La capitale congolaise Kinshasa s’étend sur la rive sud d’un coude turbulent et boueux du fleuve Congo. C’est ici que Glenn Bush, chercheur associé de Woodwell Climate, et Joseph Zambo, coordinateur des forêts et du changement climatique, ont rejoint d’autres chercheurs et responsables gouvernementaux dans les salles de conférence d’un hôtel du centre-ville pour un atelier de trois jours sur la tourbe.
Glenn Bush est un économiste et spécialiste des sciences sociales qui travaille depuis 16 ans en République démocratique du Congo (RDC), où il étudie les structures sociales et économiques qui déterminent l’utilisation des terres. Zambo est le reponsable de Woodwell Climate en RDC, et assure la liaison entre les résidents locaux, le gouvernement national et les chercheurs internationaux. Ces deux chercheurs se sont engagés à conseiller le gouvernement de RDC afin de l’aider à créer sa « contribution déterminée au niveau national » (CDN), qui définit l’engagement du pays à réduire ses émissions dans le cadre des Nations unies sur le changement climatique.
Les tourbières, un type d’écosystème humide, pourraient constituer un élément essentiel de la contribution de la RDC. Ces sols riches en carbone qui s’étendent sur de vastes surfaces de la forêt tropicale congolaise doivent impérativement être protégés. Des activités telles que l’agriculture, la déforestation et le changement climatique ont cependant déjà commencé à grignoter le précieux stock de carbone. Et une fois libérée, la tourbe prend des millénaires à se renouveler.
Qu’est-ce qu’une tourbière ?
Les tourbières du Congo se trouvent principalement dans les forêts humides et marécageuses dans le « centre du bassin » du Congo. Elles se forment sur les rives humides des cours d’eau – un environnement pauvre en oxygène qui ralentit le processus de décomposition, permettant à la matière organique de s’accumuler au fil du temps pour former un sol spongieux qui emprisonne le carbone, l’empêchant ainsi de rejoindre l’atmosphère.
La stabilité d’une tourbière dépend du taux d’humidité et des matières organiques. En cas d’assèchement d’un marais tourbeux, le carbone en contact avec l’air est immédiatement exposé à la décomposition et à l’érosion.
« Dès que les bactéries aérobies commencent à pénétrer dans la tourbière, explique Bush, tout ce carbone commence alors à devenir instable. Il est donc crucial d’éviter autant que possible de perturber cette tourbe. »
Mais, cette mesure est une action difficile à entreprendre de nos jours. La croissance démographique pousse les populations à s’enfoncer vers des marais boisés, exploités souvent pour l’agriculture, notamment pour la production du riz dans les zones humides ou la pisciculture, afin de subvenir aux besoins de leurs familles et de leurs communautés.
Les tourbières sont également extrêmement sensibles à la dégradation et à la déforestation dans le biome de la forêt tropicale. Au cœur du bassin du Congo, la forêt tropicale est en fait le moteur de la création de la plupart de ses propres pluies – la saison des pluies de printemps est déclenchée par l’humidité insufflée dans l’atmosphère par les plantes, plutôt que par le vent de la mer qui pénètre les terres. Face aux effets desséchants de la déforestation, le Congo est donc encore plus fragile que l’Amazonie.
« Pour chaque hectare de forêt perdu en Afrique, on perd proportionnellement plus de précipitations que pour une quantité similaire de forêt perdue en Amérique latine ou en Asie du Sud et du Sud-Est », explique Dr Mike Coe, directeur du programme Woodwell Climate Tropics.
Ce que nous ne savons pas sur les tourbières du Congo
Quelle est la superficie exacte des tourbières du bassin du Congo ? Et quelle serait la gravité de leur disparition en termes d’émissions ? La réponse à ces deux questions est « nous n’avons aucune donné précise ».
La recherche commence à peine à cartographier cet écosystème critique. Récemment, une équipe de chercheurs congolais et britanniques dirigée par le Dr Simon Lewis de l’université de Leeds a parcouru deux transects de 20 à 30 kilomètres de forêt marécageuse pour prélever des échantillons afin d’évaluer l’existence de tourbières. Ils en ont trouvé partout dans la forêt. Au total, on estime à 145 000 kilomètres carrés la superficie de la région.
