Environmental Engineering Reference
In-Depth Information
specifications as those used in the flask study. Bioaugmentation consisted of
P. aeruginosa
strain 64 on vermiculite. Cell density at the time of application
to the vermiculite was 10
6
cells/ml.
Microorganisms in the soil consume soil pore oxygen and release carbon
dioxide (CO
2
) as they grow. This process, respiration, is a segment of the
short-term organic carbon cycle in which carbon is converted to CO
2
(min-
eralization). Several ecosystem-level effects can be seen when a soil microbial
community is stressed by the presence of a toxin. First, the total community
respiration level decreases as the metabolic activity decreases. Then, the
respiration-to-biomass ratio increases. As exposure time to the toxin
increases, the nutrient turnover and the rate of organism turnover increase.
Microbial community succession demonstrates a decline in species diversity
and an overall decrease in growth and respiration with each succession. The
most sensitive biomarkers of both soil degradation and repair are those
associated with microbial metabolism, such as respiration, biomass, enzyme
activity, and nitrogen mineralization. Although CO
2
production is not a
completely accurate assessment of biodegradation of the contaminant, res-
piration remains the most widely used indirect method to estimate biodeg-
radation in contaminated soils (Li, 1998; Zibilske, 1994).
Dry wells for soil respiration analysis were designed at ERDC (Figure
7.13) and built from parts supplied by Plastic Supply, Inc. (Brandon, MS).
The probes were constructed from a 6-in. upper ring and cap of PVC
superimposed on a 12-in. vertical dry well made of standard 2-in. slotted
Figure 7.13
Diagram of soil gas sampling probe used to monitor microbial respiration
in situ
.
