| Wetland ecosystems play an important role in maintaining climate stability,sustaining biodiversity,and serving human livelihoods.However,increasing anthropogenic activities are continuously threatening the sustainability of global freshwater ecosystems,and there is urgent need to conduct studies related to quantifying the impacts of anthropogenic activities on freshwater ecosystems.In the past 20 years,sand mining has significantly affected the wetland landscape and Yangtze finless porpoise habitats of Poyang Lake,but the existing studies lack quantitative analysis to guide targeted ecosystem conservation and restoration measures.In this study,support vector machine(SVM)and suspended sediment concentration(SSC)inversion methods were used to identify sand mining vessels and determine the impact areas of sand mining based on US landsat images from 2000 to 2020.Subsequently,the spatiotemporal distribution of sand mining vessels was ananlyzed by standard deviation ellipses,and the landscape index was used to explore the changes of wetland landscape in the area affected by sand mining.Based on the habitat distribution data of Yangtze finless porpoise(Neophocaena asiaeorientalis asiaeorientalis)of Poyang Lake,the direct impact of sand mining on the habitat and the indirect impact of underwater noise from sand mining vessels were analyzed by sand mining vessel movement distance and sound propagation model.With the aim to serve the formulation anthropogenic activities control measures and the conservation of Yangtze finless porpoise,and provide research methods for other basins threatened by sand mining.The main conclusions are:(1)The number of sand mining vessels increased from 2000 to 2016 but rapidly decreased from 2017 to 2020,with multi-year average of 427,419 and 345 vessels in the flood,normal and dry seasons,respectively.Sand mining vessels were mainly distributed in the northern channel from 2000 to 2006,moved toward the center of the lake from 2007 to 2010,then moved northward in 2017.The sand mining vessels of southern lake multi-year average proportion under different seasons were 0.12(51vessels),0.11(46 vessels)and 0.08(27 vessels).The change tendency of the sand mining permit quantity and the number of sand mining vessels is relevant with positive,the quantity of sand mining permit is one of the factors affecting the number of sand mining vessels.(2)The area affect by sand mining distribute from northern channel to the Songmen Mountain,and the part of Ganjiang River west branch was affected during the flood,normal and dry seasons from 2000 to 2010,and expand to the southern lake after 2010.The lake southwestern and South Lake Village under all seasons in the last20 years were not affected by sand mining.The affected area in last 20 years of Poyang Lake was flood(352.46 km~2),normal(243.44 km~2),and dry(201.78 km~2),the all seasons was 408.66 km~2.(3)Within the area affected by sand mining,water and mudflats declined,grassland and sandbars increased,with multi-year averages of 198.67±55.97 km~2,114.53±40.09 km~2,79.13±22.58 km~2,and 21.21±12.64 km~2,respectively,the number of the patches increased and the landscape discontinuity increased.(4)In recent 20 years,the habitats of Yangtze finless porpoise with high degree of direct impact by sand mining in the flood,normal and dry seasons of Poyang Lake were mainly distributed in Tongjiang waterway and the west branch of Ganjiang River,and the habitats with medium and low degree of impact were mainly in the southern lake.The habitats with high,medium and low degree of direct impact by sand mining showed an increasing trend:(1)In the flood season the correlation coefficients is 0.24(P=0.05),0.57(P<0.01),0.71(P<0.01),with a multi-year average total impact area of 345.51±101.17 km~2,accounting for 49.68% of the flood season habitats,(2)In the normal season the correlation coefficients is 0.13(P=0.10),0.50(P<0.01),0.60(P<0.01)),average impact area of 179.36±45.51 km~2,accounting for 43.15% of the normal habitat,(3)In the dry season the correlation coefficients is 0.14(P=0.08),0.43(P<0.01),0.50(P<0.01),average impact area of 108.55±23.80 km~2,accounting for 51.45% of the dry season habitats.(5)In recent 20 years,the area of Yangtze finless porpoise habitat affected by underwater noise from sand mining vessels in the flood,normal and dry seasons of Poyang Lake significantly increased the correlation coefficients of 0.70,0.63,0.58 respectively,P< 0.01,and the total affected habitat areas for multi-years were 442.89±134.12 km~2,269.98±53.59 km~2,151.50±25.10 km~2,was 71.81%(dry),65.05%(normal),and 63.69%(flood)of the total habitat areas.The porpoise habitats in the northern channel and the west branch of the Ganjiang River are more seriously effected by the underwater noise than the southern lake. |
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