Cela représente environ 30 milliards de tonnes de carbone, soit plus de 20 fois les émissions annuelles de combustibles fossiles des États-Unis.
« Il ne s’agit que de deux transects dans l’ensemble du bassin du Congo, mais qui nous ont permis de recalibrer les modèles existants d’étendue et de qualité des tourbières, et cela démontre que nous visitons un trésor de carbone tropical », insiste Bush.
Protéger les tourbières, c’est lutter contre la pauvreté
Protéger les tourbières est crucial, mais dans la pratique, elle est difficile à mettre en œuvre. Pourquoi ?
À l’heure actuelle, les tourbières sont plus utiles pour les congolais en tant que ressources foncières permettant de produire de la nourriture, de chasser, de pêcher et de récolter des plantes et des matériaux de construction, qu’en tant que forêt intacte. Selon certaines estimations, plus de 90 % de la déforestation dans le pays a pour but de soutenir l’agriculture de subsistance. C’est une nécessité pour près des trois quarts de la population du pays qui vit avec moins de 2,15 $ par jour.
En 2020, Zambo et Bush, accompagnés de Kathleen Savage, chercheuse principale à Woodwell, ont mené des études sur les méthodes d’intensification agricole dans les rizières humides, qui sont souvent créées sur des tourbières déboisées. L’application de techniques agricoles différentes, consistant à désherber et à s’occuper des plants de riz tout au long de la saison plutôt que de voyager et de revenir pour la récolte, permettaient un augmentation considérable des rendements sur la même surface, ce qui réduit la nécessité d’augmenter de grignoter la forêt pour augmenter la productivité.
« Rien qu’en s’occupant du riz, on pourrait peut-être sauver environ 30 % de la forêt », explique Savage.
Les agriculteurs ont reconnu les avantages de cette méthode, mais hésitent à l’adopter. En attendant la croissance du riz, le temps est souvent consacré à gagner un revenu supplémentaire pour les charges immédiates. Tabler sur un revenu plus conséquent à la fin de la saison est un risque qu’ils ne veulent pas toujours se permettre. Une bonne récolte n’est pas garantie ; les parasites, la sécheresse ou les inondations peuvent anéantir le travail d’une année, laissant les agriculteurs sans revenu. Cette fragilité pousse les populations à prendre des décisions difficiles quant à l’utilisation des forêts.
« La RDC ne dispose d’aucun filet de sécurité sociale », rappel Savage. « En fait, le filet de sécurité sociale, c’est la forêt – la chasse, l’abattage d’un arbre et la vente du bois parce qu’il vaut beaucoup d’argent. »
Les marchés du carbone pourraient orienter l’argent vers les communautés forestières
Afin d’éviter la déforestation et la dégradation des tourbières, les communautés rurales devront trouver une autre source de revenus. Bush et Zambo ont discuté du potentiel des marchés du carbone pour fournir ces revenus.
Les marchés du carbone sont des systèmes d’échange qui attribuent une valeur monétaire à la prévention de l’émission de carbone dans l’atmosphère ou à son élimination active. Ils fonctionnent sur la base de la vente de « crédits carbone » qui représentent théoriquement une tonne métrique de carbone stockée ou séquestrée grâce à des pratiques de gestion des terres. Idéalement, l’argent provenant de leur achat va directement aux personnes qui gèrent les terres, qu’il s’agisse d’un agriculteur qui protège les forêts ou d’un groupe communautaire qui restaure les zones dégradées.
En réalité, les crédits carbone sont difficiles à vérifier en raison de la faiblesse des réglementations et du manque de données.
« Le problème du crédit carbone est que personne n’est vraiment sûr de la qualité et des normes de livraison, ni de la manière de les mesurer et de les contrôler, car il est évident que quelqu’un ne se présente pas à votre porte avec un sac rempli de carbone », nuance Bush.
