茅尾海钦江河口光滩时空变化过程研究

Spatial-temporal variations of bare flats in the Qinjiang River estuary,Maowei Sea

河口潮滩一般由生长于中高潮滩的植被和植被前缘光滩(裸滩)构成,光滩的时空变化直接关联潮滩冲淤及植被演替状态。本文基于Landsat 5 TM及Sentinel-2 MSI等多期遥感影像,利用随机森林分类算法与数字岸线分析系统探讨茅尾海钦江河口光滩在1986—2021年期间的变化过程。结果表明:①近40年钦江河口光滩面积总体呈现明显损失的状态,可分为1986—2002年冲淤平衡、2002—2007年快速淤积、2007—2014年急剧降低和2014—2021年缓慢淤涨4个阶段;②光滩淤积的区域主要分布于钦江沙井河口口门及内侧河槽与潮汐通道边缘,侵蚀出现在钦江沙井河口及钦江沙冲河口航道及潮沟区域;③茅尾海清淤工程是引起钦江河口光滩自2008年到2014年面积减少的直接因素,潮间带植被扩张和2015年之后大范围生蚝养殖引起的水动力减弱导致光滩向海淤涨。当前海平面上升未对光滩造成明显影响,但入海泥沙的变化一定程度上影响光滩冲淤演变。本研究可为区域河口潮滩资源的可持续高效利用提供部分理论与技术支撑。

Estuarine tidal flats generally consist of vegetated wetlands in upper-middle intertidal zones and fringed bare flats in middle-lower intertidal zones.Spatial-temporal variations of bare flats directly regulate geomorphic erosions-accretions and vegetation successions of the whole tidal flats.Based on multi-satellite remote sensing imageries from Landsat 5/8 TM/OLI and Sentinel-2 MSI collections,random forest classification algorithm and Digital Shoreline Analysis System were used to examine the variations and characteristics of bare intertidal flats in the Qinjiang River estuary(QRE),Maowei Sea(MWS)of Beibu Gulf in 1986—2021.Results indicate that,(1)the overall area of bare flats in the QRE has shown obvious losses during the past four decades,which can be divided into four stages:maintained equilibrium of erosion-accumulation between 1986—2002,accumulated rapidly between 2002—2007,declined sharply between 2007—2014 and slowly deposited between 2014—2021.(2)Tidal flat accretions distributed mainly in the secondary Shajing outlet(SJO)and its inner channel of the QRE along the edges of tidal channels,while erosions occurred in the secondary SJO,Shachong outlet(SCO)and inner tidal channels.(3)Dredging projects in the MWS were the direct driven force that triggered the losses of bare intertidal flats in the QRE from 2008 to 2014,and the expansions of intertidal vegetation and weakened hydrodynamics followed by extensive oyster cultivations after 2015 caused seaward progradation of the bare flats.In addition,the modern sea-level rise has not significantly affected the dynamics of bare flats,and the losses were partly due to the reduced riverine suspended sediment load into the MWS.This study provided theoretical and technical supports for the sustainable and efficient utilizations of estuarine tidal flats.