2 Manmade Marshes: One Planted, One Left to Nature March 8, 2012, 4:45 pm Wetlands development has always been a bit of an oxymoron. So perhaps it comes as little surprise that when Ohio State University studied two manmade wetlands - planting marsh varietals in one and letting nature take its course in the other - it found that over a 15-year period, both produced nearly identical plant life. Still, the natural one managed to sequester more carbon. The analysis appears in the March issue of the journal BioScience. Although wetlands creation has been an integral part of American land development policy for decades, there has been scant research on the long-term ecological viability of such human-engineered projects, said William Mitsch, a professor of environment and natural resources at Ohio State who led the study. The test wetlands were created in 1994 and fed with water pumped from the Olentangy River to mimic natural conditions. The difference was that one was consciously planted with 13 varietals of marsh plant and one was left bare and built up its plant life from seeds floating in the air and water or attached to animals migrating through. Along the way, the planted marsh exhibited more diversity. But over time, the marshes have come to contain roughly the same 100 species of plant life. And the unplanted marsh had one notable advantage: it sequestered more carbon - 266 grams per square meter per year, compared with 219 in the planted wetland. Still, both newer marshes sequestered more carbon than mature local marshes, where the rates range from 125 to 160 grams of carbon per square meter per year, the report said. Dr. Mitsch said he would stop short of advising developers of wetlands not to bother to plant their marshes. He pointed out that the planted marsh did show more biodiversity in its early years and also sequestered more methane, which like carbon dioxide is a heat-trapping greenhouse gas. Still, he said, the unplanted marsh was less work over time and was "essentially converging" in function with the planted marsh.