Jusqu’à présent, la mise en œuvre du marché a été entravée par des accusations d’écoblanchiment de la part des entreprises polluantes qui achètent des compensations et par des programmes réglementaires gouvernementaux qui peinent à prouver le bénéfice sur le climat et la biodiversité. Bush et Zambo estiment néanmoins qu’une version de cette solution pourrait apporter des revenus plus conséquents directement aux agriculteurs si elle est bien appliquée.
Bush travaille avec l’équipe carbone de Woodwell Climate à l’élaboration d’un indice de capital paysager (ICP) qui utilise des normes scientifiques pour évaluer le potentiel de toute parcelle de terre à atténuer les effets du changement climatique et à offrir d’autres avantages tels que la biodiversité et le cycle de l’eau. Une fois affiné, l’indice fournira des données permettant de vérifier les crédits carbones.
Zambo s’est beaucoup a mené des discussions approfondies avec le ministère de l’Environnement sur le plan national zéro émission. Avec Bush, il espère qu’un marché du carbone soutenu par la science pourrait générer des moyens économiques pour financer de nombreux projets de développement durable décrits dans le plan.
« La validation du carbone stocké dans cet écosystème pourrait générer beaucoup d’argent dans le pays pour le développement », déclare Zambo.
Renforcer les capacités du Congo
Un autre obstacle à la mise en œuvre d’un marché du carbone efficace est de trouver des données disponibles pour alimenter l’ICP. Comme souligné par Bush, les données actuelles sur le carbone des tourbières ne sont basées que sur une fine tranche de l’ensemble du bassin. Le financement des projets de conservation au niveau local nécessite une compréhension beaucoup plus détaillée de l’étendue et de la qualité du carbone présent dans l’ensemble de l’écosystème. La collecte de ce type de données nécessitera davantage de scientifiques – des scientifiques congolais – et davantage de compétences techniques chez les fonctionnaires qui pourraient être responsables de la gestion des programmes de conservation à l’avenir.
« La RDC doit renforcer ses capacités en matière de cartographie des tourbières afin d’élaborer une stratégie nationale spécifique aux tourbières », explique Zambo.
L’atelier auquel ont participé Bush et Zambo à Kinshasa étaient principalement basé sur le renforcement des capacités.
« Cet atelier revêtait d’une importance capitale dans la mesure où il a permis le partage des connaissances et des avancées au sujet de la collecte de données sur les tourbières, devant permettre au gouvernement congolais d’identifier les données manquantes, de sensibiliser les parties prenantes et de créer des synergies entre les tourbières et d’autres initiatives climatiques », explique M. Zambo.
Il faudrait également appuyer les capacités scientifiques avec des ressources technologiques supplémentaires. Savage a travaillé avec l’assistante de recherche Zoë Dietrich pour mettre au point des chambres de surveillance du méthane portables et peu coûteuses, qui seront utilisées sur des sites de recherche de terrain au Brésil et en Alaska. Savage estime qu’il est possible d’adapter la conception de ces chambres pour la situation en RDC, afin de surveiller les flux de carbone dans les forêts des zones humides.
« Actuellement, en termes de comptabilisation du carbone, [la RDC] utilise des mesures estimées à partir d’un autre pays similaire et l’on suppose que c’est également ce que font leurs forêts. Mais pour obtenir des chiffres précis, il faut vraiment passer à des mesures directes », explique Savage.
L’avenir durable de la RDC
Beaucoup reste à faire pour que les marchés du carbone deviennent un mécanisme de financement viable pour les grands efforts de conservation en RDC. La durabilité et la croissance économique se résumeront en fin de compte à fournir aux ménages ruraux des alternatives pragmatiques de subsistance et à développer un sentiment de sécurité financière. Mais Bush espère que l’enthousiasme suscité par leur potentiel pourrait contribuer à faire traverser l’impasse des discussions, non seulement sur la conservation et le climat, mais aussi sur la gouvernance économique du pays à plus grande échelle.
Après tout, le marché du carbone est un marché au même titre que ceux qui vendent des sacs de riz ou du bois de valeur.
