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Soil organic carbon variability in Australian temperate freshwater wetlands: Temperate wetland soil organic carbon variability

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Globally, there is little information on freshwater (non-tidal) wetland below ground soil organic carbon (SOC) stocks, sequestration rates and, in particular, their within-wetland variation. This basic information is critical for designing programs to sample SOC stocks and identifying areas that sequester large amounts of carbon so that they can be managed to prevent degradation and carbon loss. Here, focusing on temperate seasonally inundated freshwater wetlands in south-eastern Australia, we compared SOC stocks and sequestration rates (via radiometric dating) among wetlands, within wetland locations (High water mark, Edge and Middle), and with adjacent terrestrial locations. SOC stocks varied most among wetlands but also varied inconsistently within wetlands. Wetland SOC stocks (20.4 ± 0.1 kg C m−2) were significantly greater than adjacent terrestrial locations (13.3 ± 0.1 kg C m−2). Wetland SOC sequestration rates were similar among all locations (i.e., within a wetland, ranging from 70 g C m−2 yr−1 to 87 g C m−2 yr−1). The relative lack of difference in SOC stocks among wetland locations allows for reduced within-wetland sampling and subsequently greater replication at the wetland level, at least for temperate ephemeral freshwater wetlands, although these findings need to be confirmed over a range of wetland types. This study also produced the first estimates of temperate freshwater wetland SOC stocks and sequestration rates in Australia, and is among the first studies globally to demonstrate that seasonally inundated wetlands can sequester carbon at significant rates. It therefore provides important justification to support the protection and rehabilitation of temperate freshwater wetlands worldwide.
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Soil organic carbon variability in Australian temperate
freshwater wetlands
Alex L. Pearse,
1
Jan L. Barton ,
1
Rebecca E. Lester,
1,2
Atun Zawadzki,
3
Peter I. Macreadie
4
*
1
School of Life and Environmental Sciences, Deakin University, Warrnambool, Victoria, Australia
2
Centre for Regional and Rural Futures, Deakin University, Geelong, Victoria, Australia
3
Australian Nuclear Science and Technology Organisation, Lucas Heights, New South Wales, Australia
4
School of Life and Environmental Sciences, Deakin University, Burwood, Victoria, Australia
Abstract
Globally, there is little information on freshwater (non-tidal) wetland below ground soil organic carbon
(SOC) stocks, sequestration rates and, in particular, their within-wetland variation. This basic information is
critical for designing programs to sample SOC stocks and identifying areas that sequester large amounts of
carbon so that they can be managed to prevent degradation and carbon loss. Here, focusing on temperate
seasonally inundated freshwater wetlands in south-eastern Australia, we compared SOC stocks and sequestra-
tion rates (via radiometric dating) among wetlands, within wetland locations (High water mark, Edge and
Middle), and with adjacent terrestrial locations. SOC stocks varied most among wetlands but also varied
inconsistently within wetlands. Wetland SOC stocks (20.4 60.1 kg C m
22
) were significantly greater than
adjacent terrestrial locations (13.3 60.1 kg C m
22
). Wetland SOC sequestration rates were similar among all
locations (i.e., within a wetland, ranging from 70 g C m
22
yr
21
to 87 g C m
22
yr
21
). The relative lack of dif-
ference in SOC stocks among wetland locations allows for reduced within-wetland sampling and subse-
quently greater replication at the wetland level, at least for temperate ephemeral freshwater wetlands,
although these findings need to be confirmed over a range of wetland types. This study also produced
the first estimates of temperate freshwater wetland SOC stocks and sequestration rates in Australia, and is
among the first studies globally to demonstrate that seasonally inundated wetlands can sequester carbon at
significant rates. It therefore provides important justification to support the protection and rehabilitation of
temperate freshwater wetlands worldwide.
Between 1750 and 2016, atmospheric CO
2
concentrations
increased dramatically, from 280 ppm to 403 ppm, or 44%
(www.esrl.noaa.gov/gmd/ccgg/trends, last accessed: 14
th
April
2016). This increase is contributing substantially to climate
change events and, as a result, there has been increased inter-
est into the use of natural ecosystems to mitigate climate
change via bio-sequestration (Kayranli et al. 2010). Bio-
sequestration involves the removal of CO
2
from the atmo-
sphere via photosynthesis and its subsequent storage within
either living or dead organic matter (Mitsch and Gosselink
2007; Kayranli et al. 2010). Historically, bio-sequestration has
focused on the biomass of terrestrial forest ecosystems
(Jobb
agy and Jackson 2000), but recent research has demon-
strated that coastal aquatic ecosystems are also globally signifi-
cant carbon sinks (Nellemann et al. 2009; Ewers Lewis et al.
2017). However, forest biomass only sequesters carbon for dec-
ades or centuries whereas aquatic ecosystems typically bury
soils progressively through time and can keep soil organic car-
bon (SOC) locked in for millennia (Mitsch et al. 2013). While
information about the bio-sequestration capabilities of tidal
“blue carbon” ecosystems is increasing exponentially, less is
known quantitatively known about non-tidal (e.g., freshwater)
wetlands.
All wetlands have three essential features: the presence of
water both at the surface or within the root zone; unique
anaerobic soil conditions which differ from adjacent soils;
and the presence of biota adapted to flooding (Mitsch and
Gosselink 2007). These features, which generally promote
high rates of net primary productivity and low rates of
decomposition, make wetlands ideal SOC sinks (Bernal and
Mitsch 2012). It is estimated that 20–30% of the terrestrial
carbon pool is stored in freshwater wetlands, yet they only
cover 5–8% of the land surface (Mitsch and Gosselink 2007).
Like other bio-sequestration systems, wetland vegetation
takes up atmospheric CO
2
via photosynthesis. Dead and
*Correspondence: p.macreadie@deakin.edu.au
Additional Supporting Information may be found in the online version
of this article.
1
LIMNOLOGY
and
OCEANOGRAPHY Limnol. Oceanogr. 00, 2017, 00–00
V
C2017 Association for the Sciences of Limnology and Oceanography
doi: 10.1002/lno.10735
decaying plant organic matter (OM) enters the system as
organic sediment and is then preserved in the soil and added
to the system’s carbon stock as anaerobic conditions in wet-
land soils retard decomposition (Mitsch and Gosselink
2007). The term “carbon stock” refers to the amount of
organic carbon stored at a particular location. In the context
of wetlands, carbon stock mainly refers to organic carbon
stored below-ground in soils (the “SOC” pool) but, to a lesser
extent, organic carbon stored within living plant biomass
and litter. SOC stocks are typically measured in the top 1 m
but, in reality, many studies take core to the point of refusal,
which could be shallower or deeper than 1 m. Freshwater
wetlands are also known to release substantial amounts of
methane, a greenhouse gas with a global warming potential
25 times that of CO
2
over a 100-yr period (Page and Dalal
2011; Mitsch et al. 2013). It is estimated that wetlands
account for 20–25% of global methane emissions (Mitsch
et al. 2013). Greenhouse gas production from freshwater
wetlands has been highlighted as an important area of future
research to ascertain whether freshwater wetlands are net
carbon sinks or sources (Page and Dalal 2011). Quantifying
greenhouse gas flux budgets is outside the scope of this cur-
rent study, which is instead focused on quantifying below-
ground SOC stock and sequestration rates.
Much of the previous work on wetland SOC stocks and
sequestration rates has been conducted in the peat soils of
boreal and subarctic wetlands (Armentano and Menges 1986;
Bernal and Mitsch 2012; Yu 2012), with some additional
work in tropical and subtropical wetlands (Bernal and Mitsch
2008; Mar
ın-Mu~
niz et al. 2014; K
ochy et al. 2015; Villa and
Mitsch 2015). While there is growing literature on temperate
freshwater wetland SOC stocks and sequestration rates, the
focus has largely been on more permanent and flow-through
wetlands, and few studies have looked at smaller isolated
seasonally inundated wetlands (but see Euliss et al. 2006).
Furthermore, most studies to date have been focused in the
Northern Hemisphere (Armentano and Menges 1986; Bridg-
ham et al. 2006; Craft et al. 2008; Bao et al. 2011; Bernal
and Mitsch 2012; Ma et al. 2015). The carbon sequestration
rates estimated among these studies on temperate wetlands
ranges over an order of magnitude from 20 g C m
22
yr
21
in
Europe (Armentano and Menges 1986) to 384 g C m
22
yr
21
for wetlands of the Sanjiang floodplains in China (Bao et al.
2011). In the arid Australian Macquarie Marshes, ephemeral
Phragmites australis beds had higher sequestration rates
(465 g C m
22
yr
21
and 554 g C m
22
yr
21
) than persistent
reed beds (5 g C m
22
yr
21
). Reported SOC stocks are also var-
iable, ranging from 16 kg C m
22
in Europe (Armentano and
Menges 1986) to 10 kg C m
22
in New Zealand (Ausseil et al.
2015).
Temperate and tropical wetlands are usually found close
to densely populated regions, subjected to high levels of
anthropogenic pressure including drainage and development
(Bao et al. 2011). Thus the potential for future (and ongoing)
degradation is high, so it is important to quantify SOC
stocks and sequestration rates of these systems to assess what
may be lost. The temperate climate of Australia is limited to
a narrow band of southern Australia encompassing parts of
Western and South Australia and most of the state of Victo-
ria. Prior to European settlement, Victoria alone contained
over 12,500 wetlands. Since European settlement, over two-
thirds of those wetlands have been either lost or degraded
due to agricultural land clearing and many that are left are
located on private property. It is imperative that SOC stocks
and sequestration rates of those wetlands are measured to
improve knowledge on their storage capabilities and to
provide restoration incentives for private landholders. On a
global scale, data on temperate seasonally inundated fresh-
water wetland SOC stocks and sequestration rates will help
to improve estimates of global wetland storage and inform
greenhouse gas abatement plans.
