Blue Carbon ecosystems such as saltmarshes are natural carbon (C) stores, accumulating organic carbon (OC) in their soils and storing it for decades to millennia (Mcleod et al., 2011; Duarte et al., 2013; Saintilan et al., 2013). Globally, saltmarshes are estimated to store 0.4–6.5 Gt of OC (Mcleod et al., 2011; Duarte et al., 2013; Temmink et al., 2022). It is estimated that annually a further 167–245 g C m−2 yr−1 accumulates within saltmarshes resulting in an additional 10–53.65 Mt. of OC entering these ecosystems each year worldwide (Chmura et al., 2003; Ouyang and Lee, 2014; Wang et al., 2021). The ability of saltmarshes to rapidly accumulate and store OC means these blue carbon habitats have the potential to be a key nature-based solution in mitigating climate change through the additional accumulation and long-term storage of OC (Intergovernmental Panel on Climate Change (IPCC), 2019), while also providing a range of other key ecosystem services including enhanced water quality, coastal protection, and biodiversity gain (Temmerman et al., 2013). Yet saltmarshes and other blue carbon ecosystems are under threat, with global annual losses of saltmarsh extent averaging 0.28 % between 2000 and 2019 (Campbell et al., 2022).
盐沼等蓝碳生态系统是天然碳 （C） 储存，在其土壤中积累有机碳 （OC） 并将其储存数十年至数千年（Mcleod 等人，2011 年;Duarte 等人，2013 年;Saintilan 等人，2013 年）。在全球范围内，盐沼估计储存了 0.4-6.5 Gt 的 OC（Mcleod 等人，2011 年;Duarte 等人，2013 年;Temmink 等人，2022 年）。据估计，每年在盐沼中 −1 再积累167-245 g C m −2 yr，导致全世界每年有10-53.65 Mt.的OC进入这些生态系统（Chmura等人，2003年;Ouyang 和 Lee，2014 年;Wang 等人，2021 年）。盐沼快速积累和储存碳的能力意味着这些蓝碳栖息地有可能通过碳的额外积累和长期储存来缓解气候变化的关键自然解决方案（政府间气候变化专门委员会 （IPCC），2019 年），同时还提供一系列其他关键生态系统服务，包括提高水质， 海岸保护和生物多样性增加（Temmerman等人，2013）。然而，盐沼和其他蓝碳生态系统正受到威胁，2000 年至 2019 年间，全球盐沼范围的年平均损失为 0.28%（Campbell 等人，2022 年）。
Establishing the rate at which saltmarshes accumulate OC is crucial for quantifying the past, present, and potential future benefit of these ecosystems to climate change mitigation. Furthermore, without robust estimations of saltmarsh OC accumulation rates (OCAR), their inclusion into climate frameworks (e.g., United Nations Framework Convention on Climate Change) and C markets (Friess et al., 2022) will be challenging. To date, national OC accumulation estimates are rare (e.g., Macreadie et al., 2017; Miller et al., 2023), with most nations relying on global averages (Chmura et al., 2003; Ouyang and Lee, 2014) to estimate the quantity of OC accumulating in their saltmarshes. The large data compilations that these global estimates are based upon potentially bias the global mean OCAR value towards well-studied areas such as the OC-rich saltmarshes of North America (Chmura et al., 2003; Ouyang and Lee, 2014). Together, spatial clustering and variability in the quality of the data within these global data compilations likely result in the global mean OCAR being an overestimation, thereby limiting the applicability of these values in many regions. Refined approaches to systematically quantifying accumulation rates at national and regional scales are therefore required.
确定盐沼积累OC的速度对于量化这些生态系统对减缓气候变化的过去、现在和未来潜在益处至关重要。此外，如果没有对盐沼OC积累率（OCAR）的可靠估计，将其纳入气候框架（例如，《联合国气候变化框架公约》）和C市场（Friess等人，2022）将具有挑战性。迄今为止，国家OC积累估计很少（例如，Macreadie等人，2017;Miller et al.， 2023），大多数国家依赖全球平均水平（Chmura et al.， 2003;Ouyang 和 Lee，2014 年）来估计盐沼中积累的 OC 数量。这些全球估计所依据的大数据汇编可能会使全球平均OCAR值偏向于经过充分研究的地区，例如北美富含OC的盐沼（Chmura等人，2003年;Ouyang和Lee，2014）。总之，这些全球数据汇编中的空间聚类和数据质量的可变性可能导致全球平均OCAR被高估，从而限制了这些值在许多区域的适用性。因此，需要采取改进的办法，在国家和区域范围内系统地量化积累率。
As with many nations, there are growing ambitions for the United Kingdom (UK) to include saltmarsh ecosystems in national emission reporting (UK Climate Change Committee, 2022; Burden and Clilverd, 2021), natural capital accounting (Hooper et al., 2019) and C markets (Mason et al., 2022). Nevertheless, OC accumulation data for GB saltmarshes are spatially poorly resolved with the majority of the data originating in Scotland (Miller et al., 2023) and Essex (Burden et al., 2019), with little elsewhere. Here, we build on recent assessments of the stock and accumulation rates of OC in Scottish saltmarshes (Miller et al., 2023) and the OC stock held in British saltmarshes (Smeaton et al., 2022a, Smeaton et al., 2023) by providing a comprehensive assessment of OC accumulation in British saltmarshes. We estimate the total quantity of OC accumulating across all British saltmarshes annually and determine the source of that OC. In doing so, this study contributes to understanding and exploring the climate regulation potential of saltmarshes. The OC accumulation estimates allow comparisons with other global systems, enable the development of GB-specific policy and management approaches to prioritise saltmarsh conservation, restoration, and management for OC storage, and provide a foundation to discuss the appropriate inclusion of saltmarsh habitat in national emission reporting and C markets.
与许多国家一样，英国 （UK） 将盐沼生态系统纳入国家排放报告的雄心越来越大（英国气候变化委员会，2022 年;Burden 和 Clilverd，2021 年）、自然资本会计（Hooper 等人，2019 年）和 C 市场（Mason 等人，2022 年）。然而，GB盐沼的OC积累数据在空间上解析度很差，大部分数据来自苏格兰（Miller等人，2023年）和埃塞克斯（Burden等人，2019年），其他地方几乎没有。在这里，我们通过对英国盐沼中OC积累的全面评估，建立在最近对苏格兰盐沼中OC的储量和积累率的评估（Miller等人，2023）和英国盐沼的OC储量（Smeaton等人，2022a，Smeaton等人，2023）的基础上。我们估计了每年在所有英国盐沼中积累的 OC 总量，并确定该 OC 的来源。在此过程中，本研究有助于理解和探索盐沼的气候调节潜力。OC积累估计允许与其他全球系统进行比较，能够制定针对GB的政策和管理方法，以优先考虑盐沼的保护、恢复和管理OC储存，并为讨论将盐沼栖息地适当纳入国家排放报告和碳市场提供基础。
Saltmarsh ecosystems occupy 451.65 km2 of the coastline of GB, with ~74 % of the total area of GB saltmarsh located in England, and Wales and Scotland each accounting for ~13 % (Haynes, 2016; Natural Resources Wales, 2016; Environment Agency, 2023). The diverse nature of the British coastline results in the development of six main types of saltmarshes (Haynes, 2016): estuarine, embayment, back-barrier, and fringing (fluvial) marshes are found throughout GB, while loch-head are exclusively found in Scotland and perched marshes occur in Scotland and Wales. The vegetation composition of saltmarshes varies throughout GB, but in general these marshes are dominated by Puccinellia maritima and Festuca rubra communities (Adam, 1978; Burd, 1989; Haynes, 2016). Additionally, Smeaton et al. (2023) classified the saltmarshes by bringing together a range of variables (climatic, geomorphological, oceanographic, ecological) for each of GB's 448 mapped saltmarshes (Fig. 1A) with a k-medoids cluster analysis based upon the partitioning around medoids (PAM) algorithm (Kaufman and Rousseeuw, 1990) to cluster (group) saltmarshes with similar characteristics. This approach groups the British saltmarshes into eight clusters (Fig. 1B).
盐沼生态系统占大不列颠海岸线的451.65公里 2 ，英格兰占大不列颠盐沼总面积的~74%，威尔士和苏格兰各占~13%（Haynes，2016;威尔士自然资源，2016年;环境署，2023 年）。英国海岸线的多样性导致了六种主要类型的盐沼的发展（Haynes，2016）：整个英国都发现了河口、海湾、后屏障和边缘（河流）沼泽，而湖头只在苏格兰发现，栖息沼泽发生在苏格兰和威尔士。盐沼的植被组成在大不列颠各地各不相同，但总的来说，这些沼泽以Puccinellia maritima和Festuca rubra群落为主（Adam，1978年;Burd，1989 年;Haynes，2016 年）。此外，Smeaton 等人（2023 年）通过将 GB 的 448 个制图盐沼中每个盐沼的一系列变量（气候、地貌、海洋学、生态学）汇集在一起对盐沼进行分类（图 1A），并基于 k-medoids 聚类分析（PAM）算法（Kaufman 和 Rousseeuw，1990）对盐沼进行分类（组）具有相似特征的盐沼。这种方法将英国盐沼分为八个集群（图1B）。
Fig. 1. Saltmarshes of Great Britain (A) Sampling locations alongside the mapped extent of saltmarsh habitat (exaggerated by 1.5 times for visibility). (B) Great British saltmarshes grouped into eight clusters identified by partitioning around medoids cluster analysis (Smeaton et al., 2023). Stars represent the 21 saltmarshes in this study and the colour represents their associated cluster. Descriptions of each of the eight groups can be found in Supplementary Table 1.
图 1.大不列颠盐沼 （A） 盐沼栖息地地图范围旁的采样位置（为提高能见度而夸大 1.5 倍）。（B） 大不列颠盐沼分为八个簇，通过围绕 medoids 聚类分析进行分区确定（Smeaton 等人，2023 年）。在这项研究中，星星代表21个盐沼，颜色代表它们的相关星团。八组中每组的描述见补充表1。
To assess rates of OC accumulation, we integrate data from a total of 21 saltmarshes located around the coasts of England, Scotland, and Wales (Fig. 1A), including five sites previously sampled by Miller et al. (2023). Of the five sites sampled by Miller et al. (2023) additional samples were collected from three sites (Fig. 1A). The 21 saltmarshes sampled within this study cover all eight groups as classified by the cluster analysis (Smeaton et al., 2023) and are in-turn considered representative of the entire GB saltmarsh habitat (Fig. 1B; Supplementary Table 1).
为了评估 OC 积累率，我们整合了位于英格兰、苏格兰和威尔士海岸周围的总共 21 个盐沼的数据（图 1A），其中包括 Miller 等人（2023 年）先前采样的五个地点。在Miller等人（2023）采样的五个地点中，从三个地点收集了额外的样本（图1A）。本研究中采样的 21 个盐沼涵盖了聚类分析分类的所有 8 个组（Smeaton 等人，2023 年），反过来又被认为是整个 GB 盐沼栖息地的代表（图 1B;附表1）。
Together, the sampled saltmarshes occupy an area of 80.02 km2, equivalent to 18 % of the areal extent of saltmarsh in GB (Haynes, 2016; Natural Resources Wales, 2016; Environment Agency, 2023).
