Ewers Lewis Carolyn J, Baldock Jeffrey A, Hawke Bruce, Gadd Patricia S, Zawadzki Atun, Heijnis Henk, Jacobsen Geraldine E, Rogers Kerrylee, Macreadie Peter I
School of Life and Environmental Sciences, Centre for Integrative Ecology, Deakin University, 221 Burwood Highway, Burwood, Victoria 3125, Australia.
Commonwealth Scientific and Industrial Organisation, Agriculture and Food, PMB 2, Glen Osmond, South Australia 5064, Australia.
Sci Total Environ. 2019 Jul 1;672:427-437. doi: 10.1016/j.scitotenv.2019.03.345. Epub 2019 Mar 25.
Tidal marsh ecosystems are among earth's most efficient natural organic carbon (C) sinks and provide myriad ecosystem services. However, approximately half have been 'reclaimed' - i.e. converted to other land uses - potentially turning them into sources of greenhouse gas emissions. In this study, we applied C stock measurements and paleoanalytical techniques to sediments from reclaimed and intact tidal marshes in southeast Australia. We aimed to assess the impacts of reclamation on: 1) the magnitude of existing sediment C stocks; 2) ongoing C sequestration and storage; and 3) C quality. Differences in sediment horizon depths (indicated by Itrax-XRF scanning) and ages (indicated by lead-210 and radiocarbon dating) suggest a physical loss of sediments following reclamation, as well as slowing of sediment accumulation rates. Sediments at one meter depth were between ~2000 and ~5300 years older in reclaimed cores compared to intact marsh cores. We estimate a 70% loss of sediment C in reclaimed sites (equal to 73 Mg C ha), relative to stocks in intact tidal marshes during a comparable time period. Following reclamation, sediment C was characterized by coarse particulate organic matter with lower alkyl-o-alkyl ratios and higher amounts of aromatic C, suggesting a lower extent of decomposition and therefore lower likelihood of being incorporated into long-term C stocks compared to that of intact tidal marshes. We conclude that reclamation of tidal marshes can diminish C stocks that have accumulated over millennial time scales, and these losses may go undetected if additional analyses are not employed in conjunction with C stock estimates.
潮间带湿地生态系统是地球上最有效的天然有机碳汇之一，并提供多种生态系统服务。然而，大约一半的潮间带湿地已被“开垦”，即转变为其他土地用途，这可能使其成为温室气体排放源。在本研究中，我们对澳大利亚东南部已开垦和完整潮间带湿地的沉积物进行了碳储量测量和古分析技术研究。我们旨在评估开垦对以下方面的影响：1）现有沉积物碳储量的大小；2）持续的碳固存和储存；3）碳质量。沉积物层深度（通过Itrax-XRF扫描显示）和年龄（通过铅-210和放射性碳测年显示）的差异表明，开垦后沉积物出现了物理损失，沉积物积累速率也有所减缓。与完整湿地岩芯相比，开垦岩芯中一米深处的沉积物年龄大约在2000年至5300年之间。我们估计，与同期完整潮间带湿地的碳储量相比，开垦地点的沉积物碳损失了70%（相当于73 Mg C/公顷）。开垦后，沉积物碳的特征是粗颗粒有机物，其烷基-氧-烷基比率较低，芳香碳含量较高，这表明与完整潮间带湿地相比，其分解程度较低，因此被纳入长期碳储量的可能性也较低。我们得出结论，潮间带湿地的开垦会减少在数千年时间尺度上积累的碳储量，如果在碳储量估计中不采用额外分析，这些损失可能无法被发现。
