The Study On The Surface Elevation Change With The Spartina Alterniflora Invasion In Coastal Wetlands Of China

Coastal wetlands,as a transitional zone between land and sea,are the primary habitats of aquatic benthic organisms with important ecological and scientific research values,acting as one of the most vulnerable ecosystems.Global climate change and the non-native species invasion are the two important factors affecting coastal wetlands.However,sea-level rise directly threatens coastal wetlands,and the invasion of Spartina alterniflora seriously endangers the balance and sustainable development of coastal wetland ecosystems in China.Under the combining effects of sea-level rise and surface subsidence,the vertical accretion rates are virtual factors affecting the development of coastal wetlands.Therefore,it is of great significance to determine the coastal wetland sedimentary dynamics after S.alterniflora invading into natural habitats and can help explain the vulnerability of coastal wetlands under the future rising sea level,as well as maintaining the balance of coastal wetland ecosystem and its sustainable development.In this study,three typical coastal wetlands were selected,which were the Yellow River Delta wetlands in Shandong,the Yancheng wetlands in Jiangsu,and the Minjiang River Estuary wetlands in Fujian.We established 36 targeted monitor stations,called Surface Elevation Table-Marker Horizon(SET-MH),in the field of these three sites,and monitoring surface elevation change(SEC),vertical accretion(VA)and the root zone expansion in each station.We also carried out field surveys on the coastal wetlands along in China from 2017 to 2019.With the comprehensive analysis for the trends between SEC and the affecting factors between S.alterniflora and native species,we explained the capable of coastal wetlands to meet sea level rise by combining the community and biomass surveys of S.alterniflora and native salt marshes,as well as the tidal monitoring and topographic analysis surveys.The main results we got are as follows.1.The SEC rate of S.alterniflora in the Yellow River Delta was 58.8±11.2 mm/a,which was much higher than the rates in the native salt marshes,Suaeda salsa and Tamarix chinensis(-9.9±5.2 mm/a and-14.7±0.7 mm/a,respectively).Similarly,there was the similar trend in the Minjiang River Estuary,where the SEC rate of S.alterniflora(ranged from 25.7±19.1 to 39.5±14.3 mm/a)was much higher than that of the native salt marsh of reeds(Phragmites communis),Cyperus malaccensis and the mangroves Kandelia obovata(2.1±3.3 mm/a,1.1±6.3 mm/a and 25.0±2.7 mm/a,respectively).However,the SEC within the various communities in the Yancheng wetlands showed a significant downward trend,where the mudflat(no vegetationcovered area)erosion was the most pronounced at a rate of-71.5±7.8 mm/a,which was significantly lower than those of S.alterniflora(-13.5±2.7 mm/a)and the native species S.salsa(2.2±4.8 mm/a).2.Except for Yancheng wetlands,the VA rate of S.alterniflora was higher than those of the native vegetation.Among them,the VA rate of each vegetation type in the Yellow River Delta wetlands ranged from 16.2±0.2 to 74.7±3.0 mm/a,and ranged from 24.3±6.1 to 54.3± 11.2 mm/a in the Culu Island wetlands,and ranged from 17.9±1.7 to 56.0±2.7 mm/a in the Shanyu Beach wetlands of Minjiang River Estuary.However,in Yancheng wetlands,the VA rate of S.alterniflora community was slightly lower than that of the native S.salsa,and the overall rate within the region ranged from 7.2±0.8 to 9.1±0.8 mm/a.3.The rate of shallow root zone changes(RE for root expansion)of the invasive species S.alterniflora community in each study site was higher than those of the native vegetation community.The RE changes of each vegetation type in the Yellow River Delta wetlands ranged from-5.8±0.2 to-1.1±3.7 mm/a,that of Yancheng wetlands was-6.7±1.3 to-9.7±1.5 mm/a.In Culu Island wetlands and Shanyu Beach wetlands in Minjiang River Estuary,the ranges of RE were-8.1±2.4 to-11.6±3.9 mm/a and11.9±5.4 to 24.7±0.0 mm/a,respectively.4.The correlation between the growth of S.alterniflora and shallow root zone changes(AGB:slope=0.0439,R2=0.5578;BGB:slope=0.0162,R2=0.5040)was higher than that with native species(slope<0.001,R2<0.05,both AGB and BGB).The biomass of S.alterniflora(AGB:1731±88 to 33748±2548 g/m2,BGB:1368±425 to 3401±980 g/m2)in Yellow River Delta and Minjiang River Estuary wetlands were significantly higher than those of the native species were(AGB:31.5± 10.0 to 32156 ±155 g/m2,BGB:14.5±1.7 to 1106±106 g/m2).Although,the SEC of all kinds of communities in Yancheng wetland showed a significant downward trend,while the S.alterniflora showed a remarkable positive effect in shoal consolidation.5.Based on the simulation of the WARMER model,this study demonstrated that the elevations of S.alterniflora communities in the Yellow River Delta and Minjiang River Estuary wetlands will increase significantly in 2030,while the elevations of all communities in the Yancheng wetlands will decrease rapidly.In future climatic scenarios,Yancheng wetlands will be the most vulnerable during the pace of rising sea level,followed by the Yellow River Delta wetlands and Shanyu Beach wetlands in Minjiang River Estuary,while the effects of sea level rise on the Culu Island wetlands in Minjiang River Estuary will be the smallest.