| Due to the special geographical location,the costal wetlands was occupied with extremely sensitive habitat,and intricate ecological structures and functions.Recently,because of intensive human activities and global climate change,which contained coastal wetlands development,reclamation,rising sea levels and the storm surge intensified,the large area of coastal wetlands was destroyed variously.It concentrated on the dramatic landscape fragmentation,the imbalance of water and salt,biodiversity loss and ecosystem disorder.Therefore,how to mitigate degradation pressures and rebuild the ecosystem habitat was the hot spots in wetlands ecology internationally.Based on the analysis result of the landscape pattern change in Yangtze delta,the study selected the Nanhui east tidal flat as the research region,where was a fresh wetland by reclamation project.And we investigated the response mechanism between the vegetation and soil sedimentary environment and analyse the interaction quantitatively.The study aimed to provide scientific theoretical basis for ecological restoration in Yangtze estuary wetlands.(1)The characteristic of landscape pattern change and its driving factors in Yangtze Delta coastal wetlands.In this section,the study used the vector data of LUCC in 1960,1980,1990,2000,2010 and 2015,to approach the landscape pattern change.The results showed: 1)in the landscape level,the total area increased,the landscape fragmentation and contagion risen,presented a balanced trend totally and the types of wetlands varied sophisticated.Additionally,2000 was the significant point for the transfer of all the landscape indexes.2)in the class level,the study offered the isobath 6m,tidal flat,reservoir,salt marsh and culture pond to illustrate.The area of tidal flat and salt marsh revealed a trend of fluctuation,and others keep growing.The culture pond had the most fragmentation index,when the reservoir had the least conversely.The contagion of reservoir and culture pond increased gradually.The maximum dominance was the sea with 6m isobath,while the tidal flat took the second place in the dominance.In 1990,the salt marsh come to the ultimate dominance distinctively.Combined the indicators of society and economic,the population,GDP,industrial,urban road and fishery had the significant statistics with the total landscape fragmentation.Meanwhile,the urban infrastructure construction and fishery both correlated with the fragmentation in the class level.Given all that,the transmutation of landscape pattern in Yangtze estuary presented complicated and diversified.The fragmentation in this region continued to aggravate.Urban construction predominated the landscape change.(2)Soil characteristics and their potential thresholds associated with Scirpus mariqueter distribution on a reclaimed wetland coast.How various soil characteristics were associated with Scirpus mariqueter growth and spatial heterogeneity on Shanghai Nanhui Dongtan wetlands was studied.In September and October 2015,twelve soil characteristics(soil organic carbon,total phosphorus,total nitrogen,nitrate,nitrite,ammonia,orthophosphate,pH,moisture content,particle size,salinity,and tidal elevation)were analyzed in 101 soil samples.The key factors affecting S.mariqueter spatial distribution were determined using principle component analysis and curve fitting analysis.Results showed that,1)for the vegetation inter annual distribution variation,the TOC,salinity and moisture were the key factors.However,there were various soil factors in the different season.In spring,the TOC,TN and Nitrate were positively correlated(P < 0.05)with its growing.In the summer and autumn,the coefficient of correlation was greater than other factors.2)Scirpus mariqueter were mainly distributed in tidal flats elevations of 2.0–3.4 m.Plant coverage and density were positively correlated(P < 0.05)with total nitrogen and soil salinity.Based on the curve-fitting and independent samples t-test analyses,thresholds of total nitrogen,conductivity,and tidal flats elevation of soil were 0.5475(g/kg),0.8368(ms/cm),and 2.75(m)respectively.This study has critical significance for future coastal wetlands remediation around the world.(3)Interaction of vegetation-soil system and their response to spatial sedimentary differentiation on coastal wetlandsUnderstanding the interaction of vegetation-soil system in costal wetland is essential for coastal vegetation rehabilitation project.In this paper,the study we aim to answer:(1)what model could be used to reveal the interacting mechanism between the vegetation index and soil physiological parameters;and(2)how Scirpus mariqueter responded to coastal sedimentation spatial difference on Nanhui coastal area.Soil physiochemical characteristics of 32 soil sampling in 2015 and 2017 and 7 spectral reflectance of Scirpus mariqueter with high-density vegetation cover were collected and analyzed.The interaction between vegetation index and soil physiochemical characteristics and their response to tidal flats elevation dynamics were computed and analyzed using regression analysis,correlation analysis and spatial analysis by ArcGIS.Results showed that after reclamation both elevation and NDVI tremendously increased on the study site.By raster reclassifying computation the increase of NDVI and elevation could be divided into 11 categories.The bigger the category value,the faster the NDVI or elevation increased.It was founded that the area proportion was 51.45% with both NDVI and elevation had a category value of no less than 6 by raster calculator.Most of these areas located at east side of the study area.80.45% of area with NDVI increasing category value bigger than 6 was contained in the area with elevation increasing category value bigger than 6.It revealed that soil salinity and soil moisture were spatial correlated with tidal flats elevation by geostatistics analysis,while soil salinity and soil moisture were both the controlling factors affecting Scirpus mariqueter spatial distribution.NDVI-based vegetation analysis could provide a holistic and time-saving approach to know the vegetation spatial sprawling dynamics.Tidal elevation was the key factor affect Scirpus mariqueter spatial expansion.This research is helpful to understand the sprawling mechanism of Scirpus mariqueter and build the quantitative interaction model between sedimentation,hydrology and vegetation response,which in turn promote the fast coastal wetlands rehabilitation.Given all that,the operation about landscape pattern analysis was based on the definition of coastal wetlands from ?Convention on Wetlands of International Importance Especially as Waterfowl Habitat?.The study succeeded extract the thresholds by regression models,and build spatial statistics models between NDVI and soil environmental factors by spatial analysis.Completed the quantitative analysis,what the study obtained would guide the practice of ecological restoration.And it provided theoretical support with the application of hyperspectral remote sensing to real-time monitor the vegetation distribution in Nanhui east tidal flat.It is essential to carry out the further examination to emphasize the effect of coastal wetlands in the development of economic belts in Yangtze delta. |
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