Microbial mats associated with mangroves provide soil stabilization and modify nutrient chemistry over monsoon cycles

We examined sediment characteristics and water nutrient levels in channels of the Sandspit backwater mangroves. Using the bell jar method and analyzing soil physico-chemical parameters, we identified seasonal variations in water nutrients and edaphic features. Soils covered with microbial mats predominantly comprised fine sands, while fringe area soils showed higher medium sand content. The microbial mat positively impacted the mangrove soil, enhancing its nutrient profile. Statistical analysis revealed significant positive correlations (p < 0.05) between key soil variables temperature, pH, salinity, bulk density, chlorophyll a/b, total carbon, organic matter, moisture content, water holding capacity, and carbon–nitrogen ratio) and water channel nutrients (nitrite NO₂⁻, nitrate NO₃⁻, ammonia NH₄⁺, phosphate PO₄³⁻). Principal component analysis identified soil salinity-temperature, organic matter, water holding capacity, soil moisture, NH₄⁺, and PO₄³⁻ as significant variables differentiating the two soil types, and cluster analysis supported these findings. Seasonal variations within each soil type were minimal; rather, sediment properties were more influenced by the presence of microbial mats than by pre-monsoon, monsoon, or post-monsoon changes. The microbial mats played a major role in increasing total nitrogen and carbon percentages, whereas wastewater runoff predominantly influenced inorganic nitrogen and phosphate concentrations. These results highlight the complex interactions between hydrological and edaphic factors and offer valuable insight for future modeling and restoration of similar mangrove ecosystems. This study aids in establishing effective management strategies for tropical mangroves by interpreting how seasonal dynamics interact with sediment properties and nutrient fluxes. It provides baseline ecological knowledge relevant for Sandspit and other mangrove ecosystems impacted by marine pollution, with global implications.