Spatial Heterogeneity,Temporal Changes And Driving Mechanisms Of The Wetland Landscapes In Huaihe River Basin,China

The Huaihe River Basin locates in warm temperate zone,which is a part of the transitional zone between South and North China.As a representative wetland region in China,Huaihe River Basin is rich in wetlands in terms of both coverage and diversity.Unfortunately,in recently years,wetlands are subject to adverse impacts,more than any other ecosystem type.Multiple threatening factors(e.g.climate change,biological invasion,human reclamation,hydrological modification and water pollution)can separately or additively reduce ecological functions and services of wetlands.Of those,human activities have been recognized as a major cause of these wetland problems.The objective of this dissertation was to study the rule of spatial and temporal heterogeneity of wetlands,and identification of the driving mechanism of wetland dynamic changes.We organized a synthesis paper that first to distinguish the rule of spatial and temporal variation of wetlands in Huaihe River Basin.Then representative wetland region was chosen to investigate the conversion trajectory of the natural wetlands and map the hotspots of natural w-etland reduction.Finally,the driving mechanism of wetlands changes was discussed.The main research contents and results as follows:(1)Aquatic Ecoregion Zoning(AEZ)refers to the process of dividing a certain study area into various aquatic ecoregions according to the similarities and dissimilarities of regional eco-environmental characteristic.This was based on the application of modern ecology theory and GIS,on the analysis of regional eco-environmental characteristics(such as hypsography,physiognomy,climate,soil,water resource,vegetation,biodiversity,etc.)with their formation mechanisms,and also on the combination of qualitative methods and quantitative methods.Based on the above research,we then put forward the principles,criteria and index of Huaihe River Basin AEZ system.As a result,Huaihe River Basin was divided into 5 aquatic ecoregions and 16 aquatic sub-ecoregions.For every aquatic ecoregion,specific eco-environmental characteristics and aquatic biology characteristics were illustrated.The achievements of the study would provide a scientific foundation for decision-making such as regional eco-environmental conservation and construction,reasonable natural resources utilization,spatial allocation of agricultural and industrial production,and also to develop information and approach for environmental management department.(2)Human activities produced great impacts on wetlands worldwide.Taking Jiangsu Province,China as a representative wetland region subject to extensive human activities,the aim of this study is to understand the conversion trajectory and spatial differentiation in wetland change from a multi-scale perspective.Based on multi-temporal Landsat images,it was found that the natural wetlands decreased by 11.2%from 1990 to 2006 in Jiangsu Province.Transition matrices showed that the conversion of natural wetlands to human-made wetlands(mostly aquaculture ponds)was the major form of natural wetland reduction,accounting for over 60%of the reduction.Percentage reduction and area reduction of natural wetlands were respectively quantified within different wetland cover zones using a moving window analysis.Average percentage reduction showed a decreasing tendency with increasing wetland cover.The high-cover and mid-cover zone presented the largest area reduction at the scales of 1-2 km and 4-8 km,respectively.Local hotspots of natural wetland reduction were mapped using the equal-interval and quantile classification schemes.The hotspots were mostly concentrated in the Lixiahe marshes and the coastal wetland areas.For the area reduction hotspots,the quantile classification presented larger area and more patches than the equal-interval classification;while an opposite result was shown for the percentage reduction hotspots.With respect to the discontinuous distribution of the natural wetlands,area reduction could be more appropriate to represent reduction hotspots than percentage reduction in the study area.These findings could have useful implications to wetland conservation.(3)This study attempted to differentiate the impact of human activities on reductions in wetland vegetation in the Lixiahe wetlands,China,at multiple spatial scales.The reduction in wetland vegetation from 1988 to 2006 was quantified using Landsat data,and moving window analysis was used to detect hotspots of vegetation reduction in the wetlands at window sizes of 150,1,000 and 2,500 m.Logistic regression was used to examine the influence on occurrence of the hotspots of landscape variables representing accessibility to human settlements and roads.Over the study period,wetland vegetation declined by 69%,which was largely attributable to aquaculture development.The hotspots of wetland vegetation reduction exhibited increasing patch size but decreasing patch number with increasing window size.The occurrence probability of the hotspots rose significantly with increasing proximity to rural settlements and secondary roads,with only a minor response to the presence of towns.With increasing window size,however,the density of secondary roads and rural settlements were less influential,whereas the presence of major roads had more influence on hotspot occurrence.These trends are reasonable in that wetland use activities in the study area are directly associated with the settlements and roads in the rural areas at local scales,but are also indirectly associated with the major transportation network from a regional perspective.Overall,these results suggested that different human activities,as distinguished by their sources on the landscape,could have different environmental consequences at different scales for scale-dependent features.Huaihe River Basin,as one of the most developed regions in China.Understanding spatial heterogeneity,temporal changes and driving mechanisms of the wetland landscapes in Huaihe River Basin could provide supports to future decision making of wetland conservation and restoration in China in the context of rapid socioeconomic development.