Seagrass meadows store globally significant organic carbon (C_org) stocks which, if disturbed, can lead to CO₂ emissions, contributing to climate change. Eutrophication and thermal stress continue to be a major cause of seagrass decline worldwide, but the associated CO₂ emissions remain poorly understood. This study presents comprehensive estimates of seagrass soil C_org erosion following eutrophication‐driven seagrass loss in Cockburn Sound (23 km² between 1960s and 1990s) and identifies the main drivers. We estimate that shallow seagrass meadows (<5 m depth) had significantly higher C_org stocks in 50 cm thick soils (4.5 ± 0.7 kg C_org/m²) than previously vegetated counterparts (0.5 ± 0.1 kg C_org/m²). In deeper areas (>5 m), however, soil C_org stocks in seagrass and bare but previously vegetated areas were not significantly different (2.6 ± 0.3 and 3.0 ± 0.6 kg C_org/m², respectively). The soil C_org sequestration capacity prevailed in shallow and deep vegetated areas (55 ± 11 and 21 ± 7 g C_org m⁻² year⁻¹, respectively), but was lost in bare areas. We identified that seagrass canopy loss alone does not necessarily drive changes in soil C_org but, when combined with high hydrodynamic energy, significant erosion occurred. Our estimates point at ~0.20 m/s as the critical shear velocity threshold causing soil C_org erosion. We estimate, from field studies and satellite imagery, that soil C_org erosion (within the top 50 cm) following seagrass loss likely resulted in cumulative emissions of 0.06–0.14 Tg CO_2‐eq over the last 40 years in Cockburn Sound. We estimated that indirect impacts (i.e. eutrophication, thermal stress and light stress) causing the loss of ~161,150 ha of seagrasses in Australia, likely resulted in the release of 11–21 Tg CO_2‐eq since the 1950s, increasing cumulative CO₂ emissions from land‐use change in Australia by 1.1%–2.3% per annum. The patterns described serve as a baseline to estimate potential CO₂ emissions following disturbance of seagrass meadows.

中文翻译：

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自20世纪中叶以来海草的损失加剧了土壤碳储量的二氧化碳排放量。

海草草甸在全球范围内存储大量的有机碳（C _org）储备，如果受到干扰，会导致CO ₂排放，从而导致气候变化。富营养化和热应激仍然是全世界海草数量下降的主要原因，但是与之相关的CO ₂排放仍然知之甚少。这项研究提出了在Cockburn Sound（1960年代至1990年代之间23 km ²）富营养化驱动的海草流失后海草土壤C _org侵蚀的综合估计，并确定了主要驱动力。我们估计，在50 cm厚的土壤中（4.5±0.7 kg C _org / m ²）浅海草草甸（深度小于5 m）的C _org储量明显较高。）比以前的植被（0.5±0.1 kg C _org / m ²）高。然而，在更深的地区（> 5 m），海草和裸露但先前已植被的地区的土壤C _org储量没有显着差异（分别为2.6±0.3和3.0±0.6 kg C _org / m ²）。土壤C _org的固存能力主要分布在浅植物区和深植被区（分别为55±11 g C _org  m - ² 年- ¹年和21±7 g C _org m - ²年^-1），而在裸露的地区则消失了。我们发现仅海草冠层损失并不一定驱动土壤C _org的变化。但是，当结合高动能时，就会发生严重的侵蚀。我们的估计值约为0.20 m / s，它是引起土壤C _org侵蚀的临界剪切速度阈值。通过实地研究和卫星图像，我们估计，海草流失后土壤C _org侵蚀（在顶部50厘米以内）很可能导致了过去40年里，库克本峡的累积排放量为0.06-0.14 Tg CO _2当量。我们估计，间接影响（即富营养化，热应力和光应力）在澳大利亚造成约161,150公顷海草损失，很可能导致1950年代以来释放11–21 Tg CO _2当量，从而增加了累积CO ₂澳大利亚土地利用变化带来的排放每年增加1.1％–2.3％。所描述的模式用作基线，以估计海草草甸受到干扰后的潜在CO ₂排放。