滨海滩涂土壤磷吸附解吸特征及其对覆被变化/盐分动态的响应

Phosphorus plays a key role in the stability of coastal ecosystem. However, anthropogenic activities such as reclamation and leaching/ desalination have altered the land-use pattern of coastal tidal flat, which might have changed the biogeochemical processes of phosphorus at the land-sea interface, and then greatly affect the ecological function of coast, but the processes and mechanism are still unclear. In this project, we choose the typical coastal tidal flat in Yancheng as our study area, and the soils of pristine vegetation successions (intertidal mudflat, Spartina alterniflora flat, Suaeda salsa flat, and Phragmites communis flat) and reclaimed coastal tidal flat (barren land, farmland, and woodland) as research subjects, and phosphorus adsorption/desorption on water-soil interface as the key biogeochemical process to study the mechanism of influence of anthropogenic activities on the key biogeochemical processes of phosphorus, through conducting experiments of adsorption/desorption simulation and soil column leaching/desalination. The main research contents are as follows: 1) the changes of phosphorus fractions, adsorption/desorption characteristics as well as the key factors controlling these variables before and after reclamation; 2) the differences of adsorption/desorption behaviors under various salinity gradients; 3) the responses of phosphorus adsorption/desorption characteristics to land cover change and salt dynamics. Our results will offer scientific proof for protecting and rationally exploiting coast, considering both land demand and sustainable ecological function of coastal zones.

围垦造田/淋洗脱盐等人类活动改变了滨海滩涂土地利用格局，驱动了磷等生源要素在陆-海界面生物地球化学过程的变化，进而影响了整个滨海生态系统的稳定。然而关于人类活动对滨海滩涂磷关键生物地球化学过程的影响强度和机制目前尚缺乏系统的实验研究。本项目选择盐城地区典型滨海滩涂，以原生植被演替带（光滩、互花米草滩、碱蓬滩、芦苇滩）和围垦造田（荒地、耕地、林地）后土壤为对象，水土界面吸附、解吸为关键生物地球化学过程，采用吸附、解吸模拟和土柱淋洗脱盐实验，通过分析：1）磷赋存形态、吸附、解吸特征及其物理化学控制因子在围垦前、后的变化；2）不同脱盐水平下磷吸附、解吸行为的差异；3）磷吸附、解吸特征参数与覆被变化/盐分动态的响应关系，揭示人类活动对滨海滩涂磷关键生物地球化学过程的影响机制。为保护与合理开发滨海滩涂资源，寻求兼顾土地需求与海岸生态保护的可持续发展之路提供基础依据。

滨海滩涂土地利用/覆被变化主要由辐射沙洲转化为原生滩涂的自然演化过程和由原生滩涂转化为农田的人为演化过程（围垦造田）两部分组成。为分析围垦等人类活动对滩涂磷关键生物地球化学过程的影响强度和机制，采用空间换时间的方式，以辐射沙洲、滩涂原生植被演替、围垦农田土壤为研究对象，分析了磷吸附解吸特征、赋存形态、生物可用磷在滩涂自然演化和人为演化以及不同脱盐水平下的变化。.结果发现：.1）滩涂自然演化和人为演化过程均可使土壤理化性质发生显著改变，总体上自然演化的影响远高于人为演化，滩涂发展到原生植被演替阶段，主要物化性质和土壤质量已接近农田。.2）自然演化过程促进了磷吸附容量的快速升高，并显著降低了解吸率和磷释放风险；而围垦导致的人为演化过程对磷吸附容量和解吸率影响不大，但可导致磷吸附阈值和饱和度上升，磷释放风险显著提高。.3）自然演化过程不影响总磷、无机磷含量与分布，而人为演化则可显著提高总磷含量和有机磷赋存比例。两者均可显著提高活性磷组分和生物可用磷含量，相比而言，人为演化提高幅度远高于自然演化过程。.4）原生滩涂内部植被演替也对磷行为具有显著影响。随着滩涂植被的正向演化，磷吸附容量升高，吸附阈值、解吸率、活性磷组分、生物可用磷及释放风险均显著下降，滩涂植被的正向演化有助于磷的吸附固定，降低磷风险。.5）围垦脱盐时间对磷行为具有显著影响。吸附容量随脱盐时间逐渐降低，饱和度和释放风险则逐渐升高，三者在脱盐40年后均趋于稳定。吸附阈值和生物可用磷在脱盐40年达到峰值。围垦脱盐40年左右可能是磷行为转化的关键阶段。.6）单纯淋洗不改变滩涂土壤的磷吸附容量、吸附阈值和赋存形态，但可使磷饱和度和释放风险显著下降。.7）在滩涂土地利用/覆被变化过程中土壤粘粒是磷吸附解吸、赋存形态变化的主要驱动力，盐度等起到辅助作用。.以上研究结果为认识人类活动对滩涂生源要素的影响过程，保护与合理开发滩涂资源提供了一定依据。