In addition to the lack of studies into freshwater wetland
SOC stocks, there is a corresponding lack of standardized
approaches for sampling SOC stocks such systems. Previous
studies have focused on identifying factors controlling SOC
storage and sequestration rates (Bernal and Mitsch 2008,
2012; Villa and Mitsch 2015) in shallow soils rather than
methods to conduct wetland SOC stock assessment. While
standardized sampling techniques exist for blue carbon eco-
systems (e.g., Fourqurean et al. 2014), this is not the case for
freshwater systems. Decomposition, a vital process influenc-
ing SOC accumulation (Mitsch and Gosselink 2007), varies
with inundation level and also soil depth (Clarkson et al.
2014). Anaerobic waterlogged soils prevent aerobic microor-
ganisms from breaking down litter and soil organic matter
(Clarkson et al. 2014), forcing decomposition to occur via
less efficient pathways (Mitsch and Gosselink 2007). Thus,
locations within wetlands with a longer inundation period,
such as in the middle, may hold more SOC (Bernal and
Mitsch 2008, 2012) than the outer edge and high water
mark. If true, estimates of a wetland’s SOC stock could
change depending on the locations within the wetland that
are sampled. Within-wetland variability in SOC stocks could
also influence sampling and analysis costs, as costs will
change depending on the number of locations that are
required to be sampled to gain an accurate estimate for the
wetland as a whole. Thus, a greater understanding of the
within-wetland variability in SOC stocks is needed to
improve the accuracy of freshwater SOC stock estimates and
sampling procedures.
For any sampling program, it is often the case that the
ideal sampling design is too costly or too time consuming to
fully implement (Downes et al. 2002). This leaves researchers
in the position of needing to identify trade-offs in the
research design to maximize the likelihood that research
aims will be met (i.e., that inferential power will be sufficient
to address the hypothesis) when undertaking a feasible sam-
pling design (i.e., in terms of cost and time) (Downes et al.
Pearse et al.Temperate wetland soil organic carbon variability
2
2002). Common approaches for those trade-offs include
stratification of samples within identified groups, composit-
ing of sub-samples within replicates and using planned sta-
tistical comparison (Downes 2010). Another key tool to
achieving such a trade-off is to identify the primary sources
of variability within a system and then target sampling
accordingly (Downes et al. 2002). For many carbon account-
ing aims, for example, individual wetlands will be the appro-
priate unit of replication. However, if there is substantial
within-wetland variation, depending on the location at
which the cores are taken, then extrapolating from a single
(or few) core(s) will provide a misleading estimate of wetland
SOC stocks. This is particularly true if differences among
wetland locations vary inconsistently among wetlands. Thus,
we aim to address this question and identify the relative var-
iability within a wetland, compared with among wetlands of
the same type, to enable more robust study design for simi-
lar systems in the future.
Therefore, the specific aims of this study were to: (1)
assess the within-wetland variability in carbon stocks in Aus-
tralian temperate seasonal freshwater wetlands by sampling
multiple locations within wetlands that should have differ-
ent inundation regimes; (2) use those results to recommend
sampling designs for SOC stock assessments; and (3) quantify
SOC stocks and sequestration rates in seasonally inundated
freshwater wetlands of temperate Australia. We hypothesized
that there would be a trend of increasing soil carbon stocks
from the High water mark to the Middle location in the wet-
land due to the greater inundation period of the latter. We
also hypothesized that wetland locations would have higher
SOC stocks than adjacent terrestrial locations. Together,
these would suggest that studies aiming to quantify total
SOC stocks for the wetland would need to sample multiple
locations within a wetland in order to extrapolate SOC
stocks with accuracy. A lack of difference in SOC stocks
within individual wetlands would mean that less emphasis
on multiple within-wetland samples would be possible for
this wetland type and that greater replication at the wetland
level would be possible, depending on the aims of future
studies.
Methods
Study site
This study was conducted in six seasonally inundated
freshwater wetlands in Cobboboonee National and adjacent
Forest Park, in south-west Victoria. The Cobboboonee
National and Forest Park was chosen because it contains rela-
tively undisturbed freshwater wetlands (Fig. S1 in the Sup-
porting Information). In contrast the majority of freshwater
wetlands in south-west Victoria have been subject to sub-
stantial degradation due to farming practices (Parks Victoria
2015), especially small seasonally inundated wetlands, which
were the focus of this study. In selecting wetlands that had
experienced minimal disturbance, we aimed to understand
underlying differences in SOC stocks and sequestration rates
due to differences in inundation period and other wetland
characteristics, rather than as a result of differences in land
use and other anthropogenic factors.
The parks cover 27,500 ha and, along with the adjacent
Lower Glenelg National Park, provides the largest tract of
remaining natural vegetation in the region (Parks Victoria
2015). Prior to 2008, the area was state forest which allowed
logging and public firewood collection. Terrestrial vegetation in
the parks is predominantly dry sclerophyll forest that is
characterized by Eucalyptus obliqua,Eucalyptus radiata,and
Eucalyptus viminalis interspersed with heathland (Silberbauer
1992). The surrounding land is privately owned, cleared of native
vegetation and used for sheep grazing or cropping. On the north-
eastern border of the park there is 750 ha of pine plantation.
The parks include a mosaic of small shallow seasonally
inundated freshwater palustrine wetlands, which typically
fill with water in June and then dry out by December each
year. Six of these were chosen based on their proximity
(within 30 km
2
) and similarity in physico-chemical charac-
teristics (Table S1 in the Supporting Information). All wet-
lands were isolated, depressional wetlands with no distinct
inflow which fill through local rainfall and soil saturation.
The wetlands all possessed organic soils and were surrounded
by dry sclerophyll forest riparian vegetation. Catchment
land use was consistent, except for Wetland 6 which was
close to the aforementioned pine plantation. Minor differ-
ences among wetlands were observed in their surface area,
water depth and dominant aquatic vegetation (Table 1).
Sampling was conducted in October 2015. At each wetland,
four locations were sampled: Middle of the wetland (water
depth >20 cm); Edge of the wetland (water depth <20 cm);
the High water mark (no water, soft soils and vegetation
adapted to inundation); and an adjacent terrestrial location
(minimum distance of 20 m from wetland, hard dry mineral
soils and terrestrial vegetation).
Field procedures
At each location in each wetland, one 20-m transect ran
parallel to the shoreline. Soil cores were taken following the
procedures of Ewers Lewis et al. (2017). Six soil cores were
taken at random along the transect using 5-cm diameter
sharpened PVC pipe. While the aim was to take a core of
1 m depth, this was not always possible due to soil hardness.
A minimum of 80 cm of soil was collected from all wetland
locations, while a minimum of 30 cm of soil was collected
from terrestrial locations due to the hard soil cracking and
breaking the PVC pipe.
Before cores were retrieved, the distance from the top of
the corer to the soil within the corer was compared with the
distance from the top of the corer to the ground level
outside of the corer. This was to test for incomplete recovery
of soils due to compaction (Skilbeck et al. 2017). Cores that
Pearse et al.Temperate wetland soil organic carbon variability
3
showed substantial evidence of compaction (>15 cm differ-
ence between measurements between the inside and outside
measurements) were discarded and another was taken. This
affected approximately 10% of cores. By discarding cores
that were substantially affected by compression, we poten-
tially biased our sampling toward those cores with soil con-
ditions that made them less susceptible to compression (i.e.,
high dry bulk density, consolidated soils) but in the absence
of a robust method to deal with compaction, this was
unavoidable.
For core retrieval, a rubber plug was inserted into the top
of the corer creating internal suction and then lock-grip pli-
ers were used to manually pull out the corer and its core. On
retrieval, excess water in the corer was carefully drained off,
a foam stopper was inserted to prevent sediment movement
during transport and both ends of the core were capped and
stored in a 58C cool room. All cores were processed within a
week of sampling to prevent significant loss of carbon due to
aerobic decomposition.
Soil carbon analysis
Three of the six soil cores from each location within each
wetland were sub-sampled after extrusion via a winch-
operated manual core extruder. Five 2-cm sections, at 0–2,
14–16, 28–30, 48–50, and 74–76 cm depths, were removed
for soil carbon content analysis following the method of Kel-
leway et al. (2015). All the soils were very fine, with minimal
plant material and negligible fractions greater than 2 mm so
we did not sieve. Cores that were retained but still showed
signs of compaction (<15 cm) were mathematically decom-
pressed using the procedures of Fourqurean et al. (2014, Eqs.
S1 and S2 in the Supporting Information). Compaction-
corrected depths were then used to locate the desired sub-
sample sections in each core. Sub-samples were oven dried at
608C until constant mass (approximately 2 d), cooled in a
desiccator and weighed to four decimal places. Dry bulk den-
sity was calculated by multiplying the dry weight of the sam-
ple by the sample volume (g cm
23
).
Soil carbon analysis was conducted at the University of
Hawaii Hilo Analytical Laboratory in Hawaii, U.S.A. using
the method set out in Campbell et al. (2015). Soil total
carbon content (%) was determined by passing 28 mg of soil
through an automated elemental analyser (detection limit
C50.005 mg, with two quality controls per batch; Costech,
ECS 4010). Soil inorganic carbon content (%) was deter-
mined using the dry-oxidation procedures described by Four-
qurean et al. (2012) (Eq. S3 in the Supporting Information).
