Australian vegetated coastal ecosystems as global hotspots for climate change mitigation

Data on C stocks and sequestration rates in Australian tidal marshes, mangrove forests and seagrass meadows were compiled from published data. In addition, unpublished studies from the CSIRO Marine and Coastal Carbon Biogeochemistry Cluster project and other studies by the co-authors were included. Data from 1,553 study sites (593 from tidal marshes, 323 from mangrove forests and 637 from seagrass meadows) on soil C stocks (1,103 cores in total), soil C sequestration rates (352 cores in total) and standing C stocks in aboveground biomass (98 measurements in total) were used in this study. Detailed methods are provided in the manuscript linked to this dataset.\nLineage: Soil cores were sampled using different coring mechanisms. The cores were sliced at regular intervals, each slice/sample was weighed before and after oven drying to constant weight at 60-70°C (i.e. dry weight, DW).\nThe Champagne test’ was used to determine whether soil samples contained inorganic carbon. The soil core sub-samples containing carbonates were acidified with 1 M HCl, centrifuged (3500 RPM; 5 minutes) and the supernatant with acid residues was removed, then washed in deionized water, centrifuged again and the supernatant removed and dried before C elemental analyses. Where carbonates were absent, bulk soil samples were milled and encapsulated without acid pre-treatment before C analyses. The C content was obtained using a dry combustion elemental analyser or mass spectrometer. \nData on soil accumulation rates from 315 cores derived by means of 210Pb and 14C was compiled. Concentration profiles of 210Pb were determined by alpha spectrometry using Passivated Implanted Planar Silicon (PIPS) detectors after acid digestion of the samples. Selected samples from each core were analysed for 226Ra by ultra-low background liquid scintillation counting (LSC, Quantulus 1220) or gamma spectrometry. Gamma spectrometry measurements were conducted in some cores using semi-planar intrinsic germanium high purity coaxial detectors. Sediment accumulation rates were obtained by applying the Constant Rate of Supply (CRS) or the Constant Flux:Constant Sedimentation models (CF:CS). \nSamples of bulk soil, plant debris and shells along the cores were radiocarbon dated following standard procedures. The 14C dates from seagrass cores were calibrated using the marine13 calibration curve considering a local Delta R ranging from 3 to 71 years as a function of study site. The corrected ages were used to produce an age-depth model (linear regression) to estimate sediment accumulation rates.\nTo allow direct comparison among study sites, the C storage per unit area (cumulative stocks, mass C m-2) was standardized to 1 m-thick deposits (extrapolating linearly integrated values of C content with depth when necessary). The C sequestration rates (mass C m-2yr-1) were calculated by multiplying average C concentration by the sediment accumulation rate (mass m-2 yr-1) in each core. Estimates of aboveground biomass per unit area were obtained by drying and weighing aboveground materials for tidal marshes and seagrasses, and using field measurements and allometric equations (specific to the region and species) for mangroves. \nAll analyses were performed using Generalized Linear Model procedures in SPSS v. 14.0. All response variables were square-root transformed prior to analyses and had homogenous variances. Climate region (arid, semi-arid, temperate, subtropical and tropical) and ecosystem type (tidal marsh, mangrove and seagrass) were treated as fixed factors in all statistical models (probability distribution: normal; link function: identity).\nThe upscaling of each habitat polygon was performed by multiplying the average ± SD soil C stocks, sequestration rates, and standing C stocks in the aboveground biomass for each ecosystem within each climate region by the specific ecosystem area to obtain blue carbon estimates at climate region scale (arid, semi-arid, temperate, subtropical and tropical) and administrative jurisdictions within Australia (Northern Territory, Queensland, New South Wales, Victoria, Tasmania, South Australia and Western Australia). \nPotential C stock losses (mass C) and CO2 emissions (mass CO2-e yr-1) were estimated based on 0.03% annual ecosystem area loss for tidal marshes and mangroves, and 0.1% yr-1 for seagrass, and accounted for the sum of C stocks in aboveground biomass and the top meter of soils, assuming that 50% of total C stocks are lost and remineralized to CO2 after disturbance.

