The Mapping Method Of Tidalflat Deposition Rate In The Cencral Jiangsu Coast,Eastern China

Coastal salt-marshes represent an important part of the coastal system and one of the ecosystems with the richest biological productivity which has a great value of ecosystem products and services.The coastal wetlands of Jiangsu with a total area of 5100 km2 are important natural resources.The intensity of coastal tidal flats reclamation has been increasing because of the driving force of the rapid growth of economy and social development within a region with a relatively small amount of land per capita with.In order to obtain more land resources,Spartina angelica and Spartina alterniflora were introduced into the Jiangsu coast successively.The two Spartina species have made an important contribution in dissipating wave and protecting coasts,with S.alternifora having a more significant effect in this regard.Futhermore,the introduction of Spartina also has had a significant impact on the patterns of coastal vegetation and the geomorphology evolution of tidal flats.Based on field investigations on the Jiangsu coast,eastern China,a proxy derived from the morphology of S.alterniflora plants was used to estimate deposition rates of salt-marshes associated with a tidal flat environment.This method is based on the assumptions that the root and stem system of the plant,below the bed surface,is quite stable for living plants,and that buried,old plants can be found in the strata.For such an analysis,the colonization time of S.alterniflora must be known;if the timing for any site within the salt-marsh can be determined,then it is feasible to apply this technique to mapping the deposition rate over a large area.In the present study,the position of the S.alterniflora front for different years was detected using remote sensing imageries;thus,the time series of S.alterniflora covered areas was obtained.On such a basis,the age of the old plants in the sediment layers was determined and the deposition rate was estimated.Based on twenty-three phases of satellite imageries from 1992 to 2014 and field observation data,the salt-marshes on the central Jiangsu coast are characterized by a deposition rate of 2.0-6.0 cm a-1.Where short sediment cores were available,210Pb measurements were carried out to obtain independent estimates.The results from the two methods were generally consistent.This preliminary study shows that the methodology proposed has a potential for deposition rate mapping over a large area.Futhermore,using the deposition rate measurements of each station in the study area,an interpolating method was applied to depict the distribution pattern of the plant S.alterniflora in the study area,in order to achieve the deposition rate mapping.Finally,a geostatistical method was used to analyse the effect of promoting the deposition quantitatively based on the distribution trend of deposition rate in the S.alterniflora salt-marsh.The results showed that the study area has a significant effect of accretion since the introduction of S.alterniflora.The volume of sediment traped by S.alterniflora salt-marsh is about 2.38 × 104 m3 per year,1.35”104 m3 higher than bare flats.The effect of enhancing deposition is twice as that of the bare flat.In the future,field observations for,e.g.,ground water level,the concentration of suspended sediment,and sediment dynamic processes should be strengthened for the S.alterniflora salt-marsh to improve our understanding of the spatial and temporal characteristics of various dynamic parameters,i.e.,the settling law and the changing processes for the deposition rate in S.alterniflora salt-marshes can be studied well.Furthermore,numerical modelling should be applied to analyse the sediment dynamic processes and to identify the mechanisms of the geomorphology evolution in S.alterniflora salt-marshes.