Suitability Assessment Of Returning Mariculture Ponds To Mangrove In The Intertidal Zone Of China Target At Mangrove Restoration

Returning mariculture ponds to mangrove forest was one of the important ways for mangrove ecological restoration.How to scientifically predict the potential maximum ecologically-suitable areas for rebuilding mangrove forest and carry out reconstruction efficiently is an urgent task to be solved.Based on remote sensing monitoring of mangrove changes,a set of feasibility assessment system for converting abandoned aquaculture ponds in intertidal zone into mangrove restoration land was proposed and applied in five coastal provinces of China,including Zhejiang,Fujian,Guangdong,Guangxi and Hainan.Based on the study on spatio-temporal trend of mangroves,the spatial distribution of mangroves and major landscape metrices(forest area,patch number,patch density,maximum patch index and shape index)were quantitatively analyzed.The spatial distribution and area of abandoned mariculture ponds in study area were obtained by using similar slope angle principle and visual interpretation method based on remote sensing images and tidal data.In addition,Maxent model evaluation system was established to identify the dominating environmental factors affecting the growth of mangroves and classify habitat suitability level of abandoned ponds for planting mangroves into four categories.The main environmental variables affecting the distribution of mangroves in the study area were bioclimate variables,where temperature,precipitation,topography,and salinity were the dominating influential factors.Six environmental factors,including the mean temperature in warmest season,the monthly mean sea surface temperature,mean temperature in the wettest season,rainfall in the coldest season,DEM,and the average salinity of surface seawater,were selected as main influencing factors for mangrove growth.The results showed that:(1)During the past 46 years from 1973 to 2019,the area of mangroves in the five provinces showed a trend of decreasing at first and then increasing.During the periods of 1973-1993,the mangrove area decreased significantly from 45811 hm~2 to 16705 hm~2.Afterwards,the ecosystem services of mangrove were gradually recognized,and a serial of restoration projects were carried out in coastal areas,resulting in an added 7062 hm~2 of mangroves since 1990s.However,the mangrove patches density increased significantly,while the maximum patch area decreased year by year,indicating that the mangrove forests were more fragmentated.Moreover,the patch shape index of mangrove increased,showing that the patches of mangrove tended to more irregular.Finally,mariculture is one of the main factors leading to the reduction of mangrove area.(2)The average temperature in warmest season greater than or equal to27.80℃is the suitable ranges of temperature for the growth of coastal mangroves.The suitable range of monthly mean sea surface temperature is26.44～27.66℃with the most suitable value of 27.00℃;while the suitable range of the average temperature in the wettest season is 28.36～28.85℃with the optimum value of 28.47℃.Meanwhile,the suitable rainfall range in the coldest season is 97.02～118.97mm with the optimum rainfall value of 114.46 mm,while the suitable range of elevation dem is-4.38～6.62 m with the optimum value of-0.72 m.Finally,the suitable range of monthly average salinity of surface seawater is 31.50‰～32.50‰.(3)According to the output results of Maxent model,the area of abandoned mariculture ponds for mangrove restoration planting with high,medium and low suitable level is 844 hectares,765 hectares,and 2059 hectares respectively,totaling 3668 hectares in the five coastal provinces of China,accounting for 21%of the total area of abandoned aquaculture ponds in the intertidal zone.The areas with medium and high suitable level in Zhejiang,Fujian,Guangdong,Guangxi and Hainan provinces were 0,286,392,754 and 131 hectares respectively,accounting for 0%,11%,57%,100%and 59%of the total area of abandoned mariculture ponds in intertidal zone of each province respectively.The framework proposed in this study for evaluating habitat suitability of abandoned mariculture ponds for restoring mangrove forests provided valuable information in scientifically determining the suitable restoration areas of mangrove target at improving the overall quality of mangrove ecosystem.