LTREB experimental chironomid mesocosms at Myvatn, Iceland

During the summer of 2014, we conducted experiments testing whether increasing numbers of chironomid larvae would increase primary production and standing chlorophyll a concentrations. We incubated experimental mesocosms with varying numbers of chironomid larvae for 12 days in July. We tested sediments for chlorophyll a concentrations, as sediments are primarily composed of benthic diatoms. We tested the oxygen production in these mesocosms. We did this by sealing the mesocosms and incubating them in Lake Myvatn for 3 hours, and taking measurements of dissolved oxygen before and after the incubations. We were also interested in whether this increase in food resources might translate to increased growth rates of chironomid larvae at high larval densities. After stocking experimental mesocosms with varying numbers of chironomid larvae, we set these mesocosms in Lake Myvatn for 12 days. We collected the larvae at the end of the 12 day experiment and obtained the average dry weights of the Chironomus islandicus larvae in each mesocosm. We hypothesized that the tubes that chironomid larvae build would be a superior substrate for algal growth, as compared to loose sediments. Because there are two taxa (Chironomus islandicus and Tanytarsus gracilentus) that are overwhelmingly dominant at our study site, we wondered whether there would be differences in this effect between the two species. We stocked mesocosms with larvae from one of the two species, and mesocosms were then incubated in Lake Myvatn. We collected sediments and larval tubes from each mesocosm and tested their chlorophyll a concentrations. We hypothesized that one mechanism that chironomid larvae might alleviate algal nutrient limitation by depositing concentrated nutrients near algae in the form of larval excretions. We collected chironomid larvae from Lake Myvatn and placed them in distilled water. We then sieved out the larvae and their fecal passings, and transported the water samples to Madison, WI, USA, where nutrient concentrations were analyzed