2.6 Effect of Environmental Factors on Metals and Microbial
Communities
Visual analysis and correlation analysis in SPSS ®were undertaken to determine the correlation, if any, between the
concentrations of different metals, microbial richness and diversity,
bed water field water quality parameters, grain size and TOC levels.
Moreover, a Principal Component Analysis (PCA) using environmental
factors including water quality parameters, total water depth, grain
size distribution, and TOC was performed to reduce the number of
variables and observe any possible clustering behaviors based on
measured environmental factors. To investigate the effect of
environmental factors on microbial diversity, the results of UniFrac
PCoA were compared with the developed environmental PCA to determine if
there were supporting similarities between the two approaches.
In addition to the assumed linear response in PCA, and to consider
unimodal species response to environmental factors, a canonical
correspondence analysis (CCA) with log-transformation was performed
using the environmental factors and microbial data at the phylum level.
To consider the effect of trace metals, a separate CCA was conducted;
only samples with measured metal data were considered due to the
approach within the statistical software in treating missing data points
(e.g., using the column average). Due to the limited number of samples
for metals and multitude of environmental factors, the sum of all six
measured metal concentrations was used as a single variable representing
the metal effect, and the clay plus silt percentage was used to
represent the sediment grain size effect. The Monte Carlo permutation
test (N= 5,000) was performed to test if the effect of environmental
variables on the observed abundance of different phylum is significant.
In other words, using such high number of N increases the likelihood of
capturing random correlations. The CCA analysis and Monte Carlo
permutation test were both performed in the PAST Package (Hammeret al. , 2001).
3. Results and Discussion