THE IMPACT OF SEA LEVEL RISE ON THE PHOTOCHEMICAL RELEASE OF
DISSOLVED ORGANIC MATTER FROM RESUSPENDED RIVER AND ESTUARINE
SEDIMENTS
Lauren E. Thompson
A Thesis Submitted to the
University of North Carolina Wilmington in Partial Fulfillment
of the Requirements for the Degree of
Master of Science
Center for Marine Science
University of North Carolina Wilmington
2010
Approved by
Advisory Committee
Robert Kieber
Steve Skrabal
Ralph Mead
Melissa Southwell
Jen Culbertson
Gene Avery
Chair
Accepted by
DN: cn=Robert D. Roer, o=UNCW,
ou=Dean of the Graduate School &
Research, email=roer@uncw.edu,
c=US
Date: 2010.10.28 10:25:53 -04'00'
Dean, Graduate School
i
TABLE OF CONTENTS
ABSTRACT ................................................................................................................................... iii
ACKNOWLEDGEMENTS ........................................................................................................... iv
LIST OF TABLES ...........................................................................................................................v
LIST OF FIGURES ....................................................................................................................... vi
INTRODUCTION ...........................................................................................................................1
METHODS ......................................................................................................................................4
Site Description ....................................................................................................................4
Sample Collection and Preparation ......................................................................................4
Collection of Sediments from Sites .....................................................................................5
Photochemical Resuspension Experiments..........................................................................6
Analytical .............................................................................................................................7
RESULTS AND DISCUSSION ......................................................................................................8
Photolytic DOC release from Cape Fear River and Elizabeth River Resuspended
Sediments .............................................................................................................................8
Biogeochemical Setting (sulfate reduction vs. methanogenisis) .......................................10
Photolytic Release of Nutrients .........................................................................................11
Implications of Photolytic Release of Resuspended Sediments ........................................12
REFERENCES ..............................................................................................................................42
ii
ABSTRACT
Fine grain estuarine and riverine sediments are naturally resuspended and remain in the
photic zone by wind, waves, and water currents. Once transported into the photic zone, these
sediments can significantly impact a variety of important biogeochemical processes such as trace
metal mobilization, nutrient dynamics, and organic matter cycling. The current study examined
the effect of biogeochemical setting, controlled by salinity regime, on the photolytic release of
dissolved organic carbon (DOC), dissolved organic nitrogen (DON), dissolved inorganic
nitrogen (DIN), and phosphate (PO43-) from resuspended estuarine sediments. Biogeochemical
setting had no effect on photochemical processes with any of the measured analytes with the
exception of one site, Paradise Creek, which showed increased photolytic release of DOC as its
biogeochemical setting shifted from sulfate reduction to methanogenesis. This suggests that there
will be no direct impacts of salinity alterations such as sea level rise on the photolytic release of
either DOC or nutrients from resuspended particles when biogeochemical setting changes from
methanogenesis to sulfate reduction. Significantly higher increases in release of DOC, DON,
and PO43- were observed for fine grain sediments exposed to simulated sunlight compared to
dark controls. Photolytic release of the various analytes was also compared between sites and
over the course of incubation period lasting as long as two years. Cape Fear River sediments had
a higher photolytic release of DOC compared to Elizabeth River sediments. Other controls on
photochemical release from these particles such as their percent organic carbon (%OC), nitrogen
(%ON) and carbon to nitrogen (C:N) ratios were also examined. Experiments conducted during
the current study using only fine grain sediments displayed a much higher rate of DOC release
compared to a previous study using whole sediments. Therefore the intensity of the resuspension
event likely impacts the photochemical processes occurring in the water column.
iii
ACKNOWLEDGEMENTS
Thanks to everyone working in the Marine and Atmospheric Chemistry Research
Laboratory group, family and friends. Special thanks to Dr. Whitehead for immense help with
instrumentation and to undergraduate assistants, Zackary Gillum and Angela Carrol, for their
help. I‟d also like to thank my advisor Dr. Avery for always having an open door and Melissa
Southwell for help with experimental design and data analysis. Finally, I would like to thank
Sheena for always going on walks.
This work was supported by the National Science Foundation (NSF Grant OCE0285538).
iv
LIST OF TABLES
Table
Page
1. Percent Organic Carbon, Nitrogen, and C:N ratio for all collected sediments and sites .........14
2. Total Dissolved Nitrogen, dissolved organic nitrogen, nitrate, and ammonium .....................15
3. Site, treatment, date of experiment, and net flux of phosphate (Δ µmol/g/hr) ........................17
v
LIST OF FIGURES
Figure
Page
1. Map of Cape Fear River Estuary .............................................................................................18
2. Map of Elizabeth River Estuary ...............................................................................................18
3. A-K Photolytic release of DOC during resuspension experiments .........................................19
4. A-G Net flux of DOC during resuspension experiments .........................................................24
5. Rate of photolytic DOC release as a function of percent organic carbon content ..................28
6. Average changed in percent sedimentary organic carbon between initial and final ...............28
7. Average changes in percent sedimentary organic nitrogen between initial and final ..............29
8. Average changes in C:N ratio between initial and final sediments ........................................29
9. Changes in photolytic release of DOC from initial and final photolytic resuspension exp .....30
10. A-K Photolytic release of TDN during resuspension experiments ..........................................30
11. A-K Photolytic release of PO43- during resuspension experiments .........................................36
vi
INTRODUCTION
Estuarine and riverine sediments are naturally resuspended and mobilized by wind,
waves, and water currents. Anthropogenic sources of resuspended sediments in estuaries include
dredging, bow waves, propeller wash, and fishing activities. In the typically shallow waters of
estuaries and coastal waters, sediment-water interactions can significantly impact a variety of
important biogeochemical processes such as trace metal mobilization, nutrient and organic
matter cycling, and release of anthropogenic contaminants (Komada and Reimers, 2001;
Komada et al., 2002; Koelmans and Prevo, 2003). While earlier studies demonstrated the
importance of dark release from resuspended estuarine sediments, recent studies have addressed
the potentially more significant role photochemical transformations play in the mobilization of
organic matter and metals from these sediments. Mayer et al. (2006) reported that particulate
organic carbon (POC) in suspended sediments from the Mississippi River system decreased after
long-term exposure (6 h d-1 for 7-9 d) to simulated sunlight, showing that DOC was produced
from light exposed sediments. Kieber et al. (2006) demonstrated that DOC is produced from
estuarine sediments after more realistic 9-h exposures to full-spectrum simulated sunlight.
