Evaluating Edaphic Conditions Favoring Reed Canary Grass Invasion in a Restored Native Prairie

Abstract

Curtis Prairie, renowned as the world’s earliest ecological restoration site, was invaded by reed canary grass (Phalaris arundinacea) after urban stormwater inflows cut a creek and inundated a 2000-m² floodplain. We evaluated the edaphic conditions directly downstream from a stormwater retention pond to determine if sedimentation, nutrients, or elevated groundwater might have favored growth of this wetland weed. A definite signature of urban stormwater influence on reed canary grass expansion is strongly indicated by enriched nutrients (bioavailable phosphorus, nitrate-nitrogen), salt (sodium), and metals (copper and zinc), each of which was significantly elevated in the invasion area and downstream in a sedge meadow. Sodium could have dispersed clays and reduced the soil’s infiltration capacity, thereby impounding water. We evaluated soil and hydrologic conditions in order to develop a conceptual model of the invasion process in Curtis Prairie. We suggest that 1) stormwater outflow from the retention pond initiated erosion; 2) reed canary grass established alongside the eroded creek and expanded vegetatively into the prairie as native plants succumbed to flooding; 3) contaminants were continuously delivered onto the floodplain, degrading soil structure and promoting aggressive growth of reed canary grass; and 4) fine-grained sediments and organic matter were transported downstream to the sedge meadow, possibly contributing to future reed canary grass expansion into this area.