Introduced to the Great Lakes Region from Europe before 1900, invasive Flowering rush (Butomus umbellatus) forms monotypic stands that crowd native species and cover open water systems across Great Lakes shorelines and reservoirs in the northern US. Factors contributing to invasion persistence and impacts on ecosystem function by this species are poorly understood. This study characterizes vegetation and environmental factors at the Ottawa National Wildlife Refuge, which borders Lake Erie, to understand how sediment nutrient levels in watersheds affect Flowering rush invasion. We hypothesized that increased sediment nutrient levels are important drivers of Flowering rush invasion success. Sediment nutrient levels, organic matter, water depth, and vegetation were sampled within 1m2 plots throughout the management units of the marsh complex. Vegetation of Flowering Rush and 18 other species present were harvested or canopy characteristics measured to estimate biomass.
Results/Conclusions
Flowering Rush was the most abundant of all identified emergent invasive species found, occurring at 55% of the surveyed plots. Flowering rush rhizome bud count averaged 509 per plot, with a range of 0-2760. Flowering rush was found both with and without native species and other invasive species. While sediment nutrient analysis of phosphorus, nitrate-nitrite, and ammonia showed heterogeneity within and across management units, nutrient levels did not predict Flowering rush abundance, although water depth and other species biomass did. Average water depth across all plots was 38.15cm, whereas average water depth at locations with Flowering rush present was 31.58cm. Sediments with increased total N (but not P) increased storage of P and N in rhizomes. Vegetative propagule production via rhizome buds actually decreased with increased nutrients and when biomass of other species increased. These data will assist managers in identifying timing and approaches for controlling spread of this invasive and restoring wetland biodiversity.