Long-term trends and spatial contrasts in Soil Organic Carbon (SOC) of Kolkata, India

Abstract Soil Organic Carbon (SOC) is used as a proxy to assess the degree of natural as well as anthropogenic stress factors. In an over populated urban zone, the values of SOC is regulated by several factors such as deposition of dust by running vehicles, atmospheric fall out, deposition of plant litter, transference of materials from the surrounding urban environment etc. This research analyzed an yearly SOC dataset for four sites in the megacity of Kolkata, namely Moulali, Rajabazar, Manicktala and Shyambazar, covering more than three decades (1990–2025) of timescale. Over the 36-year period, SOC increased from 0.62 to 1.34% at Moulali, from 0.71 to 1.61% at Rajabazar, from 0.49 to 1.03% at Manicktala and from 0.51 to 1.12% at Shyambazar. Linear trends were positive at all four sites, with fitted slopes between 0.0140 and 0.0207 percentage points per year. A noticeable dip occurred in 2020, followed by only a modest recovery in 2021 and a stronger hike thereafter. Both natural phenomenon and anthropogenic stress factors contribute to this spatio-temporal variations. The study therefore treats the present series as a baseline record and aims to explore the SOC patterns across the four selected sites. The spatio-temporal analysis of SOC is essential to understand the carbon sequestration potential of urban soils. This may further help environmentalists to understand carbon dynamics across urban ecosystems and ways to mitigate the carbon-dioxide through sequestration of terrestrial carbon.