Production of episodically large quantities of DOC from photolyzed resuspended
sediments has significant implications for the cycling of carbon in the coastal ocean. Using
measured DOC photoproduction rates from the irradiated suspensions applied to waters
containing a moderate concentration of 100 mg L-1 of suspended material yields a flux of 0.56
mmol m-2 h-1 in the top 1 m (Kieber et al., 2006). The magnitude of this flux is high compared to
the major DOC fluxes resulting from benthic exchange (0.004 to 0.12 mmol m-2 h-1; Burdige and
Homstead, 1994; Burdige et al., 1999) and riverine discharge to the coastal ocean (0.04 mmol m2
h-1) based on global riverine discharge of 18 x 1012 mol y-1 (Meybeck, 1982) and coastal ocean
1
area of 52 x 106 km2 (Stacey, 1992). Therefore, photoproduction can represent a significant,
albeit poorly constrained, episodic source of DOC to the coastal ocean (Kieber et al., 2006).
Nutrients have also been shown to be photochemically released from resuspended
sediments (Riggsbee et al., 2008; Southwell et al., 2010). Southwell et al. (2010) reported
photolytic release of total dissolved nitrogen (TDN) and phosphate in laboratory resuspension
experiments of Bradley Creek sediments in 0.2 µm filtered seawater (2010). Estuaries have
varying nutrient limitation based on seasonality and salinity therefore the photolytic release of
nutrients from resuspension events could be an important source to coastal environments. For
example, the Cape Fear River (CFR) estuary, one of the study sites of the current study has
nitrogen limitation during the summer and fall and phosphate limitation during spring and winter
(Mallin et al. 1999).
The microbial breakdown of sedimentary organic matter has been shown to affect the
photolytic release from particles. Photochemical reactivity of algal detritus increased with
microbial decomposition in a study by Mayer et al. 2009. Processes by which organic matter is
remineralized have profound effects on sediment biogeochemical conditions and directly impact
sediment and water column processes due to varying redox conditions and reactions involving
remineralization byproducts (Lovely and Phillips 1987). Rates of remineralization of organic
matter may be affected by variations in microbial processes occurring in these dynamic estuarine
systems. Sexton (2002) compared sediment remineralization rates in freshwater and estuarine
sediments with and without additions of sulfate (Sexton, 2002). Results of these experiments
suggest that the breakdown of organic material by sulfate reduction (typical of marine sediments)
is approximately twice as fast as breakdown of organic matter by methanogenesis (typical
2
freshwater sediments). Therefore, changing rates in organic matter breakdown could alter
photolytic release from resuspended sediments.
In estuaries, where salinity can vary drastically both temporally and spatially, modes of
organic matter breakdown are very dynamic. Oxic microbial processes can be important in
surface sediments but anoxic microbially mediated processes often dominate remineralization in
the majority of the sediment column. In anoxic sediments with the oxidant sulfate supplied by
sea salts, the majority of organic material is decomposed by sulfate reduction (Skyring, 1987,
Capone and Kiene, 1988). In sulfate-depleted brackish and marine sediments anaerobic
respiration occurs primarily by methanogenesis (Capone and Kiene, 1988, Day et al., 1989).
Both sulfate reduction and methanogenesis can occur at the same time, although they are usually
mutually exclusive (Lovley and Phillips, 1987; Capone and Kiene, 1988) due to biogeochemical
zonation in which sulfate reducers outcompete methanogens (Martens and Klump, 1984, Lovley
and Klug 1986; Kuivila et al., 1989).
Salinity can be altered by rising sea levels, tides, and morphological changes due to
dredging and inlet management. Alterations in biogeochemical decomposition of sediments due
to variations in salinity could cause changes in photolytic reactivity of sediments. The primary
purpose of this study was to examine the impact of variations in salinity on the photolytic release
of DOC, DON, DIN, and phosphate from resuspended sediments. Additional potential controls
on these processes including biogeochemical decomposition, particle size, percent organic
carbon, percent organic nitrogen and carbon to nitrogen ratio of the particles were also examined.
3
METHODS
1. Site Description
a. Cape Fear River
The Cape Fear River, located in southeastern North Carolina has previously been
characterized as a moderately impacted system with low dissolved trace metals (Shank, et al.,
2004; Skrabal, et al.,2006) and high dissolved organic carbon (Avery, et al., 2003). Three sites
were studied on the Cape Fear River: two freshwater sites dominated by methanogenic
remineralization, Fishing Creek and Prince George, and one which historically experienced more
saline conditions and remineralization by sulfate reduction, Town Creek (Figure 1). All
locations have been documented in terms of biogeochemical and hydrological cycles by an
ongoing monitoring program (Hackney, et al., 2006).
b. Elizabeth River
The Elizabeth River (ER) was sampled on the Southern Branch and located in
southeastern Virginia. Extremely high levels of metals and organics have been reported for the
Elizabeth River and it has been described as being industrialized and heavily modified (Walker
and Dickhut, 2001; Conrad and Chisholm-Brause, 2004). Sulfate reduction should be the
dominant remineralization process for this system due to the low freshwater flow, high organic
content, and sulfidic sediments. Elizabeth River sites include Paradise Creek and Scuffletown
Creek (Figure 2). Results from the Elizabeth River were compared to Town Creek to contrast the
effects of human impact.
2. Sample Collection and Preparation
Surface sediment was collected at a depth of 0.5 cm. This depth was chosen because this
is the sediment likely to be resuspended due to tide, wind (Kalnejais, et al. 2007), or
4
anthropogenic effects (Kieber, et al. 2006). Collected sediment samples were placed in plastic
bags and stored at 4 ºC until placed in serum vials. Sediment incubation followed by
photochemical resuspension experiments similar to those reported in Southwell et al. (2010)
were performed after each sampling event by methods below.
Collected sediments were homogenized before being placed into glass serum vials to
incubate for a period of 1 to 2 years. Sample aliquots were delivered to serum vials by a 60 mL
catheter syringe with the tip cut off to increase the diameter of the opening. Serum vials were
flushed with N2(g) before placing Teflon lined caps and crimp seals to create anoxic conditions
(Avery et al. 1999). Vials containing Cape Fear River freshwater collected sediments were
injected with a 1 mL of a 6 mM sodium sulfate (Na2SO4) and 4 mL milli-Q solution or 5 mL
milli-Q water to create slurry and assess biogeochemical setting. Initial sulfate addition to 2008
collected sediments were not the correct concentration of sodium sulfate, but this does not seem
to have affected incubated sediments as they are comparable to 2009 collected sediments from
the same sites. Sulfate additions were made every two months.
