|Ibekwe, Abasiofiok - Mark|
Submitted to: Journal of Applied Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/31/2006
Publication Date: 3/23/2007
Citation: Ibekwe, A.M., Lyon, S.R., Leddy, M., Jacobson-Meyers, M. 2007. Impact of plant density and microbial composition on water quality from a free water surface constructed wetland. Journal of Applied Microbiology. 102:921-936 Interpretive Summary: Diseases related to water sanitation are estimated to account for four percent of all deaths and about six percent of the total disease burden occurring worldwide. Health risks rise sharply with the ingestion of unsafe water. Therefore, research into wastewater treatment is needed in order to reduce the risks associated with improper sanitation, particularly in terms of wastewater reuse for crop irrigation and other domestic purposes. One way of treating wastewater is to utilize constructed wetlands, an easy to handle technique that is considered to be relatively inexpensive in developing countries. Benefits for constructed wetlands include water quality improvement, water reclamation, and habitat for species conservation, flood control, and recreational and educational activities. The Prado Wetlands in Chino, CA was used for this study. It is an approximately 186 ha, free water surface (FWS) constructed wetland consisting of 50 interconnecting shallow ponds that treats approximately 50 percent of Santa Ana River water prior to its passage to Orange County, CA where it is used for groundwater recharge. The primary functions of the wetlands are to reduce nitrate levels and other contaminants in Santa Ana River water destined for groundwater storage basins in Orange County, California. We showed that the wetland ponds with 50% plant cover were the most effective ponds for nitrate removal. The high efficiencies of these ponds were derived from the availability of energy sources from plants to bacteria for contaminant removal from the wetland effluent. Our findings highlight that the composition of different bacterial species was responsible for the breaking down of contaminants and thus the improvement of water quality.
Technical Abstract: Aims: To determine the effects of plant density and microbial community composition associated with wetland plants from different wetland pond on water quality of a free water surface (FWS) constructed wetland. Methods & Results: Water chemistry was monitored weekly for nitrate, orthophosphate and suspended solids at various sites throughout the wetland for six months. Community profile using denaturing gradient gel electrophoresis (DGGE) of total DNA was used to determine the major microbial composition associated with the wetland sediment, rhizosphere, and surface water. Bacterial 16S rRNA cloned libraries were also constructed and 300 clones were analyzed by amplified ribosomal DNA restriction analysis (ARDRA) and grouped into operational taxonomic units (OTUs). A total of 35, 31, and 36 different OTUs were obtained from soil, rhizosphere, and surface water, respectively. The most dominant group of our clone library was allocated to an unidentified bacterium followed by the phylum Proteobacteria. The dominant organisms within the class were in the gamma, beta, and delta classes. The ponds with 50% plant cover had about a 99 percent nitrate removal. The average changes between the influent and effluent water samples were 50-60 percent nitrate removal and 40-50 percent orthophosphate removal. Conclusion: Free surface constructed wetland with 50 percent plant cover to 50 percent surface water produced the most efficient wetland units for contaminant removal from wetland water. Significance: This study provides evidence that wetlands with 50 percent plant cover may promote the growth of diversed microbial communities that play important roles in decomposing chemical pollutants in surface water for the improvement of water quality.