Print PageUnderstanding the cumulative impacts of multiple stressors on north-temperate lake ecosystems is increasingly important as resource managers work to develop regional mitigation and adaptation plans. Our study investigated changes in phytoplankton communities in two northern Wisconsin lakes subjected to multiple stressors over a ten-year period that included both a four-year drought and a dramatic increase in rainbow smelt populations. We tested whether drought or rainbow smelt had the strongest relationship with resultant changes in phytoplankton communities, and whether community response differed depending on lake landscape position. Phytoplankton were collected fortnightly over a ten-year period (1984-1993), enumerated, and identified to species. We used ordination, MANOVA, and classification and regression trees to identify the response of phytoplankton communities to multiple stressors.
Results/Conclusions
Results showed that changes in phytoplankton community structure were significantly associated with the drought in a groundwater-dominated lake (p < 0.02, permutational MANOVA), but were not apparent in a precipitation-dominated lake. Changes in the rainbow smelt populations were not associated with changes in the phytoplankton communities over this ten-year period. Phytoplankton responses to the drought were characterized by a decline in the Chrysophyte taxa relative to Cryptophyte taxa and may suggest a decline in the availability of groundwater-derived silica, a nutrient of particular importance to the Chrysophyte community.