« Une fois que les acheteurs et les vendeurs ont compris la valeur fondamentale de ce qu’ils achètent et vendent, ils ont besoin des mêmes conditions-cadres pour fonctionner que n’importe quel marché », explique Bush. « Bonne gouvernance, transparence et respect de l’État de droit. »
Zambo envisage également une solution. En raison des avantages qu’elles procurent à l’écosystème, la valorisation des tourbières peut contribuer à améliorer la situation partout en RDC.
« J’espère que la conservation, la protection, la gestion et le développement des tourbières et des forêts congolaises pourront être un moteur clé du développement durable du pays », conclut Zambo.
On the southern bank of a turbulent, muddy-brown bend in the Congo River, sits the Congolese capital of Kinshasa. Here, Woodwell Climate Associate Scientist, Dr. Glenn Bush and Forests and Climate Change Coordinator, Joseph Zambo, have joined other researchers and government officials in the conference rooms of a downtown hotel for a three-day workshop about peat.
Bush is an economist and social scientist who has worked in the Democratic Republic of Congo (DRC) for 16 years, studying the social and economic structures that shape land use. Zambo leads Woodwell Climate’s work from the DRC side, liaising between local residents, the national government, and international researchers. The pair of them are hard at work advising on the creation of the DRC’s Nationally Determined Contribution (NDC), which outlines the country’s commitment to emissions reductions within the UN climate change framework.
Peatlands, a type of wetland, could be a critical element in the DRC’s contributions. Underlying large swaths of the Congo Rainforest, these carbon-packed soils are critical to protect. But disturbances like agriculture, deforestation, and climate change have already begun nibbling at the valuable stock of carbon. And once it is released, it takes millennia to replace.
What is a peatland?
Congo peatlands are found primarily in the wet, marshy forests of the country’s “Cuvette Central” or Central Basin. They form on the water-soaked banks of stream channels—an oxygen-poor environment that slows the decomposition process, allowing organic matter to build up over time into a spongy soil that locks away carbon, preventing it from re-joining the atmosphere.
A stable peatland relies on wetness. Draining a peat swamp immediately exposes that carbon to decomposition and erosion when it touches air.
“As soon as aerobic bacteria start getting in there,” says Bush. “Then all that carbon starts to become unstable. So the idea is, we just need to not disturb that peat as much as possible.”
But avoiding disturbance is a difficult thing to do these days. As populations grow, people are pushing further into forested marshland margins, often modifying them for agricultural uses like wetland rice production or fish farming to support their families and communities.
Peatlands are also extremely sensitive to degradation and deforestation across the rainforest biome. In the Congo Basin, the rainforest is actually responsible for creating most of its own rain—the spring rainy season is triggered by moisture breathed into the atmosphere by plants, rather than blown inland from the sea. This makes the Congo even more sensitive than the Amazon when it comes to the drying effects of deforestation.
“For every hectare of forest you lose in Africa, you lose proportionately more rainfall than you do for a similar amount of forest loss in Latin America or in South and Southeast Asia,” says Woodwell Climate Tropics Program Director, Dr. Mike Coe.
What we don’t know about the Congo’s peatlands
So exactly how much peatland does the Congo Basin hold? And how bad would it be in terms of emissions to lose them? The answer to both is “we don’t know for certain.”
Research has only just begun to give size and shape to this critical ecosystem. Recently, a collaborative Congolese and British team led by Dr. Simon Lewis of the University of Leeds walked two 20-30 kilometer transects of marshy forest, taking core samples to assess the existence of peatland. They found it everywhere beneath the forest. All told, an estimated 145,000 square kilometers across the entire region.
That translates to an estimated 30 billion metric tons of carbon—more than 20 times the United States’ annual fossil fuel emissions.
“It’s only two transects in the whole of the Congo Basin, but using that, we’ve been able to recalibrate existing models of peatland extent and quality, and it basically shows we’re sitting on a tropical carbon treasure trove,” says Bush.
Peatland protection is poverty alleviation
So protecting peatlands is important, but in practice, it’s a hard thing to accomplish. Why?
Right now, peatlands are more valuable to the people of DRC as a land resource to produce food, hunt, fish and harvest plants and materials for building, than as untouched forest. Some estimates indicate more than 90% of deforestation in the country occurs to support subsistence agriculture. It’s a necessity for the nearly three quarters of the country’s population that lives on less than $2.15 a day.
