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The biogeomorphologic effect of forest edge on the sediment transportation and carbon accumulation along the mangrove coast of Leizhou Peninsula, southern China
Received:May 24, 2013  Revised:January 10, 2014
Key words:mangroves  edge effect  grain properties  Leizhou Peninsula
中文关键词:  红树林,边缘效应,粒度特征,雷州半岛
Author NameAffiliationAddress
yangjuan* 中国地质大学(北京)海洋学院 北京市海淀区学院路29号中国地质大学(北京)海洋学院
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      Mangroves play an important role in sequestrating carbon and trapping sediments. But the effectiveness of such functions is unclear due to the restriction of knowledge on sedimentation process across the vegetation boundaries. In this paper, the edge effects of mangrove forests on sediment transportation and long term sedimentation processes are compared by investigating 4 typical mangrove distribution sites along the coast of Leizhou Peninsula. Surface and core sediments were collected for grain size analysis and organic carbon content test. The results showed that the grain size spectrum of surface sediments are dominated by fine and poorly sorted grains with insignificant differences among different vegetation subzones. However the decrease in energy condition from the mudflat zone to the interior zone is highlighted by the cumulative frequency curve of FC and TC surface samples, where energy condition driven by marine action is relatively strong. Due to the friction caused by vegetation on water movement and contribution of mangrove debris, the interior surface sediments contain a significantly higher concentration (1.64±0.79%) of TOC (total organic carbon) and organic carbon density (13.95±6.51 g/m3) than the mudflat sediments regardless of locations. In contrast, the moment and graphic parameters of core sediments reflect the textual facies range widely from sand to mud, resulting from different sedimentation processes under specific hydrogeomorphic settings. The sedimentary environments are generally controlled by fluvial and shallow marine forces under comparatively low to moderate low energy conditions. Fluvial deposition force decreases from TM (riparian mangroves), via GQ and FC(estuarine mangroves), to TC (tidal mangroves). In response, the highest TOC was preserved under the stable and relative weak energy conditions, like TM (riparian mangroves), while low TOC with dominant mangrove derived organic carbon stored in the tidal mangrove sediments, like TC (tidal mangroves).
      红树林在固碳和捕集沉积物中发挥了重要作用。但是,由于缺乏植被林缘沉积过程的深入认识,这些功能的有效性目前还不清楚。本文通过调查雷州半岛沿岸4个典型的红树林分布点,对收集的表层和柱状沉积物进行粒度分析和有机碳含量测试,比较了红树林林缘对泥沙输移和沉积过程的边缘效应。结果表明,表层沉积粒径谱主要以细粒为主,分选较差,不同的植被亚带之间的差异不显著。然而,从光滩带到植被中心带的输移动力的减弱,在能量条件相对强的FC和TC地点的表层沉积物粒径分布累计频率曲线上表现较突出。由于植被对水流的阻力和自身碎屑的贡献,植被中心带的表层沉积物均比光滩带含有显著较高TOC(总有机碳)含量(1.64±0.79%)和有机碳密度(13.95±6.51 g/m3)。比较而言,由于特定的水文地貌下不同的沉积过程,柱状沉积物粒径参数反映出沉积相的变化范围很宽,从砂到泥。沉积环境主要由相对较低到低的能量条件下河流和浅海作用控制。河流的沉积驱动从TM(河岸红树林),经GQ和FC(河口红树林)至TC(潮汐红树林)递减。相应的,沉积物中最高的TOC含量保存在稳定和相对较弱的能量条件下,如TM(河岸红树林),而较低的TOC含量,主要来源于红树林的有机碳储存于潮汐红树林沉积物中,如调查点TC。
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