采样的盐沼总面积为80.02公里 2 ，相当于大不列颠盐沼面积的18%（Haynes，2016;威尔士自然资源，2016年;环境署，2023 年）。
At each of the 16 study sites, we used prior knowledge of type, thickness, and relative position of sedimentary layers underlying the vegetated saltmarsh derived from three transects of equally spaced narrow diameter (3 cm) gouge cores (n = 15–18) from across each site, as reported by Smeaton et al. (2023). Representative large diameter (master) cores were collected using a Russian corer or wide (6 cm diameter) gouge corer for radionuclide dating and geochemical analyses. In addition to the 16 newly sampled sites, three sites from Miller et al. (2023) were revisited with an additional master core being collected at the Tay, Skinflats and Wigtown (Fig. 1A). In total 27 new master cores were collected from sites around GB (Fig. 1A) which is further supplemented with data from seven cores in Scotland (Miller et al., 2023; Supplementary Table 2).
在 16 个研究地点中的每一个，我们都使用了植被盐沼下沉积层的类型、厚度和相对位置的先验知识，这些沉积层来自每个地点的三个等距窄直径 （3 cm） 凿岩芯 （n = 15-18） 的横断面，正如 Smeaton 等人（2023 年）所报告的那样。使用俄罗斯取芯器或宽（直径6厘米）气凿取芯收集具有代表性的大直径（主）岩心，用于放射性核素测年和地球化学分析。除了 16 个新采样的地点外，还重新访问了 Miller 等人（2023 年）的三个地点，并在 Tay、Skinflats 和 Wigtown 收集了额外的主岩芯（图 1A）。总共从大不列颠各地的地点收集了 27 个新的主岩心（图 1A），并进一步补充了来自苏格兰七个岩心的数据（Miller 等人，2023 年;附表2）。
These 34 master cores were collected from the high and mid-low marsh zones as defined following the modified EUNIS scheme which classifies the saltmarsh into different zones using vegetation communities (Environment Agency, 2023). Together, these two saltmarsh zones represent ~77 % of all GB saltmarsh. High marsh was not present at some sites; in these cases, cores were collected from the seaward edge and the rear of the mid-low marsh zone, this marsh configuration accounted for 10 of the sites. Due to restricted access, only one master core was collected at some sites (e.g., Morrich More). Supplementary Table 2 provides sampling information for the 21 saltmarshes; supplementary figs. 1–21 and Supplementary Table 3 display the core locations. The use of gouge and Russian corers results in negligible soil compaction (Smeaton et al., 2020). We described the sedimentary sequence in each master core following Troels-Smith (1955) and further classified sediments into basal sediments, which accumulate prior to saltmarsh colonisation (e.g., intertidal flat), and saltmarsh soils, following the approach of Miller et al. (2023) and Smeaton et al. (2023). This classification is primarily based on the proportion of organic sediment (see Fig. 3 in Smeaton et al. (2023)). The position and elevation of all cores was recorded using differential GPS, with an average precision of 2 cm. Master cores were recovered whole and stored at <4 °C prior to analysis. Sample collection was undertaken between November 2018 and July 2021.
这 34 个主岩芯是从高沼泽和中低沼泽区收集的，该方案是根据修改后的 EUNIS 方案定义的，该方案使用植被群落将盐沼分类为不同的区域（环境署，2023 年）。这两个盐沼带加起来占所有GB盐沼的~77%。一些地点没有高沼泽;在这些情况下，岩心是从向海边缘和中低沼泽区的后部收集的，这种沼泽配置占了10个地点。由于访问受限，在一些地点（例如Morrich More）只收集了一个主核心。补充表2提供了21个盐沼的取样信息;补充图 1-21 和补充表 3 显示了核心位置。使用凿孔机和俄罗斯取芯机导致土壤压实可以忽略不计（Smeaton 等人，2020 年）。在Troels-Smith（1955）之后，我们描述了每个主岩芯中的沉积序列，并按照Miller等人（2023）和Smeaton等人（2023）的方法，进一步将沉积物分为在盐沼定殖之前积累的基底沉积物（例如潮间带平原）和盐沼土壤。这种分类主要基于有机沉积物的比例（见Smeaton et al. （2023）中的图3）。使用差分GPS记录所有岩心的位置和高度，平均精度为2厘米。在分析之前，将主岩心整体回收并储存在<4°C下。样本采集于2018年11月至2021年7月期间进行。
The master cores were sliced at 1 cm depth intervals, resulting in a total of 1575 samples of known volume. The samples were freeze dried to assure sample integrity prior to subsequent analyses. Before and after drying, samples were weighed to calculate dry bulk density values following standard methodologies (Appleby and Oldfield, 1978).
主岩芯以 1 厘米深度的间隔切片，总共有 1575 个已知体积的样品。在进行后续分析之前，对样品进行冷冻干燥，以确保样品的完整性。在干燥之前和之后，对样品进行称重，以按照标准方法计算干堆积密度值（Appleby和Oldfield，1978）。
The freeze-dried samples were homogenised to a fine powder prior to analysis. To determine the bulk elemental (OC and nitrogen (N)) and stable isotope (δ13Corg and δ15N) composition, ~12 mg of milled soil was placed into tin capsules and sealed. A further 12 mg of soil was placed into silver capsules. To remove carbonate (from CaCO3), the samples encapsulated in silver underwent acid fumigation (Harris et al., 2001; Bao et al., 2019). The stable isotope analyses were undertaken using an elemental analyser coupled to an isotope ratio mass spectrometer (Thermo Scientific Delta V EA-IRMS). The acidified samples were analysed for OC and δ13Corg, while N and δ15N values were produced from the samples encapsulated in tin. By analysing the N and δ15N separately, the risk of altering the isotopic values through the acid fumigation step is negated (Kennedy et al., 2005). Triplicate measurements of samples (n = 160) produced standard deviations (1σ) of 0.02 % for N and 0.06 ‰ for δ15N, 0.03 % for OC and 0.07 ‰ for δ13Corg. Further quality control was assured by repeat analysis of high OC sediment standard (B2151, Elemental Microanalysis) with reference values of C = 7.45 ± 0.14 %. N = 0.52 ± 0.02, δ13C = −28.5 ± 0.1 % and δ15N = 4.32 ± 0.2 %. The reference standards (n = 310, 2 standards for every 10 samples) deviated from the known values by: OC = 0.08 %, δ13C = 0.10 ‰, N = 0.03 % and δ15N = 0.13 ‰. The isotope values are reported in standard delta notation relative to Vienna Peedee belemnite (VPDB) and air. The C/N ratios are reported as molar ratios: C/N = (OC/12)/(N/14).
在分析之前，将冻干样品均质化为细粉。为了确定本体元素（OC和氮（N））和稳定同位素（δ 13 Corg和δ 15 N）的组成，将~12mg碾磨的土壤放入锡胶囊中并密封。将另外12mg土壤放入银胶囊中。为了除去碳酸盐（从CaCO 3 ），封装在银中的样品经过酸熏蒸（Harris等人，2001;Bao 等人，2019 年）。使用与同位素比质谱仪（Thermo Scientific Delta V EA-IRMS）耦合的元素分析仪进行稳定同位素分析。酸化样品的OC和δ 13 C org 含量分析，而封装在锡中的样品产生N值和δ 15 N值。通过分别分析氮和δ 15 氮，消除了通过酸熏蒸步骤改变同位素值的风险（Kennedy等人，2005）。样品 （n = 160） 的三份测量得出的标准偏差 （1σ） 为 N 为 0.02 %，δ 15 N 为 0.06 ‰，OC 为 0.03 %，δ 13 C org 为 0.07 ‰。通过对高OC沉积物标准品（B2151，元素显微分析）的重复分析，确保了进一步的质量控制，参考值为C = 7.45 ± 0.14%。N = 0.52 ± 0.02，δ 13 C = −28.5 ± 0.1 %，δ 15 N = 4.32 ± 0.2 %。参考标准品（n = 310，每 10 个样品 2 个标准品）与已知值的偏差幅度为：OC = 0.08 %、δ 13 C = 0.10 ‰、N = 0.03 % 和 δ 15 N = 0.13 ‰。同位素值以相对于维也纳 Peedee belemnite （VPDB） 和空气的标准 delta 符号报告。C/N 比以摩尔比表示：C/N = （OC/12）/（N/14）。
The δ13Corg, δ15N and C/N values were used with the open-source Bayesian isotope mixing model FRUITS (Fernandes et al., 2014) to estimate the fraction of terrestrial/in situ and marine OC input to the saltmarsh soils (Smeaton and Austin, 2017; Miller et al., 2023). Published bulk elemental and isotopic values representing the terrestrial (n = 148) and marine (n = 104) environments local to the marshes, alongside saltmarsh above (n = 228) and belowground biomass (n = 33) from around GB (Smeaton et al., 2022b) were compiled for use as OC source values in the mixing model. Due to the diversity of the underlying bedrock geology in GB (Waters et al., 2016), it is likely that fossil/petrogenic C is incorporated into the saltmarsh soils in unknown and varying quantities, potentially altering the δ13Corg values. Except for the west coast of Scotland, where petrogenic OC input to the coastal zone is estimated to be below <0.1 % (Smeaton et al., 2021), it has not been possible to quantify the fossil/petrogenic C input or its influence on the δ13Corg values in the saltmarsh soils of this study.
将δ 13 C org 、δ 15 N 和 C/N 值与开源贝叶斯同位素混合模型 FRUITS 一起使用（Fernandes 等人，2014 年）来估计陆地/原位和海洋 OC 输入到盐沼土壤的比例（Smeaton 和 Austin，2017 年;Miller 等人，2023 年）。已发表的体元素和同位素值代表了沼泽地当地的陆地 （n = 148） 和海洋 （n = 104） 环境，以及来自大不列颠附近的盐沼 （n = 228） 和地下生物量 （n = 33）（Smeaton 等人，2022b） 被编译为混合模型中的 OC 源值。由于大不列颠底层基岩地质的多样性（Waters等人，2016），化石/岩性碳很可能以未知和不同的数量被掺入盐沼土壤中，可能会改变δ 13 碳 org 值。除了苏格兰西海岸，沿海地区的石化碳输入估计低于 <0.1%（Smeaton 等人，2021 年），无法量化化石/岩石碳输入或其对本研究盐沼土壤中 13 δ C org 值的影响。
Age-depth models for each core were produced based on the radionuclides 210Pb and 137Cs, measured using gamma spectroscopy using Ortec gamma spectrometers at the Consolidated Radio-Isotope Facility (CoRIF) at the University of Plymouth, United Kingdom. We measured activities of 210Pb and its parent isotope 226Ra in 1–cm slices from each core. The number of samples per core varied between 20 and 44 according to core length and stratigraphy. A Bayesian framework within the rplum package (Blaauw et al., 2022) in R (R Core Team, 2023) was used to develop age-depth models. Rather than using 137Cs data to corroborate 210Pb-based age-depth models, we achieved smaller temporal uncertainties by combining the ~1963 CE and/or Sellafield discharge 137Cs peak with the 210Pb data in a single model for each core (Aquino-López et al., 2018, Aquino-López et al., 2020). The rplum approach alleviates the need for using the lowermost samples to estimate the equilibrium depth where total and excess 210Pb activities become indistinguishable (Appleby, 2001) and is applicable to 210Pb profiles where the equilibrium depth has not been reached. From each age-depth model, we obtained age estimates and 2σ uncertainties in calibrated years CE, along with 1-cm resolution sedimentation rates (cm yr−1), the average sedimentation rate for each core was calculated using all depth intervals.
