Short-Term Variability in Sediment Carbon Sequestration in Tropical Indian Wetlands: Physicochemical Controls and Policy Relevance

Wetlands are critical components of the global carbon cycle, functioning as both carbon sinks and sources depending on environmental conditions. This study assessed short-term variability in sediment carbon storage and its physicochemical controls across five tropical wetlands in southern India. Sediment samples collected in March 2024 and March 2025 were analyzed for pH, macronutrients (N, P, K), bulk density (BD), organic carbon (OC), total organic carbon (TOC), and derived carbon indices, including carbon mass (CM), total mass carbon (TMC), and carbon density (CD). Results indicated consistent increases in OC (0.6–2.4% to 0.7–2.65%) and TOC (1.2–6.2% to 1.5–7.1%), accompanied by increases in CD (1.71–10.69 to 2.18–12.57 kgm⁻²), suggesting enhanced short-term carbon accumulation. Correlation and principal component analyses revealed strong associations among carbon-related variables, while BD and pH contributed to secondary gradients. However, these relationships partly reflect mathematical dependencies among derived indices and should be interpreted with caution. Effect size analysis (Cohen’s d) indicated substantial short-term differences for carbon-related variables (d = 2.04–2.46), along with strong effects for OC and BD, reflecting consistent directional changes across sites. Nitrogen showed a supportive role in organic matter accumulation, whereas phosphorus exhibited limited short-term influence. Slightly acidic conditions (pH 4.2–6.0) were associated with reduced decomposition and enhanced carbon preservation. Despite these findings, the study is constrained by its short temporal scope and the absence of key biogeochemical parameters such as redox potential and greenhouse gas fluxes. Overall, the results provide baseline insights into sediment carbon dynamics and inform future wetland carbon monitoring and management strategies.