10.15146/R3K59Z
Schile, Lisa
0000-0001-8565-3825
Smithsonian Institution
Kauffman, J. Boone
Oregon State University
Megonigal, J. Patrick
Smithsonian Institution
Fourqurean, James
Florida International University
Crooks, Stephen
Silvestrum Climate Associates
Abu Dhabi Blue Carbon project
Dryad
dataset
2016
nded by the Abu Dhabi Global Environmental Data Initiative
2016-12-10T19:22:35Z
2016-12-10T19:22:35Z
en
2529455 bytes
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CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Coastal ecosystems produce and sequester significant amounts of carbon
(‘blue carbon’), which has been well documented in humid and semi-humid
regions of temperate and tropical climates but less so in arid regions
where mangroves, marshes, and seagrasses exist near the limit of their
tolerance for extreme temperature and salinity. To better understand these
unique systems, we measured whole-ecosystem carbon stocks (above- and
belowground biomass and soil) in 58 sites across the United Arab Emirates
in natural and planted mangroves, salt marshes, seagrass beds, microbial
mats, and coastal sabkha (inter- and supratidal unvegetated salt flats)
and were funded by the Abu Dhabi Global Environmental Data Initiative.
Plant carbon for mature mangrove trees were measured following methodology
from Kauffman and Donato (2012). Due to their smaller structure, all trees
with stems > 3 cm diameter at breast height (DBH; 1.3 m in height)
within the 7 m plot were measured instead of restricting measurement to
trees with DBH > 10 cm. Standing dead trees and downed woody debris
were found at some Gulf of Oman sites and pools were quantified
appropriately (Kauffman and Donato 2012). In the planted mangrove sites,
five 2-m radius plots were established at 10-m intervals along a 40-m
transect. When stands contained individuals < 1.3 m tall, we
measured the crown diameter and main stem diameter at 30-50 cm in height.
In the 3, 5, and 10 year old planted mangrove sites in Abu al Abyad, trees
were planted in an evenly-spaced grid; therefore, the plant density was
calculated by measuring the average plant spacing and main stem and crown
diameter of 50-75 trees.Salt marsh transect length and plot spacing were
the same as with the mature mangroves, although the plot radius ranged
from 1-4 m depending on plant density. The height and elliptical crown
area (perpendicular crown widths centered on the canopy) were measured on
every plant rooted in each plot.Biomass for A. marina and A. macrostachyum
were calculated using allometric equations. Global tree carbon percentages
of 48 and 39% for above- and belowground biomass, respectively, were
applied (Kauffman and Donato 2012). To examine differences in average
annual carbon sequestered in planted mangrove trees, we divided total
biomass for each stand by the number of years since plantation
establishment. We developed allometric equations for A. macrostachyum
aboveground biomass, as none previously had been published. Twenty-four
plants were collected from three sites and measured for crown dimensions
and succulent woody tissue fresh weight. A subsample of each tissue type
from every plant was weighed fresh and dry (constant weight at 50°C) to
calculate a wet-to-dry mass conversion factor for the entire plant. Simple
linear regression of natural log-transformed oven-dry biomass and plant
volume (height x elliptical crown area) were calculated, producing two
different relationships depending on plant size. Tissue samples were
analyzed for percent carbon and nitrogen; carbon content of woody (n = 12)
and succulent (n = 10) tissue averaged 45.5 and 34.0%, respectively (SE ±
0.7% for both). We used the proportion of 52% woody tissue reported in
Neves et al. (2010) to calculate carbon content for aboveground biomass as
40.3 ± 1.4%C. The reported root to shoot ratio of A. macrostachyum
measured in Portugal (Neves et al. 2010) is likely a conservative estimate
of root biomass, as soil cores were taken to a depth of 15 cm instead of
20-30 cm as in other studies (reviewed in Curcó et al. 2002).Soil Carbon
PoolsAt mangrove and salt marsh plots, undisturbed soil samples were
collected following methodology from Kauffman and Donato (2012) using a 1
m-long gouge auger with an open-face, semi-cylindrical chamber of 5.1 cm
radius. Soils were cored to 3 m or until coarse marine sands or coral
rubble representing the parent material was encountered. The soil core was
divided into depth intervals of 0-15, 15-30, 30-50, 50-100, and
>100 cm, or until refusal. Subsamples collected from center of each
interval were analyzed for bulk density (dry mass per unit volume) and
carbon concentration (organic and inorganic). If encountered, unique soil
layers were sampled separately. The same soil sampling methodology was
used within microbial mats and coastal sabkha; the number of plots sampled
per transect varied from 3-6 plots spaced at 20 m intervals along a
transect. We determined soil carbon stocks following methods outlined in
Fourqurean et al. (2012a), which are designed to account for soils
containing carbonates. A variety of soil biogeochemical measurements, soil
respiration, elevation, and tidal data were collected in selected
mangroves, salt marsh, microbial mats, and sabkha sampled in 2013;
mangroves sampled in 2014 were not sampled. Redox potential (Eh) was
estimated from five replicate platinum-tipped electrodes inserted 10 cm
into the soil for a period of 1-20 minutes and corrected for the potential
of the calomel reference electrode by adding 244 mV (Megonigal and
Rabenhorst 2013). At sites that had a shallow water table, soil pore-water
was collected from corer boreholes at 5-10 cm below the surface and
analyzed by the standard methods described in Keller et al. (2009).
Salinity was determined either by refractometer (values < 160) or
calculated from [Cl-] (values > 160). pH was measured in the field
with a portable electrode. Porewater dissolved methane (CH4) was measured
by headspace equilibration following Keller et al. (2009) and stored in
evacuated Exetainer vials until analysis by Varian 450-GC gas
chromatography. Porewater [SO42-] and [Cl-] were determined by Dionex
ICS-2000 ion chromatography on filter-sterilized (0.22 µm), HCl-acidified
samples, and the sulfate depletion ratio was calculated per Keller et al.
(2009). Gas and filtered porewater samples were stored for four weeks
before analysis, which is well within the capacity of the storage methods
used. We quantified instantaneous CO2 gas exchange rates as a simple index
of activity to assist with comparisons across the ecosystems in this
study. Soil surface CO2 emissions were measured with a LICOR 6400 soil
respiration analyzer, with a range of 2-18 measurements per site,
depending on time spent at each site and the rate of soil respiration;
more measurements were possible at higher respiration rates.
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Abu Dhabi, United Arab Emirates