每个岩芯的年龄深度模型是根据放射性核素 210 Pb和 137 Cs制作的，在英国普利茅斯大学综合放射性同位素设施（CoRIF）使用Ortec伽马能谱仪使用伽马能谱法测量。我们测量了每个核心 1 厘米切片中 210 Pb 及其母体同位素 226 Ra 的活性。根据岩心长度和地层，每个岩心的样品数量在20至44个之间变化。R （R Core Team， 2023） 中 rplum 包（Blaauw 等人，2022 年）中的贝叶斯框架用于开发年龄深度模型。我们没有使用 137 Cs 数据来证实基于 210 Pb 的年龄深度模型，而是通过将 ~1963 CE 和/或 Sellafield 放电 137 Cs 峰值与每个岩心的 210 Pb 数据相结合，实现了较小的时间不确定性（Aquino-López 等人，2018 年，Aquino-López 等人，2020 年）。rplum 方法减轻了使用最低样品来估计总铅活性和过量 210 铅活性变得无法区分的平衡深度的需要（Appleby，2001 年），并且适用于 210 尚未达到平衡深度的铅剖面。从每个年龄深度模型中，我们获得了校准年份CE的年龄估计值和2σ不确定性，以及1厘米分辨率的沉降速率（厘米年 −1 ），使用所有深度区间计算每个岩心的平均沉降速率。
In addition to 210Pb and 137Cs analyses, we selected six pairs of samples from six cores at five sites for radiocarbon (14C) dating. Each pair consisted of a plant macrofossil sample and a bulk (humin) sample recovered from the same core depth. The humin fraction was chosen for dating over humic compounds as it is insoluble in water at all pH values and immobile within the soil (Balesdent, 1987). The humin fraction was extracted following the acid–alkali–acid method (Pessenda et al., 1996). The extracted humin fraction was combusted to carbon dioxide (CO2), cryogenically purified, and converted to graphite using zinc/iron reduction (Slota et al., 1987). Sample graphites were analysed using an accelerator mass spectrometer at the Natural Environment Isotope Facility (East Kilbride, UK). A lack of sufficient identifiable above-ground terrestrial plant macrofossils and substantial and inconsistent offsets between macrofossil and humin samples meant that we did not sample further cores for 14C dating and we do not incorporate 14C data in any of the age-depth models. The 14C dates are reported in Supplementary Table 3.
除了铅和 137 铯分析外 210 ，我们还从五个地点的六个岩心中选择了六对样品进行放射性碳（ 14 C）测年。每对都由一个植物大型化石样本和一个从相同岩心深度回收的散装（腐殖质）样本组成。选择腐殖质组分来测年腐殖质化合物，因为它在所有pH值下都不溶于水，并且在土壤中不动（Balesdent，1987）。腐殖质馏分采用酸-碱-酸法提取（Pessenda等人，1996）。将提取的腐殖素馏分燃烧成二氧化碳（CO 2 ），低温纯化，并使用锌/铁还原转化为石墨（Slota等人，1987）。在自然环境同位素设施（英国东基尔布赖德）使用加速器质谱仪分析样品石墨。由于缺乏足够可识别的地上陆生植物宏观化石，以及宏观化石和腐殖质样本之间大量且不一致的偏移，这意味着我们没有对更多岩心进行 14 C测年，也没有将C数据纳入 14 任何年龄深度模型中。 14 C日期见补充表3。
To determine the OCAR (g C m−2 yr−1), the soil OC density (g C cm−3) was calculated by combining the dry bulk density values and OC content for each of the 1-cm slices. The soil OC density was then multiplied by the corresponding sedimentation rate derived from the age-depth models. The mean OCAR for each core was calculated by averaging the centimetre-resolution OCARs for the saltmarsh soil unit.
为了确定OCAR（g C m −2 yr −1 ），通过结合每个1 cm切片的干堆积密度值和OC含量来计算土壤OC密度（g C cm −3 ）。然后将土壤OC密度乘以从年龄深度模型得出的相应沉降速率。通过平均盐沼土壤单元的厘米分辨率OCAR来计算每个岩心的平均OCAR。
To test if OC density, sedimentation rate and OCAR differ between marsh zones across individual GB saltmarshes, ANOVA and Tukey-Kramer (TK) statistical tests (Driscoll, 1996) were utilized. Prior to undertaken the statistical analysis the data was tested for normality using Shapiro-Wilk Test (González-Estrada and Cosmes, 2019). If the dataset was not normal it was first checked for outliers and if none were found the data was transformed using the Box-Cox transformation approach (Sakia, 1992).
为了测试单个GB盐沼的沼泽带之间的OC密度，沉降速率和OCAR是否不同，使用了方差分析和Tukey-Kramer（TK）统计测试（Driscoll，1996）。在进行统计分析之前，使用夏皮罗-威尔克检验（González-Estrada and Cosmes，2019）对数据进行了正态性检验。如果数据集不正常，则首先检查异常值，如果没有找到异常值，则使用 Box-Cox 变换方法（Sakia，1992）转换数据。
Saltmarsh soil OC accumulation was estimated for the 21 saltmarshes following the approach of Miller et al. (2023). For each saltmarsh, the mean (and standard deviation) OCAR for the high and mid-low marsh zones were multiplied with the areal extent of those respective zones (Haynes, 2016; Natural Resources Wales, 2016; Environment Agency, 2023) to calculate the annual OC accumulation at each marsh.
按照 Miller 等人 （2023） 的方法估计了 21 个盐沼的盐沼土壤 OC 积累。对于每个盐沼，高沼泽和中低沼泽带的平均值（和标准差）OCAR乘以这些区域的区域范围（Haynes，2016;威尔士自然资源，2016年;环境署，2023 年）来计算每个沼泽的年碳排放量。
This study estimates OCAR from the high and mid-low marsh zones but lacks data in the pioneer and Spartina zones, which occupy ~4 % and ~ 7 % of the total areal extent of GB saltmarsh, respectively (Haynes, 2016; Natural Resources Wales, 2016; Environment Agency, 2023). To facilitate the estimation of total OC accumulation across the marshes, the mid-low OCAR is used as a surrogate value for the pioneer and Spartina zones. Additionally, at sites where we do not have a high marsh OCAR value we utilise the mid-low OCAR value from that marsh. Because a large proportion of saltmarsh mapping took place over a decade ago (Haynes., 2016; Natural Resources Wales, 2016), an error of ±5 % was applied to the areal data to account for expansion and/or contraction of the saltmarshes (Smeaton et al., 2022a).
本研究估计了高沼泽和中低沼泽区的OCAR，但缺乏先锋和斯巴达区的数据，它们分别占GB盐沼总面积的~4%和~7%（Haynes，2016;威尔士自然资源，2016年;环境署，2023 年）。为了便于估计整个沼泽的总OC积累，使用中低OCAR作为先锋区和Spartina区的替代值。此外，在沼泽OCAR值不高的地点，我们利用该沼泽的中低OCAR值。因为很大一部分盐沼测绘发生在十多年前（Haynes.，2016;威尔士自然资源，2016 年），对区域数据应用了 ±5% 的误差，以解释盐沼的扩张和/或收缩（Smeaton 等人，2022a）。
The calculations were undertaken in a Markov Chain Monte Carlo (MCMC) framework. MCMC analysis was applied within the OpenBUGS software package (Lunn et al., 2009) by taking 1,000,000 out of 10,000,000 random samples from a normal distribution of each variable (area, OCAR) from each marsh zone and multiplying the area by the OCAR to generate a pool of results. Applying standard descriptive statistical techniques to the pool of generated solutions allows calculation of the mean, median, standard deviation, and the 5th and 95th percentiles.
计算是在马尔可夫链蒙特卡洛（MCMC）框架中进行的。MCMC分析在OpenBUGS软件包（Lunn等人，2009）中应用，方法是从每个沼泽区每个变量（面积，OCAR）的正态分布中抽取10,000,000个随机样本中的1,000,000个，并将面积乘以OCAR以生成结果池。将标准描述性统计技术应用于生成的解决方案池，可以计算平均值、中位数、标准差以及第 5 个和第 95 个百分位数。
To upscale the OC accumulation measurements from the 21 saltmarshes in this study to all saltmarsh habitat in GB, the classification approach developed by Smeaton et al. (2023) was utilized. The clustering approach developed by Smeaton et al. (2023) as advantages over other classification and upscaling methods such as using the saltmarsh type or vegetation communities (Adam, 1978; Burd, 1989; Haynes, 2016; Smeaton et al., 2022a). These alternative approaches negate to take local conditions into consideration when classifying saltmarsh, for example an estuarine marsh in the North of Scotland and the South of England would be determined to be similar when in reality this is unlikely. By using variables, that take in to consideration local variation the clustering approach (Smeaton et al., 2023) allows marshes with similar climatic, oceanographic, geomorphic, and ecological characteristics to be grouped, which provides foundation for upscaling. Even with this approach the 21 saltmarshes only represent 18 % of the total GB saltmarsh area. Therefore, it is probable that the variation in OC accumulation across all GB marshes will not be fully captured.
为了将本研究中 21 个盐沼的 OC 积累测量值提升到大不列颠的所有盐沼栖息地，使用了 Smeaton 等人 （2023） 开发的分类方法。Smeaton 等人（2023 年）开发的聚类方法优于其他分类和放大方法，例如使用盐沼类型或植被群落（Adam，1978 年;Burd，1989 年;海恩斯，2016 年;Smeaton 等人，2022a）。这些替代方法否定了在对盐沼进行分类时考虑当地条件的情况，例如，苏格兰北部和英格兰南部的河口沼泽将被确定为相似，而实际上这不太可能。通过使用考虑局部变化的变量，聚类方法（Smeaton 等人，2023 年）允许对具有相似气候、海洋、地貌和生态特征的沼泽进行分组，这为放大提供了基础。即使采用这种方法，21个盐沼也只占GB盐沼总面积的18%。因此，可能无法完全捕获所有GB沼泽中OC积累的变化。
To estimate the OC accumulation of all GB saltmarshes, the areal extent of each marsh zone within each of the eight clusters was multiplied with the corresponding mean OCAR for each marsh zone calculated from the sampled saltmarshes that fall into each cluster (Fig. 1B). Again, a ± 5 % error was applied to the areal extent of all marsh zones to account for changes since the surveys were undertaken. All calculations were carried out within the MCMC framework.
