eosFD chambers now measuring soil CO2 flux at Howland Forest

A set of eosFD chambers are enjoying their new home as part of a Mitacs-funded graduate internship, co-installed alongside existing automated soil respiration chambers at the Howland Forest in central Maine (See insert for more details about the amazing Howland Forest).

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Lesson learned: A basketball pole is an excellent sturdy structure upon which to mount a solar panel!

Two weeks ago, I headed down to the forest, a tidy 7.5 hour drive from Dartmouth, NS, accompanied by Stephanie MacIntyre, a grad student from St. FX, to deploy a set of eosFD chambers. Our mission? To test the deployment of a set of esoFD chambers, and to obtain a dataset that could demonstrate the utility of soil respiration data for eddy covariance towers (see previous blog post about WHY researchers should use soil respiration data), using Eosense’s low cost and low power solution for soil CO2 flux.

Howland Forest – Background

Eddy covariance tower in Howland ForestThis forest is a 558 acres tract of old growth Acadian forest (red and black spruce dominated with Eastern hemlock, white pine and Eastern cedar), with some trees over 300 years old. Howland Forest hosts an amazing amount of diversity, as a result of a wide variety of soil drainage types across the site and a lack of human-induced disturbance.

The Howland Forest site was initially set up to study atmospheric chemistry in the 1980’s (acid rain); researchers are now primarily studying carbon cycling, by measuring environmental variables and carbon uptake, including atmospheric carbon dioxide and water concentrations and fluxes, and the isotopic composition of carbon and oxygen, the canopy, soil, forest floor, and bole respiration. An eddy covariance tower at the site is one of the oldest running and founding sites of the AmeriFlux network, measuring carbon uptake and loss since 1996.

Carbon is also meticulously accounted for with biometric surveys, alongside carbon in soil and water. Interestingly, research at the site has uncovered evidence that this “over-mature” site is still sequestering carbon (link to paper). Research at this site also considers the impact of forest management practices on carbon balance in softwood forests. The site is ideal for eddy covariance studies as the footprint is derived from an almost perfectly flat landscape with a homogeneous canopy and a large fetch.

Over 10,000 published peer reviewed journal articles have included Howland Forest in their work. This site also has the reputation for being one of the most photographed on the planet: NASA has been taking spatial imagery of the site as part of the Forest Ecosystem Dynamics study for years.

The instrumented part of the Howland Forest site  (appx. 100 m2) spans a range of moisture regimes, from an “upland” well drained area, near the eddy covariance tower, down a slight decline (<10 degrees) to a more poorly drained region that transitions to a wetland. All along this moisture gradient, a series of long-term automated soil respiration chambers are located, which have been measuring during the field season for over a decade. This range of sites is an interesting moisture gradient that has better elucidated the controls on soil respiration, and therefore C release.

The eosFD has low power requirements (< 1.6 W on average), and so all 10 FD chambers were powered from a single deep cycle battery, which was then charged with a single 100 W solar panel. So, what’s the best place? While the rest of the forest floor is shaded by the tall canopy, in the wettest part of the forest sun streams into the forest, providing an excellent location for our solar panel…(…and the occasional moose…).

Solar Panel MacGyvering

So, you may ask, “How do you mount a solar panel in a swamp?” Eosense’s Darren Wall came up with an innovative solution: mount it on a basketball net stand, of course! This was possible with the assistance of several clever and helpful people onsite at Howland Forest that day (yes, I am talking about you, Holly Hughes, Kathleen Savage and John Lee). There was a pre-existing wooden platform and so, to minimize disturbance, we decided that this would be the most cost effective (compared to traditional tripod mounts) and sturdy (base can be weighted with water and provides a home for the electrical components).

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Cables were run through the forest connecting each eosFD to the terminal assembly/panel

In the swamp, I found a peaceful setting for wiring, was surrounded by Sphagnum and sundew, and rescued from the horseflies by dragonflies. A set of cables extended from the terminal block connected to a charge converter (photo) to the eosFD chambers through the forest. These were housed in a plastic bin, with the charge converter and terminal block.

Installing the eosFD in Howland Forest

Each FD collar was inserted into through an organic layer, most often sphagnum, using a knife to minimize disturbance and to ensure a tight fit. Eosense’s FD chambers were installed alongside existing automated soil respiration chambers which measure on a 2 hour basis.

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Installing the eosFD with a knife to ensure minimal soil disturbance.

The absolutely satisfying moment came when I connected the set of FD’s to the power. I could instantly hear the gentle humming of the eosFD’s through the forest site, joining the existing chorus of birds (especially hermit thrushes) and insects.

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eosFD measuring next to the site’s existing custom automated chamber system

Howland Researchers are Great

During our week long adventure at Howland, the highlight of the trip was the opportunity to meet some great people. Howland Forest is cared for by Holly Hughes, University of Maine, a tough and dedicated steward of this site. We met John Lee, site manager (also a fellow Canuck) and his pal Tayga. Their passion for the forest and its teachings was evident.

Eosense has teamed up with fellow Canuck Kathleen Savage (Woods Hole Research Centre, Falmouth, US) who has been carrying out ecological research on carbon cycling, especially soil respiration, at this site for over a decade. Her newest research focuses on trace greenhouse gas (CH4 and N2O) emissions from the site.

Postdoc Debjani Sihi (University of Maryland) is studying soil carbon storage and soil respiration and was sampling soils across the site at that time, along with a research intern, Liomari from University of Texas (Austin). We also met Julie Shoemaker in the swamp sites: She is a methane biogeochemist, and Assistant Professor at Lesley University, who makes a regular habit of the trek up to Howland to sample water for methane.

Biometric work is carried out by Aaron Livingstone and Shaun Fraver at University of Maine, and several of their students were busy at work in the forest. Jack and Hunter (in group photo, below) were carrying out tree surveys at the time and were instrumental to our project success.

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Science party at Howland! Site and group shot
[Clockwise from front left: Jack , Hunter, Liomari, Kathleen, Stephanie, Debjani and Holly]

Research Goals

The eosFD chambers are now happily deployed, nestled among the the vegetation in this incredible old growth forest, watched by careful eyes. We anticipate that the data from this deployment will be an important step in bringing this quality soil respiration data to a wider audience, including eddy covariance researchers. Furthermore, this set up will also provide a unique dataset: as these chambers are robust (with earlier prototypes surviving in Antarctica!) with low power requirements, there is an opportunity to collect wintertime soil respiration data, which has never been collected at this site, further demonstrating the utility of the eosFD’s at this eddy covariance site.

Watch for updates! It’s going to be an interesting year!