Warming temperatures and its effects on lower trophic levels in Arctic tundra ponds

Background/Question/Methods

While it is well established that the Arctic is warming, the impact of this warming on Arctic aquatic ecosystems is largely unknown, due in large part to the absence of long-term data. High percentages of the total land in the Arctic tundra consist of ponds and lakes with low production and biodiversity. The International Biological Program (IBP) ponds in Barrow, Alaska, represent one of the few locations where historic data on Arctic aquatic ecosystems exist; these ponds were first sampled in the early 1970s. Recently, with warmer temperatures, we observed changes in these aquatic systems such as increased algae biomass and nutrient levels. We hypothesized that these changes would also affect the biodiversity and abundance of zooplankton and algae, both planktonic and benthic, over the past 40 years. Water chemistry, algae and zooplankton were sampled weekly from multiple small ponds in both the 1970s and 2009-2012. We calculate correlation coefficients to find any relationship between species and between temperature and species with their statistical significance. We also make bar and line graphs to better identify differences between actual and historical data.

Results/Conclusions

Preliminary results from Pond E and C indicate that zooplankton community seasonal dynamics vary among ponds in close proximity to each other. Samples from IBP Pond E indicate much higher zooplankton abundances in samples from 2010-2012; however, the IBP Pond C community shows very little difference among decades. Species such as Daphnia middendorffiana and Diaptomus spp. were among the most abundant taxa. Reproduction of D. middendorffiana was also highly variable among years. There was a 400% increase in asexual reproduction of Daphnia in 2012 as compared to 2010, 2011 and 1970’s. Production of offspring in D. middendorffiana was positively related to water temperature the week prior to sampling.  The increase in water temperatures over the past 40 years will likely have a positive impact on Daphnia populations. Surprisingly, the reproduction of D. middendorffiana was not significantly related to phytoplankton CHL-a levels. High variability among ponds has made it difficult to generalize about changes in the zooplankton community through time.  However, the recent increase in temperature in the ponds may play a role in controlling zooplankton reproduction. In 2012, we found more noticeable changes in Daphnia reproduction, although the reason for this massive reproductive event is unclear.