为了估计所有GB盐沼的OC积累，将8个集群中每个沼泽带的面积范围乘以每个沼泽带的相应平均OCAR，该平均值由属于每个集群的采样盐沼计算得出（图1B）。同样，对所有沼泽带的区域范围应用了±5%的误差，以解释自进行调查以来的变化。所有计算均在MCMC框架内进行。
Of the 21 marshes studied, six are estimated to have formed prior to 1900, eleven between 1900 and 1950, and a further four after 1950 (Fig. 2A). Fig. 2 summarises age-depth models for 34 cores from 21 sites, including 6 cores from 5 sites originally sampled by Miller et al. (2023). Individual age models with 2σ temporal uncertainties are provided alongside radionuclide results in Supplementary Fig. 22–26. Average sedimentation rates in saltmarsh soils vary between 0.12 cm yr−1 at Morrich More (northeast Scotland) to 1.28 cm yr−1 at Dornoch Point (northeast Scotland). Across all sites, the mean sedimentation rate is 0.41 ± 0.16 cm yr−1 (Fig. 2B). Sedimentation rates for all cores are provided in Supplementary Fig. 27.
在所研究的21个沼泽中，估计有6个在1900年之前形成，11个在1900年至1950年之间形成，另外4个在1950年之后形成（图2A）。图 2 总结了来自 21 个地点的 34 个岩心的年龄深度模型，其中包括最初由 Miller 等人 （2023） 采样的 5 个地点的 6 个岩心。在补充图22-26中提供了具有2σ时间不确定性的个体年龄模型以及放射性核素结果。盐沼土壤的平均沉积速率在Morrich More（苏格兰东北部）的0.12厘米/年 −1 和Dornoch Point（苏格兰东北部）的1.28厘米/年 −1 之间变化。在所有地点，平均沉降速率为0.41±0.16厘米（ −1 图2B）。所有岩心的沉降速率见补充图27。
Fig. 2. (A) Mean age-depth models for 34 cores developed from 210Pb and 137Cs data using rplum (Blaauw et al., 2022). (B) Centimetre-resolution sedimentation rates derived from the age-depth models, arranged by latitude (furthest north on the left-hand side). The solid line within the boxes represents the median values, and the triangles illustrate the 5th and 95th percentiles. The dashed line represents the mean sedimentation rate calculated from all cores in this study. Supplementary Figs. 22–26 display age models and sedimentation rates from all 34 cores.
图 2.（A） 使用 rplum 根据 210 Pb 和 137 Cs 数据开发的 34 个岩心的平均年龄深度模型（Blaauw 等人，2022 年）。（B） 按纬度（左侧最北端）排列的年龄深度模型得出的厘米分辨率沉积速率。框内的实线表示中值，三角形表示第 5 个和第 95 个百分位数。虚线表示从本研究中所有岩心计算的平均沉降速率。补充图22-26显示了所有34个岩心的年龄模型和沉降速率。
Across GB saltmarshes, there is high variability in both the dry bulk density and OC content of the soils. We observe the common trend that dry bulk density decreases as OC content increases (Fig. 3A). The saltmarsh soil's dry bulk density and OC content differ significantly across the sites. The mean dry bulk density across all sites is 0.52 ± 0.27 g cm−3 with values ranging from 0.05 g cm−3 in the surficial fibrous peat layers found in the northern Scottish saltmarshes (e.g., Waulkmill Bay) to 1.66 g cm−3 in the silts and sands found deeper in the profile at marshes such as Lindisfarne and Sunderland. The mean OC content of the saltmarsh soils is 8.54 ± 7.09 %, with values ranging between 0.11 % in the sandy soils at Dornoch Point to 37.66 % in the fibrous peat layers at Skinflats (Fig. 1). The variation in dry bulk density and OC content across the sites results in mean core OC density values ranging between 0.011 g C cm−3 in the mid-low marsh at Wigtown Bay to 0.078 g C cm−3 in the mid-low marsh at the Kyle of Tongue. Across all cores, the average OC density of the saltmarsh soils is 0.034 ± 0.010 g C cm−3 (Fig. 3B). At sites with cores from both high and mid-low marsh zones, the OC density in the high zone is always higher than those measured in the mid-low marsh (Fig. 3B). When statistically tested using an ANOVA the difference between OC densities in the high and mid-low marsh are generally deemed to be statistically significant, yet in several cases (Black Rock, Sunderland, and Dornoch Point) the difference between the groups is not statistically significant (Supplementary Table 15).
在大不列颠盐沼中，土壤的干堆积密度和OC含量都存在很大变化。我们观察到一个共同的趋势，即干堆积密度随着OC含量的增加而降低（图3A）。盐沼土壤的干容积密度和OC含量在不同地点之间存在显着差异。所有地点的平均干堆积密度为0.52±0.27克厘米 −3 ，其值范围从苏格兰北部盐沼（例如沃克米尔湾）的表层纤维泥炭层的0.05克厘米 −3 到林迪斯法恩和桑德兰等沼泽地剖面更深处的淤泥和沙子的1.66克厘米 −3 。盐沼土壤的平均OC含量为8.54±7.09%，在Dornoch Point的沙质土壤中，OC含量在0.11%之间，在Skinflats的纤维泥炭层中为37.66%（图1）。各地点干散装密度和OC含量的变化导致平均核心OC密度值在威格敦湾中低层沼泽的0.011 g C cm −3 到Kyle of Tongue的中低层沼泽的0.078 g C cm −3 之间。在所有岩心中，盐沼土壤的平均OC密度为0.034±0.010 g C cm −3 （图3B）。在具有来自高沼泽和中低沼泽带岩心的地点，高区的OC密度总是高于中低沼泽中测得的OC密度（图3B）。当使用方差分析进行统计检验时，高沼泽和中低沼泽中 OC 密度之间的差异通常被认为具有统计学意义，但在一些情况下（Black Rock、Sunderland 和 Dornoch Point），组之间的差异在统计学上并不显着（补充表 15）。
Fig. 3. Organic carbon density of Great British saltmarsh sediments. (A) Dry bulk density vs organic carbon (OC) content. Black line reflects the correlation (y = 2.3874×-1.053) between the dry bulk density and OC (%). (B) Centimetre-resolution OC density (g C cm−3) of the saltmarsh cores (core identification along the x-axis) arranged by latitude (furthest north on the left-hand side). The solid line within the boxes represents the median value, and the triangles illustrate the 5th and 95th percentiles. The black dashed line represents the mean OC density calculated from all cores in this study. Supplementary Fig. 28 displays downcore OC content records for all 34 cores.
图 3.大不列颠盐沼沉积物的有机碳密度。（A） 干散体积密度与有机碳（OC）含量的关系。黑线表示干散装密度与OC（%）之间的相关性（y = 2.3874× -1.053 ）。（B） 按纬度（左侧最北端）排列的盐沼岩心的厘米分辨率OC密度（g C cm −3 ）（沿x轴的岩心识别）。框内的实线表示中值，三角形表示第 5 个和第 95 个百分位数。黑色虚线表示从本研究中所有内核计算的平均 OC 密度。补充图 28 显示了所有 34 个内核的下核 OC 内容记录。
Organic carbon accumulation rates for saltmarsh soils average 110.88 ± 43.12 g C m−2 yr−1 across all sites and range between 27.57 g C m−2 yr−1 at Loch Laich to 343.68 g C m−2 yr−1 at Wigtown Bay (Fig. 4). Across all sites, on average, the high marsh zone cores accumulate OC at a greater rate (115.52 ± 64.07 g C m−2 yr−1) in comparison to the cores from the mid-low marsh zone (108.90 ± 76.33 g C m−2 yr−1).
盐沼土壤 −1 的有机碳积累率在所有地点的平均为110.88±43.12 g C m −2 yr，范围在Loch Laich的27.57 g C m −2 yr −1 至 −1 Wigtown Bay的343.68 g C m −2 yr之间（图4）。平均而言，在所有地点，与中低沼泽区岩心（108.90 ± 76.33 g C m −2 yr −1 ）相比，高沼泽区岩心的OC积累速率更高（115.52 ± 64.07 g C m −2 yr −1 ）。
Fig. 4. Centimetre-resolution organic carbon (OC) accumulation rates (g C m−2 yr−1) for the 34 cores (Fig. 1) derived from the age-depth models and sedimentation rates (Fig. 2), arranged by latitude (furthest north on the left-hand side).The solid line within the boxes represents the median value, and the triangles illustrate the 5th and 95th percentiles. The black solid line represents the mean OC accumulation rate (110.88 g C m−2 yr−1) calculated from all cores in this study. Grey dashed lines highlight previously published regional and global average OC accumulation rates (i) Ouyang and Lee (2014), (ii) Ouyang and Lee (2014) and (iii) Chmura et al. (2003). Supplementary Fig. 29 displays downcore OCAR records for all 34 cores.
图 4.34个岩心（图1）的厘米分辨率有机碳（OC）积累速率（g C m −2 yr −1 ）来自年龄-深度模型和沉积速率（图2），按纬度排列（左侧最北端）。框内的实线表示中值，三角形表示第 5 个和第 95 个百分位数。黑色实线代表本研究中所有岩心的平均OC积累率（110.88 g C m −2 yr −1 ）。灰色虚线突出显示了先前公布的区域和全球平均OC积累率（i）Ouyang和Lee（2014），（ii）Ouyang和Lee（2014）和（iii）Chmura et al.（2003）。补充图 29 显示了所有 34 个内核的下核 OCAR 记录。
GB saltmarsh soils are characterised by δ13Corg values of −26.2 ± 2.1 ‰, δ15N values of 5.2 ± 2.0 ‰, and C/N ratios of 16.6 ± 4.3. As with the OC content, these values vary between cores with δ13Corg values ranging between −17.5 ‰ to −31.4 ‰, δ15N values 0.29 ‰ to 9.8 ‰ (Fig. 5), and C/N ratios ranging from 7.5 to 35.5. When compared, the high and mid-low marsh zones vary little with mean values mirroring those of the whole dataset; however, the most depleted δ13Corg values are observed in the high marsh (Fig. 5). In comparison, the δ13Corg and δ15N values of the basal soils (the sediments related to the pre-saltmarsh intertidal flat) are enriched and the C/N ratios are lower than those observed in the saltmarsh (Fig. 5).
