Responses of Above- and Belowground Carbon Stocks to Degraded and Recovering Wetlands in the Yellow River Delta

Abstract

Wetlands reserve a large amount of organic carbon (C), playing a key role in contributing global C stocks. It is still uncertain to evaluate wetland C stocks due to wetland disturbance or degradation. In this study, we performed the degraded and recovering wetlands to estimate aboveground C stocks and soil organic C (SOC) stocks at the depth of 1 m in the Yellow River Delta. Our results showed that the recovering wetland sequestered 1.67 Mg C ha–1 aboveground, approximately three times higher than those (0.56 Mg C ha–1) of degraded wetland, and recovering wetland stored more SOC of 51.86 Mg C ha–1 in the top 1 m soils, approximately two times higher than those (26.94 Mg C ha–1) of degraded wetland. These findings indicate that the transformation between degraded and recovering wetlands is associated with the conversion of wetland C sources and sinks. The shifts in aboveground C stocks and SOC stocks were mainly attributed to changed biotic (i.e., aboveground biomass and photosynthetic C) and abiotic (i.e., soil water, salinity, SOC and N contents, and SOC compounds) factors. The improved soil water, salinity, and nutrient enhance C reservoir, sequestering more C in aboveground vegetation and storing more SOC via photosynthetic C input of plant litter and root exudates in recovering wetland than in degraded wetland with poor soil conditions. The relationships among wetland C stocks, plant, and soil properties indicate plant-soil interaction driving wetland ecosystem C stocks in degraded and recovering wetlands. Our research suggests that wetland restoration highlights a positive response to “carbon neutrality” by efficiently sequestering C above- and belowground.

Restoring blue carbon ecosystems

“…Annual aboveground carbon production was 200 to 1,700 g C m -2 in constructed wetlands of the United States (from placement of dredged material) at 2 to 3 years old (Madrid et al, 2012). Restored wetlands in China also observed aboveground biomass stocks near 167 g C m -2 , which were three times higher than degraded wetlands (Shao et al, 2022). The total carbon soil stock (to 1 m) of restored marshes can be about 51.86 Mg C ha -1 , approximately two times higher than degraded wetlands (Shao et al, 2022).…”

“…Restored blue carbon stocks (above-and belowground, AGB and BGB) tend to be 2-800 times higher than in degraded/converted/bare sites, and methane (CH4) fluxes can be 4 times less than degraded/converted/bare sites, depending on habitats and age. For example, a) seagrasses, bare versus (vs) restored; (Oreska et al, 2020); b) Mangrove, converted/degraded vs restored (Sasmito et al, 2019;Rosentreter et al, 2021); c) Tidal marshes; converted/degraded vs restored (Kelsall et al, 2023;Iram et al, 2022;Stagg and Mendelssohn 2010;Shao et al, 2022) The following describes the major stock and flux components separately for each blue carbon ecosystem, and is indicative of the magnitude of stock and flux change that can be expected following restoration. Kirwan et al (2023).…”

“…The time needed for tidal marsh restoration to achieve ecological equivalence to natural marshes can vary between 3 to >15 years (Billah et al, 2022;Broome et al, 2019) but significant increases in carbon stocks (up to 3 times; Shao et al, 2022) can be reached as early as four years (O'Connor et al, 2020).…”

Aboveground biomass estimation of wetland vegetation at the species level using unoccupied aerial vehicle RGB imagery

“…Aboveground biomass (AGB) of wetland vegetation serves as a key indicator to evaluate the health status and the carbon storage capacity of wetland ecosystems ( Shen et al., 2021 ). Monitoring the AGB of wetland vegetation can provide a scientific basis for the conservation and restoration of wetland ecosystems, which is essential for achieving carbon neutrality targets ( Shao et al., 2022 ). Due to the poor accessibility of wetlands and the influence of complex environmental factors, traditional manual harvesting methods for obtaining the AGB is not only time-consuming and labor-intensive, but also difficult to implement on a large scale.…”

Herbivores shape the seascape : Cascading effects of herbivores on the functioning of tropical seagrasses in a changing world

“…In macrophyte dominated ecosystems, the focus is often on measuring aboveground recovery (Macreadie et al 2014, Smith et al 2016, Castagno et al 2021. However, knowledge of belowground dynamics is key for understanding the resilience of these ecosytems (Nyman et al 2006, Vonk et al 2015, because belowground biomass includes the carbon reserves important for recovery potential (Hagedorn et al 2016, Yang andLi 2022) and the root structure that provides stability and resistance to waves and storms (Sasser et al 2018, Battisti and Griffin 2022, Infantes et al 2022. Assessing factors that determine both above-and belowground recovery rates is therefore essential to provide management recommendations to conserve and protect coastal ecosystems in times of change and to help build resilience in vulnerable ecosystems facing multiple threats (Senf et al 2019).…”