South Bay, VA, seagrass sediment and autotroph source stable isotope compositions, 2014

Abstract text from Oreska et al. (2017): Non-seagrass sources account for 50% of the sediment organic carbon (SOC) in many seagrass beds, a fraction that may derive from external organic matter (OM) advected into the meadow and trapped by the seagrass canopy or produced in situ. If allochthonous carbon fluxes are responsible for the non-seagrass SOC in a given seagrass bed, this fraction should decrease with distance from the meadow perimeter. Identifying the spatial origin of SOC is important for closing seagrass carbon budgets and "blue carbon" offset-credit accounting, but studies have yet to quantify and map seagrass SOC stocks by carbon source. We measured sediment d13C, d15N, and d34S throughout a large (6 km2), restored Zostera marina (eelgrass) meadow and applied Bayesian mixing models to quantify total SOC contributions from possible autotroph sources, Z. marina, Spartina alterniflora, and benthic microalgae (BMA). Z. marina accounted for <40% of total meadow SOC, but we did not find evidence for outwelling from the fringing S. alterniflora salt-marsh or OM advection from bare subtidal areas. S. alterniflora SOC contributions averaged 10% at sites both inside and outside of the meadow. The BMA fraction accounted for 51% of total meadow SOC and was highest at sites furthest from the bare subtidal-meadow edge, indicative of in situ production.

Oreska等人（2017）的摘要文本如下：在多数海草床中，非海草来源贡献了50%的沉积物有机碳（sediment organic carbon, SOC），该部分碳或来自被海草冠层截留并输入至草甸的外源有机物质（organic matter, OM），亦或是在草甸内原位生成。若某一海草床内的非海草源SOC由异地碳通量主导，则该碳组分占比应随距草甸边缘的距离增加而降低。明确沉积物有机碳的空间来源，对闭合海草碳收支与“蓝碳”（blue carbon）抵消信用核算均具有重要价值，但目前尚无研究依据碳源类型对海草床SOC储量进行量化与空间制图。
本研究在一片面积达6 km²的修复型大叶藻（Zostera marina, 鳗草）草甸中，测定了沉积物的碳同位素比值δ¹³C、氮同位素比值δ¹⁵N及硫同位素比值δ³⁴S，并运用贝叶斯混合模型，量化了三类潜在自养生物源对总SOC的贡献：大叶藻、互花米草（Spartina alterniflora）以及底栖微藻（benthic microalgae, BMA）。
结果显示，大叶藻对草甸总SOC的贡献占比不足40%，但未发现来自边缘互花米草盐沼的碳外输，或是裸露潮下带区域有机物质平流输入的相关证据。互花米草对SOC的贡献在草甸内外的采样点中平均占比均为10%。底栖微藻贡献了草甸总SOC的51%，且在距裸露潮下带-草甸边界最远的采样点中占比最高，这表明其贡献主要来源于原位生产。