Invasive plants constitute nearly 90% of Hawaiian flora; many are found at low elevations where human impacts (i.e., agriculture, urbanization) are greatest.  While this threatens Hawaiian biodiversity, invasive N-fixing plants, like Falcataria moluccana (albizia) threaten ecosystem function through alteration of nutrient budgets and cycling. To examine the effects of invasive plants and land use on riverine organic matter dynamics, we compared leaf breakdown of albizia and native Metrosideros polymorpha (ohia) trees in forested and developed reaches of the Wailuku River during wet and dry seasons (2005-2006). During 2005, breakdown rates of albizia leaves were significantly faster than ohia (1.5 – 2X) and were attributed to greater initial fungal colonization.  However, by the end of the experiments, fungal biomass on ohia was similar to and often exceeded that on albizia litter. Breakdown rates of litter from both species did not differ between forested and developed reaches of the river.  Breakdown rates were greatest during dry seasons for both litter types, which was attributed to increased river flow (100-500X) resulting from storms. Elevated leaf litter inputs and higher litter breakdown rates for albizia suggest that this invasive riparian tree could dramatically alter N dynamics in Hawaiian rivers and their downstream coastal areas.