All plastic, glassware, and quartz were acid washed in 10% HCl and rinsed with Milli-Q
water. Glassware and quartz were additionally combusted over night at 450 ºC to remove
organics. Glass fiber filters (GF/F) used for filtration were similarly combusted, but only for a
period of two hours.
3. Collection of Sediments from Sites
Sediments were collected twice to form two separate collections. Freshwater Cape Fear
River sediments were collected in August 2008 and June 2009. Salty sediments were collected
from the Elizabeth River in October 2008 and Cape Fear River June 2009. All collected
sediments were placed in serum vials within 1 week of collection and stored in the dark.
5
4. Photochemical Resuspension Experiments
Sediments placed in glass serum vials were sacrificed at four month increments and
resuspended in filtered (0.2 µm) Wrightsville Beach seawater. Resuspension occurred due to
vigorous shaking of water and sediment. Resuspended sediment was allowed to settle for a
period of 41 minutes, to exclude coarse sediment, according to Stokes‟ Law. Sediment material
that remained suspended in the top twenty centimeters was of the size fraction <10 µm and was
siphoned into a clean 4-L HDPE carboy. This water was then split among six 250 mL quartz
flasks with magnetic stir bars. After 60 mL were taken from each flask and filtered for initial
measurements of nutrients (ammonium NH4+, nitrate and nitrite NOx-, and phosphate, PO43-) and
organics (DOC/DON), all flasks were placed in the solar simulator equipped with a water bath to
maintain a constant temperature of 22º C. Three flasks were covered in aluminum foil to serve
as dark controls. The solar simulator contained a 1,000 watt Xe arc lamp, a sun lens diffuser,
and an AM1 filter to remove wavelengths not found in the solar spectrum. Laboratory irradiance
measurements showed that the solar simulator emits light typical of the mid-summer solar
spectrum at 40º N. Quartz flasks were left in the solar simulator for a period of 6 hours which
was equivalent to one 12 hour day. Throughout the photochemistry experiment, all 6 flasks were
stirred with magnetic stir bars to ensure sediments remained in suspension. At the completion of
the experiment, flasks were removed from the solar simulator and a final measurement was taken
for nutrients and organics.
Samples for nutrients and DOM were filtered through tared GF/F filters which were then
frozen, freeze dried and reweighed for determination of particle organic carbon (POC) and
nitrogen (PON) by CHN analysis after vapor acidification (Hedges and Stern 1984).
6
The initial 10 mL filtrate was discarded as a sample rinse, 20 mL was allotted for dissolved
organic carbon (DOC) and total dissolved nitrogen (TDN), and the remaining 30 mL was used in
the measurement of nutrients. DOC/TDN samples were placed in glass scintillation vials and
acidified with 50 µL of 6 M HCl. After two 4 mL aliquots were removed for ammonium
measurement, nutrient samples were frozen. Ammonium measurements were measured on the
day of the experiment while all other measurements were run within two weeks of sampling.
Remaining water, sediment suspensions from each flask were filtered through 47 mm precombusted GF/F filters. Filters were frozen, freeze dried, reweighed, and along with volume
filtered, total suspended solids (TSS) was calculated for all 6 flasks.
5. Analytical
A Shimadzu TOC-5050A total organic carbon analyzer coupled to an Antek 9000N TDN
analyzer equipped with an ASI autosampler was used for determination of DOC/TDN (Avery et
al. 2003). Detection limits for DOC and TDN for this instrument are 5µM and 0.51µM
respectively. Nutrients (NOx-and PO43-) were measured by continuous flow analysis with a Bran
+ Luebbe Auto-analyzer 3 using EPA methods with a detection limit of <0.5 µM. An ophthalaldehyde (OPA) fluorometric method described by Holmes et al. (1999) was used to
measure ammonium. One alteration made to the Holmes et al. (1999) method was to reduce the
sample volume to 2 mL and 4 mL of OPA reagent. The detection limit of ammonium method
was 0.14 µM in this study. DON was obtained by subtracting ammonium and nitrate from TDN.
The standard deviation was calculated from triplicate light and dark flasks. An unpaired
T-test was also performed to determine if the light flask were significantly different from the
dark (significance determined at p< 0.05).
7
RESULTS AND DISCUSSION
1. Photolytic DOC Release from CFR and ER Resuspended Sediments
Release of DOC in all resuspended sediment experiments conducted in this study was
always higher upon exposure to light compared to dark controls (p<0.05, n=52) (Figure 1 a-k).
Dark fluxes of DOC were typically in the range of 0- 25 µmol DOC g-1-hr-1with a few
experiments showing a slight consumption of DOC (<-8 µmol g-1 hr-1). In a previous study of
CFR estuarine samples utilizing whole sediments (Kieber et al, 2006), dark experiments typically
showed consumption of DOC as opposed to the positive fluxes of DOC measured in the current
study where only suspended fine sediments were photolyzed (Figure 3 a-k). This may indicate
that bacterial assemblages, and therefore bacterial consumption of DOC, are more robust in
whole sediments resuspension experiments as opposed to experiments conducted on the fine
grain sediments that stay in suspension. Therefore under severe short time-frame resuspension
events such as dredging or high wave energy, bacterial consumption may mediate more of the
photochemical release of DOC compared to longer term resuspension of fine grain sediments.
Light DOC fluxes during the current study were in the range of 50-250 µmol DOC g-1hr-1
which were much higher than those reported by Kieber et al. (2006) for CFR estuarine whole
sediment resuspension (2.5-13.5 µmol DOC g-1hr-1). In both studies the net photolytic flux of
DOC (light-dark) was always positive (Figure 4 a-g). Differences in photolytic release between
whole sediment resuspension and fine grain sediments resuspension appear to be due to greater
photolytic labiality of fine grain sediments because percent organic carbon values are similar for
both sediment fractions (1-10 %OC).
Kieber et al. (2006) also reported increases in net photolytic DOC flux with increasing
percentage of sediment organic carbon (%OC) for resusupension experiments using bulk CFR
8
sediments. In the current study, experiments using only the suspended fine grain sediments from
the CFR, the differences in net photolytic fluxes of DOC for the individual CFR sites did not
show this trend with %OC (Figure 5). This suggests that for fine grain sediments resuspended in
the water column, controls on CFR photolytic DOC fluxes are different than those for bulk
sediments.
