压实作用下广西典型红树林区沉积速率及海平面上升对红树林迁移效应的制衡

Sediment Compaction Rates in Mangrove Swamps of Guangxi and Its Mangrove Migration Response to Sea-level Rise

气候变化造成的海平面上升是迫使红树林向陆迁移的主要驱动力,而其自身通过捕沙促淤不同程度的减缓了海平面上升速率的影响。基于广西典型红树林区8根短柱的210Pb测年和含水率分析,以考虑/未考虑沉积物压实作用为研究情景,通过对比研究红树林区潮滩地表高程抬升速率和相对海平面上升速率的大小关系,揭示当前海平面上升对广西红树林向陆/向海迁移的驱动机制。研究发现:未考虑压实作用下的沉积速率约是考虑压实作用下沉积速率的1.00~1.34倍(平均1.12倍),压实作用明显;压实沉积速率介于0.16~0.78 cm/a,其底层压实沉积速率与潮滩地表高程抬升速率相等。压实作用下,英罗湾和丹兜海红树林区的地表高程抬升速率小于相对海平面上升速率;与未考虑压实作用得到的结论相悖。由于广西红树林海岸大都建有防波堤,限制了红树林向陆的迁移;表明英罗湾和丹兜海的红树林正面临海平面上升的威胁。压实作用校正与否对地表高程抬升速率与相对海平面上升速率相当的区域尤为重要。

Rising sea levels caused by climate change is the major driving force in landward migration of mangrove communities,and its overlying plants can slow down the rate of sea-level rise deriving from sediment trapping. In the paper,six sediment cores were collected from the typical mangrove swamps in Guangxi,China. Based on moisture contents and210 Pb analysis,the average sedimentary rates were calculated using the CIC model in different cases of considering / no-considering sediment compaction. Compared between the rate of regional sea-level rise and the sedimentary rates,it reveals the relationship of landward mangrove migration in response to relative sea-level rise. The sediment compaction rates are between 0.16 ~ 0.78 cm / a,but no-considering sediment compaction rates are approximately 1.00 ~ 1.34 times( mean 1. 12 times) more than the rates of sediment compaction. The sediment compaction rates are lower than the rate of regional sea-level rise in mangrove swamps of Yingluo Bay and Dandou Sea,however,the sediment compaction rates are obviously higher in the Maowei Sea. Owing to the seawall preventing the landward mangrove migration,the mangrove plants are currently under threat from sea-level rise in the Yingluo Bay and Dandou Sea. It is obviously different with previous reports. Taking no account of sediment compaction,the sediment rates were be overestimated in the recent studies.