Lateral detrital C transfer across a Spartina alternifora invaded estuarine wetland

Background:The lateral movements of mass and energy across the terrestrial-aquatic interface are being increasingly recognized for their importance in the carbon(C)balance of coastal/estuarine wetlands.We quantifed the lateral fux of detrital C in the Yangtze estuary where invasive Spartina alternifora has substantially and extensively altered the ecosystem structure and functions.Our overall objective was to close the C budget of estuarine wetlands through feld sampling,tower-based measurements,and modeling.Methods:A lateral detrital C exchange evaluation platform was established in a case study of the Yangtze River Estuary to investigate the efect of ecosystem structural changes on lateral detrital C transfer processes.This study estimated the lateral detrital C exchange based on the gross primary production(GPP)by performing coupled modeling and feld sampling.Tower-based measurements and MODIS time series and CH4 outgassing and biomass simultaneously measured the lateral detrital C fux to characterize the relative contributions of lateral(i.e.,detritus)C fuxes to the annual marsh C budget.Results:The C pools in the plants and soil of Spartina marshes were signifcantly higher than those of the native community dominated by Phragmites australis.The GPP based on MODIS(GPPMODIS)was 472.6 g C m^(−2) year^(−1) and accounted for 73.0%of the GPP estimated from eddy covariance towers(GPPEC)(646.9±70.7 g C m^(−2) year^(−1)).We also detected a higher GPPMODIS during the pre-growing season,which exhibited a similar lateral detrital C fux magnitude.On average,25.8%of the net primary production(NPP),which ranged from 0.21 to 0.30 kg C m^(−2) year^(−1),was exported during lateral exchange.The annual C loss as CH4 was estimated to be 17.9±3.7 g C m^(−2) year^(−1),accounting for 2.8%of the GPPEC.The net positive detrital C fux(i.e.,more detritus leaving the wetlands),which could exceed 0.16 kg C m^(−2) day^(-1),was related to daily tides.However,the observed lateral detrital C fux based on monthly sampling was 73.5%higher than that based on daily sampling(i.e.,the sum of daily sampling),particularly in March and October.In addition,spatiotemporal granularities were responsible for most of the uncertainty in the lateral detrital C exchange.Conclusion:This research demonstrated that an integrated framework incorporating modeling and feld sampling can quantitatively assess lateral detrital C transport processes across the terrestrial-aquatic interface in estuarine wetlands.However,we note some limitations in the application of the light-use efciency model to tidal wetlands.Spartina invasion can turn the lateral C balance from a C source(209.0 g C m^(−2) year^(−1))of Phragmites-dominated marshes into a small C sink(-31.0 g C m^(−2) year^(−1)).Sampling over a more extended period and continuous measurements are essential for determining the contribution of diferent lateral detrital C fux processes to closing the ecosystem C budgets.The sampling spatiotemporal granularities can be key to assessing lateral detrital C transfer.