Inorganic carbon made up less than 1% of the total carbon
content within each soil core. As such, only values relating
to organic carbon are reported herein.
The below-ground soil organic carbon (SOC) content (%)
was calculated by subtracting inorganic carbon from total
carbon content. Final values were expressed as percentage of
dry weight. The SOC concentration (g C kg
21
) of each sam-
ple was calculated using the formula from Bernal and Mitsch
(2012) (Eq. S4 in the Supporting Information). The SOC den-
sity (g C cm
23
) and then SOC stock of individual soil sam-
ples (g C cm
22
) were calculated using the formulae described
by Fourqurean et al. (2014) (Eqs. S5 and S6 in the Supporting
Information).
Using the R computer package Rstudio (Rstudio Team
2015), natural cubic splines were fitted to the data points of
each soil core and the SOC stock of each 2-cm section was
estimated. Summation of each interpolated 2-cm SOC stock
section then gave an approximation of the total SOC stock
(kg C m
22
) of each core. Soil organic carbon stock was calcu-
lated to a soil depth of 75 cm for all wetland locations and
to a depth of 30 cm for terrestrial locations. To allow com-
parisons with other studies, SOC stocks were also extrapo-
lated to a soil depth of 1 m.
Sediment accumulation and carbon sequestration rates
Soil core chronology was determined using the lead-210
(
210
Pb) dating method. One soil core from each location
(Middle, Edge, High water mark and terrestrial) at a single
wetland (Wetland 3) underwent
210
Pb dating. Lead-210 is a
radionuclide of the uranium-238 decay series, which accu-
mulates in the soil profile via in situ production (supported
210
Pb) and atmospheric fallout (unsupported
210
Pb). Unsup-
ported
210
Pb activities from selected depths in a sediment
core are used in age-dating models to calculate sediment
ages and accumulation rates. It is calculated by subtracting
Table 1. Coordinates and differing physico-chemical characteristics of the six freshwater wetlands in this study. Refer to Supporting
Information Table S1 for additional physico-chemical characteristics.
Wetland no.
Coordinates
Latitude Longitude
Surface area
(ha)
Water
depth (cm)
Dominant aquatic
vegetation
1238.2141858141.50150984.4 50 Lepidosperma longitudinale
2238.2121068141.50330680.9 53 L. longitudinale
3238.1516018141.38460883.8 43 L. longitudinale
4238.0112688141.42535081.2 46 Juncus pallidus
5238.0115498141.42749382.0 46 J. pallidus
6238.0082768141.43422782.2 53 J. pallidus
Pearse et al.Temperate wetland soil organic carbon variability
4
the supported
210
Pb from the total
210
Pb activity in the soil
sample (Appleby and Oldfield 1978; Eq. S7 in the Supporting
Information). Lead-210 dating was conducted at the Austra-
lian Nuclear Science and Technology Organisation (ANSTO)
in Sydney by alpha spectrometry following the methods of
first, six 1-cm samples were taken from the top 20 cm of soil
for
210
Pb dating. Additional samples from the same core (i.e.,
to 30 cm) were analyzed for each of the High water mark
and terrestrial locations as
210
Pb activity had not yet reached
background levels at the 20-cm soil depth.
The calculated unsupported
210
Pb activities from each
core were used to calculate sediment ages and rate of accu-
mulation using constant rate of supply (CRS) and constant
initial concentration (CIC) models (Appleby and Oldfield
1978). All
210
Pb profiles from the three wetland locations
exhibited a monotonic decay profile, enabling the use of the
CIC model to calculate a single mass accumulation rate. The
terrestrial location exhibited a semi-monotonic profile, indi-
cating a change in the sediment accumulation rate in recent
years. Thus, a modified CIC model to calculate two CIC sedi-
ment accumulation rates, between 0–3 cm and 3–20 depths,
was used (Brugam 1978). To determine SOC sequestration
rates, the mean SOC concentration (%) over the soil depth
aged via
210
Pb (20–24 cm) was calculated for each location
from Wetland 3 and then multiplied by the sediment accu-
mulation rate (g m
22
yr
21
) to give the SOC sequestration
rate (g C m
22
yr
21
).
Statistical analysis
Statistical analyses were performed using PRIMER V.7
(Clarke and Gorley 2015) with the PERMANOVA 1add-on
(Anderson et al. 2008). Univariate data included SOC con-
centration (g C kg
21
) depth profiles and SOC stocks (kg C
m
22
). To be able to compare SOC stocks among all loca-
tions including terrestrial, a dataset containing SOC stocks
from all locations to a depth of 30 cm was analyzed. When
only comparing among wetland locations, a dataset of
SOC stocks to a depth of 75 cm (i.e., the maximum consis-
tent depth across wetland cores) was analyzed. No normal-
ization or transformation was required for either analysis.
A Euclidean distance similarity matrix was generated for
each dataset. Both the 30-cm and 75-cm datasets were ana-
lyzed using a 2-factor PERMANOVA (Location and Wet-
land). For the 30-cm dataset, a planned comparison
between the terrestrial location and the wetland locations
(High water mark, Edge and Middle) was also performed to
analyze differences in SOC stock between the terrestrial
and wetland environments. For the 75-cm dataset, a pair-
wise comparison was performed to investigate differences
in SOC stock among locations within each wetland. A sta-
tistical analysis was also performed to assess differences in
SOC concentrations with depth among locations and wet-
lands. A 2-factor PERMANOVA (Location and Wetland)
was run using depth (cm) as a co-variate to account for
differences in sampling depth between the wetland and
terrestrial locations. Results were considered significant at
p0.05 (a50.05).
Results
Soil organic carbon stock for wetland locations
Soils at all wetlands were organic in nature, with organic
matter (OM) content ranging from 29% to 62% with a mean
of 50% 61.3% over all six wetlands. At every location within
each wetland, soil carbon content was >99% organic, with
very low levels of carbonate material present. Dry bulk den-
sity profiles for each wetland location exhibited the typical
gradual increase with depth (Fig. S2 in the Supporting Infor-
mation). Soil organic carbon (SOC) stock showed a signifi-
cant interaction between wetland and location (Pseudo-F
10,
36
51.84, p50.05, Fig. 1; Table 2). Stocks also varied signifi-
cantly among wetlands (Pseudo-F
5, 36
514.99, p50.001). A
pairwise comparison of locations for each wetland revealed
that, among all wetlands, SOC stocks were not significantly
different between the High water mark and Edge locations,
with the interaction being driven by the variation among wet-
lands in SOC stock of the Middle location (Fig. 1). Pooling wet-
lands, the mean SOC stock was 51.1 612.1 kg C m
22
,
55.2 618.5 kg C m
22
, and 54.9 613.1 kg C m
22
for each of the
High water mark, Edge and Middle locations, respectively.
Soil organic carbon stock for terrestrial vs. wetland
locations
Terrestrial soils had much lower OM content compared to
the wetland locations (at a reduced soil depth of 30 cm),
ranging from 20% to 39% with a mean of 32% 63% over all
terrestrial locations. There was a significant interaction in
SOC stock between wetland and location (Pseudo-
F
15,48
54.22, p50.001, Table 2), as was observed for the test
including only wetland locations (above). A planned com-
parison between the terrestrial location and the pooled
within-wetland locations found significant differences in
SOC stock (Pseudo-F
1,5
5104.37, p50.003, Table 2), with
the terrestrial location containing 13.34 61.2 kg C m
22
and
the pooled within-wetland locations containing 20.39 6
1.1 kg C m
22
. There was no significant interaction between
the terrestrial location and wetland (Pseudo-F
5,60
50.44,
p50.812, Table 2). These results suggested that SOC stock
varied across all locations (i.e., wetland and terrestrial) and
among wetlands but that the pattern was consistent across
those wetlands. Despite this, the terrestrial location consis-
tently had the lowest SOC stock for each wetland. Mean
terrestrial SOC stocks ranged from 10.3 61.3 kg C m
22
at
Wetland 3 to 16.3 60.8 kg C m
22
at Wetland 1.
Variation in soil organic carbon concentration
Mean SOC concentration in the wetland locations for the
top 75 cm of soil was highest at the Middle location
(264.0 612.4 g C kg
21
) but was similar between the Edge
Pearse et al.Temperate wetland soil organic carbon variability
5
and High water mark locations (194.3 612.3 g C kg
21
and
196.3 613.9 g C kg
21
, respectively). When compared with the
terrestrial location for the top 30 cm of soil, the Middle location
again had the highest SOC concentration (286.0 615.8 g C
kg
21
) and the terrestrial location had the lowest at
161.7 619.4 g C kg
21
.
Overall, SOC concentrations tended to decrease with soil
depth at all locations and all wetlands, however there were
some localized exceptions to this trend (Fig. 2). Terrestrial SOC
concentrations exhibited a sharp decline (>50%) over the top
15 cm (Fig. 2a) after which SOC concentrations gradually
decreased with increasing depth. All wetland locations show a
much more gradual decline in SOC concentration with depth
(Fig. 2b–d). There were significant interactions in SOC concen-
tration between location and wetland (Pseudo-F
15, 287
57.10,
p50.001, Table 2) and between depth and location (Pseudo-
F
3, 300
525.22, p50.001, Table 2).
Sediment age, accumulation rate, and carbon
sequestration
For the terrestrial location at Wetland 3, the unsupported
210
Pb decay profile was semi-monotonic (Fig. 3a), and so two
CIC accumulation rates were calculated, one for 0–3 cm section
(Recent) and another for the 3–20 cm section (Past, Table 3). In
contrast, all the wetland locations had a monotonic
210
Pb
profile (Fig. 3b–d), so a single CIC sediment accumulation rate
was calculated (Table 3).
