Table_3_Sediment Stocks of Carbon, Nitrogen, and Phosphorus in Danish Eelgrass Meadows.DOCX

Seagrass ecosystems provide an array of ecosystem services ranging from habitat provision to erosion control. From a climate change and eutrophication mitigation perspective, the ecosystem services include burial and storage of carbon and nutrients in the sediments. Eelgrass (Zostera marina) is the most abundant seagrass species along the Danish coasts, and while its function as a carbon and nutrient sink has been documented in some areas, the spatial variability of these functions, and the drivers behind them, are not well understood. Here we present the first nationwide study on eelgrass sediment stock of carbon (Cstock), nitrogen (Nstock), and phosphorus (Pstock). Stocks were measured in the top 10 cm of eelgrass meadows spanning semi-enclosed estuaries (inner and outer fjords) to open coasts. Further, we assessed environmental factors (level of exposure, sediment properties, level of eutrophication) from each area to evaluate their relative importance as drivers of the spatial pattern in the respective stocks. We found large spatial variability in sediment stocks, representing 155–4413 g C m-2, 24–448 g N m-2, and 7–34 g P m-2. Cstock and Nstock were significantly higher in inner fjords compared to outer fjords and open coasts. Cstock, Nstock, and Pstock showed a significantly positive relationship with the silt-clay content in the sediments. Moreover, Cstock was also significantly higher in more eutrophied areas with high concentrations of nutrients and chlorophyll a (chl a) in the water column. Conversely, silt-clay content was not related to nutrients or chl a, suggesting a spatial dependence of the importance of these factors in driving stock sizes and implying that local differences in sediment properties and eutrophication level should be included when evaluating the storage capacity of carbon, nitrogen, and phosphorus in Danish eelgrass meadows. These insights provide guidance to managers in selecting priority areas for carbon and nutrient storage for climate- and eutrophication mitigation initiatives.

海草生态系统可提供一系列生态系统服务，涵盖栖息地供给与海岸侵蚀防控等范畴。从气候变化与富营养化减缓的视角来看，此类生态系统服务还包括将碳与养分埋藏并储存在沉积物中。鳗草（Zostera marina）是丹麦沿岸分布最广泛的海草物种，尽管其作为碳与养分汇的功能已在部分区域得到证实，但此类功能的空间变异特征及其背后的驱动机制尚未得到充分解析。本研究开展了丹麦首个全国性鳗草沉积物碳储量（Cstock）、氮储量（Nstock）与磷储量（Pstock）调查：研究团队在覆盖半封闭河口（内峡湾与外峡湾）至开阔海岸的鳗草草床中，对其0~10 cm表层沉积物开展了储量测定。此外，研究人员针对每个采样区域评估了环境因子（暴露水平、沉积物属性与富营养化程度），以解析各类因子对各储量空间分布格局的相对贡献强度。结果显示，沉积物储量存在显著空间变异，碳储量范围为155~4413 g C m⁻²，氮储量为24~448 g N m⁻²，磷储量为7~34 g P m⁻²。内峡湾的碳储量与氮储量显著高于外峡湾与开阔海岸区域。碳、氮、磷储量均与沉积物中的粉砂-黏土含量呈显著正相关关系。此外，水体中养分与叶绿素a（chl a）浓度较高的富营养化程度更高的区域，其碳储量同样显著更高。与之相反，沉积物粉砂-黏土含量与水体养分及chl a并无显著关联，这表明两类驱动因子对储量的影响强度存在空间依赖性；同时提示，在评估丹麦鳗草草床的碳、氮、磷储存能力时，应纳入沉积物属性与富营养化程度的区域差异。本研究结果可为管理者遴选碳与养分储存优先区域提供科学依据，以支撑气候变化与富营养化减缓相关行动的开展。