The sites in this study showed varying photolytic responses. In the current study, CFR
sediment resuspension experiments resulted in higher photolytic DOC fluxes compared to ER
sediments. In the initial experiments conducted (first time point on the time series experiments),
CFR sites had DOC flux values in the 150-250 µmol DOC g-1-hr-1 range while ER sediment
DOC fluxes were typically in the 50 µmol DOC g-1-hr-1 range. These differences in photolytic
release of DOC do not appear to be driven by differences in percent organic carbon, percent
organic nitrogen or C:N ratios because these parameters were similar for all the sites in this study
(Table 1, Figures 5). Therefore the differences between CFR and ER sites must be due to
organic matter compositional differences between the sediments or perhaps differences in the
bacterial assemblages between the sites.
Both CFR and ER sediments were incubated and analyzed over a 1-2 years period in
order to assess the effect of biogeochemical decomposition on the photochemical release of the
various analytes. For CFR sediments, time series experiments typically displayed a decrease in
photolytic release and net flux of DOC with time (Figure 3 a-i, 4 a- e). The rate and net flux of
DOC decreased by approximately one half over these long-term incubations (Figure 9). Longterm incubation of Elizabeth River sediments did not show consistent temporal changes in rate or
net flux of DOC (Figures 3 j-k, 4 f-g, 9). The Elizabeth River site, Paradise Creek, actually
showed significant increase in photolytic release over the course of the incubation period and
9
will be further discussed in the next section. Over the course of the incubation period all
collections and sites showed increasing percentage organic carbon, nitrogen and C: N ratio
(Figures 6-8).
Time series experiments conducted during this study provide further evidence relating
biogeochemical decomposition of sediments to controls on the photolytic release of DOC.
Differences in photolytic release from resuspended sediments suggest different molecular
composition for these sediments which could affect the photolytic lability or that the diagenetic
compositional changes occurring in the CFR sediments are not occurring within the ER
sediments. Generally, when long-term CFR sediment incubations resulted in a decrease in the
photolytic flux of DOC, the decrease was accompanied by an increase in both percentage organic
carbon and nitrogen (Figure 7- 8). This is consistent with the argument presented above
suggesting aging of the sediments results in compositional changes in the composition of the
resuspended fine component therefore resulting in less photolability of the organic material.
This has important implications for photochemical DOC release from sediments resuspended
from depth where aged material is typically present.
2. Biogeochemical Setting (sulfate reduction vs. methanogenesis)
During the long-term sediment incubation described above, sediments were exposed to
either sulfate reducing or methanogenic conditions in order to assess how these conditions might
affect photochemical release of the various analytes. In the case of the freshwater CFR
sediments, biogeochemical setting was amended by sulfate additions to create sulfate reducing
conditions versus methanogenic controls; for sulfate reducing sites, sulfate was allowed to be
consumed shifting the biogeochemical setting to methanogenesis with time. The addition of
sulfate to CFR freshwater sediments did not affect the photolytic release of dissolved organic
10
carbon (DOC) (Figure 2 a- d). Therefore biogeochemical setting changes that would occur due
to sea level rise do not appear to impact the organic material to any extent as no significant
differences were seen in photolytic release of Cape Fear River freshwater sites. In fact, in the
long-term incubation experiments on CFR freshwater sites described above, the decrease in DOC
photolytic release was very similar for treated and untreated sediments over time suggesting the
controls on DOC flux was the same under both sulfate reducing and methanogenic conditions.
For the higher salinity CFR site, and ER sites, depletion of sulfate and conversion of
these systems only showed differences in the photolytic release of DOC at one site, Paradise
Creek (Figure 2 e- g). Paradise Creek showed increased photolytic release of DOC from
resuspended sediments possibly due to the change in biogeochemical setting as sulfate was
depleted in incubated sediment vials and driven to methanogenesis. The other Elizabeth River
site showed no temporal trends of photolytic release and the Cape Fear River saltwater site
showed decreased photolytic release similar to Cape Fear River freshwater sites. Molecular
composition of sediments could explain differences seen in the photolytic release from
resuspended sediments and alterations of biogeochemical decomposition.
3. Photolytic Release of Nutrients
a. Nitrogen (TDN, DON, NOx, NH4+)
Photochemical release of TDN was observed in the current study for CFR sediments similar
to that reported By Southwell et al., (2009) for resuspended tidal creek and coastal shelf
sediments. The majority of TDN was DON (Table 2) with less than ten percent inorganic
nitrogen also similar to that reported by Southwell et al., (2010). Upon exposure to light, CFR
sediments release of TDN was significantly higher than dark controls for the majority of
experiments (p<0.05, n=37); fifteen experiments showed no significant difference (Figure 10 a-
11
i). Although average TDN release of ER sediments was higher than dark controls they were not
statistically different (p>0.05, n=11); with the exception of one individual time point (Figure 10
j- k). Initial concentrations of NOx- and NH4+ were very low in all experiments and significant
changes were rarely observed after exposure to light or in dark controls (Table 2). Of forty one
laboratory experiments three showed significant release of NOx- and five showed significant
release of NH4+( p>0.05). Therefore, in terms of nitrogen as a nutrient, these photochemical
experiments suggest organic nitrogen as the only significant form of nitrogen released
photochemically by these resuspended sediments.
b. Phosphate
Generally, resuspended sediments exposed to light had a higher release of PO43compared to dark controls (p<0.05, n=41); five experiments did not show significant increase in
the release of PO43- upon exposure to light. While light release was always greater, dark release
did occur. Release of PO43- from dark controls is attributed to desorption due to sediments being
resuspended in filtered seawater. Average photolytic rate and net flux of PO43- from resuspended
sediments did not vary temporally or spatially (Table 3, Figure 11 a-k). Photolytic release of
PO43- in these sediments has important implications for estuarine systems. In the upper estuary,
where PO43- is typically the limiting nutrient, resuspension events may increase primary
productivity. In the Cape Fear River estuary, phosphate is the limiting nutrient in the winter and
spring; therefore, resuspension of surface sediments could be important to the Cape Fear River
during these times of year.
12
4. Implications of Photolytic Release of Resuspended Sediments
On the basis of this study, sea level rise or other salinity alterations will not affect photolytic
release from resuspended sediments. Therefore, unlike many other important biogeochemical
processes that will be impacted by climate change, these processes should remain constant. The
differences in photolytic release between fine grain sediments in the current study and bulk
sediments in previous studies indicate that the severity of resuspension events has a great impact
on this photochemical process. Fine particles typically entrained in the estuarine waters should
release more DOC on a per gram basis compared to bulk sediments. Therefore previous
published estimates of photolytic release of DOC (0.56 mmol m-2 h-1 in the top 1 m (Kieber et
al., 2006)) are likely underestimated by at least one order of magnitude. Microbial
decomposition, regardless of microbial process, can alter composition of the and thereby impact
the photochemical release from these resuspended sediments in some cases. In general, the more
decomposed resuspended sediment is the lower the rate of photochemical release of DOC.
