Lexie Lucassen

2015 Summer Internship Program

Geomorphic Controls on Hyporheic Steam Temperture Fluctuations in Alaska

Lexie LucassenAs a JISAO intern at the Alaska Salmon Program, I helped wherever was needed to run the Aleknagik and Nerka field camps and contribute to the monitoring of the Wood River System that has run continuously since the late 1940’s. The program focuses not only on monitoring sockeye salmon, but rather the entire ecosystem that revolves around this keystone species.

Most days were spent in the field running projects and collecting data and samples, with some lab work on the side to process samples or prepare for the field. Long-term data collection included limnology, in which we sampled the lakes’ chlorophyll and zooplankton abundance, clarity, and thermal profile. I also helped with specific projects, ranging from bear hair collection to stream carbon sampling, as well as sampled resident fish species and our focus species, sockeye salmon. We did things like measure size, species abundance, gastric lavage to monitor diets, take genetic samples, conduct scarring surveys, and tag the fish. Later in the season as salmon started to spawn and die off, we surveyed the number if sockeye salmon in different habitats throughout the watershed and collected otolith, or ear stone samples from dead specimens. Otoliths are used to determine their age and strontium isotope levels, which can be used to estimate which freshwater habitats an individual salmon used when it was a juvenile.

I conducted my own project measuring hyporheic temperatures of streams, found in the area of a stream’s gravel bed where Lexie working in Alaskagroundwater and stream water mix. Because water temperature controls so many biological and chemical processes in streams, and a lot happens ecologically below the gravel line, it is important to understand how the hyporheic zone temperature fluctuates throughout the day. I attached temperature loggers to rebar poles, pounded them into streambeds at different depths, and let them run for several days. I then compared them to the features of each individual stream, and found that there were pronounced differences in temperature between hyporheic and open channel temperatures as little as 20 cm below the gravel surface. However, this lack of mixing between the channel water and the interstitial water was most prominent in low gradient streams with small particle sizes. In steeper streams with larger gravel and cobble, channel water mixed much deeper into the hyporheic habitat.



Lexie's research poster

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