Overall, for wetland locations, sediment accumulation
rates were highest at the High water mark grading to the
lowest rate at the Middle location (Table 3). The terrestrial
Fig. 1. Comparison of soil organic carbon (SOC) stock (kg C m
22
) among locations for six periodically inundated freshwater wetlands. Locations are
High water mark (HWM, white fill), Edge (E, gray fill) and Middle (M, black fill). Bars indicate mean (61 SE) SOC stock (kg C m
22
) to a soil depth of
75 cm. (a) is Wetland 1; (b)2;(c)3;(d)4;(e) 5; and (f) 6. Letters above individual bars of each wetland show the results of the pairwise comparison
with bars with different letters indicating a significant difference in SOC stock for that wetland.
Pearse et al.Temperate wetland soil organic carbon variability
6
location below the top 3 cm had a sediment accumulation
rate of 1370 g m
22
yr
21
, which was an order of magnitude
greater than the other locations. However, there was an
abrupt decrease in the sediment accumulation rate at Wet-
land 3’s terrestrial location over the past 50 yr, with the
recent rate being only 220 640 g m
22
yr
21
. Soil organic car-
bon sequestration rates were similar among all locations
(Table 3). Again, the past SOC sequestration rate for the
terrestrial location was much higher than the recent
SOC sequestration rate (178 62 vs. 64 613 g C m
22
yr
21
,
Table 3).
The age of the top 20 cm of soil was similar among all
wetland locations (ranging from 121 to 173 yr, Table S1 in
the Supporting Information). For the terrestrial location, CIC
and CRS ages were dissimilar. (Table S2 in the Supporting
Information) and an independent method to validate the
210
Pb chronology is therefore needed to determine which
model is more reliable. Throughout this paper, the mass
accumulation rates calculated from the CIC dating model
were used to determine the carbon sequestration rates at the
terrestrial location. All wetland locations had similar sedi-
ment accretion rates (Table 3). The terrestrial location had
the lowest accretion rate at 0.55 mm yr
21
for the recent
period, although the past accretion rate for the terrestrial
location was much higher (1.83 mm yr
21
).
Discussion
This study found that seasonally inundated freshwater
wetlands sequester substantial amounts of organic carbon
within their soils. The amount of soil organic carbon (SOC)
stored varied inconsistently among locations across the wet-
lands sampled, but the major source of variability appeared
to be the individual wetlands rather than locations within
wetlands. Wetland SOC stocks were also significantly greater
than terrestrial stocks, implying that seasonally inundated
freshwater wetlands may be important SOC sinks. The SOC
sequestration rates, representing the first estimates for tem-
perate freshwater wetlands in Australia, were similar among
wetland locations for the one wetland type analyzed despite
this type not being among those likely to sequester most
SOC (e.g., due to periodic inundation). This suggests that
other types of temperate freshwater wetlands in Australia
may sequester even more SOC.
The effect of location on soil organic carbon stock
Bernal and Mitsch (2008) found soil carbon stock to a
depth of 24 cm to be significantly greater in permanently
flooded compared to intermittently flooded locations in a
freshwater wetland in Ohio, U.S.A. Longer inundation peri-
ods allow anaerobic soil conditions to persist in waterlogged
soils, slowing decomposition rates and increasing SOC stor-
age potential (Mitsch and Gosselink 2007). These findings
were not consistent with those presented here (to a depth of
75 cm) where SOC stocks were comparable among locations
in five of the six wetlands. Only one wetland had higher
stock at the more-frequently inundated Middle location
than the nearby Edge and High water mark locations, where
higher SOC may be a result of longer or more consistent
inundation, for example. Surface water was not observed at
the High water mark despite sampling in spring when water
Table 2. PERMANOVA table showing results from statistical tests of significance on wetland soil organic carbon (SOC) stock (kg C
m
22
) and concentrations (g C kg
21
). df is the numerator and denominator degrees of freedom in the Pseudo-Ftest. Bold type indi-
cates pvalues that are significant at a50.05.
Variable Factor df Pseudo-Fp
SOC stock (75 cm) Location 2, 10 0.65 0.525
Wetland 5, 36 15.00 0.001
Location 3wetland 10, 36 1.84 0.050
SOC stock (30 cm) Location 3, 15 6.58 0.002
Wetland 5, 48 11.82 0.001
Location 3wetland 15, 48 4.22 0.001
Terrestrial SOC stock*
(30 cm)
Location
(terrestrial vs. wetland)
1, 5 104.37 0.003
Terrestrial (location) 3wetland 5, 60 0.44 0.812
SOC concentration Location 3, 15 8.40 0.004
Wetland 5, 287 59.58 0.001
Depth 1, 292 197.91 0.001
Depth 3location 3, 300 25.22 0.001
Depth 3wetland 5, 287 0.91 0.454
Location 3wetland 15, 287 7.10 0.001
Depth 3location 3wetland 15, 287 1.27 0.210
* Planned comparison between the terrestrial location and the combined wetland locations.
Pearse et al.Temperate wetland soil organic carbon variability
7
levels are likely to be relatively high, but all High water
mark cores were nonetheless waterlogged. Recharge of sub-
surface soils by local groundwater lenses, similar to that
observed by Van der Kamp and Hayashi (1998) in North
American semi-arid wetlands, would allow sub-surface soils
to remain waterlogged, potentially resulting in higher SOC
stocks than would be expected otherwise. The seasonally
inundated nature of the wetlands in this study also allows
for high plant production throughout the entire system
(Clement and Proctor 2009). Robust reed and sedge species
(including J. pallidus and L. longitudinale) are able to
dominate throughout the wetlands, not just at the Edge
location. As such, soils throughout the entire wetland
receive autochthonous OM inputs, potentially resulting in a
Fig. 2. Distribution of soil organic carbon (SOC) concentration (g C kg
21
) with soil depth (cm) and location in six freshwater wetlands. Locations
are: (a) terrestrial; (b) High water mark; (c) Edge; and (d) Middle. Black points indicate depths sampled and the line connecting points indicates
interpolated values. The shading around each line is 61 SE. Each color represents one of the six wetlands, Wetland 1 5blue, 2 5green, 3 5yellow,
45red, 5 5orange, 6 5purple.
Pearse et al.Temperate wetland soil organic carbon variability
8
large build-up of SOC over time at most within-wetland
locations.
Soil organic carbon stocks were more variable when
locations were compared at a shallower depth of 30 cm.
Shallow surface soils are likely to experience wetting and
drying more often than deeper soils and this pulsing is likely
to exert greater control over shallow soil anaerobic condi-
tions than it does for deeper sub-surface soils (Clarkson et al.
2014). The increased variability may also be due to differ-
ences in vegetation communities which have been found to
influence the amount of OM stored at these shallower
depths (Bernal and Mitsch 2012; Villa and Mitsch 2015). The
finding that the amount of variation in SOC stocks among
locations changed with depth has important implications
for future freshwater temperate wetland carbon stock assess-
ments and their sampling design.
Implications for freshwater wetland soil organic
carbon sampling
The relatively low variation among locations within a
wetland suggests that sampling from a small number of loca-
tions is likely to give an accurate estimation of a wetland’s
SOC stock when sampling deeper than 30 cm for seasonally
inundated wetlands. The increased variability for shallow
cores indicates that more locations should be sampled com-
pared with the number of locations that may need to be
sampled for deep cores (e.g., 1 m). Having said this, the
interaction between wetland and location (suggesting incon-
sistencies in within-wetland variability with wetland) mean
that additional research is needed to verify this recommen-
dation. Furthermore, this study focused on a specific wetland
type, isolated depressional seasonally inundated wetlands
with no distinct inflow. Hydrogeomorphology influences the
Fig. 3. Depth profile of unsupported lead-210 (
210
Pb) activity (Bq kg
21
) on a log scale at three locations within a freshwater wetland and one adjacent
terrestrial location, all at Wetland 3. Locations are: (a) terrestrial; (b) High water mark; (c) Edge; and (d) Middle. The circled point in plot b is an outlier
which was excluded from further analyses. The black line within each plot indicates the monotonic (or semi-monotonic) decline in
210
Pb activity. Error bars
are 61 SE.
Pearse et al.Temperate wetland soil organic carbon variability
9
carbon sequestration rate and SOC stocks of freshwater wet-
lands (Bernal and Mitsch 2012; Mitsch et al. 2013). Thus,
these results should not be extrapolated to wetlands of a dif-
ferent type without confirmation that these findings hold.
The high variation in SOC stocks among wetlands within
the Cobboboonee National and Forest Parks illustrates the
need for greater replication at the wetland scale in compari-
son to the within-wetland scale for individual wetland types.
Variation among individual wetlands may be driven by
small-scale differences in hydrogeomorphology, soil struc-
ture or vegetation types, for example, even when located in
close proximity as was the case here. Previous studies into
wetland soil carbon stocks and sequestration rates tend have
low replication at the within-wetland scale, instead focusing
on other factors such as climate and wetland type (Bernal
and Mitsch 2008) or hydrological regime (Mar
ın-Mu~
niz et al.
2014). In this study, SOC stocks among individual wetlands
of a single climatic zone (cool temperate) and hydrogeomor-
phological type (isolated depressional) varied significantly.
This suggests that replication of these factors is important
and multiple wetlands need to be sampled to gain a reliable
estimation of SOC stocks for a given wetland type. This may
be more feasible if within-wetland sampling need not be as
intensive, if these findings hold for other wetland types.
