Assimilative capacity and the dynamics of subsurface microbial ecology
Abstract
An assessment of the assimilative capacity, the capability to attenuate contaminants, of subsurface soils for pesticides is essential to estimate their fate as well as to propose bioremediation techniques. This study was conducted to estimate the assimilative capacity of subsurface soils for atrazine, to evaluate the responses of the microbial population to nutrients preexposure, and to estimate how seasonal variations impact microbial function in subsurface soil. Soil was (i) incubated with atrazine and its sorption, mineralization, and transformation (formation of bound residues and metabolites) measured; (ii) preexposed to glucose, N, NPK, atrazine, 2,4-D, glucose + NPK, atrazine + NPK, and 2,4-D + NPK, and (iii) collected in the winter and summer and the microbial biomass and activity measured. Sorption coefficients for atrazine, K$\sb{\rm f},$ declined from 8.17 in the surface to 3.31 in the vadose zone. Rates of atrazine mineralization and bound residues formation were 12- and 2.3-fold lower in the vadose zone than in the surface soil. Sorption, mineralization, and formation of bound residues were correlated to chemical and biological properties of the soil. Small amounts of the metabolite deethylatrazine (DEA) were formed and degraded in the vadose zone during 205 days. Preexposure to atrazine increased microbial biomass 1.7 times and atrazine mineralization by a 3.5-fold factor. Preincubation with N, NPK or 2,4-D had no effect on atrazine mineralization, but mineralization of 2,4-D increased up to 76% with preexposure to 2,4-D. This implies a specific population is needed for degradation. Microbial biomass in the subsurface soil was the same in the winter and in the summer, but microbial activity in the summer was up to 49 times greater than in the winter due to higher temperatures. Assimilative capacity for atrazine in the subsurface is lower than at the surface. Conditions that favor the microbial population, such as preexposure to the contaminant and high temperatures, increase the assimilative capacity of this environment.
Degree
Ph.D.
Advisors
Turco, Purdue University.
Subject Area
Agronomy|Microbiology|Agricultural engineering|Soil sciences
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