Biomass and carbon stocks in deltaic wetlands across active and inactive basins in the Mississippi River Delta, USA

Abstract

Deltaic wetlands in coastal Louisiana are experiencing widespread changes in vegetation dynamics and distribution due to rising sea level and long-term modifications in hydrology and sediment supply. Using field and remote sensing data, we investigated how aboveground biomass (AGB) and C stocks change in response to seasonality along salinity and soil nutrient gradients across different wetland habitats in two coastal basins with active (Atchafalaya - AB) and inactive (Terrebonne - TB) hydrological regimes. The highest seasonal changes in AGB and C stocks across both basins occurred in saline (SL) sites (AGB range: 343 ± 101 to 1214 ± 210 g m− 2) in early growing and peak biomass season, respectively. Biomass productivity rates varied across basins, with SL sites being the most productive, albeit less species-diverse. Foliar nutrient uptake was higher in the mineral-rich soils of AB freshwater (FW) site. In contrast, Terrebonne FW plants (as well as brackish and SL) had lower tissue nutrients and higher biomass allocation, indicating greater nutrient use efficiency with increasing salinity stress. Seasonal variation in AGB was positively correlated with porewater salinity and with soil nutrients (total nitrogen (N) and phosphorus). As hypothesized, changes in plant and soil isotopic signatures in both basins paralleled the spatiotemporal patterns in environmental stressors (e.g., elevated salinity and nutrient availability). Our findings show that in both active and inactive coastal delta basins, herbaceous wetlands maintain high biomass and C stocks by developing adaptive strategies in response to the distribution of environmental stressors and availability of resources.