Soil organic carbon stock in temperate freshwater
wetlands
There have been few previous assessments of the SOC stock
of temperate freshwater wetlands (but see Euliss et al. 2006; Ber-
nal and Mitsch 2008; Ausseil et al. 2015; Ma et al. 2015 for
examples). Those assessments that have been done occur over a
large range of geographic locations and wetland types, meaning
that comparisons between those studies and this one should be
made cautiously given that this study used only one wetland
type and/or geographic location. The mean SOC stock for the
wetlands in this study was 20.4 60.1 kg C m
22
to a depth of
30 cm and 68.3 618.0 kg C m
22
when extrapolated to 1 m.
These estimates fall within the range of values previously
reported for SOC stocks in temperate and boreal freshwater wet-
lands (see Fig. 4, Armentano and Menges 1986; Eswaran et al.
1993; Yu 2012; Ma et al. 2015; Ricker and Lockaby 2015). They
are much greater than the estimates for tropical freshwater wet-
lands (Fig. 4, K
ochy et al. 2015), which are known to have
higher decomposition rates due to the inherently warmer tem-
peratures of the tropics (Bernal and Mitsch 2008). In Australia,
no estimates have been given for temperate freshwater wetlands
with the exception of Grover et al. (2012) who estimated peat
stores of a temperate peatland in the Australian Alps to be
49.7 kg C m
22
to a depth of 1.4 m.
Terrestrial SOC stocks measured here were within the
range of previously reported values for temperate forest eco-
systems (see Fig. 4, Jobb
agy and Jackson 2000) and were
approximately half that of the corresponding wetland SOC
stocks in this study (13.3 60.1 kg C m
22
and 20.4 60.1 kg C
m
22
, for terrestrial and wetland locations, respectively). This
is in line with previous studies which have found significant
differences in SOC stocks between wetlands and their adja-
cent terrestrial environment (Bernal and Mitsch 2008, 2012).
In this study, the top 30 cm of soil accounted for less than
30% of the wetland SOC stocks, with SOC stocks increasing
by 240% over the next 70 cm (when extrapolated to 1 m).
In comparison, the top 30 cm of soil in the terrestrial loca-
tions accounted for nearly 75% of the total SOC stocks.
This study is the first to estimate SOC stocks in seasonally
inundated isolated, depressional wetlands in temperate Aus-
tralia. The high SOC stock indicates the potential importance
of these systems as carbon sinks, however, freshwater wetlands
can also produce large amounts of methane when wet (Page
and Dalal 2011). Further research into greenhouse gas emis-
sions from freshwater wetlands is needed to determine
whether they truly are net carbon sinks and not sources (Kayr-
anli et al. 2010; Page and Dalal 2011). Nonetheless, these
results highlight the importance of the inclusion of temperate
seasonally inundated freshwater wetlands in future carbon
stock estimates. Estimates of SOC given in this study might be
toward the upper limit for this type of wetland due to their
Table 3. Constant initial concentration (CIC) sediment accumulation rates, sediment accretion rates and soil organic carbon (SOC)
sequestration rates of three wetland locations and one adjacent terrestrial location at one freshwater wetland (Wetland 3). Values are
presented as means 61 SE with the exception of sediment accretion rate where only one value per core was obtained.
Location
Sediment accumulation
rate (g m
22
yr
21
)
Sediment accretion
rate (mm yr
21
)
SOC sequestration rate
(g C m
22
yr
21
)
Terrestrial (recent)* 220 640 0.55 64 613
Terrestrial (past)
1370 6200 1.83 17862
High water mark
460 610 1.66 87 62
Edge
§
290 610 1.37 64 62
Middle
§
180 620 1.33 70 68
* Rates and ages for top 0–3 cm soil profile, recent (<50 yr).
Rates and ages for 3–20 cm soil profile, past (>50 yr).
Rates calculated over the top 24 cm of soil.
§
Rates calculated over the top 20 cm of soil.
Pearse et al.Temperate wetland soil organic carbon variability
10
location within a forested national park providing a large
source of allochthonous OM, as well as protection from degra-
dation or drainage.
Freshwater wetland sediment accumulation
and carbon sequestration
Soil organic carbon sequestration rates, which were mea-
sured at a single wetland, were similar among wetland locations
despite differences in sediment accumulation rates. The ability
of these locations to sequester similar amounts of SOC irrespec-
tive of those differences indicates that sediment accumulation
mechanisms may differ among locations. The higher sediment
accumulation rates observed at the High water mark and Edge
locations may be due to vegetation in these shallow outer loca-
tions restricting overland water flow and trapping allochtho-
nous mineral sediments before it can reach Middle locations
(Mitsch and Gosselink 2007). Sedimentation at the Middle loca-
tion may instead be driven by the continual deposition of
autochthonous organic sediments. This is potentially supported
by the much higher SOC concentration of the Middle location
(393.5 611.0 g C kg
21
) when compared to the High water mark
and Edge locations of Wetland 3 (224.5630.3 g C kg
21
and
237.1 622.7 g C kg
21
, respectively).
Previously reported SOC sequestration rates for temperate
freshwater wetlands vary considerably, ranging over an order
of magnitude from 24 g C m
22
yr
21
to 473 g C m
22
yr
21
(Fig.
4, Armentano and Menges 1986; Bridgham et al. 2006; Craft
et al. 2008; Bao et al. 2011; Bernal and Mitsch 2012). The SOC
sequestration rates reported in this study (64–87 g C m
22
yr
21
) are at the lower end of these previously reported values.
Bernal and Mitsch (2012) reported an average sediment accu-
mulation rate of 2300 g m
22
yr
21
for isolated depressional
wetlands, which is an order of magnitude greater than the sed-
iment accumulation rates estimated in this study (180–460 g
m
22
yr
21
). The soils of these previous studies are all classed as
mineral (Mitsch and Gosselink 2007; Fourqurean et al. 2014),
indicating that carbon sequestration may be driven more by
allochthonous mineral sedimentation from overland flooding,
adjacent rivers and snow melt, whereas sediments in the cur-
rent study were organic and SOC sequestration appears to be
driven mainly by the deposition of autochthonous organic
sediments. The terrestrial carbon sequestration rates measured
here were much higher than global estimates for temperate
forests (Fig. 4, Schlesinger 1997; Zehetner 2010; Batjes 2011).
These results from a single wetland type indicate that temper-
ate seasonally inundated freshwater wetlands are able to accu-
mulate large amounts of organic carbon within their soils,
comparable to that of other freshwater wetlands.
Interestingly, we observed a 3-fold decline in recent
accretion rates at our terrestrial location compared to histori-
cal accretion. Further research would be needed to test the
potential causes of such a change, as there are several possi-
bilities. One is that recent soils are more compacted—a pos-
sibility that could be further explored through fine-scale
analysis of grain size and dry bulk densities. However, we do
not think this is likely since deeper soils are normally more
compacted than surface soils (i.e., the opposite of what we
found). If we therefore assume that soil type/structure and
compaction are consistent throughout the soils, then there
might have been a genuine decline (as opposed to an arte-
fact of preservation) to the accretion rate at the terrestrial
site. For example, there might have been a recent decline in
material (e.g., plant litter) that would normally contribute to
soil accretion at the terrestrial location; a change in litter
Fig. 4. Range of values reported for (a) soil organic carbon (SOC) stocks to a depth of 1 m and (b) SOC sequestration rates, for freshwater wetlands
in differing climates (temperate, tropical, and boreal), as well as for blue carbon ecosystems (seagrass, saltmarsh, and mangroves) and terrestrial forests
(temperate). Light gray bars represent the range of values reported in the literature, with the line indicating the reported global mean. Dark gray bars
representing the range of values from the current study. There is no line shown when there is no known published current global mean for a given
ecosystem. Refer to in-text citations for the source of data presented.
Pearse et al.Temperate wetland soil organic carbon variability
11
quality leading to less recalcitrant (more labile) material
being delivered in recent times; and/or accelerated break-
down of such material by heterotrophic soil microorganisms.
All of the aforementioned possibilities could occur as a result
of climate-driven changes in carbon cycling dynamics.
Conclusions
This study is the first step in understanding the carbon stor-
age capabilities of Australia’s temperate freshwater wetlands
and quantifying their potential to mitigate climate change via
bio-sequestration. Australian temperate freshwater wetlands
were shown to store large amounts of SOC, far greater than the
adjacent terrestrial forest ecosystem. Given the relatively small
variation in SOC stocks within wetlands, replication at the wet-
land scale should be prioritized over within-system replication
for isolated depressional seasonally inundated wetlands. These
findings thus allow the standardization of SOC stock sampling
designs for freshwater wetlands of this type. While future stud-
ies should quantify stocks over a larger range of wetland types,
these results provide important justification for the protection
and rehabilitation of temperate freshwater wetlands.
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Acknowledgments
We gratefully acknowledge the assistance of Lachlan Farrington and
Adam Miller from Glenelg Nature Trust, as well as the Glenelg-Hopkins
CMA, for assistance in locating study sites. We also thank Paul Carnell,
Saras Windecker, Steve Krueger, and Alistair Drew for field assistance
and sample preparation. We thank the Hilo Analytical Laboratory in
Hawaii for performing the carbon content analyses and Jack Goralewski
and Brodie Cutmore at ANSTO Environmental Radioactivity Measure-
ment Centre for performing the lead-210 dating of wetland soils. We
acknowledge Courtney Cummings for assistance in formatting this man-
uscript and the constructive comments of two anonymous reviewers.