GB盐沼土壤的特点是δ 13 C org 值为-26.2±2.1‰， 15 δ N值为5.2±2.0‰，C/N比值为16.6±4.3。与OC含量一样，这些值在内核之间变化，δ 13 C org 值在−17.5‰至-31.4‰之间，δ 15 N值在0.29‰至9.8‰之间（图5），C/N比范围为7.5至35.5。比较时，高沼泽区和中低沼泽区变化不大，平均值反映了整个数据集的平均值;然而，在高沼泽中观察到最耗尽的δ 13 C org 值（图5）。相比之下，基底土壤（与潮前盐沼潮间带滩相关的沉积物）的 13 δ C org 和 15 δ N值富集，C/N比值低于盐沼（图5）。
Fig. 5. Cross plots of (A) δ13Corg versus δ15N and (B) δ13Corg versus C/N for soil samples from the 21 saltmarshes. Terrestrial, marine and saltmarsh source values derived from samples collected from across Great Britain (Smeaton et al., 2022b). Full details of the source values can be found in Supplementary Table 3.
图 5.21个盐沼土壤样品的（A）δ 13 C org 与δ 15 N和（B）δ 13 C org 与C/N的交叉图。陆地、海洋和盐沼源值来自从英国各地收集的样本（Smeaton 等人，2022b）。源值的完整详细信息可在补充表 3 中找到。
The variation in the isotopic and elemental ratios of these bulk soil samples are indicative of OC originating from multiple sources (terrestrial, in situ and/or marine). As observed in other studies (Saintilan et al., 2013; Geraldi et al., 2019; Miller et al., 2023), there is an overlap in the δ13Corg, δ15N and C/N values of saltmarsh biomass and terrestrially derived soil and vegetation (Supplementary Table 4), which prevents the differentiation of in situ OC production from other terrestrial OC inputs to the saltmarshes. The outputs from the Bayesian isotope mixing model estimates that, across all cores and sedimentary units, 66.1 ± 15.0 % of the OC originates from terrestrial and/or in situ sources, with values ranging between 10.1 % in the Arne marsh and 98.7 % in the fjord-head systems at the Kyle of Tongue and Loch Laich. If averaging the 1-cm resolution data across the saltmarsh soils, the model estimates that 72.0 ± 14.4 % of the OC is derived from terrestrial/in situ sources. Up to 92.8 ± 18.7 % of OC in the Skinflats saltmarsh soils comes from terrestrial/in situ sources, while the OC within the Arne saltmarsh largely originates from the marine environment with only 28.9 ± 17.1 % sourced from terrestrial/in situ sources. On average, 77.7 ± 14.9 % of the OC in the high marsh cores is derived from terrestrial/in situ sources compared to 69.7 ± 14.2 % in the mid-low marsh cores. Down core estimates of terrestrial/in situ OC accumulation are detailed in Supplementary Fig. 30.
这些散装土壤样品的同位素和元素比的变化表明OC来自多个来源（陆地、原位和/或海洋）。正如在其他研究中观察到的那样（Saintilan 等人，2013 年;Geraldi 等人，2019 年;Miller et al.， 2023），盐沼生物量和陆生土壤和植被的 δ 13 C org 、δ 15 N 和 C/N 值存在重叠（补充表 4），这阻碍了原位 OC 生产与盐沼其他陆地 OC 输入的区别。贝叶斯同位素混合模型的输出估计，在所有岩心和沉积单元中，66.1%±15.0%的OC来自陆地和/或原位来源，其值在Arne沼泽的10.1%和舌头凯尔和莱奇湖的峡湾源系统的98.7%之间。如果对盐沼土壤的 1 厘米分辨率数据进行平均，该模型估计 72.0 ± 14.4% 的 OC 来自陆地/原位来源。Skinflats盐沼土壤中高达92.8%±18.7%的OC来自陆地/原位来源，而Arne盐沼中的OC主要来自海洋环境，只有28.9%±17.1%来自陆地/原位来源。平均而言，高沼泽岩心中77.7%±14.9%的OC来自陆地/原位来源，而中低沼泽岩心中的OC为69.7%±14.2%。陆/原位OC积累的下部岩心估计详见补充图30。
The 21 saltmarshes in this study accumulate 8873 ± 2840 t of OC annually, of which we estimate that 5961 ± 1908 t of OC originate from terrestrial and/or in situ sources. Significantly different OC accumulation rates are observed between the individual marshes. Gedney, for example, gains 2771 ± 991 t of OC annually, whereas Loch Laich only accumulates 4 ± 1 t annually (Fig. 6A). However, this disparity in OC accumulation is largely driven by areal extent of the marshes, as illustrated by Gedney and Waulkmill Bay occupying areas of 20.49 km2 and 0.11 km2, respectively.
本研究中的21个盐沼每年积累8873±2840吨OC，我们估计其中5961±1908吨OC来自陆地和/或原位来源。在各个沼泽之间观察到显着不同的OC积累率。例如，Gedney 每年获得 2771 ± 991 吨的 OC，而 Loch Laich 每年仅积累 4 ± 1 吨（图 6A）。然而，OC积累的这种差异主要是由沼泽的面积范围驱动的，如Gedney和Waulkmill Bay分别占据20.49公里 2 和0.11公里 2 的区域所示。
Fig. 6. Saltmarsh organic carbon (OC) accumulation in Great Britain. (A) Annual OC accumulation (tonnes C yr−1) across the 21 saltmarshes with the contribution of marine and terrestrial and/or in situ OC sources highlighted. (B) Total annual OC accumulation in the saltmarsh habitat of Great Britain and its constituent nations. A full breakdown of the OC accumulation can be found in Supplementary Tables 6–11.
图 6.英国盐沼有机碳（OC）积累。（A） 21个盐沼的年OC积累量（吨C年 −1 ），并强调了海洋和陆地和/或原位OC来源的贡献。（B） 大不列颠及其组成国盐沼生境的OC年总积累量。OC累积的完整明细见补充表6-11。
The 451.65 km2 of saltmarsh habitat in GB is estimated to accumulate 46,563 ± 4352 t of OC annually, with 5th and 95th percentile estimates of 39,338 and 53,754 t OC yr−1 (Fig. 6B). Of this total, 68 % (31,809 ± 3418 t OC) of OC originates from terrestrial and/or in situ sources, with the marine environment providing the remaining 32 % of OC (Fig. 6B). English saltmarshes, which represent ∼74 % of the total area of GB saltmarsh, accumulate 32,276 ± 2992 t of OC yr−1, the largest quantity of the three nations. Welsh and Scottish marshes accumulate 7726 ± 977 t OC yr−1 and 6561 ± 1050 t OC yr−1 respectively (Fig. 6B). Per saltmarsh area, English marshes accumulate the lowest quantity of OC (98.59 ± 8.62 g C m−2 yr−1 on average), followed by Scottish (113.32 ± 17.86 g C m−2 yr−1) and Welsh (129.07 ± 15.84 g C m−2 yr−1) marshes. Supplementary Tables 5–11 provide a full breakdown of the data.
据估计，大不列颠451.65公里 2 的盐沼生境每年累积46,563±4352吨碳，第5和第95个百分位估计分别为39,338和53,754吨碳 −1 （图6B）。其中，68%（31,809 ± 3418 t OC）来自陆地和/或原位来源，其余 32% 的 OC 来自海洋环境（图 6B）。英国盐沼占英国盐沼总面积的74%，累积了32,276±2992吨的OC yr −1 ，是三个国家中数量最多的。威尔士沼泽和苏格兰沼泽的年累积量 −1 分别为7726±977吨， −1 6561吨±1050吨（图6B）。每个盐沼面积，英国沼泽积累的OC量最低（平均98.59±8.62 g C m −2 yr −1 ），其次是苏格兰沼泽（113.32 ± 17.86 g C m −2 yr −1 ）和威尔士沼泽（129.07 ± 15.84 g C m −2 yr −1 ）。补充表5-11提供了数据的完整分类。
Terrestrial/in situ OC constitutes 66 % and 69 % of the OC accumulating in English and Welsh saltmarshes respectively, while in Scotland 77 % of the OC originates from terrestrial/in situ sources. Northern Ireland saltmarshes occupy an area of 2.38 km2 (Joint Nature Conservation Committee, 2013), approximately 0.5 % of the GB total. It is therefore reasonable to assume that the quantity of OC accumulating in total United Kingdom (i.e., Great Britain and Northern Ireland) saltmarshes would only be marginally greater than the GB estimate.
陆生/原位OC分别占英格兰和威尔士盐沼中积累的OC的66%和69%，而在苏格兰，77%的OC来自陆地/原位来源。北爱尔兰盐沼面积为2.38公里 2 （联合自然保护委员会，2013年），约占大不列颠总面积的0.5%。因此，可以合理地假设，英国（即大不列颠及北爱尔兰）盐沼中累积的OC数量只会略高于GB的估计数。
By upscaling high-resolution OC accumulation records from 34 cores across 21 sites, we estimate that 46,563 ± 4352 t of OC are accumulating annually, supplementing the estimated 5.20 ± 0.65 Mt. of OC currently stored in GB saltmarshes (Smeaton et al., 2023). Previous attempts to estimate OC accumulation in GB saltmarshes used either a limited number of cores from only one region (Miller et al., 2023) or a single OCAR value across the areal extent of all marshes (Luisetti et al., 2019; Pearson, 2020).
通过升级 21 个地点的 34 个岩心的高分辨率 OC 积累记录，我们估计每年有 46,563 ± 4352 吨 OC 正在积累，补充了目前储存在 GB 盐沼中的估计 5.20 ± 0.65 Mt. 的 OC（Smeaton 等人，2023 年）。以前估计 GB 盐沼中 OC 积累的尝试要么只使用来自一个地区的有限数量的岩心（Miller 等人，2023 年），要么使用所有沼泽区域范围内的单个 OCAR 值（Luisetti 等人，2019 年;皮尔逊，2020 年）。
On average, saltmarshes in Great Britain accumulate OC at a rate of 110.88 ± 43.12 g C m−2 yr−1, with values ranging between 27.57 and 343.68 g C m−2 yr−1 (Fig. 3).The young and shallow nature of saltmarsh deposits in GB (Miller et al., 2023; Smeaton et al., 2023) means that the OC does not reach a state of inert long-term storage as it is still degrading, albeit at a decreasing rate with depth (Supplementary Figs. 28). Therefore, OC burial in these saltmarsh soils, as with any natural burial system (e.g., Middelburg, 2018), are not in long-term equilibrium, but instead reflect a balance of gains and loss terms, which are spatially and temporally complex resulting in the large range of OCARs calculated within and across saltmarshes in this study.
