Algal responses to road run-off in an urbanized catchment

Road run-off containing excess nutrients, heavy metals, and other organic contaminants often flows directly into streams during storm events, impacting both water quality and stream ecosystem structure and function. This run-off can be a potential stressor or stimulant for algae. We used controlled experiments in mesocosms (~1,300 liter tanks) to evaluate the effect of storm water on algal biomass and metabolism. Storm run-off was collected from Little Black Creek, MI and used to create the following treatments: 0% storm water (control; n=4), 50% (n=4), or 100% (n=3). Nested within each mesocosm were four exclosure treatments containing different combinations of algae, snails (Physa sp.) and Pumpkinseed Sunfish (Lepomis gibbosus). Storm water concentration did not have a significant impact on either algal biomass or metabolism. Within each storm water treatment, significantly less algal biomass was present on the tiles exposed to fish, suggesting fish movement in the exclosures removed algae. Measures of algal production and respiration did not show clear patterns in response to the storm water treatments. The limited algal response may be because the storm water run-off used in this experiment contained low levels of contaminants or because exposure to storm water conferred resistance to the algal communities.