Habitat Suitability Assessments Under The Impact Of Coastline And Topographical Alteration In The Pearl River Estuary

As the heart of the land-sea interface,estuaries are among the most biologically productive areas and are often an important base for socio-economic development.60%of the world’s population and 70%of the world’s cities are located in estuaries.In order to meet the needs of urbanization and industrialization,a large number of anthropogenic activities(e.g.hydraulic engineering,polder farming,industrial production,port construction)are carried out that depend on the rich natural resources and environmental conditions of the estuary,and at the same time can bring about serious pressures and negative effects on the estuary,leading to the destruction of the ecosystem and the reduction or even disappearance of biological habitats.At present,a number of studies have been carried out on the ecological flow of estuaries in relation to changes in freshwater input caused by hydraulic projects,resulting in changes in estuarine hydrodynamic and water quality conditions,which in turn affect habitat suitability for organisms.Among these,the habitat simulation method has received keen attention from experts in hydraulics and ecology and has developed a mature theoretical framework and basic methodology.However,current studies are less likely to take the changes in the estuarine coastline and topography created by anthropogenic activities as a starting point and explore their possible effects on the suitability of biological habitats based on numerical simulations of the hydrodynamic-water quality model coupled with fuzzy.Therefore,this paper takes the Pearl River Estuary(PRE)with high-intensity anthropogenic activities as the research object,uses RS and GIS technology to analyze the evolution of coastline change and underwater topography in the Pearl River Estuary,and sets up different coastline and topography change scenarios,constructs the corresponding coupled hydrodynamic-water quality model to obtain the spatial and temporal distribution characteristics of the hydrodynamic-water quality conditions under the coastline and topographic changes of the estuary.Finally,an evaluation model of biological habitat suitability was established based on the fuzzy logic method combined with landscape structure analysis,and the spatial distribution,weighted usable area,and fragmentation degree of typical biological habitats in the Pearl River Estuary were analyzed to investigate the influence mechanisms of the coastline and topographic changes on biological habitat suitability in the Pearl River Estuary.The results of the study have important implications for estuarine coastal urban development planning and estuarine biodiversity conservation,and can also provide references for relevant habitat evaluation in other estuarine areas affected by high-intensity anthropogenic activities.The main findings are as follows:1.Under the influence of high-intensity anthropogenic activities,the coastline of the Pearl River Estuary has changed significantly,with the underwater topography showing a characteristic of"shallow shoals becoming shallower and the deep troughs becoming deeper".In the last 30 years,the length of the coastline of the PRE has increased by74.813km and the land area has increased by 679.253km~2.As of 2017,the proportion of artificial coastlines has reached 80.90%,while the proportion of natural coastlines is only19.10%.Most of the water depths in the West and East Shoals areas of the PRE are shallower than 4m,with maximum water depths of over 20m in the West and East Troughs areas,and many sand pits with water depths of over 10m occurring near Inner Lingding Island in the Middle Shoal area.Among them,the reduction in the amount of inlet sand caused by the construction of water conservancy projects is the main reason for the contraction of the natural coastline in the PRE;while urbanization and agricultural reclamation are the main reasons for the expansion of the artificial coastline on the east and west coasts respectively;sand mining and dredging are the main reasons for the deepening of the underwater topography in the"two troughs"of the PRE and near Inner Lingding Island.2.In this paper,based on the coastline and topographic data in different periods,a series of coupled hydrodynamic-water quality models were constructed based on the MIKE 21 FM platform to simulate the spatial and temporal variation characteristics of hydrodynamic-water quality in the estuary under different coastline and topographic conditions.The results show that the spatial-temporal distributions of the hydrodynamics and water quality in the PRE are affected to some extent by changes in the estuarine coastline and topography.Specifically,with the change in topographic conditions,the tidal levels at stations such as Shanbanzhou,Neilingding Island,Zhuhai Xiangzhou,Shenzhen Airport,Guishan Island,and Dong’ao Island were were relatively insignificant..There is a large variation in flow velocity in the West and East Troughs areas,less variation in flow velocity in the West and East Shoals areas,and a significant shift in flow direction in the West,Middle and East Troughs areas,central and eastern troughs.From the simulation results of salinity and water temperature,the saline water intrusion in the PRE tends to be obvious due to the influence of coastline and topographic changes,while the water temperature in the estuary is relatively limited by the influence.3.By analyzing the biological data obtained from fieldwork and literature,six dominant species and economically important species of the PRE(Scylla paramamosain,Coilia mystus,Exopalaemon carinicauda,Collichthys lucidus,Metapenaeus ensis and Portunus sanguinolentus)were selected as objects for evaluation,considering the key life histories of the species such as reproductive and juvenile stages,and selecting water depth,temperature and salinity as key environmental factors affecting the habitat,and constructing an evaluation model for the suitability of typical biological habitats under different coastline and topographic conditions.The results show that the spatial pattern of the area of suitable habitat for typical estuarine organisms has changed significantly under the influence of morphological changes in the PRE.Specifically,from 1987 to 2017,the higher suitability habitat for all six typical species extended northwards along the river;the weighted usable areas all showed a decreasing trend from 1987 to 2010,and a significantly increasing trend in 2017 compared with the previous period.Higher suitability habitat fragmentation increased for species adapted to very shallow depths and low salinities(e.g.Scylla paramamosain),shallow depths and low salinities(e.g.Coilia mystus,Exopalaemon carinicauda)and medium depths and high salinities(e.g.Collichthys lucidus),while higher suitability habitat fragmentation improved for species adapted to high depths and high salinities(e.g.Metapenaeus ensis,Portunus sanguinolentus).In addition,the magnitude of changes in the area of suitable habitat for the typical species under changes in the coastline and topographic of the estuary and changes in the gradient of the inlet flow were further compared,and the results showed that coastline and topographic changes had a greater impact on the area of suitable habitat for the above organisms than changes in inlet flow.