Our newest NSF project is a large, integrated study that will assess the potential of a warming climate to change how terrestrial organic carbon is processed by forest stream networks. One component of the research involves field manipulations of water temperature in stream-side channels and in a natural stream reach. Over the last year, we have worked very hard to get these manipulations up and running. They are finally both online. Below is a thermal image overlaying a photo of half of our stream-side channel array. The channels provide a range of five temperatures (ambient, +1C, +2C, +3C and +4C), each replicated four times. Our first three-month experiment just ended, during which we measured responses in coarse and fine particulate matter, chironomid midges and Tallaperla stoneflies.
The channel array has worked amazingly well. Below is a plot of mean (+/- 1 SE) temperatures for the first few weeks of this spring's experiment, showing how tightly we're able to maintain the treatment differences, while maintaining all the natural temporal variation in temperature.
The second temperature manipulation is more ambitious. We are heating an entire stream reach by 3-4C for two years and studying a suite of community- and ecosystem-level responses (everything from midge consumption rates to entire organic matter budgets). The stream-warming infrastructure was completed on time in May 2019 and we are now warming. Below is a shot of our set-up, which diverts the stream flow at the top of the reach into a holding tank, where it is warmed to target temperature by cartridge heaters. The heaters are controlled electronically based on the difference between inflow and outflow temperatures. Overall, very exciting. Fingers crossed that it all goes smoothly for the next two years!