平均而言，英国盐沼的OC积累率为110.88±43.12 g C m −2 yr −1 −1 ，其值在27.57至343.68 g C m −2 yr之间（图3）。大不列颠盐沼沉积物的年轻和浅层性质（Miller et al.， 2023;Smeaton 等人，2023 年）意味着 OC 不会达到惰性长期储存状态，因为它仍在降解，尽管随着深度的增加速度而降低（补充图 28）。因此，与任何自然埋藏系统（例如，Middelburg，2018）一样，这些盐沼土壤中的OC埋藏并不处于长期平衡状态，而是反映了收益和损失的平衡，这在空间和时间上都很复杂，导致本研究中盐沼内部和盐沼之间计算的OCAR范围很大。
The range of OCAR values observed in GB marshes are comparable with recent studies of northern European natural saltmarshes in Denmark (Graversen et al., 2022; Leiva-Dueñas et al., 2024), Germany (Mueller et al., 2019) and realigned marshes that have reached maturity (~100 years from creation) in southern England (Burden et al., 2019). However, newly created marshes, such as Steart Marsh in Somerset, report mean sedimentation rates of 4.7 cm yr−1 and OCAR of up to 1960 g C m−2 yr−1 (Mossman et al., 2022) which are an order of magnitude higher than the sedimentation rates (0.07–1.18 cm yr−1) and OCARs (27.57–343.68 g C m−2 yr−1) reported in this study and across the wider literature (Cundy and Croudace, 1995; Callaway et al., 1996; Andrews et al., 2008; Teasdale et al., 2011; Adams et al., 2012; Burden et al., 2019; Miller et al., 2023). The disparity between these published rates and the unusually high rates of Mossman et al. (2022) are almost certainly due to the rapid and early infill of newly created accommodation space following managed realignment of the site in 2014. This early infill process is significantly faster than the rate at which natural saltmarshes can accumulate material and the OCAR in these locations must therefore be treated with caution and are not comparable to naturally functioning saltmarsh ecosystems. This highlights the importance of defining when a realigned area can be considered a saltmarsh (Intergovernmental Panel on Climate Change, 2013; McMahon et al., 2023).
在大不列颠沼泽中观察到的OCAR值范围与丹麦北欧天然盐沼的最新研究相当（Graversen等人，2022年;Leiva-Dueñas 等人，2024 年）、德国（Mueller 等人，2019 年）和英格兰南部已经成熟（~100 年）的重新排列的沼泽（Burden 等人，2019 年）。然而，新创建的沼泽，如萨默塞特郡的 Steart 沼泽，报告的平均沉降速率为 4.7 厘米/年 −1 ，OCAR 高达 1960 克 C m −2 年 −1 （Mossman 等人，2022 年），这比 −1 −2 −1 本研究和更广泛的文献（Cundy 和 Croudace， 1995;Callaway等人，1996年;Andrews 等人，2008 年;Teasdale 等人，2011 年;Adams等人，2012;Burden等人，2019;Miller 等人，2023 年）。这些公布的比率与 Mossman 等人（2022 年）异常高的比率之间的差异几乎可以肯定是由于在 2014 年对场地进行管理调整后，新创建的住宿空间被快速和提前填充。这种早期的填充过程明显快于天然盐沼积累物质的速度，因此必须谨慎对待这些地点的OCAR，并且无法与自然运作的盐沼生态系统相提并论。这凸显了定义何时可以将重新调整的区域视为盐沼的重要性（政府间气候变化专门委员会，2013 年;McMahon 等人，2023 年）。
While it might seem logical to conclude that high saltmarsh OCAR would equate to high OC storage values (kg C m−2) and OC stocks (t C), this is not the case (Fig. 7). The main driver for the magnitude of the OC stock is the areal extent of the saltmarshes, with large marshes such as Llanrhidian, Morrich More and Stiffkey possessing the largest stocks. Variation in OCAR is governed by sedimentation rates and OC density, which are themselves driven by factors such as sediment supply, geomorphology, and vegetation composition. In contrast, OC storage (i.e. the amount of OC per unit area) in GB saltmarshes is potentially driven by an underlying regional history of relative sea-level change and sediment availability (Allen, 2000; Smeaton et al., 2023; Gore et al., 2024). The saltmarshes in the north of Scotland are the oldest of the marshes in this study and have experienced an extended period of comparatively stable relative sea level (Barlow et al., 2014; Shennan et al., 2018), resulting a longer duration of organic saltmarsh sediment accumulation and elevated OC storage when compared to the younger sites (Fig. 7). The south of England, by contrast, has experienced more rapid relative sea-level rise during the early and mid-Holocene, enhanced by continued isostatic subsidence (Shennan et al., 2018). This has favoured the drowning of estuaries and river valleys, increased accommodation space, and resulted in the deposition of predominantly minerogenic sediments (Allen, 2000; Waller and Long, 2003). Reduced rates of sea-level rise in the late Holocene, combined with enhanced sedimentation from terrestrial sources linked to anthropogenic activities including forest clearance and mineral exploitation, allowed estuaries to “catch up” (Pye and Blott, 2014; Vis et al., 2015). Sediments infilled the available accommodation space and provided conditions suitable for the accumulation of organic saltmarsh deposits, although the onset occurred substantially later than in northern GB (Long et al., 2000).
虽然得出高盐沼OCAR等同于高OC储存值（kg C m −2 ）和OC储量（t C）的结论似乎是合乎逻辑的，但事实并非如此（图7）。OC储量规模的主要驱动因素是盐沼的面积范围，Llanrhidian，Morrich More和Stiffkey等大型沼泽拥有最大的储量。OCAR的变化受沉积速率和OC密度的控制，而沉积速率和OC密度本身受沉积物供应、地貌和植被组成等因素的驱动。相比之下，大不列颠盐沼的OC储存量（即每单位面积的OC量）可能受到相对海平面变化和沉积物可用性的潜在区域历史的驱动（Allen，2000年;Smeaton 等人，2023 年;Gore 等人，2024 年）。苏格兰北部的盐沼是本研究中最古老的沼泽，并且经历了较长时间的相对稳定的相对海平面（Barlow等人，2014年;Shennan et al.， 2018），与较年轻的地点相比，有机盐沼沉积物堆积持续时间更长，OC储存量增加（图7）。相比之下，英格兰南部在全新世早期和中期经历了更快的相对海平面上升，持续的等静压沉降加剧了这种情况（Shennan et al.， 2018）。这有利于河口和河谷的淹没，增加了住宿空间，并导致主要成矿沉积物的沉积（Allen，2000年;Waller和Long，2003）。全新世晚期海平面上升速度的降低，加上与森林砍伐和矿产开采等人为活动相关的陆地来源的沉积增加，使河口能够“迎头赶上”（Pye和Blott，2014;Vis 等人。, 2015).沉积物填满了可用的住宿空间，为有机盐沼沉积物的积累提供了合适的条件，尽管发病时间比大不列颠北部晚得多（Long等人，2000年）。
Fig. 7. Organic carbon (OC) accumulation rates (g C m−2 yr−1) compared to soil OC storage (kg C m−2) and OC stock (tonnes) estimates – the latter from Smeaton et al. (2023). Colours represent the cluster in which each saltmarsh is grouped (Fig. 1B; Smeaton et al., 2023).
图 7.有机碳 （OC） 积累率 （g C m −2 yr −1 ） 与土壤 OC 储存量 （kg C m −2 ） 和 OC 储量（吨）估计值相比——后者来自 Smeaton 等人（2023 年）。颜色表示每个盐沼分组的簇（图1B;Smeaton 等人，2023 年）。
Estimates of saltmarsh OC accumulation from this study differ significantly from global estimations (Table 1), raising questions on the applicability of such global datasets in calculating OC accumulation for individual nations or regions where such data are absent. Global estimates of the rate at which OC accumulates in saltmarshes range between 210 and 250 g C m−2 yr−1, resulting in total accumulation in the range of 10.2–59.0 Mt. OC yr−1 (Table 1). These rates significantly exceed the 110.88 ± 43.12 g C m−2 yr−1 observed in the GB marshes (Table 1). The disparity in the OCAR is driven by spatial biasing of sampling location towards high OCAR areas, methodological approaches, and data quality of records within these global datasets (Chmura et al., 2003; Ouyang and Lee, 2014). Both Chmura et al. (2003) and Ouyang and Lee (2014) use the same dataset compiled from 143 saltmarsh OCAR records, yet while Chmura et al. (2003) estimate global OCAR to be 210.0 ± 24.0 g C m−2 yr−1, Ouyang and Lee (2014) estimate 244.7 ± 26.1 g C m−2 yr−1. The difference in these is driven by the exclusion of a number of datasets by Ouyang and Lee (2014) due to perceived quality control issues. The disparity between these studies is further highlighted by the fact that Chmura et al. (2003) and Ouyang and Lee (2014) estimate that 44.6 and 10.2 Mt. of OC yr−1 accumulates in global marshes, respectively. These significant differences are due to upscaling methodologies; Chmura et al. (2003) apply a mean OCAR to the global marsh extent while Ouyang and Lee (2014) calculate regional OCAR, which are then applied to region-specific areal extents.
本研究对盐沼OC积累的估计与全球估计有很大不同（表1），这引发了对此类全球数据集在计算缺乏此类数据的个别国家或地区的OC积累的适用性的问题。全球估计盐沼中OC的积累速率在210至250 g C m −2 yr之间 −1 ，总积累量在10.2-59.0 Mt. OC yr −1 范围内（表1）。这些速率大大超过了在大不列颠沼泽中 −1 观察到的110.88±43.12克立米 −2 年（表1）。OCAR的差异是由抽样位置向高OCAR区域的空间偏差、方法和这些全球数据集中记录的数据质量驱动的（Chmura等人，2003年;Ouyang和Lee，2014）。Chmura et al. （2003） 和 Ouyang and Lee （2014） 都使用相同的数据集，该数据集由 143 个盐沼 OCAR 记录汇编而成，但 Chmura 等人 （2003） 估计全球 OCAR 为 210.0 ± 24.0 g C m −2 yr −1 ， Ouyang and Lee （2014） 估计为 244.7 ± 26.1 g C m −2 yr −1 。这些差异是由于Ouyang和Lee（2014）由于感知到的质量控制问题而排除了一些数据集。Chmura et al. （2003） 和 Ouyang and Lee （2014） 估计全球沼泽中分别 −1 积累了 44.6 和 10.2 Mt. of OC yr，这一事实进一步凸显了这些研究之间的差异。这些显著差异是由于方法的升级;Chmura et al. （2003） 将平均 OCAR 应用于全球沼泽范围，而 Ouyang 和 Lee （2014） 计算区域 OCAR，然后将其应用于特定区域的区域范围。
Table 1. National saltmarsh organic carbon accumulation rates (OCAR) and total organic carbon (OC) accumulation estimates from this study in comparison to national, regional, and global datasets and sequestration (†) and accumulation rates for other ecosystems. *Error presented as standard error opposed to standard deviation.
