Nitrogen isotope additions finally start

This year the weather did a good job delaying the start of the planned simultaneous nitrogen isotope additions to our four focal streams (two warm, two cold), as we cannot start them if the streams are too high. We finally got a forecast for a break in the weather, so Mick and Jon started the drippers yesterday evening (in truly awful weather, as it happened). The good weather has now arrived and all 8 drippers (one for ammonium nitrate and one for 15N-enriched ammonium chloride and potassium nitrate in each stream) were behaving well when we changed the batteries after one day out of the scheduled five days of isotope addition. Fingers crossed that those five days go off without a hitch.

Tomorrow we take our first food web samples from the four streams, followed two days later by comprehensive water sampling for nitrogen concentrations and isotopes. More posts to follow.

The Other Valley

Typically, most of my time in Hengill is spent running the side-stream channel experiment, so I rarely get a chance to visit the other streams that our group studies. However, earlier this month I had the opportunity to assist with checking the nutrient drippers in the “landscape” streams, which allowed me venture away from the channel site and see what else Hengill has to offer.

All I can say is that I’ve been missing out on some beautiful views-

This year we’re adding nitrogen to our four study streams using a rather elegant dripper system that is controlled entirely by gravity. It’s essentially the same setup as the drippers we use for the channel experiment, but slightly modified to fertilize an entire stream as opposed to a small plastic channel. 

 VS.

Although this dripper system maintains a remarkably consistent drip rate once set up, it does require the occasional check, and an occasional refill of the reservoir to maintain the nitrogen supply. Here’s Kate and Bonnie in refill action:

 Just add water...

and stir!

It was a nice change of pace to hike around the streams of Hengill’s “other” valley, and a good reminder of the interconnectedness of the work done with the channels and the landscape streams. We’re all excited to see the results of this year’s nitrogen additions, and I’m particularly interested in how these results might compare (and/or contrast) with our channel data!

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!

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!