A case study on structural development and ecological services of restored mangroves in Adyar Estuary, India

Mangroves, critical coastal wetlands, face global degradation, necessitating conservation and restoration efforts. This study evaluates mangrove restoration in the Adyar Estuary, Chennai, along the Bay of Bengal, degraded by urbanization and anthropogenic pressures. It evaluates afforested mangroves' structural development, restored ecological functions, and factors enabling their establishment. Spanning 56.6 acres, the estuary hosts six mangrove species, with Avicennia marina dominant. The afforested mangroves showed a median density of 3900 trees ha-1, vegetation biomass of 222.26 Mg ha-1, and sequestered 99.89 Mg C ha-1 (366.60 Mg CO2e ha-1). Total carbon storage was 2288.00 Mg C (8397.05 Mg CO2e), with annual sequestration at 325.71 Mg C year-1 (1195.42 Mg CO2e year-1). Reduced self-thinning indicated enhanced self-tolerance. Despite pollution, mangroves thrived due to locally adapted species, replanting efforts, and community involvement. This study highlights mangrove restoration as a strategy for climate resilience, aligning ecological and socio-economic goals.

Methods
This dataset was collected from Adyar Estuary along the Bay of Bengal in Chennai, India. Field surveys were conducted at nine stations with a minimum spacing of 50 m between them along the Adyar Estuary and Creek during August 2022 to assess the vegetation structure of the afforested mangroves. At each station, random plots measuring 10 m x 10 m were established to study the vegetation characteristics of the afforested mangroves. A total of 49 sampling plots were used, and the age of the mangrove stands in each station was determined based on information provided by Chennai Rivers Restoration Trust. Within each sampling plot, all mangroves were identified and counted. Girth at breast height (GBH) and tree height were measured using a distometer (Leica Disto D510, Hungary). Based on these data, basal area (m2 ha-1) and stand density (stems ha-1) were calculated. In the present study, two carbon pools, namely above-ground vegetation biomass (AGB) and below-ground vegetation biomass (BGB), were considered to measure the vegetation carbon stock of the afforested mangroves in the estuary. The allometric equations for Southeast Asian mangroves were applied to estimate AGB and BGB. 

AGB = 0.251 × r ×  D2.46 

BGB = 0.199 × r0.899 × D2.22

where, AGB is the above-ground vegetation biomass (kg), BGB is the below-ground vegetation biomass (kg), r is the species’ wood density, and D is the diameter derived from GBH using the equation D = GBH/(22/7). The wood density for the afforested mangrove species present in the estuary was obtained from the Global Wood Density Database.