Therefore, in older sediments, these photochemical processes will provide less DOC to the water
column. Furthermore, sediments resuspended from depth, which are typically older sediments,
may have less impact than those resuspended from the surface. The compositional changes in
the %OC, %ON and C:N of the fine grained sediments from resuspension experiments
conducted on sediment from long-term incubations were not constant with changes predicted for
decomposed sediments. Future studies should focus on these compositional changes at the
molecular level in order to determine the compositional alterations to the organic material that
are driving the changes in photolytic release. Molecular composition could also explain the
difference in photolytic release from the difference in resuspended sediments.
13
Table 1. Percent Organic Carbon, Nitrogen, and C:N ratio for all collected sediments and sites.
Averages are from all 6 flasks. Standard deviations from averages reported within parenthesis.
Site
Treatment
Fishing Creek
„08
Sulfate
No Sulfate
Fishing Creek
„09
Sulfate
No Sulfate
Prince George
„08
Sulfate
No Sulfate
Prince George
„09
Sulfate
No Sulfate
Town Creek
„09
N/A
Elapsed
time (Days)
37
236
281
407
519
37
236
281
407
519
8
121
239
337
121
239
337
50
175
287
450
562
50
175
287
450
562
15
121
239
352
121
239
352
23
146
238
336
14
C:N
%OC
%ON
18.43
19.80
20.73
21.55
17.44
18.59
20.74
20.34
17.96
19.06
8.53
35.41
25.89
19.91
15.06
21.07
22.44
18.61
18.02
18.40
18.54
18.68
16.31
15.98
20.30
20.35
18.68
20.18
22.58
20.35
22.47
22.06
19.51
20.61
19.24
23.46
20.49
23.00
3.80(0.62)
3.55(0.53)
4.50(0.34)
10.20(1.39)
7.67(1.74)
5.33(1.77)
4.14(0.32)
4.39(0.41)
11.16(1.22)
8.74(0.65)
1.99(0.08)
3.49(0.30)
6.24(1.0)
8.38(2.37)
2.97(0.13)
11.32(2.78)
5.96(1.46)
5.32(1.05)
3.81(0.36)
5.11(1.00)
9.72(2.57)
10.76(1.28)
4.01(0.78)
3.52(0.10)
4.70(0.95)
13.72(0.78)
10.76(1.28)
4.19(0.66)
3.30(0.28)
6.09(1.31)
13.27(4.58)
4.41(2.52)
8.65(1.54)
9.18(3.37)
2.96(0.22)
1.76(0.23)
4.01(2.52)
3.54(0.71)
0.24(0.04)
0.20(0.03)
0.26(0.03)
0.67(0.12)
0.47(0.12)
0.32(0.11)
0.24(0.03)
0.25(0.04)
0.67(0.10)
0.58(0.03)
0.08(0.01)
0.18(0.01)
0.28(0.06)
0.50(0.15)
0.15(0.01)
0.63(0.20)
0.28(0.08)
0.26(0.01)
0.22(0.02)
0.29(0.06)
0.60(0.15)
0.70(0.08)
0.22(0.06)
0.19(0.01)
0.28(0.04)
0.89(0.03)
0.70(0.08)
0.24(0.04)
0.17(0.00)
0.34(0.08)
0.65(0.18)
0.23(0.05)
0.52(0.09)
0.52(0.21)
0.18(0.02)
0.09(0.01)
0.23(0.03)
0.18(0.04)
TABLE 1 CONT.
Site
Treatment
Scuffletown Creek
„08
N/A
Paradise Creek
„08
N/A
Elapsed time
(Days)
95
274
328
460
90
271
327
461
572
C:N
%OC
%ON
17.13
15.23
19.48
18.24
17.24
16.71
14.92
18.28
20.21
3.47(0.51)
3.00(0.58)
3.36(0.08)
5.97(0.80)
3.20(0.32)
2.51(0.24)
2.80(0.48)
4.42(2.08)
3.48(0.90)
0.25(0.04)
0.23(0.04)
0.23(0.01)
0.39(0.13)
0.27(0.20)
0.18(0.02)
0.22(0.04)
0.28(0.13)
0.22(0.07)
Table 2 Total Dissolved Nitrogen, dissolved organic nitrogen, nitrate, and ammonium for all
collected sediments and sites. Averages are of net photolytic resuspension experiments (Δ µmol
g-1 hr-1). Standard deviations of averages reported within parenthesis. “X” records photolytic
experiments without samples.
Site
Treatment
Elapsed TDN
DON
NOxNH4+
Time
(Days)
Fishing Creek
Sulfate
37
15.78(7.42) 13.62(7.51) 0.08(0.16) 0.82(0.71)
„08
236
-6.01(9.01) -6.03(9.12) 0.03(0.05) -0.13(1.3)
281
6.31(5.73)
X
X
-0.53(1.0)
407
3.65(2.31) 0.36(2.23) -0.06(0.14) 0.44(0.92)
519
3.98(2.31)
X
X
0.06(0.98)
No Sulfate 37
6.93(3.48) 5.73(3.64) 0.17(0.14) 0.64(0.48)
236
-1.96(1.73) 0.57(14.95) 0.31(0.07) 0.11(1.02)
281
5.20(4.72)
X
X
0.25(0.46)
407
4.48(4.72) 5.80(2.81) -0.07(0.11) 0.53(0.77)
519
4.48(2.15)
X
X
1.03(1.18)
Fishing Creek
Sulfate
8
2.00(2.93)
X
X
0.12(0.48)
„09
121
3.83(2.40)
X
-0.11(0.16)
X
239
3.90(2.86) -1.86(5.27) -0.47(1.42) 1.11(1.74)
337
-1.01(7.0)
-2.29(8.49) 0.22(0.19) 0.48(0.71)
No Sulfate 121
4.47(2.03)
X
0.01(0.20)
X
239
6.01(3.57) 3.25(5.06) -0.10(0.37) 2.04(1.81)
337
5.05(7.38) 0.41(0.68) -0.13(0.21) 0.18(2.04)
15
TABLE 2 CONT.
