Role of Plant Architecture and Cuticular Features in Removing Iron From Wetlands Constructed to Treat Abandoned Mine Drainage Rachel Giroux, Beth Karwaski, Kenneth Klemow, Donald Mencer, Therese Wignot, and Brian E. Whitman College of Science and Engineering, Wilkes University, Wilkes-Barre, PA Background Abandoned mine drainage (AMD) is a primary contributor to aquatic pollution nationwide. Heavy metals dissolved in AMD become oxidized, forming insoluble metal hydroxides deposited in stream beds. AMD kills aquatic vegetation and impairs macroinvertebrate communities needed for healthy aquatic food chains. AMD is often treated by diverting contaminated mine water into constructed wetlands. In the mid-1990s, an interdisciplinary team of Wilkes biologists and environmental engineers designed two wetland systems that successfully removed iron from mine water. These wetlands improve water quality by adsorbing particulate iron onto the surface of individual plants, including introduced and naturally colonizing species. Some plant species remove iron more effectively than others. Plants with diffuse submerged stem and root structures appear to bind more iron than those with unbranched stems. However, the proportion of the plant covered by non-polar vs. polar non-cuticled plant surfaces may also affect the adsorption of polar hydroxides. Statement of Problem Identify the species of wetland plant best suited to remove the most iron per unit area in order to achieve maximum iron removal potential. Hypothesis The plant species able to trap the most iron will most likely have broad ridged leaves with a branched structure, such as the bur-reed. Plants with smoother, less branched leaves, such as the great bulrush and soft rush, will accumulate less iron. Plants with a thick waxy cuticle will most likely prevent heavy iron accumulation as opposed to plants with a thinner cuticle layer. Materials and Methods Several dozen plants of four species were collected removed from an AMD-treatment wetland near Nanticoke in Luzerne County, PA. The potions of the plants exposed to the water column were isolated. The plant structures were rinsed with tap water to remove the iron material. The water containing iron material was oven dried. The iron material was ignited at 800°C for 2 hours to burn off any organic matter, evaporate any remaining water, and convert the material into Fe 2 O 3. This material was then weighed. The surface areas of the plant structure were determined by first spray painting the plants black and then using a CI-202 Area Meter. Iron weight was graphically correlated to plant surface area for each species. Conclusions Bur reed accumulates a greater amount of iron per unit area compared to the cattail, great bulrush and softrush. Preliminary cuticle analysis proved to be inconclusive. Further experiments may be done to optimize cuticle wax extraction. Typha latifolia: Cattail The common cattail has long, broad, slightly waxy leaves. A thick cylindrical column of tightly bound leaves is exposed to the water in the wetland. Sparangium americanum: Bur reed Plant Species Juncus effusus: Softrush The stem of bur reed produces short, broad, ridged leaves. The column exposed to the water in the wetland can be branched or tightly bound as in the cattail. Scirpus validus: Great bulrush Softrush has long, thin, smooth tubular leaves. They are frequently found in large clumps where the columns exposed include a collection of tubular leaves. Great bulrush also has long tubular leaves. Many of the plants also included an outer smooth layer of dead matter. The columns exposed to the water often contained a collection of plant leaves. Results Literature Cited Matthew A. Jenks, Hillary A. Tuttle, Sandford D. Eigenbrode, and Kenneth A. Feldmann. Leaf Epicuticular Waxes of the Eceriferum Mutants in Arabidopsis. Plant Physiology. (1995) 108: Abdelali Hannoufa, John McNevin, and Betrand Lemieux. Epicuticular Waxes of Echeriferum Mutants of Arabidopsis thaliana. Phytochemistry. (1993). 33: Future Work Examination of biofilms (bacteria or other micro-organisms) may reveal additional insight concerning the adherence of iron to plant cuticles. Chemical analysis of the iron material found in mine drainage would also be useful when deciding how to remove the material from the environment. A study comparing the live plant material to the dead plant matter could determine whether the dead matter in the wetland accumulates a greater amount of iron. Analysis of plant densities throughout the wetland may also be performed to determine if groups of a particular species optimize iron removal. Surface Area (cm 2 ) Iron (Fe 2 O 3 ) Weight (grams) Figure 3: Great bulrush: Iron Weight vs. Surface Area Iron (Fe 2 O 3 ) Weight (grams) Surface Area (cm 2 ) Figure IV: Softrush: Iron Weight vs. Surface Area Surface Area (cm 2 ) Iron (Fe 2 O 3 ) Weight (grams) Figure I: Bur reed: Iron Weight vs. Surface Area Surface Area (cm 2 ) Iron (Fe 2 O 3 ) Weight (grams) Figure II: Cattail: Iron Weight vs. Surface Area* Figure 1 shows the relationship between iron accumulation and surface area for bur-reed. For the most part, there is an upward trend, indicating an increase in accumulation with an increase in surface area as expected. There is significant scatter indicating that other factors are involved when determining a plants ability to trap iron. Inset graphs contain rescaled versions for cattail, great bulrush and soft rush respectively to allow for a more detailed view of the data. Figure 2 shows cattail’s iron accumulation per square centimeter of plant matter. There is a much smaller iron mass for each square centimeter compared to the bur- reed. The cattail data also included a degree of scatter, which is a topic of future study. Figure 3 depicts the great bulrush’s iron accumulation: surface area relationship. The great bulrush was notably smaller in size and collected a much smaller amount of iron than bur reed. Cattail adsorbed a slightly larger amount of iron where the surface areas were similar. Scatter was also an issue when dealing with the detailed great bulrush graph. Figure 4 illustrates the relationship between iron accumulation and surface area of softrush. Softrush and great bulrush adsorbed similar amounts of iron. Softrush, however, included a larger variety of plant surface area where accumulation increased. Scatter was again observed with the softrush. Funding for this project was provided by a grant from Merck / AAAS to Wilkes University