally earlier in a single event.
White Clay Creek POM with published sediment values
Organic carbon (%)
10
8
leaf litter,
algae
POM from
White Clay Creek
Rivers draining
deserts
<1
<1
Larger, temperate
rivers
(data from Keil et al.
1997, Mayer et al.
1994, Onstad et al.
2000)
<1
26
6
<1
4
2
73
139
52
29
32 49 107
36
330
1100
<1
0
0
20
40
60
80
Mineral Surface Area (m2/g)
100
Oxygen exposure
times for marine
sediments
on the Washington
shelf & slope and
suboxic Mexican
margin (data from
Hartnett et al. 1998,
Hedges et al. 1999,
Keil et al. 2004)
Preliminary Results
Preliminary Results - POM
•POM from White Clay Creek is relatively high in organic carbon content.
• Organic carbon to surface area ratios closely resemble the surface soil
from the land cover types in the catchment – agriculture and forest.
•OC and mineral surface area change with season, but their ratio remains
constant and characteristic of relatively ‘fresh’ material.
Acknowledgements
Anthony Aufdenkampe
Steve Hicks
Dave Montgomery
Stephanie Dix
Denis Newbold
Sara Geleskie
Fred Shaw
Erika Vazquez
Jim Pizzuto
Del Levia
Adam Pearson
Elyse Williamson
Rolf Aatlo
Julia Marquard
CRB CZO work was funded by the National Science Foundation
[NSF EAR 0724971]
SSH CZO work funded by an NSF EAR Postdoctoral Fellowship
[NSF EAR 1144760]