本数据集汇编了已发表文献中关于澳大利亚潮间带沼泽（tidal marshes）、红树林（mangrove forests）及海草床（seagrass meadows）的碳储量与固碳速率数据。此外，本研究还纳入了澳大利亚联邦科学与工业研究组织（Commonwealth Scientific and Industrial Research Organisation, CSIRO）海洋与海岸碳生物地球化学集群项目的未发表研究，以及合作作者开展的其他相关研究数据。
本研究共纳入1553个调查点位的数据：其中潮间带沼泽点位593个、红树林点位323个、海草床点位637个，涵盖土壤碳储量（总计1103根岩心）、土壤固碳速率（总计352根岩心）以及地上生物量现存碳储量（总计98组测定数据）。本数据集关联的手稿中详细记载了实验方法。

实验流程：采用不同的取芯装置采集土壤岩心。将岩心按固定间隔切割分样，每份样品在60~70℃烘箱中烘干至恒重后，分别称量其湿重与干重（dry weight, DW）。
采用香槟测试（Champagne Test）判定土壤样品是否含有无机碳。对于含碳酸盐的岩心分样，先用1 mol/L盐酸进行酸化处理，随后以3500转每分钟的转速离心5分钟，弃去含酸残留的上清液；再用去离子水洗涤样品，再次离心并弃去上清液，烘干后进行碳元素分析。对于不含碳酸盐的散装土壤样品，则无需酸预处理，直接研磨封装后开展碳元素分析。碳含量通过干式燃烧元素分析仪或质谱仪测定。
汇编了315根岩心的土壤沉积速率数据，其测定基于210Pb与14C同位素示踪技术。对样品进行酸消解后，采用钝化植入型平面硅探测器（Passivated Implanted Planar Silicon, PIPS），通过α能谱法测定210Pb的浓度剖面。从每根岩心中选取部分样品，采用超低本底液体闪烁计数法（liquid scintillation counting, LSC, Quantulus 1220）或γ能谱法分析226Ra含量。部分岩心采用半平面本征锗高纯同轴探测器开展γ能谱测定。通过应用恒定供给速率模型（Constant Rate of Supply, CRS）或恒定通量-恒定沉积模型（Constant Flux:Constant Sedimentation, CF:CS）计算得到沉积物沉积速率。
沿岩心采集的散装土壤、植物碎屑与贝壳样品均按照标准流程进行放射性碳定年。针对海草床岩心的14C测年数据，采用marine13校准曲线进行校正，并根据调查点位的不同，将局域Delta R值设定为3~71年。利用校正后的年龄构建年龄-深度模型（线性回归法），以此估算沉积物沉积速率。
为实现不同调查点位间的直接对比，将单位面积碳储量（累计储量，单位：g C·m⁻²）标准化至1米厚的沉积物层（必要时通过线性外推不同深度的碳含量积分值）。固碳速率（单位：g C·m⁻²·yr⁻¹）通过将每根岩心的平均碳浓度与沉积物沉积速率（单位：g·m⁻²·yr⁻¹）相乘计算得到。单位面积地上生物量的估算方式为：对于潮间带沼泽与海草床，直接烘干并称量地上生物量；对于红树林，则结合野外实测数据与针对区域及物种的异速生长方程进行计算。
所有统计分析均采用SPSS v14.0中的广义线性模型（Generalized Linear Model, GLM）流程完成。分析前对所有响应变量进行平方根变换，以保证方差齐性。在所有统计模型中，气候区域（干旱、半干旱、温带、亚热带与热带）及生态系统类型（潮间带沼泽、红树林与海草床）均被设定为固定因子（概率分布：正态分布；连接函数：恒等函数）。
通过将各气候区域内各生态系统的平均碳储量±标准差、固碳速率及地上生物量现存碳储量，乘以对应生态系统的面积，完成各生境多边形的尺度放大，以此得到各气候区域（干旱、半干旱、温带、亚热带与热带）及澳大利亚各行政辖区（北领地、昆士兰州、新南威尔士州、维多利亚州、塔斯马尼亚州、南澳大利亚州与西澳大利亚州）的蓝碳估算值。
基于潮间带沼泽与红树林每年0.03%的生态系统面积损失率、海草床每年0.1%的面积损失率，估算潜在碳储量损失量（单位：g C）与CO₂排放量（单位：g CO₂-e·yr⁻¹）；估算范围涵盖地上生物量与表层1米土壤的碳储量总和，并假设受扰动后总碳储量的50%会发生流失并被再矿化为CO₂。