This research was conducted under a Parks Victoria National Parks Per-
mit No. 10007689 and was supported by Deakin University, an Austra-
lian Academy of Science 2015 Thomas Davies Research Grant for
Marine, Soil and Plant Biology and an Australian Institute of Nuclear Sci-
ence and Engineering Research Grant (ALNGRA 15529). P.M. acknowl-
edges the support of an Australian Research Council Discovery Early
Career Researcher Award DE130101084 and Australian Research Council
Linkage Grants LP160100242 and LP160100061.
Conflict of Interest
None declared.
Submitted 14 December 2016
Revised 30 July 2017
Accepted 18 September 2017
Associate editor: N
uria Marb
a
Pearse et al.Temperate wetland soil organic carbon variability
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... Under the existing understanding of wetland SOC storage, periodic drying of seasonally saturated wetlands might be expected to stimulate C emissions and SOC loss (Miao et al. 2017). Contrary to this expectation, seasonally saturated wetland soils can sequester large stocks of SOC (Pearse et al. 2018;Tangen and Bansal 2020), though little is known about the mechanisms that could promote long-term SOC storage in seasonally saturated wetlands. As wetting and drying cycles in wetlands are expected to become more extreme with changes in land use and climate (e.g., Fennessy et al. 2018;Lee et al. 2020), understanding the mechanisms of SOC storage in seasonally saturated wetlands is critical to predicting the vulnerability of SOC to future change. ...
... Seasonally saturated wetlands play an important role in SOC storage and stabilization (Pearse et al. 2018;Chanlabut et al. 2020), yet the mechanisms underpinning these processes are understudied. Here we show that SOC in and around seasonally saturated wetlands may be stabilized during dry periods by physical protection within macroaggregates and, to a lesser extent, by organo-mineral associations with Fe. ...
... Our results demonstrate that mean water level can be used as a continuous indicator of hydrologic conditions to examine linear and nonlinear trends in soil characteristics across wetlands, building on prior studies that study SOC across discrete topographic categories (e.g., Chanlabut et al. 2020;LaCroix et al. 2019;Pearse et al. 2018;Webster et al. 2011;Webster et al. 2008). Low relief, wet forests are ubiquitous throughout the eastern U.S., but given their complexity they have typically been neglected in forest C models (e.g., Hurtt et al. 2019) and may be poorly represented by upland SOC models (Trettin et al. 2001). ...
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Wetlands store significant soil organic carbon (SOC) globally, yet this SOC is sensitive to climate and land use change. Seasonally saturated wetlands experience fluctuating hydrologic conditions that may promote the physicochemical mechanisms known to control SOC stabilization in upland soils; these wetlands are therefore likely to be important for SOC storage at the landscape-scale. We investigated the role of physicochemical mechanisms of SOC stabilization in five seasonally saturated wetlands to test the hypothesis that these mechanisms are present, particularly at the transition zone between wetland and upland where saturation in the upper soil profile is most variable. At each wetland, we monitored water level and collected soil samples at five points along a transect from frequently saturated basin edge to rarely saturated upland. We quantified physical protection of SOC in aggregates and organo-mineral associations in mineral horizons to 0.5 m depth. As expected, SOC decreased from basin edge to upland. In the basin edge and transition zone, the majority of SOC was physically protected in macroaggregates. By contrast, overall organo-mineral associations were low, with the highest Fe concentrations (5 mg Fe g − 1 soil) in the transition zone. While both stabilization mechanisms were present in the transition zone, physical protection is more likely to be a dominant mechanism of SOC stabilization in seasonally saturated wetlands. As future climate scenarios predict changes in wetland wet and dry cycles, understanding the mechanisms by which SOC is stabilized in wetland soils is critical for predicting the vulnerability of SOC to future change.
... Carbon dynamics in the sediments and aquatic ecosystems of wetlands are shaped by geology and climate setting, geomorphology, hydrology, vegetation structure and residence time (Renschler et al. 2007;Kayranli et al. 2010;Marín-Muñiz et al. 2014;Sutfin et al. 2016). Globally, the extensive areal extent of freshwater wetlands results in substantial total stores of soil organic and inorganic carbon, that are well documented for temperate and boreal wetlands, but less so for tropical freshwater wetlands (Nahlik and Fennessy 2016;Pettit et al. 2017a;Pearse et al. 2018). To date there are no accurate global estimates of the tropical freshwater wetland soil carbon pool (Villa and Bernal 2018). ...
... As the majority of samples in this study contained [ 35% clay content, LOI 950 was adjusted with the clay correction factor of 0.09 (Hoogsteen et al. 2015). SOC density (SOC d ) is the density of carbon within a given sample analysed (Pearse et al. 2018), determined by the formula: ...
... SOC stock is the conversion of SOC density to a volumetric measure, i.e. mass of carbon contained in a given sample (Pearse et al. 2018), determined by the formula: ...
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Freshwater wetlands are a key component of the global carbon cycle. Wet–dry tropics wetlands function as wet-season carbon sinks and dry-season carbon sources with low aquatic metabolism controlled by predictably seasonal, yet magnitude-variable flow regimes and inundation patterns. However, these dynamics have not been adequately quantified in Australia’s relatively unmodified wet–dry tropics freshwater wetlands. A baseline understanding is required before analysis of land-use or climate change impacts on these aquatic ecosystems can occur. This study characterises geomorphology and sedimentology within a seasonally connected wet–dry tropics freshwater wetland system at Kings Plains, Queensland, Australia, and quantifies soil carbon stocks and wet- and dry-season aquatic metabolism. Soil carbon stocks derived from loss-on-ignition on samples to 1 m depth were 51.5 ± 7.8 kg C m−2, higher than other wet–dry tropics wetlands globally, with potential for long-term retention at greater depths. Gross primary productivity of phytoplankton (GPP) and planktonic respiration (PR) measured through biological oxygen demand bottle experiments in the water column of sediment inundated under laboratory conditions show overall low GPP and PR in both wet- and dry-season samples (all wetland samples were heterotrophic with GPP/PR < 1). Despite the short-term dominance of aquatic respiration processes leading to net release of carbon in the water column under these conditions, there is appreciable long-term storage of carbon in sediment in the Kings Plains wetlands. This demonstrates the importance of wet–dry-tropics wetland systems as hotspots of carbon sequestration, locally, regionally and globally, and consideration should be given to their conservation and management in this context.
... Hervé et al. (2020) examined SOC content in five natural and nine restored vernal pool systems in Chinon, France, and found that although Sphagnum moss cover and SOC were strongly and positively correlated across all systems, these two factors were greater in the natural pools. Furthermore, when SOC content has been examined with depth in seasonally inundated systems studies have found that the amount of SOC varies both among and within study sites (Bernal and Mitsch, 2012;Pearse et al, 2018). While great strides have been made in the last decade in our understanding of the important role vernal pools can play in C sequestration, substantial research gaps still exist, particularly in regards to the partitioning of SOC into labile versus recalcitrant pools, which has a direct bearing on long-term C storage outcomes. ...
... It is not surprising that the vernal pools studied for this work are C sinks given the known C sequestration potential in similar temperate freshwater wetlands (Bernal and Mitsch, 2012;Mazurczyk and Brooks, 2018;Pearse et al., 2018). However, our results help to clarify SOC dynamics in such wetland systems by enumerating the long-term SOC fraction with depth. ...
Article
Bryophytes are important contributors to carbon (C) sequestration and play an important role in regulating C and nitrogen (N) flux in wetland environments. We assessed bryophyte species number and biomass, and select soil chemical parameters at four depth intervals (0-5, 5-10, 10-15, and 15-20 cm) in two vernal pool systems located within two contrasting physiographic provinces (the Appalachian Plateau and the Ridge and Valley) of the U.S. northern Appalachians. Results indicated that bryophyte species number and biomass were significantly higher in the Ridge and Valley versus the Appalachian Plateau system. While total soil organic carbon (TOC) and N were significantly higher in the Ridge and Valley at the shallower depths of 0-5, 5-10, and 10-15 cm, no significant differences were found between the two physiographic provinces for either parameter at the deepest depth interval (15-20 cm). The mineral-associated fraction of soil organic C, as indicated by the recalcitrant index for C (RIC), was only found to be significantly different at the 5-10 cm depth interval. When RIC was averaged across the samples for each study area, the mineral-associated fraction of soil organic C was found to be constant with depth in all vernal pools, while the relationship between RIC and TOC varied with depth within each vernal pool. These results suggest that variations in C input due to differing bryophyte species number and biomass may explain why vernal pools in the two contrasting study areas appear to have different TOC retention capacities, yet similar potentials for long-term C sequestration.
... Although we investigated a lower number of humid grassland plots compared to the other vegetation types, our results are consistent with previous studies that demonstrated that tall humid grasslands could exceed more than double the values found in other grassland types (Fan et al. 2008). The gradient we evidenced seems to be primarily related to the dominant species growth form and strategy for resource acquisition, that account for primary productivity and the accumulation of above and below-ground biomass (Marín-Muñiz et al. 2014, Pearse et al. 2018. Coastal humid grasslands are dominated by tall grasses and sedges and have a rich and complex below-ground structure, with fine roots and below-ground organs, such as rhizomes, which have been proven to play a crucial role in carbon storage and sequestration (Fidelis et al. 2013). ...