In 2020, Zambo and Bush, alongside Woodwell Senior Research Scientist Kathleen Savage, conducted research into methods of agricultural intensification in rice paddy wetlands which are often created on deforested peatland. Applying different farming methods, involving weeding and tending to rice plants throughout the full season rather than traveling and returning for the harvest, significantly boosted yields over the same area, meaning less pressure to expand into the forest to increase productivity.
“Just by tending the rice, you could perhaps save about 30% of the forest,” says Savage.
Farmers recognized the benefit of this method, but were hesitant to adopt it. That time spent not tending to rice is often spent working to earn extra cash to pay immediate expenses. Waiting for a larger payout at the end of the season is not always a risk they are able to take. A good crop is not guaranteed; pests, drought, or floods could all wipe out a year’s worth of work, leaving farmers with no income. That uncertainty pushes people to make tough decisions about how to use forests.
“There’s no social safety net,” says Savage. “Well actually, the social safety net is the forest—hunting, chopping a tree down and selling the lumber because it’s worth a lot of money.”
Carbon markets could direct money to forest communities
To prevent deforestation and degradation of peatland, rural communities will need an alternative source of income. Bush and Zambo have been discussing the potential for carbon markets to supply that income.
Carbon markets are a finance mechanism that places a monetary value on preventing carbon from entering the atmosphere—or actively removing it. They function on the sale of “carbon credits” which theoretically represent one metric ton of carbon kept stored or sequestered through land management practices. Ideally, money from their purchase goes directly to the people managing the land—whether that’s a farmer protecting forests or a community group restoring degraded areas.
In reality, however, carbon credits have been challenging to verify because of weak regulations and lack of data.
“The problem with the carbon credit is nobody’s really sure about quality and standards for delivery or how to measure and monitor them because, obviously, somebody doesn’t turn up on your doorstep with a bag full of carbon,” says Bush.
So far, market implementation has been plagued by accusations of greenwashing for polluting corporations who buy offsets and government regulatory programs unable to prove positive climate and biodiversity impacts. But Bush and Zambo see potential for a version of this solution to bring more wealth directly into farmers’ hands if done right.
Bush is working with the Carbon team at Woodwell Climate on the development of a Landscape Capital Index (LCI) that uses scientific standards to assess the potential of any tract of land to deliver climate mitigation and other benefits like biodiversity and water cycling. Once refined, the Index will provide data against which carbon credits can be checked.
Zambo has been deeply involved in conversations with the Ministry of Environment around the country’s National Net Zero Plan. Both he and Bush hope that a science-backed carbon market could make many of the sustainable development projects outlined in the plan economically feasible.
“The validation of carbon stored in this ecosystem could generate a lot of money in the country for development,” says Zambo.
Building Congolese Capacity
Another obstacle to implementing an effective carbon market is finding available data to feed the LCI. As Bush mentioned, current information on peatland carbon is based on only a thin slice of the entire watershed. In order to provide payments for local-level conservation projects, we need a much more granular understanding of the extent and quality of carbon across the entire ecosystem. Collecting that kind of data will require more scientists—Congolese scientists—and more technical capacity among officials who could be responsible for managing conservation programs in the future.
“DRC needs capacity building in the mapping of peatland areas to develop a national strategy specific to peatlands,” says Zambo.
Capacity building was a large part of the workshop in Bush and Zambo attended in Kinshasa.
“This workshop was very important in the context of sharing knowledge and advances in data collection about peatlands, in order to enable the Congolese government to identify missing data, raise awareness among stakeholders, and create synergies between peatlands and other climate initiatives,” says Zambo.
Additional technological resources could also help bolster scientific capacity. Savage has been working with Research Assistant Zoë Dietrich to develop inexpensive, portable, methane monitoring chambers for use at field research sites in Brazil and Alaska. Savage sees the potential to adapt the chamber design for use in the DRC monitoring carbon fluxes in wetland forests.
“Right now, in terms of carbon accounting, [the DRC] is using measurements estimated from another similar country and the assumption is that’s what their forests are doing, too. But in order to get accurate numbers, they really need to move to direct measurements,” says Savage.
