Impact of an invasive exotic species on stream nitrogen levels in southern Illinois.
Autumn-olive (Elaeagnus umbellata Thunb.) is an invasive, exotic shrub that has become naturalized in the eastern United States. Autumn-olive fixes nitrogen (N) via a symbiotic relationship with the actinomycete Frankia. At the plot scale, the presence of autumn-olive has been related to elevated soil water nitrate-N (NO3--N) concentrations. This study examined the relationship between autumn-olive cover in a watershed and stream water quality. Stream water nitrate-N (NO3--N) and ammonium-N (NH4+-N) concentrations were measured in 12 first order ephemeral streams draining watersheds with mixed forest cover and a range of 0-35% autumn-olive cover. Percent autumn-olive cover was positively correlated with mean stream NO3--N concentrations, but was not correlated with mean stream NH4+-N concentrations. While other studies have demonstrated a significant relationship between native N-fixers and stream NO3--N, this is the first study to document a relationship for an invasive, exotic N-fixing species. Results suggest that this exotic species can be an additional source of NO3- in local and regional water bodies and demonstrates an additional negative ecosystem consequence of invasion beyond losses in biodiversity.