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Coastal dune vegetation has been proved to contribute to several crucial ecosystem services, as coastal protection, water purification, recreation; conversely, its capacity to regulate the concentration of greenhouse gases received less attention. To fill this gap, the present work focalized on the assessment of the contribution of coastal dune herbaceous vegetation to carbon storage and carbon sequestration rate, also in relation to possible effects of disturbance. To this aim, we measured the dry biomass and carbon sequestration rate in three different vegetation types (foredune, dry grasslands, humid grasslands), and habitat patch attributes as proxies of the disturbance regime. Relationships between disturbance, and carbon storage and sequestration rate have been analysed by GLMMs. The target vegetation types did not equally contribute to the medium-long term sequestration of carbon with a gradient that increased from the seashore inlands and related to both the growth form and the strategy of resource acquisition of dominant species, and plant community attributes. Disturbance in the form of trampling negatively affected carbon sequestration rate. Results suggest that, when different plant communities are spatially interconnected, the landscape scale results in a better understanding of ecosystem dynamics, functioning and resistance to perturbations and allows to plan coherent management strategies.
... In addition, human activities also affect wetland SOC [13,14]; previous studies have shown that when wetlands are converted to other land use types, the SOC pool decreases [15][16][17]. In view of the large wetland carbon pools and the impact of their changes on the global carbon cycle, changes in wetland soil carbon pools during degradation or restoration and their influencing factors have become one of the hot issues in wetland ecology [18][19][20][21]. ...
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Full-text available
There is a huge carbon pool in the lakeside, which is sensitive to environmental changes and can very easily be transformed into a carbon source as land from the lake is reclaimed. In this paper, West Mauri Lake was employed as a case study to examine soil organic carbon (SOC) and its controlling factors along the lakeside. Four transects of land use (i.e., vegetation) types along the landward lakeside were identified as the fluctuation zone, the beach zone, the mesozoic farmland rewetting zone and the xerophytic farmland rewetting zone. With the increase in soil depth, SOC in the lakeside decreased significantly (p < 0.05). SOC had an obvious seasonal variation (p < 0.001), ranking in order: winter (December) > spring (February) > summer (May). Among the aforementioned transects, SOC density differed significantly (p < 0.05), showing a significant increasing trend. Pearson correlation indicated that most soil physiochemical factors showed a significant correlation with SOC (p < 0.01), except total chromium, total copper, total zinc and total phosphorus. The relationship between SOC density and total nitrogen (N) has an obvious “S” curve, and total N accounts for 81% of the variation of SOC, suggesting that total N is the main controlling factor of SOC in the lakeside. The significant difference in SOC along the different vegetation (land use) types implied that land use affects the SOC in the lakeside. The long-term accumulation of N fertilizer after the man-made reclamation and aquaculture obviously controls SOC in the lakeside of West Mauri Lake.
... Seasonally saturated wetlands play an important role in SOC storage and stabilization (Pearse et al. 2018;315 Chanlabut et al. 2020), yet the mechanisms underpinning these processes during seasonally dry, oxic conditions are 316 understudied. Here we show the potential for SOC in and around seasonally saturated wetlands to be stabilized 317 during dry periods by physical protection within macroaggregates and, to a lesser extent, by organo-mineral 318 associations with Fe. ...
Preprint
Full-text available
Wetlands store significant soil organic carbon (SOC) globally due to anoxic conditions that suppress SOC loss, yet this SOC is sensitive to climate and land use change. Seasonally saturated wetlands experience fluctuating hydrologic conditions that may also promote mechanisms known to control SOC stabilization in upland soils; these wetlands are therefore likely to be important for SOC storage at the landscape-scale. We investigated the role of physicochemical mechanisms of SOC stabilization in five seasonally saturated wetlands to test the hypothesis that these mechanisms are present, particularly in the transition between wetland and upland where soil saturation is most variable. At each wetland, we monitored water level and collected soil samples at five points along a transect from frequently saturated basin edge to rarely saturated upland. We quantified physical protection of SOC in aggregates and organo-mineral associations in mineral horizons to 0.5 m depth. As expected, SOC decreased from basin edge to upland. In the basin edge and transition zone, the majority of SOC was physically protected in macroaggregates. By contrast, overall organo-mineral associations were low, with the highest Fe concentrations (5 mg Fe g -1 soil) in the transition zone. While both stabilization mechanisms were present in the transition zone, physical protection is more likely to influence SOC stabilization during dry periods in seasonally saturated wetlands. As future climate scenarios predict changes in wetland wet and dry cycles, understanding the mechanisms by which SOC is stabilized in wetland soils is critical for predicting the vulnerability of SOC to future change.
... A narrower range of carbon accumulation (4986 g C m 22 year 21 ) was reported for temperate fresh peatlands by Craft et al. (2008). A similar range was found for Australian temperate freshwater wetlands (7087 g C m 22 year 21 ) by Pearse et al. (2018). Such an amount of carbon corresponds roughly to the soil layer accretion rate between 0.5 and 2.3 mm year 21 (Craft et al., 2018). ...
Chapter
The chapter provides statistical backgrounds, based on recent research on ecosystem dynamics, for why we should be interested in forest conservation in general and, in particular, why in Chile it can play a tremendously important role. The authors show how a dynamical system (DS) given by a t-score function for some class of monotonic data transformations generates consistent extreme value estimators. The variation of their values increases the uncertainty of a proper assessment of climate change. We experience singular learning of the transitions in ecosystems, and as complexity measures, we will consider both entropy and fractal dimension. The chapter shows applications to wetlands, which are a poster example of biodiversity, endemism, and conservation challenges. It also provides an analysis of the dynamics of methane emissions from Czech wetlands in South Bohemia, as a comparing example. Together, these cases illustrate the complexity of the conservation process (The results obtained will be an integral part of the Chilean project FONDECYT 2015–2019, N1151441: Statistical and mathematical modelling as a knowledge bridge between Society and Ecology Sustainability,” in synergy with the Linz Institute of Technology Project LIT-2016-1-SEE-023: Modeling complex dependencies: how to make strategic multicriterial decisions?)
... Most researchers have estimated SOCS in wetlands at global (Batjes, 1996;Mitra et al., 2005), national (Zheng et al., 2013;Nahlik and Fennessy, 2016) or regional scales (Pearse et al., 2018). However, the estimated SOCS in global wetlands range from 202 Gt to 535 Gt with a great uncertainty (Mitra et al., 2005). ...
Article
Wetland hydrology can greatly influence the variations in soil carbon and nitrogen stocks. Soil cores were sampled to a depth of 100 cm at 10 cm intervals above 20 cm soils and 20 cm intervals below 20 cm soils in river marginal wetlands with different flooding frequencies (i.e., permanently flooded, one-year, five-year, ten-year, and one-hundred-year floodplains) in 1999 and 2009, respectively. Soil organic carbon and total nitrogen were measured to investigate spatial and temporal variations in soil organic carbon and total nitrogen stocks in five floodplains with different flooding frequencies on a small scale. The results showed that SOCS ranged from 4.62 kg C/m 2 to 13.21 kg C/m 2 and TNS from 0.41 kg N/m 2 to 2.01 kg N/m 2 in the top 1m depth in five zones in both sampling years. Higher soil organic carbon and total nitrogen stocks were observed in these floodplain wetlands with higher flooding frequencies (i.e. permanently flooded, one-year, and five-year floodplains) than those in lower-flooding-frequency floodplains (i.e., ten-year and one-hundred floodplains), and the highest soil organic carbon and total nitrogen stocks in top 10 cm appeared in one-year floodplain rather than permanently flooded floodplain in both years. This indicated that higher flooding frequencies could contribute to soil carbon and nitrogen accumulation due to better hydrological conditions compared with lower flooding frequencies. Soil organic carbon and total nitrogen stocks in top 1m depth decreased by approximately 8-53% and by 22-55% from 1999 to 2009, respectively, of which the highest change rate occurred in one-hundred fooldplain and the lowest in permanently flooded floodplain. The decline in soil carbon and nitrogen stocks of deeper soils mainly caused by heavy alkalinity, reduced water table, and elevated temperature in a ten-year period possibly contribute to explaining the total carbon and nitrogen losses in soil profiles. Correlation analysis showed that soil organic carbon and total nitrogen levels in this region were significantly correlated with flooding frequencies, soil depth, soil pH value, bulk density, soil texture, and microbial biomass. It is necessary to pay much more attention to carbon and nitrogen stocks in deeper soils and find out the key factors that cause carbon and nitrogen loss in these floodplain wetlands to improve carbon sink function of wetland soils. The findings of this work provide a potential explanation for the "missing" carbon sinks at a larger scale.
... A narrower range of carbon accumulation (4986 g C m 22 year 21 ) was reported for temperate fresh peatlands by Craft et al. (2008). A similar range was found for Australian temperate freshwater wetlands (7087 g C m 22 year 21 ) by Pearse et al. (2018). Such an amount of carbon corresponds roughly to the soil layer accretion rate between 0.5 and 2.3 mm year 21 (Craft et al., 2018). ...
Chapter
Wetlands can be defined as transitional ecotone ecosystems between terrestrial and aquatic conditions and are characterized by the waterlogged soils. Prevailing anaerobic conditions in wetland soils slow down or suspend decomposition processes of organic matter. These processes are connected with the production of soil biogenic methane (CH4) and carbon dioxide (CO2). CH4 is a product of organic decomposition under anaerobic conditions, while CO2 is a product of organic matter decomposition under aerobic conditions. Anaerobic conditions stabilized in profiles of wetland soils determine a crucial role of wetlands in the carbon cycle at both the local and the global scale. Wetlands sequestrate well carbon into the soil for a long period, and their soils contain about one-third of the global soil carbon stock. It is a bit of a paradox that ecosystems, which are responsible for creating huge carbon storage, are now under scrutiny in case of CH4 emissions into the atmosphere.
