How do multiple stressors impact zooplankton from montane lakes?

The Strecker lab has a new publication! Master’s student Jeff Brittain (M.S., 2015) studied how multiple stressors impact zooplankton communities from montane lakes. This week, his work was published in the journal Water Resources Research (co-authored with PI Angela Strecker). Here’s a summary of the findings!

Mountain lakes are often viewed as pristine ecosystems, but actually face numerous threats. Jeff studied the individual and additive effects of two threats, nitrogen deposition and acidification, on mountain lake zooplankton from two lake types: fishless or fish-stocked systems. Using tanks as lake mesocosms, Jeff had four experimental treatments: (1) no acid, no nitrogen (control); (2) acid, no nitrogen; (3) no acid, nitrogen; and (4) acid, nitrogen. He replicated this design using zooplankton communities from either fishless or fish-present lakes. Each treatment was replicated four times, for a total of 32 tanks.

In the experiment with zooplankton from the fish-present lake, zooplankton abundance tended to increase over the course of the experiment. In the acid treatment, zooplankton biomass increased with time and was largely driven by small-bodied, acid-tolerant species. In the experiment with zooplankton from the fishless lake, zooplankton abundance and biomass tended to decrease over time. The nitrogen and acid treatments had opposite effects, with nitrogen positively affecting abundance and biomass and acid having a negative effect.

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In both experiments, the nitrogen x acid treatment had more positive effects than expected, indicating that nitrogen may override negative effects of acid, and highlights the complexity in managing threats in montane lakes. Another major take-home message was that zooplankton from fish-present and fishless lakes responded differently to stressors. Fish-present lakes had acid-tolerant zooplankton species that dominated in the acid treatment, but these species were largely absent from the fishless lakes. This may make fishless lakes more sensitive to acid pollution. Overall, it may be difficult to predict zooplankton response to threats and to restore habitat through fish removals.

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