Site
Treatment
Prince George
„08
Sulfate
No Sulfate
Prince George
„09
Sulfate
No Sulfate
Town Creek „09
N/A
Scuffletown
Creek „08
N/A
Paradise Creek
„08
N/A
Elapsed
Time
(Days)
50
175
287
450
562
50
175
287
450
562
15
121
239
352
121
239
352
23
146
238
336
15
95
274
328
460
572
90
271
327
461
572
TDN
DON
NOx-
3.39(5.19)
X
3.93(6.69)
6.54(5.91)
2.85(3.50)
6.88(3.45)
X
3.71(2.65)
4.96(6.69)
3.51(3.69)
7.97(9.57)
1.51(4.33)
4.86(3.45)
3.47(2.63)
5.10(2.91)
3.23(3.13)
3.32(4.70)
4.01(3.67)
2.60(1.75)
2.31(0.83)
5.88(4.80)
2.64(1.39)
5.30(3.35)
0.44(9.53)
2.71(0.93)
4.74(1.57)
1.81(5.46)
-0.30(2.05)
2.02(3.95)
5.10(2.22)
1.68(2.98)
5.64(5.46)
2.02(3.95)
X
X
6.46(5.93)
2.33(4.37)
6.87(3.27)
X
X
4.62(6.74)
3.00(4.18)
8.75(9.52)
X
X
0.88(2.45)
X
X
5.12(4.48)
X
X
2.52(2.54)
5.63(4.76)
X
X
2.60(0.96)
X
4.01(1.63)
X
-0.71(1.92)
5.52(2.23)
1.60(2.45)
5.50(5.77)
X
0.10(0.10)
0.18(0.09)
0.22(0.40)
0.04(0.16)
0.00(0.10)
0.05(0.15)
-0.16(0.32)
-0.06(0.33)
0.07(0.14)
-0.05(0.25)
0.13(0.17)
0.60(0.15)
0.05(0.19)
-0.20(0.35)
0.04(0.32)
-0.03(0.20)
0.08(0.26)
-0.12(0.10)
-0.14(0.56)
0.03(0.05)
-0.70(0.86)
0.25(0.04)
-0.10(0.27)
0.23(0.21)
X
-0.02(0.20)
X
0.60(0.14)
X
-0.22(0.36)
-0.07(0.05)
0.09(0.12)
16
NH4+
0.84(0.63)
1.11(1.71)
-0.28(1.60)
-0.20(0.80)
-0.16(0.26)
-0.04(0.60)
0.81(1.26)
0.33(0.70)
0.76(0.57)
0.50(0.64)
0.58(0.77)
X
X
2.35(2.08)
X
X
2.58(1.94)
X
X
-0.56(0.70)
0.31(1.38)
-0.10(0.30)
0.29(0.49)
0.03(0.41)
-0.05(0.50)
0.24(0.54)
2.85(2.39)
1.71(1.84)
-0.05(0.10)
0.40(0.76)
0.21(1.03)
-0.23(1.1)
Table 3. Site, treatment, date of experiment and average net flux of phosphate from photolytic
resuspension experiments (Δ µmol/g/hr). Standard deviations of averages reported within
parenthesis.
Site
Fishing
Creek 2008
Fishing
Creek 2008
Fishing
Creek 2009
Fishing
Creek 2009
Prince
George
2009
Prince
George
2009
Town
Creek 2009
Scuffletown
Creek 2008
Paradise
Creek 2008
Treatment Day
Ave.(Stdev)
No
41
Sulfate
0.67(0.09)
Sulfate
37
0.65(0.09)
No
121
Sulfate
0.13(0.31)
Sulfate
121
0.24(0.54)
No
15
Sulfate
0.19(0.13)
Day
Ave.(Stdev)
234
0.39(0.06)
236
0.44(0.09)
239
0.34(0.07)
239
0.52(0.05)
134
0.16(0.33)
Day
Ave.(Stdev)
280
0.45(0.11)
519
0.44(0.13)
337
0.40(0.06)
337
0.43(0.20)
254
0.43(0.04)
Day
Day
Ave.(Stdev) Ave.(Stdev)
519
0.32(0.08)
Sulfate
134
0.54(0.14)
254
0.29(0.06)
352
0.31(0.04)
146
0.16(0.02)
95
0.21(0.03)
271
0.34(0.12)
238
0.13(0.05)
328
0.18(0.09)
327
0.29(0.09)
336
0.11(0.04)
460
0.17(0.04)
461
0.20(0.04)
No
Sulfate
No
Sulfate
No
Sulfate
23
0.20(0.07)
15
0.36(0.06)
90
0.35(0.07)
17
352
0.06(0.21)
572
0.10(0.06)
572
0.20(0.21)
Figure 1 Cape Fear River Map of fresh and salt water sites: Town Creek (P2), Fishing Creek
(P13), Prince George (P14).
Paradise Creek
Scuffletown Creek
Figure 2 Elizabeth River Map with labeled Creeks, Paradise Creek and Scuffletown Creek.
18
DOC (µmol g-1hr-1)
400
300
200
Light
Dark
100
0
-100
0
100
200
300
Days
400
500
Figure 3 a. Photolytic release of DOC from Cape Fear River freshwater resuspended sediments
collected at Fishing Creek in 2008. Sediments from incubated vial with no sulfate added. Error
bars represent averages from triplicate flask.
DOC (µmol g-1hr-1)
400
300
200
Light Treated
Dark Treated
100
0
-100
0
200
400
600
Days
Figure 3 b. Photolytic release of DOC from Cape Fear River freshwater resuspended sediments
collected at Fishing Creek in 2008. Sediments from incubated vial with sulfate added. Error bars
represent averages from triplicate flask.
19
DOC (µmol g-1hr-1)
400
300
200
Light
Dark
100
0
-100
0
100
200
Days
300
400
Figure 3 c. Photolytic release of DOC from Cape Fear River freshwater resuspended sediments
collected at Fishing Creek in 2009. Sediments from incubated vial with no sulfate added. Error
bars represent averages from triplicate flask.
DOC (µmol g-1hr-1)
400
300
200
Light
Dark
100
0
-100
0
100
200
Days
300
400
Figure 3 d. Photolytic release of DOC from Cape Fear River freshwater resuspended sediments
collected at Fishing Creek in 2009. Sediments from incubated vial with sulfate added. Error bars
represent averages from triplicate flasks.
20
DOC (µmol g-1hr-1)
400
300
200
Light
Dark
100
0
-100 0
100
-200
200
300
400
500
Days
Figure 3 e. Photolytic release of DOC from Cape Fear River freshwater resuspended sediments
collected at Prince George in 2008. Sediments from incubated vial with sulfate added. Error bars
represent averages from triplicate flasks.
