Microbial Response to Potential Soil-Stabilizing Polymer Amendments for Coastal Wetland Restoration

Microbes release extracellular polymeric substances during metabolism of organic matter, which accumulate to bind particles and increase soil aggregation. On a large scale, hydraulically dredged sediment can be amended with polymer and deposited on subsiding marshes, where the polymer stabilizes the sediment until marsh plants become established. However, adding a simple C source to the soil can potentially affect microbial activity. This study determined the effect of addition of two commercially available natural polymers (xanthan gum and guar gum) on microbial biomass and activity in three types of hydraulically dredged sediments (clay, silty clay, and sandy loam) saturated under a range of salinity regimes (1.49 and 7.46, 7.46 and 14.9, and 22.4 and 37.3 mS cm(-1), respectively) for four time periods (1, 8, 16, and 26 wk). The CO2 evolved in response to added polymer suggests that microbial communities rapidly degraded the polymers. Addition of polymers provided a readily available source of C that induced a priming effect on the microbial biomass leading to increased activity. Microbial activity accelerated to a much greater rate than background (control) respiration, resulting in up to an 8.7-fold increase in loss of native soil C beyond degradation of the added polymer C. Therefore, polymer additions to stabilized sediments led to a significant increase in native soil C loss with a concomitant decrease in soil quality.