... The increasing demand for global carbon markets has the Australian government, industry, and research groups considering the incentive potential of rehabilitating freshwater ecosystems for carbon sequestration, storage, and emission reduction. While wetland carbon stocks and sequestration rates are relatively well understood in semi-arid regions of Victoria, Australia (Carnell et al., 2018;Pearse et al., 2018), there is no data on carbon fluxes and the corresponding microbial communities that are responsible for carbon release during rehabilitation practices. To maintain environmental benefits such as increased carbon storage and reduced carbon FIGURE 1 | Representation of the inland wetland carbon cycle. ...
Article
Full-text available
Globally, freshwater wetlands are significant carbon sinks; however, altering a wetland’s hydrology can reduce its ability to sequester carbon and may lead to the release of previously stored soil carbon. Rehabilitating a wetland’s water table has the potential to restore the natural process of wetland soil carbon sequestration and storage. Further, little is known about the role of microbial communities that mediate carbon cycling during wetland rehabilitation practices. Here, we examined the carbon emissions and microbial community diversity during a wetland rehabilitation process known as “environmental watering” (rewetting) in an Australian, semi-arid freshwater floodplain wetland. By monitoring carbon dioxide (CO2) and methane (CH4) emissions during dry and wet phases of an environmental watering event, we determined that adding water to a degraded semi-arid floodplain wetland reduces carbon emissions by 28–84%. The watering event increased anoxic levels and plant growth in the aquatic zone of the wetland, which may correlate with lower carbon emissions during and after environmental watering due to lower anaerobic microbial decomposition processes and higher CO2 sequestration by vegetation. During the watering event, areas with higher inundation had lower CO2 emissions (5.15 ± 2.50 g CO2 m–2 day–1) compared to fringe areas surrounding the wetland (11.89 ± 4.25 g CO2 m–2 day–1). CH4 flux was inversely correlated with CO2 emissions during inundation periods, showing a 38% (0.013 ± 0.061 g CO2-e m–2 day–1) increase when water was present in the wetland. During the dry phases of environmental watering, there was CH4 uptake within the fringe and aquatic zones (−0.013 ± 0.063 g CO2-e m–2 day–1). A clear succession of soil microbial community was observed during the dry-wet phases of the environmental watering process. This suggests that wetland hydrology plays a large role in the microbial community structure of these wetland ecosystems, and is consequently linked to CO2 and CH4 emissions. Overall, the total carbon emissions (CO2 + CH4) were reduced within the wetland during and after the environmental watering event, due to increasing vegetative growth and subsequent CO2 sequestration. We, therefore, recommend environmental watering practices in this degraded arid wetland ecosystem to improve conditions for wetland carbon sequestration and storage. Further use of this management practice may improve wetland carbon storage across other arid freshwater wetland ecosystems with similar hydrologic regimes.
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In this chapter a range of sediment sampling techniques specifically suited to estuarine conditions are briefly described and discussed. Advice is provided about the selection of appropriate coring sites and techniques for a variety of conditions, including water depth, varying sediment composition, and sample analytical requirements. In the section on experimental design we briefly consider issues to do with sample replication from both a biological and geological perspective. During coring, alterations are inevitably made to the texture of the sediment, including compaction and water loss, resulting in changes to bulk density and the structure of the pore spaces, and physical disruption to layering. We comment on the nature of some of these disturbances, their dependency on sediment composition, which techniques to choose to minimise occurrence and, if necessary, how and when to make measurements to determine the amount of change caused by coring. Several factors need to be considered during the core recovery phase to ensure optimal retrieval of the core. These include use of core catchers and plugs to minimise or prevent loss of sediment during recovery. Freeze coring is recommended where the sediment-water interface is poorly defined or the sediments are particularly watery. Finally, we discuss transport and initial storage of cores.
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Freshwater wetlands provide a range of ecosystem services, one of which is climate regulation. They are known to contain large pools of carbon (C) that can be affected by land-use change. In New Zealand, only 10 % of the original freshwater wetlands remain due to conversion into agriculture. This study presents the first national estimation of C stocks in freshwater wetlands based on the compilation of soil carbon data from 126 sites across the country. We estimated C stocks for two soil sample types (mineral and organic) in different classes of wetlands (fen, bog, swamp, marsh, pakihi and ephemeral), and extrapolated C stocks to national level using GIS. Bogs had high C content and low bulk densities, while ephemeral wetlands were the reverse. A regression between bulk density and C content showed a high influence of the soil type. Average C densities (average ± standard error) were 1,348 ± 184 t C ha−1 at full peat depth (average of 3.9 m) and 102 ± 5 t C ha−1 (0.3 m depth) for organic soils, and 121 ± 24 t C ha−1 (0.3 m depth) for mineral soils. At national level, C stocks were estimated at 11 ± 1 Mt (0.3 m depth) and 144 ± 17 Mt (full peat depth) in organic soils, and 23 ± 1 Mt (0.3 m depth) in mineral soils. Since European settlement, 146,000 ha of organic soils have been converted to agriculture, which could release between 0.5 and 2 Mt CO2 year−1, equivalent to 1–6 % of New Zealand’s total agricultural greenhouse gas emissions.
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Monitoring Ecological Impacts provides the tools needed to design assessment programs that can reliably monitor, detect and allow management of human impacts on the natural environment. The procedures described are well-grounded in inferential logic. Step-by-step guidelines and flow diagrams provide clear and useable protocols, which are applicable to real situations.
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Estimating carbon sequestration and nutrient accumulation rates in Northeast China are important to assess wetlands function as carbon sink buffering greenhouse gas increasing in North Asia. The objectives of this study were to estimate accreting rates of carbon and nutrients in typical temperate wetlands. Results indicated that average soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) contents were 37.81%, 1.59% and 0.08% in peatlands, 5.33%, 0.25% and 0.05% in marshes, 2.92%, 0.27% and 0.10% in marshy meadows, respectively. Chronologies reconstructed by 210Pb in the present work were acceptable and reliable, and the average time to yield 0–40 cm depth sediment cores was 150 years. Average carbon sequestration rate (Carbonsq), nitrogen and phosphorus accumulation rates were 219.4 g C/(m2·yr), 9.16 g N/(m2·yr) and 0.46 g P/(m2·yr) for peatland; 57.13 g C/(m2·yr), 5.42 g N/(m2·yr) and 2.16 g P/(m2·yr) for marshy meadow; 78.35 g C/(m2·yr), 8.70 g N/(m2·yr) and 0.71 g P/(m2·yr) for marshy; respectively. Positive relations existed between Carbonsq with nitrogen and precipitations, indicating that Carbonsq might be strengthened in future climate scenarios.
Article
Shifts in ecosystem structure have been observed over recent decades as woody plants encroach upon grasslands and wetlands globally. The migration of mangrove forests into salt marsh ecosystems is one such shift which could have important implications for global 'blue carbon' stocks. To date, attempts to quantify changes in ecosystem function are essentially constrained to climate-mediated pulses (30 years or less) of encroachment occurring at the thermal limits of mangroves. In this study, we track the continuous, lateral encroachment of mangroves into two south-eastern Australian salt marshes over a period of 70 years and quantify corresponding changes in biomass and belowground C stores. Substantial increases in biomass and belowground C stores have resulted as mangroves replaced salt marsh at both marine and estuarine sites. After 30 years, aboveground biomass was significantly higher than salt marsh, with biomass continuing to increase with mangrove age. Biomass increased at the mesohaline river site by 130 ± 18 Mg biomass km(-2) yr(-1) (mean ± SE), a 2.5 times higher rate than the marine embayment site (52 ± 10 Mg biomass km(-2) yr(-1) ), suggesting local constraints on biomass production. At both sites, and across all vegetation categories, belowground C considerably outweighed aboveground biomass stocks, with belowground C stocks increasing at up to 230 ± 62 Mg C km(-2) yr(-1) (± SE) as mangrove forests developed. Over the past 70 years, we estimate mangrove encroachment may have already enhanced intertidal biomass by up to 283 097 Mg and belowground C stocks by over 500 000 Mg in the state of New South Wales alone. Under changing climatic conditions and rising sea levels, global blue carbon storage may be enhanced as mangrove encroachment becomes more widespread, thereby countering global warming.
Article
Biogeochemistry-winner of a 2014 Textbook Excellence Award (Texty) from the Text and Academic Authors Association-considers how the basic chemical conditions of the Earth, from atmosphere to soil to seawater, have been and are being affected by the existence of life. Human activities in particular, from the rapid consumption of resources to the destruction of the rainforests and the expansion of smog-covered cities, are leading to rapid changes in the basic chemistry of the Earth. This expansive text pulls together the numerous fields of study encompassed by biogeochemistry to analyze the increasing demands of the growing human population on limited resources and the resulting changes in the planet's chemical makeup. The book helps students extrapolate small-scale examples to the global level, and also discusses the instrumentation being used by NASA and its role in studies of global change. With extensive cross-referencing of chapters, figures and tables, and an interdisciplinary coverage of the topic at hand, this updated edition provides an excellent framework for courses examining global change and environmental chemistry, and is also a useful self-study guide.
Article
Small wetlands in the semi-arid northern prairie region are focal points for groundwater recharge. Hence the groundwater recharge function of the wetlands is an important consideration in development of wetland conservation policies. Most of the groundwater recharge from the wetlands flows to the moist margins of the wetlands and serves to maintain high evapotranspiration by the vegetation surrounding the wetlands. Only a small portion of the recharged water flows to regional aquifers, but this portion is important for sustaining groundwater resources. Wetland drainage eliminates the local flow systems, but may have little effects on regional aquifers other than a slight lowering of the groundwater levels. Further research should focus on the effects of wetland drainage on regional groundwater levels, the role of small ephemeral ponds in groundwater recharge, and the contribution of groundwater inflow to the water balance of large permanent wetlands.