表 1.本研究的国家盐沼有机碳积累率 （OCAR） 和总有机碳 （OC） 积累估计值与国家、区域和全球数据集以及其他生态系统的封存 （†） 和积累率进行比较。*误差表示为标准误差，而不是标准偏差。
| Nation 国家 | OCAR (g C m−2 yr−1) OCAR （g C m −2 yr −1 ） | Total OC Accumulation (Tonnes yr−1) 总OC累积量（吨年 −1 ） | References 引用 | ||||
|---|---|---|---|---|---|---|---|
| Mean (± σ) 平均值 （± σ） | 5th 第5名 | 95th 第95届 | Mean (± σ) 平均值 （± σ） | 5th 第5名 | 95th 第95届 | ||
| Scotland 苏格兰 | 113.3 ± 17.9 113.3 ± 17.9 | 83.7 | 142.6 | 6561 ± 1050 6561 ± 1050 | 4843 | 8299 | This Study 本研究 |
| England 英国 | 98.6 ± 8.6 98.6 ± 8.6 | 84.4 | 112.5 | 32,276 ± 2922 32,276 ± 2922 | 27,470 | 37,088 | |
| Wales 威尔士 | 129.1 ± 15.8 129.1 ± 15.8 | 103.4 | 155.0 | 7726 ± 977 7726 ± 977 | 6157 | 9347 | |
| Great Britain 英国 | 110.9 ± 43.1 110.9 ± 43.1 | 88.9 | 120.4 | 46,563 ± 4352 46,563 ± 4352 | 39,338 | 53,754 | |
| Scotland 苏格兰 | 83.4 ± 15.6 83.4 ± 15.6 | – | – | 4385 ± 481 4385 ± 481 | 3473 | 5621 | Miller et al., 2023 Miller 等人，2023 年 |
| Wales 威尔士 | 84.0 | – | – | 6379 | – | – | Pearson, 2020 皮尔逊，2020 年 |
| Essex, Realigned 埃塞克斯，重新调整 | 65.0–104.0 | – | – | – | – | – | Burden et al., 2019 Burden等人，2019 |
| United Kingdom 英国 | – | – | – | 37,000 | – | – | Luisetti et al., 2019 Luisetti 等人，2019 年 |
| Denmark 丹麦 | 4.6–141.6 | – | – | – | – | – | Graversen et al., 2022; Leiva-Dueñas et al., 2024 Graversen 等人，2022 年;Leiva-Dueñas 等人，2024 年 |
| Germany 德国 | 112.0–149.0 | Mueller et al., 2019 穆勒等人，2019 年 | |||||
| Portugal 葡萄牙 | 18.0–94.0 | – | – | – | – | – | Martins et al., 2022; Mazarrasa et al., 2023 Martins 等人，2022 年;Mazarrasa 等人，2023 年 |
| Spain 西班牙 | 16.5–121.0 | – | – | – | – | – | Mazarrasa et al., 2023 Mazarrasa 等人，2023 年 |
| Regional and Global Estimates 区域和全球估计数 | |||||||
| Northern Europe* 北欧* | 315.2 ± 62.9 315.2 ± 62.9 | – | – | – | – | – | Ouyang and Lee, 2014 欧阳和李，2014 |
| Europe & Scandinavia* 欧洲和斯堪的纳维亚* | 312.4 ± 50.6 312.4 ± 50.6 | – | – | 720,000 ± 120,000 720,000 ± 120,000 | – | – | |
| North West Europe* 西北欧* | 62.5–220.0 | – | – | 75,000 –385,220 | – | – | Legge et al., 2020 Legge 等人，2020 年 |
| Global* 全球* | 210.0 ± 24.0 210.0 ± 24.0 | – | – | 44,600,000 | – | – | Chmura et al., 2003 Chmura 等人，2003 年 |
| Global* 全球* | 244.7 ± 26.1 244.7 ± 26.1 | – | – | 10,200,000 | – | – | Ouyang and Lee, 2014 欧阳和李，2014 |
| Global 全球 | 167.7 ± 136.5 167.7 ± 136.5 | – | – | 48,520,000 - 59,010,000 | – | – | Wang et al., 2021 Wang 等人，2021 年 |
| Global* 全球* | 250.0 | – | – | – | – | – | Temmink et al., 2022 Temmink 等人，2022 年 |
| Other ecosystems 其他生态系统 | |||||||
| Forests, Great Britain 森林， 英国 | 103.5† | – | – | 926,431† | – | – | Zellweger et al., 2022 齐薇格等人，2022 年 |
| Forests, global 全球森林 | 110–360 | – | – | – | – | – | Requena Suarez et al., 2019; Cook-Patton et al., 2020 Requena Suarez 等人，2019 年;Cook-Patton 等人，2020 年 |
| Monoculture forest plantations, global 全球单一栽培人工林 | 90–820 | – | – | – | – | – | Bukoski et al., 2022 Bukoski 等人，2022 年 |
Of particular note is the estimate by Ouyang and Lee (2014) that northern European saltmarshes accumulate 315.2 ± 62.9 g C m−2 yr−1. This estimate exceeds the global average and is substantially higher than the average OCAR estimate both in GB (this study) and Denmark (Graversen et al., 2022) (Table 1). The Ouyang and Lee (2014) northern European estimate is derived from 20 cores collected from 5 marshes in the UK (11 cores), the Netherlands (2 sites, 4 cores), Denmark (1 core) and Poland (2 sites, 4 cores). Across these records, four different methodologies are used to calculate the sedimentation rate (surface elevation tables, marker horizons, radionuclide dating using 210Pb and also using137Cs as a single chronological marker) and only two of the cores have direct OC measurements. In comparison to the OCAR calculated in this study and others within the region (Graversen et al., 2022; Miller et al., 2023), we conclude that the Ouyang and Lee (2014) results are likely to represent a significant overestimation of OCAR in Northern European saltmarshes.
特别值得注意的是 Ouyang 和 Lee （2014） 的估计，北欧盐沼每年积累 315.2 ± 62.9 克 −1 C m −2 。这一估计值超过了全球平均水平，并大大高于英国（本研究）和丹麦（Graversen 等人，2022 年）的平均 OCAR 估计值（表 1）。Ouyang 和 Lee （2014） 的北欧估计来自英国（11 个岩心）、荷兰（2 个岩心、4 个岩心）、丹麦（1 个岩心）和波兰（2 个岩心，4 个岩心）的 5 个沼泽地收集的 20 个岩心。在这些记录中，使用四种不同的方法来计算沉降速率（地表高程表、标记层、使用 210 铅的放射性核素测年以及使用 137 铈作为单一年代标记），并且只有两个岩心具有直接的OC测量值。与本研究中计算的 OCAR 和该地区其他研究相比（Graversen 等人，2022 年;Miller et al.， 2023），我们得出结论，Ouyang 和 Lee （2014） 的结果可能代表了北欧盐沼中 OCAR 的显着高估。
Our results therefore indicate that northern European saltmarshes in fact play a smaller role in global OC accumulation. The results highlight the need for high quality national/regional OC accumulation studies, as the use of current mean global/regional OCAR (Chmura et al., 2003; Ouyang and Lee, 2014) are generating unreliable estimates across some regions; and in the case of GB and northern Europe this appears to have generated a very significant overestimation of the quantity of OC accumulating in these saltmarshes. Such overestimation could potentially result in suboptimal management decisions, undermine the evidence to support GHG emissions accounting, exaggerate natural capital accounts and ultimately weaken the confidence of investors in credible voluntary C markets linked to saltmarsh restoration projects.
因此，我们的研究结果表明，北欧盐沼实际上在全球OC积累中的作用较小。研究结果突出表明，需要高质量的国家/区域OC积累研究，因为使用当前平均全球/区域OCAR（Chmura等人，2003年;Ouyang 和 Lee，2014 年）在某些地区产生了不可靠的估计;就英国和北欧而言，这似乎严重高估了这些盐沼中积累的OC数量。这种高估可能导致次优管理决策，破坏支持温室气体排放核算的证据，夸大自然资本账户，并最终削弱投资者对与盐沼恢复项目相关的可信自愿C市场的信心。
The average OCAR of GB saltmarshes is similar to a recent estimate of carbon sequestration by GB forests (103.5 g C m−2 yr−1; Zellweger et al., 2022) and at the lower end of estimates of sequestration by global forests (110–3605 g C m−2 yr−1; Requena Suarez et al., 2019) and monoculture forestry plantations (90–820 5 g C m−2 yr−1; Bukoski et al., 2022). Estimates of carbon accumulation in forests soils over thousands to tens of thousands of years are lower (Morison et al., 2012; Vanguelova and Pitman, 2010); however, the duration of accumulated OC in GB saltmarshes (typically hundreds of years) makes the comparison with sequestration in living forest biomass more appropriate.
大不列颠盐沼的平均OCAR与最近对大不列颠森林碳封存的估计相似（103.5 g C m −2 yr −1 ;Zellweger et al.， 2022），以及全球森林封存估计值的下限（110-3605 g C m −2 yr −1 ;Requena Suarez et al.， 2019） 和单一栽培林业人工林 （90–820 5 g C m −2 yr −1 ;Bukoski 等人，2022 年）。对森林土壤中数千至数万年碳积累的估计较低（Morison等人，2012年;Vanguelova 和 Pitman，2010 年）;然而，GB盐沼中OC累积的持续时间（通常为数百年）使得与活森林生物量中的封存进行比较更合适。
Annually, the saltmarsh habitat of GB accumulates 170,885 ± 15,974 t CO2eq. It is currently unclear what quantity of the OC accumulating in these marshes is sequestered from the atmosphere (through in situ production) and therefore providing a direct climate mitigation service. In this study, it is estimated that ∼32 % of the OC held within the marsh soils originates from the marine environment (Fig. 5). The other 68 % of the OC that accumulates each year is derived from either the terrestrial environment or in situ production. As we cannot differentiate between these sources of OC, it is not possible to quantify the amount of OC directly sequestered from the atmosphere by the saltmarshes. Rather, we can only highlight that it is an as-yet unknown fraction of the 31,809 ± 3418 t of OC accumulating each year that is derived from terrestrial/in situ sources (Fig. 6B). While the accumulation of allochthonous OC in the saltmarsh soils does not directly equate to CO2 being sequestered from the atmosphere, its storage and preservation in the soils does provide a climate regulation service that should not be overlooked.
每年，大不列颠的盐沼生境积累了170,885±15,974吨一氧化碳 2 当量。目前尚不清楚这些沼泽中积累的OC数量与大气隔离（通过原位生产），从而提供直接的气候缓解服务。在这项研究中，估计沼泽土壤中约32%的OC来自海洋环境（图5）。每年累积的另外68%的OC来自陆地环境或原位生产。由于我们无法区分这些OC的来源，因此无法量化盐沼直接从大气中隔离的OC量。相反，我们只能强调，在每年积累的31,809±3418吨OC中，只有一部分来自陆地/原位来源（图6B）。虽然盐沼土壤中异色OC的积累并不直接等同于CO 2 从大气中隔离出来，但它在土壤中的储存和保存确实提供了不容忽视的气候调节服务。
Increasing the quantity of organic carbon accumulating can enhance the role of saltmarsh habitats in climate mitigation. The most direct way to increase saltmarsh OC accumulation is to increase marsh areal extent (Hudson et al., 2021). In the UK, 220 km2 of coastline has been identified as suitable for realignment to create new saltmarsh habitat to improve flood defence, biodiversity, and climate mitigation services provided by these ecosystems (Marine Management Organisation, 2019; Austin et al., 2022). If this goal was achieved and the saltmarshes reached maturity, we estimate an additional 89,525 t CO2eq yr−1 would accumulate. The small quantities of OC accumulating in GB saltmarshes do not prohibit the inclusion of these environments in national emission reporting (Burden and Clilverd, 2021) and natural capital accounting (Hooper et al., 2019), but when integrating GB saltmarshes into C markets (Friess et al., 2022; Mason et al., 2022), caution must be applied to assure that these markets are viable, considering the low OCARs.
