Bacterial Community Dynamics in Surface Flow Constructed Wetlands for the Treatment of Swine Waste.

Constructed wetlands are generally used for the removal of waste from contaminated water. In the swine production system wastes are traditionally flushed into an anaerobic lagoon which is then sprayed on agricultural fields. However, continuous spraying of lagoon wastewater on fields can lead to high N and P accumulations in soil or may contaminate surface or ground water with pathogens. Using a 454/GS-FLX pyrosequencing we assessed bacterial composition within a surface flow constructed wetland over a 12 month period to determine temporal and spatial dynamics of bacterial communities within the wetland. The results were analyzed using nonmetric multidimentional scaling (NMDS) and UniFrac, coupled with principal coordinate analysis (PCoA) to compare diversity, abundance, community structure, and specific functional groups of bacteria in the manure, lagoon, storage tank, wetland cells, and holding ponds.  PCoA analysis showed that bacterial composition from manure samples clustered together, whereas liquid samples did not follow any particular pattern suggesting changes in bacterial composition in and out of the wetland marsh throughout the year. From all the sampling points, Bacteria were numerically dominated by phyla—the Proteobacteria (27%), Bacteroidetes (22%), Firmicutes (15%), Cyanobacteria (4%), Tenericutes (4.2%), Chloroflexi (3%), and Actinobacteria (4%) accounting for the majority of taxa detected. Overall results, using the β diversity measures UniFrac, coupled with principal coordinate analysis (PCoA), showed that bacterial composition in manure and liquid samples were significantly different (P =0.0001) in time and space based on parsimony test using 454 pyrosequencing data. Our results showed that the wetland system is very rich in bacterial composition (60 phyla based on greengenes database) and this may be the major reason why most wetlands are very efficient in waste decomposition.