It's been a while since the last post, but we have been busy. The lab has published two exciting papers in the last few months. The first of these was Mick Demi's second publication from his dissertation, a paper in Functional Ecology describing how the structure of five stream communities at Coweeta Hydrologic Lab changed as a result of our experimental dissolved N:P gradient. Below is a nMDS plot from the paper showing the shift in community structure of the five streams during two years of enrichment (filled symbols) relative to pre-enrichment communities (open symbols) and how it was related to experimental increases in soluble reactive phosphorus (SRP) concentrations and resulting decreases in the C:P ratio of leaf litter, the dominant food resource. Overall, the results provide a community-level perspective on the increases in invertebrate production that Mick described in his Ecology paper, while clearly demonstrating the primacy of phosphorus limitation in these small forest stream ecosystems.
The second paper was a long time in coming, but we think it was well worth the wait. This Ecology paper followed up on our 2014 study of Ivishak Spring, in which we demonstrated the effect of seasonal cycles of light on the annual pattern of ecosystem metabolism in this high-latitude, spring-fed (and so thermally stable) stream ecosystem. The new paper finally shows the rest of the story - how the animal community exhibits similar seasonal patterns in production that are all driven by extreme arctic cycles of light and its effect on photosynthesis within the stream. The plot below is of daily production of primary consumers (mayflies, midges, etc) over the two years of the study. We are really excited about this dataset, which shows beautifully how production is tightly linked from the bottom of the food web all the way to the top (Dolly Varden char, American dipper, river otters). We're currently working on a proposal to follow up on this work. It would be good to get back to the North Slope.