Arsenic has become a contaminant of significant concern around the world due to its prevalence and toxicity. The industrial and agricultural history of northwest Ohio created a legacy of arsenic contamination in the area, leaving current and future landowners with the task of remediation. Engineered wetlands could be part of an inexpensive and aesthetically-pleasing treatment strategy for removing arsenic from contaminated water because they rely on naturally-occurring physical, chemical, and biological processes. The role that wetland plants can play in arsenic remediation in temperate climates is not well understood. We do know that in order to maximize the removal of arsenic using wetlands, these plant species need to accumulate arsenic, survive prolonged arsenic stress, function during the course of a growing season, and to survive secondary contaminants that co-occur with arsenic.
During the course of this dissertation I hypothesized that native wetland plants could be used for arsenic phytoremediation and that using mixtures of plant species would maximize arsenic removal in the temperate climate of northwest Ohio. To test this hypothesis I performed four laboratory experiments using native plant species that accumulated arsenic in preliminary tests and have different growing seasons.
(i) Carex stricta, Pycnanthemum virginianum, and Spartina pectinata tolerated an environmentally relevant concentration (1.5 mg As L-1) and continued removing arsenic when irrigated with arsenic-laden solutions for seven weeks. Their tolerance toward arsenic was evaluated in terms of contaminant uptake, growth, and chlorophyll content.
(ii) When exposed to arsenic in conditions representative of spring and summer in northwest Ohio, the warm-season species (S. pectinata) performed best in summer conditions, while the cool-season species (C. stricta) exhibited consistent uptake in both sets of conditions. A variety of warm- and cool-season species could be used to maximize the period of arsenic uptake during a growing season.
(iii) The age of C. stricta and S. pectinata did not effect uptake by roots, but older plants transferred a greater portion of arsenic to leaves and stems than younger plants. Arsenic extraction could be maximized by allowing plants to accumulate arsenic throughout the growing season, and harvesting aboveground portions in the fall.
(iv) The effects of arsenic, copper, and silicon varied in terms of uptake and toxicity in Azolla caroliniana and Lemna minor. Again, a mixture of plant species could be used to maximize the removal of each contaminant.
The results of this research indicate that native plants could be used in wetlands engineered for arsenic remediation, and that a community of plants could maximize uptake throughout the growing season. These findings will be used during the construction of microcosm and pilot-scale systems at a local, industrial site.