DOC (µmol g-1hr-1)
400
300
200
Light
Dark
100
0
-100 0
100
200
300
400
500
-200
Days
Figure 3 f. Photolytic release of DOC from Cape Fear River freshwater resuspended sediments
collected at Prince George in 2008. Sediments from incubated vial with sulfate added. Error bars
represent averages from triplicate flasks.
21
DOC (µmol g-1hr-1)
400
300
200
Light
Dark
100
0
0
100
200
300
400
Days
DOC (µmol g-1hr-1)
Figure 3 g. Photolytic release of DOC from Cape Fear River freshwater resuspended sediments
collected at Prince George in 2009. Sediments from incubated vial with no sulfate added. Error
bars represent averages from triplicate flasks.
400
300
200
Light
Dark
100
0
0
100
200
300
400
Days
Figure 3 h. Photolytic release of DOC from Cape Fear River freshwater resuspended sediments
collected at Prince George in 2009. Sediments from incubated vial with sulfate added. Error bars
represent averages from triplicate flasks.
22
DOC (µmol g-1hr-1)
400
300
200
Light
Dark
100
0
-100
0
100
200
300
400
Days
Figure 3 i. Photolytic release of DOC from Cape Fear River saltwater resuspended sediments
collected at Town Creek in 2009. Error bars represent averages from triplicate flasks.
DOC (µmol g-1hr-1)
400
300
200
Light
Dark
100
0
-100
0
200
400
600
Days
Figure 3 j. Photolytic release of DOC from Elizabeth River saltwater resuspended sediments
collected at Scuffletown Creek in 2008. Error bars represent averages from triplicate flasks.
23
DOC (µmol g-1hr-1)
400
300
200
Light
Dark
100
0
-100
0
200
400
600
Days
DOC (Δ µmol g-1hr-1)
Figure 3 k. Photolytic release of DOC from Elizabeth River saltwater resuspended sediments
collected at Paradise Creek in 2008. Error bars represent averages from triplicate flasks.
400
300
200
Treated
100
Untreated
0
0
200
400
600
Days
Figure 4 a. Net flux of DOC released during photolytic experiments from Cape Fear River
freshwater sediments collected at Fishing Creek in 2008; with and without sulfate addition. Error
bars represent averages from triplicate flasks.
24
DOC (Δ µmol g-1hr-1)
350
300
250
200
150
100
50
0
Treated
Untreated
0
100
200
300
400
Days
DOC (Δ µmol g-1hr-1)
Figure 4 b. Net flux of DOC released during photolytic experiments from Cape Fear River
freshwater sediments collected at Fishing Creek in 2009; with and without sulfate addition. Error
bars represent averages from triplicate flasks.
350
300
250
200
150
100
50
0
Treated
Untreated
0
200
Days
400
600
Figure 4 c. Net flux of DOC released during photolytic experiments from Cape Fear River
freshwater sediments collected at Prince George in 2008; with and without sulfate addition. Error
bars represent averages from triplicate flasks.
25
DOC (Δ µmol g-1hr-1)
350
300
250
200
150
100
50
0
Treated
Untreated
0
100
200
300
400
Days
DOC (Δ µmol g-1hr-1)
Figure 4 d. Net flux of DOC released during photolytic experiments from Cape Fear River
freshwater sediments collected at Prince George in 2009; with and without sulfate addition. Error
bars represent averages from triplicate flasks.
350
300
250
200
150
100
50
0
0
100
200
300
400
Days
Figure 4 e. Net flux of DOC released during photolytic experiments from Cape Fear River
saltwater sediments collected at Town Creek in 2009. Error bars represent averages from
triplicate flasks.
26
DOC (Δ µmol g-1hr-1)
350
300
250
200
150
100
50
0
0
100
200
300
400
500
600
Days
Figure 4 f. Net flux of DOC released during photolytic experiments from Elizabeth River
saltwater sediments collected at Scuffletown Creek site in 2008. Error bars represent averages
from triplicate flasks.
DOC (Δ µmol g-1hr-1)
350
250
150
50
-50 0
100
200
300
-150
400
500
600
Days
Figure 4 g. Net flux of DOC released during photolytic experiments from Elizabeth River
saltwater sediments collected at Paradise Creek in 2008. Error bars represent averages from
triplicate flasks.
27
DOC (µmol g-1hr-1)
300
R² = 0.9831
250
Cape Fear River
Freshwater
200
150
Cape Fear River
Saltwater
100
50
Elizabeth River
0
-50 0
5
% OC
10
14
12
10
8
6
4
2
0
Fishing Creek
'08
Fishing
Creek '09
Prince
George '08
Prince
George '09
Town Creek
'09
Scuffletown
Creek '08
Paradise
Creek '08
%OC
Figure 5 Rate of photolytic DOC release of resuspended sediments from Cape Fear and Elizabeth
River sediments as a function of % organic carbon content for initial sediments on the time series
experiments. Error bars represent range.
Initial
Final
Figure 6 Average changes in percent sedimentary organic carbon between initial and final
sediments from all collections and sites. Error bars represent standard deviations of those
averages.
28
Scuffletown
Creek '08
Paradise
Creek '08
Town Creek
Fishing Creek
'08
Fishing
Creek '09
Prince
George '08
Prince
George '09
%ON
1
0.8
0.6
0.4
0.2
0
-0.2
Initial
Final
25
20
15
10
5
0
Fishing Creek
'08
Fishing
Creek '09
Prince
George '08
Prince
George '09
Town Creek
'09
Scuffletown
Creek '08
Paradise
Creek '08
C:N
Figure 7 Average changes in percent sedimentary organic nitrogen between initial and final
sediments from all collections and sites. Error bars represent standard deviations of those
averages.
Initial
Final
Figure 8 Changes in C:N ratios between initial and final sediments from all collections and sites.
29
Fishing Creek
'08
Fishing
Creek '09
Prince
George '08
Prince
George '09
Town Creek
'09
Scuffletown
Creek '08
Paradise
creek '08
DOC(Δµmolg-1h-1)
300
250
200
150
100
50
0
-50
Initial
Final
TDN (µmol g-1hr-1)
Figure 9 Changes in photolytic release of DOC from initial and final photolytic resuspension
experiments calculated from averages of net flux (Δµmolg-1hr-1). Error bars represent standard
deviations of those averages.
30
25
20
15
10
5
0
-5 0
-10
Light
Dark
200
400
600
Days
Figure 10 a. Photolytic release of TDN from Cape Fear River freshwater sediments with no
sulfate added collected at Fishing Creek in 2008. Error bars represent averages from triplicate
flasks.