增加有机碳积累的数量可以增强盐沼栖息地在减缓气候变化中的作用。增加盐沼OC积累的最直接方法是增加沼泽面积范围（Hudson等人，2021）。在英国，220 公里 2 的海岸线已被确定为适合重新调整以创造新的盐沼栖息地，以改善这些生态系统提供的防洪、生物多样性和气候缓解服务（海洋管理组织，2019 年;Austin 等人，2022 年）。如果这一目标得以实现，盐沼达到成熟，我们估计每年 −1 将额外积累89,525吨二氧化碳 2 当量。在大不列颠盐沼中积累的少量OC并不禁止将这些环境纳入国家排放报告（Burden和Clilverd，2021）和自然资本核算（Hooper等人，2019年），但在将大不列颠盐沼纳入C市场时（Friess等人，2022年;Mason 等人，2022 年），考虑到 OCAR 较低，必须谨慎行事以确保这些市场是可行的。
While GB saltmarshes only accumulate a small quantity of OC annually (Table 1), this does highlight the importance of the OC already stored in these ecosystems. The OC within the soils of GB saltmarshes equates to 19.1 ± 2.4 Mt. CO2eq (Smeaton et al., 2023). Though not directly comparable, as the OC stores have built up over decades to centuries, it must be recognised that if the OC within these saltmarshes were to be remineralised and released as CO2 to the atmosphere, there would be an appreciable increase in atmospheric CO2 concentrations. While implausible that all GB saltmarshes would be lost simultaneously, these systems are under growing pressure. It has been estimated that there has been an 85 % loss in saltmarsh areal extent in England since the 1800s (Environment Agency, Chief Scientist's Group, 2023) with loss rates of up to 0.4 km2 yr−1 observed in the south of England (Hughes and Paramor, 2004; Ladd et al., 2019). These trends are predicted to continue into the 21st century as a result of rising sea level (Horton et al., 2018). The loss of saltmarsh will result in the release of OC currently stored and, due to the reduction in areal extent and the low OCARs observed in GB systems, any OC lost will not be recoverable (Goldstein et al., 2020). Consequently, it is essential that the OC currently held in the soils of GB saltmarshes is protected; the avoided emissions from the prevention of OC loss is several orders of magnitude more important to global climate than the annual accumulation of OC in these marshes.
虽然大不列颠盐沼每年只积累少量的OC（表1），但这确实凸显了已经储存在这些生态系统中的OC的重要性。GB 盐沼土壤中的 OC 相当于 19.1 ± 2.4 Mt. CO 2 eq（Smeaton 等人，2023 年）。虽然没有直接可比性，因为OC储存已经积累了几十年到几个世纪，但必须认识到，如果这些盐沼内的OC被重新矿化并作为一氧化碳释放 2 到大气中，大气中的一氧化碳 2 浓度将明显增加。虽然难以置信的是，所有大不列颠盐沼都会同时消失，但这些系统正承受着越来越大的压力。据估计，自 1800 年代以来，英格兰的盐沼面积损失了 85%（环境署，首席科学家小组，2023 年），在英格兰南部 −1 观察到的损失率高达 0.4 公里 2 （Hughes 和 Paramor，2004 年;Ladd等人，2019）。由于海平面上升，预计这些趋势将持续到 21 世纪（Horton 等人，2018 年）。盐沼的损失将导致目前储存的OC的释放，并且由于区域范围的减少和GB系统中观察到的低OCAR，任何丢失的OC都将无法恢复（Goldstein等人，2020）。因此，目前保存在大不列颠盐沼土壤中的OC必须得到保护;通过防止OC损失而避免的排放对全球气候的影响比这些沼泽中OC的年积累要重要几个数量级。
The saltmarshes of Great Britain on average accumulate organic carbon at a rate of 110.88 ± 43.12 g C m−2 yr−1, resulting in these marshes annually accumulating 46,563 ± 4353 t of organic carbon.. However, the rate at which these saltmarshes accumulate organic carbon is considerably lower than the global estimates. The organic carbon accumulation rates quantified in this study suggest the role that GB and potentially northern European saltmarshes more generally play in global climate mitigation is less than previously thought and has been overestimated in global and regional compilations and are comparable to sequestration rates in temperate forests. Enhanced understanding of GB saltmarsh OC accumulation rates must be considered if these ecosystems are to be included in emissions reporting, natural capital accounting and carbon markets. Although the small quantity of organic carbon accumulating each year in these systems does not prevent their inclusion into such areas, caution will need to be applied especially when monetising the annual accumulation of organic carbon. The findings of this study further highlight the importance of the significant quantities of organic carbon already stored in these saltmarshes. Preventing the loss (i.e. avoided emissions) of this vulnerable store of organic carbon could be up to several orders of magnitude more important to global climate than the annual accumulation of organic carbon in Great British saltmarshes.
大不列颠的盐沼平均每年积累110.88±43.12克碳 −2 −1 ，导致这些沼泽每年积累46,563±4353吨有机碳。然而，这些盐沼积累有机碳的速度远低于全球估计。本研究中量化的有机碳积累率表明，大不列颠和潜在的北欧盐沼在全球减缓气候变化方面的作用比以前认为的要小，并且在全球和区域汇编中被高估了，与温带森林的封存率相当。如果要将这些生态系统纳入排放报告、自然资本核算和碳市场，就必须考虑加强对大不列颠盐沼OC积累率的了解。虽然这些系统中每年积累的少量有机碳并不妨碍它们被纳入这些领域，但需要谨慎行事，特别是在将有机碳的年度积累货币化时。这项研究的结果进一步强调了这些盐沼中已经储存的大量有机碳的重要性。防止这种脆弱的有机碳储存的损失（即避免排放）对全球气候的影响可能比大不列颠盐沼中每年的有机碳积累要重要几个数量级。
Craig Smeaton: Writing – original draft, Visualization, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. Ed Garrett: Writing – original draft, Visualization, Methodology, Investigation, Formal analysis. Martha B. Koot: Writing – review & editing, Methodology, Investigation, Formal analysis. Cai J.T. Ladd: Writing – review & editing, Investigation, Funding acquisition, Conceptualization. Lucy C. Miller: Writing – review & editing, Methodology, Investigation, Formal analysis. Lucy McMahon: Writing – review & editing, Investigation. Bradley Foster: Investigation. Natasha L.M. Barlow: Writing – review & editing, Supervision, Methodology, Investigation, Funding acquisition, Conceptualization. William Blake: Writing – review & editing, Methodology, Investigation, Formal analysis. W. Roland Gehrels: Writing – review & editing, Supervision, Methodology, Investigation, Funding acquisition. Martin W. Skov: Writing – review & editing, Methodology, Investigation, Funding acquisition, Conceptualization. William E.N. Austin: Writing – review & editing, Methodology, Funding acquisition.
克雷格·斯米顿（Craig Smeaton）：写作 - 原始草稿，可视化，项目管理，方法论，调查，资金获取，形式分析，数据管理，概念化。埃德·加勒特（Ed Garrett）：写作——原始草稿、可视化、方法论、调查、形式分析。Martha B. Koot：写作——审查和编辑、方法论、调查、形式分析。Cai J.T. Ladd：写作 – 审查和编辑、调查、资金获取、概念化。露西·米勒（Lucy C. Miller）：写作——审查和编辑、方法论、调查、形式分析。露西·麦克马洪（Lucy McMahon）：写作 - 审查和编辑，调查。布拉德利·福斯特：调查。Natasha L.M. Barlow：写作——审查和编辑、监督、方法论、调查、资金获取、概念化。威廉·布莱克（William Blake）：写作 - 审查和编辑，方法论，调查，形式分析。W. Roland Gehrels：写作 – 审查和编辑、监督、方法论、调查、资金获取。Martin W. Skov：写作——审查和编辑、方法论、调查、资金获取、概念化。William E.N. Austin：写作 - 审查和编辑，方法论，资金获取。
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
作者声明，该研究是在没有任何可被解释为潜在利益冲突的商业或财务关系的情况下进行的。
This research was financially supported by the Natural Environment Research Council funded Carbon Storage in Intertidal Environments (C-SIDE) project (grant NE/R010846/1) with additional support from the Scottish Blue Forum. Radiocarbon dating was supported by the National Environment Isotope Facility Radiocarbon (Environment) Laboratory (allocation 2351.0321). We would like to thank Dr. Mark Garnett for assisting with the radiocarbon analysis and interpretation. We would like to extend thanks to Glenn Havelock, Robert Mills, Fiona Hibbert, Ash Taylor, Trace Laskey and Luke Andrews from the University of York, Simone Riegel, Heather Austin and Will Hiles from the University of St Andrews, Luis Rees-Hughes from the University of Leeds, Subhasree Mohantym and Joseph Apted from the Bangor University, Geoff Millward (University of Plymouth) and Alan Radbourne from UK CEH for assistance in the field and lab. Further we would like to thank members of Nature Scot, Natural Resources Wales, and Natural England for assisting in gaining the required permissions to access and sample saltmarshes around the country.
这项研究得到了自然环境研究委员会资助的潮间带环境碳储存（C-SIDE）项目（拨款NE / R010846 / 1）的财政支持，并得到了苏格兰蓝色论坛的额外支持。放射性碳测年得到了国家环境同位素设施放射性碳（环境）实验室（分配2351.0321）的支持。我们要感谢 Mark Garnett 博士协助进行放射性碳分析和解释。我们要感谢约克大学的 Glenn Havelock、Robert Mills、Fiona Hibbert、Ash Taylor、Trace Laskey 和 Luke Andrews，圣安德鲁斯大学的 Simone Riegel、Heather Austin 和 Will Hiles，利兹大学的 Luis Rees-Hughes，班戈大学的 Subhasree Mohantym 和 Joseph Apted，普利茅斯大学的 Geoff Millward和英国 CEH 的 Alan Radbourne 在现场和实验室提供的帮助。此外，我们要感谢 Nature Scot、Natural Resources Wales 和 Natural England 的成员协助获得进入和采样全国各地盐沼所需的许可。
Supplementary material
The datasets generated for this study can be found in the Environmental Information Data Centre (www.eidc.ac.uk) and Marine Scotland Data (https://data.marine.gov.scot/). The data includes Miller et al., 2022, Smeaton et al., 2022c and Koot et al., 2023.
本研究生成的数据集可在环境信息数据中心 （www.eidc.ac.uk） 和苏格兰海洋数据 （https://data.marine.gov.scot/） 中找到。数据包括 Miller 等人，2022 年，Smeaton 等人，2022c 和 Koot 等人，2023 年。
（99）00034-7 页 （78）80002-2 （87）90528-6 （95）00054-U （96）00127-1 。SP.2000.175.01.19 
