Study On Landscape Dynamics And Ecosystem Services In Liaohe River Reserve

Liaohe River basin is located in a region influenced by global climate change,with the regional ecosystem structure and function affected by changes in precipitation and temperature to a certain degree.Liaohe River Reserve,covering the areas between levees on both sides of Liaohe River,was established in 2010 to protect and restore the ecosystems in the Liaohe River.Areas within 500 m away from the river channel were restored mainly by natural recovery from fencing.By applying" 3S"techniques,InVEST model,and field surveys,this study was aimed to investigate:(1)the spatial-temporal dynamics of Normalized Difference Vegetation Index(NDVI)from 2000 to 2015 in the Liaohe River Reserve and the spatial patterns of NDVI in three typical river reaches during the initial stage of ecological restoration;(2)variations in landscape patterns before and after the establishment of Liaohe River Reserve and the dynamics of landscape patterns during ecological restoration in fenced regions;(3)dynamics of ecosystem services and the correlations with landscape pattern;and(4)spatial patterns of riparian vegetation and soils at the initial stage of ecological restoration.Major findings are as follows:1.Annual NDVI increased from 2000 to 2015.The inter-annual increases in in the Liaohe River Reserve mainly occurred in summers during 2009-2009,and in springs during 2010-2015.The significant increases in spring NDVI from 2010 to 2015 enhanced the ecosystem services in wind breaking and sand fixation.Farming practices were the dominant anthropogenic factors affecting NDVI dynamics during 2000-2009.Natural restoration and construction of small artificial wetlands increased NDVI during 2010-2015,whereas the construction of large artificial wetlands and artificial pastures had no significant effects.2.Landscape patterns showed a tendency of fragmentation after the establishment of the Liaohe River Reserve,and the degree of fragmentation decreased with time.Before establishment of the Liaohe River Reserve,landscape types of the areas were dominated by farmlands,accounting for 36.17%of the land area;following the establishment of the Liaohe River Reserve,extensive farmlands were transformed to grasslands,and the landscape was dominated by water bodies,reed marsh,grasslands and farmlands,which accounted for 24.15%,19.7%,17.45%,and 16.99%,respectively.The degree of landscape fragmentation increased areas with natural ecological restoration,but decreased along reaches restored by wetland recovery,including construction of pond wetlands,oxbow lake wetlands,and natural wetlands.Corridors(e.g.rivers and roads)and dominated landscape class were the key factors affecting landscape patterns.3.Ecosystem services of soil retention,water yield,and water purification increased,but carbon storage showed little change after the establishment of the Liaohe River Reserve.Improvement in ecosystem services mainly occurred in fenced areas and the areas restored by the tributary estuary wetlands,wetlands parks,and the large oxbow lake wetlands.For the typical reaches,with the ecological restoration processes,soil erosion along the upstream reaches decreased by 31.93%.Water yield along up-,mid-,and downstream reaches decreased by 13.25%,4.62%,and 14.65%,respectively.Carbon storage in mid-and downstream reaches increased by 18.49%and 31.34%,respectively.P export,P retention,N export,and N retention along upstream reaches decreased by 29.72%,24.97%,20.42%,and 14.29%,respectively.Complexity of patch shape and contagion of patches were significantly correlated with soil retention and water purification function.4.Riparian vegetation structures and soil physicochemical properties showed significant spatial heterogeneity at the initial stage of ecological restoration.Ecotypes of herbage plants shifted from hydric to mesic to xeric from floodplains to terraces.Phragmites australis and Artemisia selengensis were dominant species on floodplains,whereas Ambrosia trifid,Metaplexis japonica,Humulus japonicus,Glycine soja,Artemisia lavandulaefolia and Setaria glauca were dominant on terraces.Species diversity increased significantly from floodplains to terraces.Substrate and bank stability were the significant environmental drivers of vegetation structures in floodplains.Vegetation structures on terraces were mainly determined by soil moisture and human disturbance.Riparian soils in the Liaohe River Reserve were characterized by high sand content(78.88%?96.52%)and poor soil nutrients.Soil silt content,organic carbon(OC),cation exchange capacity(CEC),total nitrogen(TN),and available nitrogen(AN)increased laterally with increasing distance away from river edge,while soil sand content decreased.Soil OC,TN,AN,and CEC in upstream and midstream reaches showed negative spatial autocorrelations along the lateral gradients,and positive spatial autocorrelations in the downstream reach.Altitude,distance from river edge and distance from nearest farmland were the pronounced factors affecting soil physicochemical properties.