30
TDN (µmol g-1hr-1)
30
25
20
15
10
5
0
-5 0
-10
Light
Dark
200
400
600
Days
Figure 10 b. Photolytic release of TDN from Cape Fear River freshwater sediments with sulfate
added collected at Fishing Creek in 2008. Error bars represent averages from triplicate flasks.
TDN (µmol g-1hr-1)
30
20
Light
Dark
10
0
0
-10
100
200
300
400
Days
Figure 10 c. Photolytic release of TDN from Cape Fear River freshwater sediments with no
sulfate added collected at Fishing Creek in 2009. Error bars represent averages from triplicate
flasks.
31
TDN (µmol g-1hr-1)
30
25
20
15
Light
10
Dark
5
0
-5 0
100
200
Days
300
400
Figure 10 d. Photolytic release of TDN from Cape Fear River freshwater sediments with sulfate
added collected at Fishing Creek in 2009. Error bars represent averages from triplicate flasks.
TDN (µmol g-1hr-1)
30
25
20
15
*
Light
Dark
10
5
0
-5 0
200
400
600
Days
Figure 10 e. Photolytic release of TDN from Cape Fear River freshwater sediments with no
sulfate added collected at Prince George in 2008. Error bars represent averages from triplicate
flasks.
32
TDN (µmol g-1hr-1)
30
25
20
15
Light
Dark
10
5
0
-5 0
200
400
600
Days
Figure 10 f. Photolytic release of TDN from Cape Fear River freshwater sediments with sulfate
added collected at Prince George in 2008. Error bars represent averages from triplicate flasks.
TDN (µmol g-1hr-1)
30
25
20
15
Light
Dark
10
5
0
-5 0
100
200
Days
300
400
Figure 10 g. Photolytic release of TDN from Cape Fear River freshwater sediments with no
sulfate added collected at Prince George in 2009. Error bars represent averages from triplicate
flasks.
33
TDN (µmol g-1hr-1)
30
20
Light
Dark
10
0
0
100
-10
200
300
400
Days
Figure 10 h. Photolytic release of TDN from Cape Fear River freshwater sediments with sulfate
added collected at Prince George in 2009. Error bars represent averages from triplicate flasks.
TDN (µmol g-1hr-1)
30
25
20
15
Light
Dark
10
5
0
-5 0
100
200
Days
300
400
Figure 10 i. Photolytic release from Cape Fear River saltwater sediments collected from Town
Creek in 2009. Error bars represent averages from triplicate flasks.
34
TDN (µmol g-1hr-1)
30
20
Light
Dark
10
0
0
200
-10
400
600
Days
Figure 10 j. Photolytic release from Elizabeth River saltwater sediments collected from
Scuffletown Creek site in 2008. Error bars represent averages from triplicate flasks.
TDN (µmol g-1hr-1)
30
20
10
Light
Dark
0
0
-10
200
400
600
Days
Figure 10 k. Photolytic release from Elizabeth River saltwater sediments collected from Paradise
Creek site in 2008. Error bars represent averages from triplicate flasks.
35
PO43- (µmol g-1hr-1)
2.00
1.50
1.00
Light
Dark
0.50
0.00
0
100
200
300
Days
PO43- (µmol g-1hr-1)
Figure 11 a. Photolytic release of PO43- from Cape Fear River freshwater sediments with no
sulfate added from Fishing Creek in 2008. Error bars represent averages from triplicate flasks.
2.00
1.50
1.00
Light
Dark
0.50
0.00
0
100
200
300
Days
Figure 11 b. Photolytic release of PO43- from Cape Fear River freshwater sediments with sulfate
added from Fishing Creek in 2008. Error bars represent averages from triplicate flasks.
36
PO43-(µmol g-1hr-1)
2
1.5
1
Light
Dark
0.5
0
0
100
200
300
Days
PO43-(µmol g-1hr-1)
Figure 11 c. Photolytic release of PO43- from Cape Fear River freshwater sediments with no
sulfate added from Fishing Creek in 2009. Error bars represent averages from triplicate flasks.
2.00
1.50
1.00
Light
Dark
0.50
0.00
0
100
200
300
Days
Figure 11 d. Photolytic release of PO43- from Cape Fear River freshwater sediments with sulfate
added from Fishing Creek in 2009. Error bars represent averages from triplicate flasks.
37
PO43-(µmol g-1hr-1)
2.00
1.50
1.00
Light
Dark
0.50
0.00
0
200
400
600
Days
PO43-(µmol g-1hr-1)
Figure 11 e. Photolytic release of PO43- from Cape Fear River freshwater sediments with no
sulfate added from Prince George in 2008. Error bars represent averages from triplicate flasks.
2.00
1.50
1.00
Light
0.50
Dark
0.00
0
200
400
600
Days
Figure 11 f. Photolytic release of PO43- from Cape Fear River freshwater sediments with sulfate
added from Prince George in 2008. Error bars represent averages from triplicate flasks.
38
PO43-(µmol g-1hr-1)
2.00
1.50
1.00
Light
Dark
0.50
0.00
0
100
200
300
Days
3-
PO43-(µmol g-1hr-1)
Figure 11 g. Photolytic release of PO4 from Cape Fear River freshwater sediments with no
sulfate added from Prince George in 2009. Error bars represent averages from triplicate flasks.
2.00
1.50
1.00
Light
0.50
Dark
0.00
0
100
200
300
Days
Figure 11 h. Photolytic release of PO43- from Cape Fear River freshwater sediments with sulfate
added from Prince George in 2009. Error bars represent averages from triplicate flasks.
39
PO43-(µmol g-1hr-1)
2.00
1.50
1.00
Light
Dark
0.50
0.00
0
100
200
300
400
Days
Figure 11 i. Photolytic release of PO43- from Cape Fear River saltwater sediments from Town
Creek in 2009. Error bars represent averages from triplicate flasks.
PO43-(µmol g-1hr-1)
2.00
1.50
1.00
Light
Dark
0.50
0.00
-0.50
0
100
200
300
Days
400
500
Figure 11 j. Photolytic release of PO43- from Elizabeth River saltwater sediments from
Scuffletown Creek in 2008. Error bars represent averages from triplicate flasks.
40
PO43-(µmol g-1hr-1)
2.00
1.50
1.00
Light
Dark
0.50
0.00
0
100
200
300
400
500
Days
Figure 11 k. Photolytic release of PO43- from Elizabeth River saltwater sediments from Paradise
Creek in 2008. Error bars represent averages from triplicate flasks.
41
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