Depth, soil type, water table, and site effects on microbial community composition in sediments of pesticide-contaminated aquifer.

Microbial community compositions in pesticide-contaminated aquifers have not been studied, although such information is important for remediation and maintaining freshwater sources clean under changing climate. Therefore, phospholipid (PLFAs), glycolipid (GLFAs), and neutral lipid (NLFAs) fatty acids were determined from sand and clay sediments at depths of 0.3–24.8 m, all contaminated with triazines and dichlobenil/2,6-dichlorobenzamide. The portion of fungi and Gram-negative bacteria at 0.3 m was greater than at 0.8 m, where the percentage of Gram-positive bacteria, actinobacteria, and sulfate-reducing bacteria (SRB) increased. In deeper sediments, microbial biomass, activity, and diversity decreased. Clay sediments seemed to serve as a reservoir for slow pesticide elution to groundwater, and their biomarker portion for all bacteria except actinobacteria was greater than in sand sediments. The slow pesticide dissipation seemed to occur in the main groundwater flow zone, resulting in nitrogen release simultaneously with organic matter elution from gardening and bank filtration. As a result, microbial biomass, activity, and diversity were increased. This shift in conditions towards that in surface soil may be appropriate for enhanced natural attenuation of pesticides in groundwater sources.