DRC’s sustainable future
There is much work to be done to build carbon markets into a viable funding mechanism for large conservation efforts in the DRC. Sustainability and economic growth will ultimately come down to providing rural households with pragmatic livelihood alternatives, and developing a sense of financial security. But Bush hopes the excitement around their potential could help push forward difficult conversations, not just around conservation and climate, but about economic governance within the country on a larger scale.
The carbon market, after all, is a market just like the ones selling sacks of rice or valuable timber.
“Once the buyers and sellers understand the basic value of what is being bought and sold, then it requires the same framework conditions to operate as any market needs,” says Bush. “Good governance, transparency and adherence to the rule of law.”
Zambo sees a path forward as well. One where valuing peatlands for their ecosystem benefits can help lift up all of DRC.
“I hope that the conservation, protection, management, and development of peatlands and forests in the DRC can be a key driver for the country’s sustainable development,” says Zambo.
The MacGyver session at the annual American Geophysical Union (AGU) conference is full to the brim with scientists showing off blinking circuit boards and 3D-printed mechanisms. Research Assistant, Zoë Dietrich, stands in front of her poster and a plexiglass cube sprouting wires. As she speaks, a whizzing sound emanates from the box as it lifts itself up on one side, holding itself open long enough to flush the interior with air from the room. A laptop screen reads out numbers from the sensors in the box, detailing changes in the concentrations of carbon dioxide and methane within.
Dietrich constructed this device herself. It’s a low-cost, autonomous, solar-powered chamber designed to float on water and measure the flow of carbon into and out of the water. Dietrich has spent the past 1.5 years testing and troubleshooting various prototypes, and has already begun deploying models at research sites in Brazil and Alaska. Now she’s sharing her work with the broader scientific community in hopes of encouraging others to build their own versions.
“One of the goals of the chamber project is to make the construction very accessible so that scientists like me, without formal engineering training or background, can build the chambers pretty easily,” says Dietrich.
This was good news for Grand Valley University masters student, Jillian Greene, and her professor Dr. Sean Woznicki, who encountered Dietrich and her chambers at AGU. Though neither of them had experience with mechanical or electrical engineering, they knew immediately a device like Dietrich’s could be invaluable to their research.
Greene’s project involves sampling carbon emissions at drowned river mouth estuaries connected to Lake Michigan. She and Woznicki will then correlate that data with other ecological characteristics gleaned from satellite imagery. There are over one hundred of these freshwater estuary-like features around the region, and Greene and Woznicki are hoping to paint a complete picture of their cumulative role in carbon cycling.
“Originally, I was going to manually sample and quantify with a gas chromatograph,” Greene says. That’s a time-consuming process that limits the amount of data one team can collect. With the chambers, however, Greene can collect emissions data every 30 seconds—greatly expanding the amount of data she’ll be able to incorporate into her models.
“This is going to make our model a lot more robust and hopefully applicable to other drowned river mouth estuaries in the region,” says Greene.
Greene and her research team have already created and deployed 6 chambers. Since AGU, she has been in contact with Dietrich, troubleshooting issues as they arise and learning an entirely new set of skills as she goes.
“[the team] has learned how to solder, how to interpret the circuit diagrams, problem solve, and adjust for our kind of unique systems that we’re looking at,” says Woznicki. “It’s really been exciting to use Zoë’s design as a learning experience for masters and undergrad students.”
Dietrich has had other groups at Colgate University and the University of California, Berkeley reach out to her as well, and she is planning to publish a paper this fall that will include detailed instructions for anyone else to construct their own chambers. She’s already shared preliminary drafts of the step-by-step instructions, including photos, diagrams, and tips, as well as programming and data-processing code and a specific materials list with the other research groups. In turn, they have provided her with helpful revisions and ideas for new modifications. Dietrich is excited about the prospect of the designs being implemented by more people. More chambers means more data, which benefits the entire scientific community.
“Our sampling of carbon right now is limited by expensive instruments and where people can go and who has access to these resources,” says Dietrich. “But the goal of this project is to be low cost and more accessible to a broader set of researchers. The chambers are autonomous, and so are accessible to places and times that aren’t otherwise being sampled right now. And taking that a step further, we need to make them accessible to be built by anyone.”
