Our adventurous week started off with sampling the benthic critters (inverts, bugs, and snails) at the Fog lakes. This included eckman grabs (quantifiable “scoops” of sediment) and snorkeling transects (giving us the opportunity to elegantly slip into our stylish wetsuits to count snails). This sampling was performed at multiple sites and depths within each lake and the data will be important for understanding the food web structure and dynamics within these systems. The fish inhabiting the Fog lakes, arctic char (Salvelinus alpinus) are highly dependent on these snails (mainly Lymnaea) as their primary food source. Therefore, due to this high degree of connectivity between snails and char, alterations in the abundance of one will likely have repercussions for the other, resulting in dynamic feedback loops that are quite intriguing to any ecologist studying food webs!
Our newly adopted snorkeling transects proved to be an effective strategy for quantifying the abundance of snails and also indirectly provided info about the fish populations within each of the lakes. For example, Fog 2 has a lower population of fish (estimated via sampling and recapture data; ~163 indv) compared to Fog 3 (~670 indv). This difference in fish abundance results in different top-down predation pressures (low in Fog 2 and high in Fog 3) that structure the lake food web. This was evident during our snorkeling transects when we counted many more snails in Fog 2 compared to Fog 3 (i.e., more fish means more predation which means less snails). Our benthic sampling will continue multiple times throughout the season as well as during future seasons within the Fog lakes. This will allow us to closely monitor and analyze alterations in both the predator (fish) and prey (snail) populations over time and how they interact and respond to our warming manipulations. After all, if you want your char to grow big and strong you gotta have the right resources available! Along with our benthic sampling at the Fogs, we also got a chance to get our hands dirty while taking sediment cores with Anne Giblin and her tech Kristen Rathbun. These sediment cores are taken from various depths around the lakes and then taken back to lab and incubated with different light regimes to investigate the respiration (oxygen uptake and production of carbon dioxide) and primary production rates (production of oxygen and uptake of carbon dioxide) of the sediments. These rates play a vital role in the carbon dynamics and overall productivity within lakes and it shall be interesting to see how our warming influences these rates. We also sampled fish on a couple of the “I-lakes” this week, gladly allowing the helicopter to chauffeur us to and from. The appropriately named I-lakes are the chain of lakes along the inlet to Toolik Lake. These lakes are connected by regularly flowing streams (making them “open” systems) and thus fish, like the arctic grayling (Thymallus arcticus), are allowed to move between these lakes. It turns out that the degree of “openness” of these arctic lake systems seems to have a strong influence in determining the fish population demographics and species diversity. A future goal of the LTER site here at Toolik is to gain a better understanding of the dynamics and differences between open and closed systems. Our fishing at the I-lakes turned up much more diversity than in the Fog lakes, which is a closed system with only arctic char and slimy sculpin (Cottus cognatus) as inhabitants. Our catch included arctic grayling, round whitefish (Prosopium cylindraceum), lake trout (Salvelinus namaycush), and even a large burbot (Lota lota). As you can see, the I-series has many interacting pieces that make up the food web puzzle, making it an exciting system to investigate. During fish sampling, when a fish is captured via hook & line or gillnetting, we record and collect multiple parameters, which include length, weight, growth, diet, and age. We also tag the fish with unique readable PIT tags, which act as a type of name or identifier for the individual fish. This is useful to track growth and survival of the individual fish over time and eventually scale up to the entire population. On the plate for next week we have stable isotope sampling, which includes collecting samples from each trophic level of the food web (benthic algae, phytoplankton, benthic critters, snails, zooplankton, and fish). With these samples we will obtain unique stable isotope (C & N) signatures from each component of the food web and use this data to get an understanding of the food web structure (who eats what). Also, we plan to set the stages (i.e., large platforms) that will eventually house our warming equipment at each of the warmed Fog lakes. Then, the next week the warming crew arrives to start our setup! By the way, be sure to check out the regularly stocked “photos” tab that highlights some of the great pictures from our time here at TFS. Informative captions for each photo are coming soon, I promise!
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Author:
Nick Barrett- PhD student on Arctic Lake Warming project Check out my personal Twitter page for various tweets about the project: @WaterWorks_NB |