Saturday, June 17, 2017

Update on the whole-stream nitrogen additions

This year we're adding nitrogen to the two cold and two warm streams. Six hundred kilos of ammonium nitrate fertilizer will do the job, delivered by the same float-valve drippers we used last year to add phosphorus. 

It's now mid-June and still early days for our nitrogen additions, but we're already playing spot the difference. Here are two shots taken two days ago of one of our warm streams. The left photo is just upstream of the nitrogen dripper, while the other shot is just downstream. Note the particularly lurid green clumps of Cladophora that start directly below the dripper.

Our isotope additions to the four streams will start in the next few days (depending on weather!), so watch this space.

New publication from Iceland project

Dan Nelson's first manuscript from his dissertation is now out in Global Change Biology. In it, we describe how our experimental warming of Stream 7 at Hengill by 3.8 degrees C changed the structure of its invertebrate community. Somewhat surprisingly, average body size increased. Across all of Hengill's streams we can obviously find taxa with a wide range in thermal preference. It just happens that many of the invertebrates with higher thermal preference are relatively large-bodied (snails and black flies, for example) and these groups responded strongly to our whole-stream warming manipulation. Conversely, many cold-adapted taxa are quite small (many midges are obvious examples) and these groups declined. These results show that shifts towards lower average body size with warming are not universal, and that the combination of diversity in thermal preference and dispersal ability will dictate how communities reassemble as ecosystems warm in the future. Well done to Dan for all the hard work he put in to reveal these patterns!

Tuesday, June 13, 2017

Update and Hot Pot

Hey Everyone!
My name is Heath Goertzen. I’m the undergrad REU student helping Lyndsie with the channels experiment this year. This blog post shouldn’t be anything complicated, just a quick update on the project so far and what we’ve been doing. I’ll also be adding a few pictures, just for posterity.

The channels have been operating quite smoothly (knock on wood) so most of what we’ve been doing is relatively simple maintenance and monitoring of channel operation, with some sampling for biomass along the way. We’ve also been spending some serious time standing over the hot pot being confused. Here’s a picture of it:

 It's the thing on the bottom, on the top is the warm pond

Now, that looks like a normal hot pot. For the first 3 years of the experiment, I’m told that this hot pot sat at a nice 40 degrees C and behaved itself. Notice the tragic use of past tense because this year, things have gotten weird. Conditions are changing day to day (perfect for scientific experiments based on consistency), so this post will probably be inaccurate by the time you see it. I’ll still fill you in on some of the more notable conditions we’ve seen. First, the hot pot got sad. See Lyndsie’s posts below mine for more but essentially, it wasn’t being a hotpot (more of a refreshing bath, really). Lyndise bailed it out (see below) and that helped at least get the temps back up. After that, the hot pot started warming in cycles. This involved it going from the original consistent temperature of 40 C to a potentially face-scalding 90 degrees C. It also started having cycles of activity that I can only describe as geyser-esque (note, I have no idea what I’m talking about and this is pure, blind speculation), wherein levels and temperature would both change over time (~1000 liters of water and 10 degrees C variability), with peak periods looking like this.

 Don’t put your face in it

 And low periods looking like this.

Still not a good idea to put your face in it

This conditional behavior caused some of the treatments to get more temp variation than was allowable, so we tried clearing a channel between the warm pond and the hot pot. The added inflow solved our level problem (yes!) but the temperature continued in cycles, which in turn perpetuated the variability (no!).

We finally blocked the same channel we had previously cleared (the one leading to the warm pond). It feels a bit like playing a game with three options wherein you’re probably going to lose no matter what you do, but you’re losing anyways so you may as well try something. Last I heard, blocking the flow has made some improvements and the hot pot was looking more consistent! I’d like everyone reading this to engage in some manner of good luck superstition. Rub a rabbit's foot, I'm serious. At this point we’ll take all the help we can get in maintaining consistency. Cheers and thanks for reading!