Human-Induced Soil Acidification in the Indian Sundarbans: Implications for Carbon Dynamics in Mangrove Soil

Mangrove forests are known for their unique ability to store organic carbon, about three to five times more than terrestrial forests. The underlying soil substratum of mangrove trees holds a considerable quantum of organic carbon, thus justifying the efficacy of mangrove soil as a vital sink of carbon. However, the soil pH gradually dipped with the increase of anthropogenic footprints in the mangrove forests. We present the decadal variation of Soil Organic Carbon (SOC) and Soil pH at four stations, namely Kakdwip (Stn. 1) and Sagar South (Stn. 2) in the western sector and Sajnekhali (Stn. 3) and Harinbhanga (Stn. 4) in the eastern sector of Indian Sundarbans based on field survey between 2012 and 2022. The stations in the western sector are exposed to anthropogenic influences of different degrees due to unplanned urban development and the proliferation of shrimp farms coupled with the construction of fish landing stations at the cost of mangroves. The SOC values increased by 47.17% and 14.29% at Kakdwip and Sagar South, respectively. The Surface soil pH values decreased by 1.82% and 0.84% at Kakdwip and Sagar South, respectively, which is a clear footprint of soil acidification. In the eastern sector with luxuriant mangrove vegetation, the SOC values increased by 10.26% and 5.03% at Sajnekhali and Harinbhanga, respectively, during our survey period after a decadal interval. The surface soil pH values exhibited a relatively lesser degree of decrease by 0.49% and 0.24% at Sajnekhali and Harinbhanga, respectively. The high mangrove diversity and density and fewer anthropogenic footprints in the eastern sector may be the reason for the minimum deviation in the values of SOC and soil pH in this region. The western sector, with an extremely low density of mangroves, showed considerable variations in the soil parameters. This may have far-reaching negative consequences on the biotic community in the western Indian Sundarbans as mangroves serve as bio-buffers against acidification in the tropical estuarine ecosystem by shifting the soil pH towards neutrality.