Differentiation Of Landscape Structure And Function During Different Reclamation Time At The Changjiang River Estuary

The reclaimed zone or polder land has complicated landscape structure and functions due to the mixed influence from natural and anthropological factors.Based on the reclamation zones of different years at the Changjiang River (Yangze River) Estuary, a synthesized indicator system,including landscape, soil and vegetation factors, was established to combine landscape structure and functions together. CLUE-S model was employed to simulate the future scenarios in the reclamation zones. Following are the main results:1) Based on the TM and ETM image of the Changjiang River Estuary obtained from 1987,1995,2000 and 2006, landuse dynamics of 3 typical pilot study areas were analyzed with GIS and statistical methods. The results showed that the 3 study areas were not significantly different in terms of land use diversity indicated by Gibbs-Mirtin diversity index. The land use change rate had no spatial difference among the 3 study areas. But the change rate of Greenhouse land and built-up land were found to be significantly different among time scales, land use levels of the 3 study areas were similar with each other, with similar land transformation trends and intensities.The insignificant difference among the 3 study areas might be caused by reclamation projects and time of reclamation.2) Fengxian area was select for the study or the land use dynamics along temporal series, with combined methods of "spatial sere substituting for time sere" and Principle Component Analysis, while the 2 study areas from Nanhui were used for verification.The results indicated:(1)The comprehensive evaluation index based on PCA(F)was positively related to farmlands(Paddy field>Greenhouse land>dry land>forest land>orchards),and negatively related to coastal land cover types(breeding ponds>grass land>open water>bare flat).(2)The F-value increased with time logarithmically (R2:0.5119), and reached stable around 40 years after reclamation.Regression analysis showed that F-value can reflect the trends for both land use levels(L) and diversity index (GM).3)With multivariate analysis of variance(MANOVA),Geo-statistical analysis(GA), PCA and Canonical Correspondence analysis, soil properties and their possible control factors were analized among zones with different reclamation years.(1)With the increase of reclamation time. Soil moisture, salinity, conductivity and partical size decreased,While soil organic matter increased;Soil available phosphorus increased first, and decreased after 100 years of reclamation.No change trend was found for NO3-N, NH4+-N and pH along time series. Soil properties reached stable around 30 years after reclamation.(2) According to the PCA results, the weight values for soil nutrient factors(such as NO3--N, SOM,SAP,NH4+-N,-pH and-soil partical size) were higher than those for soil limitation factors(such as soil salinity, conductivity and soil moisture). Higher Fs values indicated better soil quality. (3) Different land use types contributed differently during the soil maturation process; (4) CCA results indicated that soil properties were mainly affected by reclamation time, and the influence from land use was secondary. The comprehensive soil function index Fs is more related to reclamation time (r=0.1905) than with land use (r=-0.1161).4) Based on the 67 quadrats data obtained in July 2009,216 soil sampling points data obtained in April 2009, as well as the TM data of 2006, the natural vegetation zones were analized with TWINSPAN, MANOVA, DCCA and CCA methods. The results indicate that:(1) the vegetation community in the reclamation zones was mainly composed of mesophytes and helophytes-mesophytes. With the increase of reclamation time, the communities showed a transitional gradient trend; Species richness (MA), species diversity (H) and above ground biomass also increased. Nevertheless, they appeared to decline slightly in the middle and late reclamation period (>30 years), being affected by land use types, (ii) The change in species richness(MA) and species diversity (H) with reclamation time also tended to increase at first and then decreased with the rise in land use degree. Species dominance (D), however, tended to decline, and above-ground biomass increased slightly, (iii) The distribution of the vegetation community was mainly influenced by the following factors:land use patterns (r=0.55, p<0.05), soil moisture (r=0.53, p<0.05), soil salinity (r=0.43, p<0.05) and reclamation time (r=0.40, p<0.05).5) Landscape dynamics of the reclamation zone is resulted from the interaction between human and natural factors. Based on the TM image data of 1990,2000 and 2009, the driving forces for landscape dynamics in the reclamation zone was analized with RDA and PCA methods. Kappa index and CLUE-S model were also employed to verify the effectiveness of the driving factors selected.Results indicated that:The contribution from human induced factors (57.10%) is higher than that from natural factors (42.9%) to the landscape dynamics in the reclamation area.The prediction accuracy from CLUE-S model reached 82%, While the kappa index for major landscape types such as farmland,unused land and breeding ponds were all higher than 0.75.Therefore the CLUE-S model could be used for future scenarios simulation, and the driving factors selected for this study were also effective in depicting the spatial distribution of landscape transformation.Future development scenarios of the study area were simulated for the next 10 years(2010-2020), which can provide scientific support for decision making in the newly reclaimed area.