Algal-periphyton population and community changes from zinc stress in stream mesocosms

Three treatments of zinc (0.05, 0.5, 1.0 mg Zn l⁻¹) and a control could be identified by different algal communities in outdoor, flow-through, stream mesocosms. Established communities were continuously exposed to Zn, and samples were collected on days 0, 2, 5, 10, 20 and 30 after treatment began. Experiments were conducted in spring, summer, and fall 1984. Control stream mesocosms could be identified by diatoms in all seasons. The 0.05 mg Zn l⁻¹ treatment could be identified by certain diatom taxa being more abundant than in the control in all seasons and by a filamentous green alga in summer and fall. The 0.5 mg Zn l⁻¹ treatment could be identified by a filamentous green alga in fall. The 1.0 mg Zn l⁻¹ treatment was dominated by unicellular green algae in all seasons and by a filamentous blue-green alga in summer. A similarity index (SIMI) indicated that Zn-stressed samples generally became less similar to control samples as Zn concentration increased from 0.05 to 1.0 mg Zn l⁻¹. Total biovolume-density of all taxa responded slower than individual taxa in spring and failed to distinguish between Zn treatments in summer and fall. Zinc bound to periphyton was much better than total Zn in water for identifying Zn treatments. Zinc treatments as low as 0.05 mg Zn l⁻¹ changed algal species composition despite 0.047 mg Zn l⁻¹ being the Criterion of the US Environmental Protection Agency for the 24-h average of total recoverable Zn.