Construction Of Ecological Network For Natural Wetlands In The Yellow River Delta

Due to the changes in natural conditions and human activities,wetland landscapes are suffering greatly from those drastic disturbances and consequently become fragmented,which lead to reduction of ecosystem functions,such as biodiversity loss.Ecological network technology could provide new opportunity for ecologists to increase landscape connectivity and rebuild wetland landscapes for proposes of conservation and management,which are widely used in landscape planning and management.Our main objects are to analyze the dynamics of wetland landscapes in recent 20years and then to design reasonable ecological networks for natural wetland conservation in the Yellow River Delta(YRD)based on the minimum cumulative resistance.Firstly,the spatio-temporal changes in the wetlands in the delta from 1991to 2013 were studied,using landscape connectivity indices at the different scales.Then,the driving factors of wetland changes were discussed;Secondly,according to the patch size,landscape spatial pattern,and ecological service value,main wetland source patches in the delta were selected.After that,four different landscape resistance regimes based on the relationship between wetland and water were designed using the minimum cumulative resistance to generate the potential ecological corridors in the delta.Finally,structure characteristics and landscape connectivity of those ecological networks have been quantitatively analyzed through both network structure method and landscape connectivity index.By the evaluation of the four ecological networks,an optimal scheme of ecological network planning was proposed for wetland conservation in this delta.The main conclusions were:(1)From 1991 to 2013,natural wetland area has decreased by 548.79 km~2 in the YRD.Generally,wetlands have degraded from the coastal area,the southeast and the southwest regions of this delta to the nature reserve.The natural wetlands in the Kenli agricultural ecological area,Estuary agricultural ecological area,and Shengli oilfield area have been severely shrunk.There were shifts between land use types such as natural wetlands and cultivated land,constructed wetlands and constructed land.(2)Overall,the landscape connectivity of the natural wetland in the YRD showed a downward trend.The integral index of connectivity(IIC)of the natural wetland in the delta has decreased from 0.035 to 0.022,and the probability of connectivity(PC)has decreased from 0.076 to 0.041.At the regional scale,the YRD Natural Reserve,including the Yiqianer station and the Yellow River mouth station,has maintained higher landscape connectivity.However,the index in the Kenli agricultural ecological area,the Estuary agricultural ecological area,and the Shengli oilfield zone were relatively low and gradually declining.(3)The landscape patterns of wetlands have been mainly influenced by those factors,such as water and sediment in the Yellow River,coastal erosion,land use changes,oil and gas exploration,road construction,and environmental pollution.(4)The conducted wetland ecological networks have increased the landscape connectivity,with the values of 0.042 above.Different water resistance schemes have specific influences on the structure and connectivity of ecological networks,which indicated that water may play important roles in maintaining those important ecological processes at the large scale.The potential ecological networks also need more new wetland habitats,as stepping stones of wetland ecosystems structure,to benefit the species movement.(5)Based on those results,we finally proposed a“one core and three axes”wetland ecological network planning framework for wetland conservation in the YRD.