Channel Sampling: Success!

It’s official- the stream-side channel experiment is over! After two weeks of sampling, our team completed both rounds of metabolism, nutrient uptake and nitrogen fixation measurements. These efforts involved 15 people, 300 chamber incubations, and scrubbing biofilm off more than 1,000 tiles. Although it’s a relief to be done with the long days, I’m a bit sad to see the channel experiment come to an end. What am I supposed to do with myself now that I don’t have any biofilm to grow or channels to maintain? I guess I’ll have to take up a hobby (gardening should be similar to growing biofilm...), and of course analyzing all that data will keep me busy for a while!

Anyways, here are some highlights from the sampling events:

Day 1: A flawless team measuring metabolism on a flawless day

Day 2: Weather not so flawless, but our crew stayed strong to complete nitrogen and phosphorus uptake measurements

Days 3 and 4: N-fixation Nation!

Annette is a MIMs Buddha

This is what learning looks like

The final sampling push

At the channels, the optimal observer-to-worker ratio is 3:1

...except for the last day of sampling, when everyone just takes a nap

If You Don't Like the Weather in Iceland, Just Wait Five Minutes...

We have a confession to make...

The majority of our blogposts give our readers a false sense of weather here in Iceland. Although the climate is mild for the latitude, rainy days are common at our field site. Here is a little dose of reality. Enjoy.

Can you see the glistening rain jackets? 

Channel Sampling is Almost Here!

The channels have been running for a whopping 45 days now (which is basically years in “channel time”), and things have been going great at the site. The hotpot that was giving us trouble in the beginning has been stable, which means we have consistent temperature treatments, and our biofilm has been busy growing under the varying temperature and nutrient treatments. Heath and I have been busy maintaining the experiment during this time, as well as collecting samples for our biomass time series. These time series data can show us differences in biofilm growth rates among the nutrient conditions (i.e., low-N vs. high-N treatments), as well as whether these nutrient effects change under different temperature regimes. We won’t have answers until the samples are processed back at OSU, so for now it’s lots of scrubbing biofilm off tiles and filtering the samples for transport back to Ohio.

A quick look at differences in biofilm growth among channel treatments

We’ve also been taking background water chemistry samples for each channel, to ensure that the nitrogen and phosphorus additions for each treatment are at the correct concentrations.

But perhaps most importantly, we’re busy gearing up for our first round of metabolism, nutrient uptake, and nitrogen-fixation measurements. This will be a 4-5 day push with the entire team involved in the sampling efforts. During sampling, we incubate the biofilm in small plastic chambers, so we’ve spent the last few days ensuring the chambers and equipment is in working order.

Chambers: Geared up and ready to sample some biofilm

Things are looking good so far, and we should be ready for sampling in the next few days. Check back for pictures and updates of the main event!

Update: 15N additions and channel experiment

I am back from Iceland, after an ultimately successful trip, despite weather that was often difficult and that postponed the start of our five-day 15N additions to the two cold and two warm streams. The shot above is of everyone sampling food web compartments in Stream 11 during the drip. The sun did come out every now and then! The channel experiment continues to go well too. Here's a shot of our REU student Heath Goertzen and MS student Lyndsie Collis collecting and processing tiles for the biomass accumulation time series. You can just make out the diversity of growth responses that are being driven by differences in temperature and nutrient concentrations. Some tiles are still effectively bare after six weeks, while a thick algal growth is threatening to overtop some channels. Maybe we'll see some interesting temperature-nutrient interactions. Time will tell.

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.