Location: Water Management ResearchTitle: Vegetation Changes and Partitioning of Selenium in 4-Year-Old Constructed Wetlands Treating Agricultural Drainage) Author
|Lin, Zhi Qing|
|Ye, Zhi Hong|
Submitted to: International Journal of Phytoremediation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2009
Publication Date: 5/26/2010
Citation: Lin, Z., Terry, N., Gao, S., Mohamed, H., Ye, Z. 2010. Vegetation Changes and Partitioning of Selenium in 4-Year-Old Constructed Wetlands Treating Agricultural Drainage. International Journal of Phytoremediation. 12:255-267. Interpretive Summary: The management of selenium (Se)-contaminated agricultural tile-drainage water is one of the major environmental issues confronting agriculture in the San Joaquin Valley, California. Currently, most of the Se-laden drainage water is disposed into evaporation ponds/basins, which continues to be a concern on potential toxicity to migrating water birds. To reduce loading of Se into evaporation ponds, flow-through constructed wetlands were tested for removal of Se from selenate-laden agricultural drainage water before its discharge into evaporation ponds. The overall Se removal efficiency and the significance of Se volatilization have been previously reported. The objective of this paper was to determine the partitioning of Se mass retained in different compartments (sediments, living plant material and litter, and standing water) of 4-year-old wetland cells. The focus was to explore the effects of invasive species on wetland plant management and the role of vegetation in Se portioning in the treatment wetlands. Data showed that plant species varied significantly in their competitiveness with invasive species and Se partitioning in sediments was greatly affected by vegetation. About 90% of the total Se was portioned in the top 10-cm layer of sediment. The accumulation of Se mass in plant materials (including invasive plants, living tissues and litter) accounted for ~ 2% of the total Se mass retained. The information is valuable for better understanding the role of vegetation in wetland to reduce Se environmental toxicity.
Technical Abstract: The knowledge of vegetation management and the partitioning of selenium (Se) in treatment wetlands is essential for long-term effective operation of constructed wetlands treating Se-laden agricultural tile-drainage water in the San Joaquin Valley, California. Vegetation changes in six vegetated wetland cells were recorded 4 years after the wetland’s inception. Samples from different compartments of treatment wetlands were collected, and potential effects of vegetation change on Se partitioning in the treatment wetlands were examined. This field study showed that saltgrass (Distichlis spicata (L.) Greene) and rabbitfoot grass (Polypogon monspeliensis (L.) Desf.) were less competitive than cattail (Typha latifolia L.) and saltmarsh bulrush (Scirpus robustus Pursh). Over 90% of the wetland cells originally vegetated with saltgrass and rabbitfoot grass was occupied by the invasive species – mainly cattail, which occurred primarily during the 4th growing season without invasive species control. More Se was found in sediments from vegetated regions, compared to sediments from unvegetated areas of the wetland cell. In particular, rhizosphere sediments accumulated up to 4-fold more Se than non-rhizosphere sediments. Among the total Se retained in the wetland by the time of sampling, about 90% of the total Se was portioned in the top 10-cm layer of sediment. The accumulation of Se mass in plant materials (living tissues and litter) accounted for ~ 2% of the total Se mass retained, which was determined according to the final species composition (including invasive plants) in each wetland after 4 years of operation.