Lateral detrital C transfer across a Spartina alterniflora invaded estuarine wetland

Tingting Zhang,Ping Zhuang,Yu Gao,Bin Zhao,Feng Zhao,Steven Mcnulty,Jiquan Chen,Haiqiang Guo

doi:10.1186/s13717-021-00340-2

Abstract

BackgroundThe 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 quantified the lateral flux of detrital C in the Yangtze estuary where invasive Spartina alterniflora has substantially and extensively altered the ecosystem structure and functions. Our overall objective was to close the C budget of estuarine wetlands through field sampling, tower-based measurements, and modeling.MethodsA lateral detrital C exchange evaluation platform was established in a case study of the Yangtze River Estuary to investigate the effect 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 field sampling. Tower-based measurements and MODIS time series and CH4 outgassing and biomass simultaneously measured the lateral detrital C flux to characterize the relative contributions of lateral (i.e., detritus) C fluxes to the annual marsh C budget.ResultsThe C pools in the plants and soil of Spartina marshes were significantly 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 flux 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 flux (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 flux 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.ConclusionThis research demonstrated that an integrated framework incorporating modeling and field 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 efficiency 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 different lateral detrital C flux processes to closing the ecosystem C budgets. The sampling spatiotemporal granularities can be key to assessing lateral detrital C transfer.

Highlights

Mass and energy exchanges across the terrestrial-aquatic interface have been increasingly examined over the last two decades, mainly through scientific investigations of the carbon (C) cycle and global change (Aufdenkampe et al 2011; Cole et al 2007; Harishma et al 2020; Jenerette and Lal 2005; Tank et al 2018)
The annual CH4 emissions measured by conventional eddy covariance techniques (March 23, 2011–December 31, 2011) were 17.9 ± 3.7 g C m−2 year−1 and exhibited a distinct seasonal pattern. These results suggest that the emission of C in non-CO2 form (i.e., CH4) accounts for 2.8% of the GPPEC (Fig. 3) and allow us to calculate the actual lateral C flux caused by tides
By coupled modeling and field sampling, this study estimated the lateral detrital C exchange based on gross primary production (GPP) with tower-based measurements and Moderate-resolution imaging spectrometer (MODIS) time series and CH4 outgassing and based on biomass and simultaneously measured the lateral detrital C flux to characterize the relative contributions of lateral C fluxes to the annual marsh C budget

Summary

Introduction

Mass and energy exchanges across the terrestrial-aquatic interface (e.g., riparian zones of streams, rivers, lakes, and coastal areas) have been increasingly examined over the last two decades, mainly through scientific investigations of the carbon (C) cycle and global change (Aufdenkampe et al 2011; Cole et al 2007; Harishma et al 2020; Jenerette and Lal 2005; Tank et al 2018). The mechanisms and consequences of uncertainty for estimating and observing lateral fluxes depend on the spatial (e.g., plot to landscape) and temporal (e.g., day—years) scales. These scale-dependent dynamics make closing C budgets more challenging (Duarte et al 2017; Taillardat et al 2019). 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. Our overall objective was to close the C budget of estuarine wetlands through field sampling, tower-based measurements, and modeling

Methods

Results

Discussion

Conclusion