Physico-chemical, biochemical and microbial characteristics of soils of mangroves of the Andamans: a post-tsunami analysis

The mangroves of the Bay Islands accounting for 18% (383 km(2)) of the total Indian mangroves were adversely affected by the December 2004 tsunami. Changes in topography, salinity and massive water inflow have led to extensive soil degradation and associated nutrient losses in these mangroves. The major aim of the study was to determine whether the December 2004 tsunami had any effects on soil physicochemical (pH, electrical conductivity of saturation extract (EC), clay, cation exchange capacity (CEC), organic carbon (OC), total N (TN), Bray phosphorus (P), exchangeable cations (Ca, Mg, K and Na)) and biochemical/microbial parameters (Microbial biomass-C (C-MIC), -N (N-MIC), N-flush, basal respiration and hydrolytic enzyme activities). The post-tsunami soil samples (disturbed sites) were characterized by higher levels of EC, Na and Mg, while the pre-tsunami soils samples (undisturbed sites) had higher levels of OC, P, K and CEC. The study also revealed marked reductions in microbial biomass and activity in the disturbed sites. C-MIC, N-MIC, N-flush, basal respiration, and activities of hydrolytic enzymes like BAA-protease, casein-protease, phosphomonoesterase, beta-glucosidase, arylsuphatase, invertase, carboxy methyl cellulase and dehydrogenase were considerably lower in the disturbed sites. Higher levels of metabolic quotient (qCO(2)) in the disturbed soils indicated comparatively more stressed soil microbial community with reduced substrate utilization efficiency. Apparently, microbial activity was limited by the supply of biologically available substrates like OC in the disturbed sites. Contrarily, the more direct supply of nutrients from decomposing plant litter and the indirect supply of nutrients from the mineralization of organic matter led to significantly higher microbial activity in the undisturbed sites.