“Why not float the aquatic greenhouse gas chamber on a surfboard?” Tropics Program Director Dr. Mike Coe suggested in one of our team meetings, and I could feel the gears in my brain begin turning. I started a sketch… If mounted on a surfboard, we would need a method to open the chamber, flushing it with outside air. Back in my office, I asked Google “what turns electrical energy into mechanical energy?” Google was quick to respond, “Motor.” Right, thank you, Google. Next, I typed, “motor that pushes something up.” Google replied, “linear actuator.” Three clicks later and I had ordered my first linear actuator for 35 bucks.
Three days later, that linear actuator sat expectantly on my desk. One red wire and one black wire, “12V DC” printed on its side. I turned back to Google, “How to wire a linear actuator?” Opening the first hit, I skimmed through the photos and diagrams. None of them striking my fancy, I moved on to the second hit: Step-by-step instructions, clear photos, even open-source code to program my Arduino microcontroller board – nice! Within an hour, my linear actuator was extending and retracting on command, ready to be mounted in an autonomous greenhouse gas chamber.
Adding the actuator to my sketch, I popped into Senior Research Scientist Kathleen Savage’s office to hear her thoughts. Savage always has new ideas brewing, and she suggested adding a feature that would allow the chamber to function on water and on land. The chambers are the product of a Fund for Climate Solutions (FCS) grant led by Savage to quantify carbon dioxide and methane emissions from small water bodies like lakes, ponds, and reservoirs. Because there are no low-cost and auto-sampling tools available on the market, we have been developing a new instrument to measure these emissions.
DIY science
“Chamber” is a fancy word for the upside-down buckets we use to measure how fast greenhouse gasses are released from different surfaces. By resting a bucket upside-down on a patch of soil or grass or water and measuring how fast gas concentrations increase or decrease inside the bucket, we can calculate a “flux” of gas over a set area and time. Common methods of measuring fluxes require manually collecting gas samples from a chamber to be processed in a lab, or connecting the chamber to a high precision analyzer that can cost around $40,000. These methods are costly in salary time and equipment, limiting where, when, and how often people can sample—usually daytime and in accessible areas and times of the year. We need new low-cost and autonomous systems that can measure around the clock to improve carbon emissions estimates. The recent commercialization of cheaper sensors and control systems to operate them, like the Arduino microcontroller, now make these developments possible.
I’m building a new floating chamber that measures aquatic fluxes autonomously using a $15 methane sensor and a $78 carbon dioxide sensor, improving previous designs published by Dr. David Bastviken’s group at Linköping University in Sweden. Powered by a solar panel and battery, the sensors measure gas concentrations, temperature, and humidity inside the chamber every 30 seconds. The data is stored on an SD card and transmitted within 50 meters via radio. The radio transmission allows us to check that the chamber is functioning properly from the shore and to see chamber measurements in real time. When gas concentrations have increased enough to discern a flux, the linear actuator extends to open the chamber, flushing the interior with outside air before retracting to close the chamber again for another flux measurement. Calibrating the chamber with a high precision analyzer in the field shows the low-cost sensors perform well, with an accuracy of approximately 1 ppm for methane and 3 ppm for carbon dioxide.
Field deployment
I first tested chamber prototypes last July on agricultural reservoirs at the Tanguro Field Station in Brazil. At the end of our field campaign, I left one chamber deployed to see how long the electronics would last and which components might eventually fail. After helping me deploy and calibrate the chamber, field technician Raimundo “Santarém” Quintino monitored it, checking its “vital signs” via radio every few weeks. In January, he noticed the linear actuator had stopped pushing the chamber open.
During a follow-up field campaign in March, I brought a couple of extra linear actuators and five more chambers to deploy on additional reservoirs at Tanguro. Tanguro staff and I worked together to modify chamber components that didn’t function well in the first deployment. These modifications included swapping the materials of the floating foam bases and improving the mounting mechanisms of the linear actuator and chamber hinge. Our adjustments were informed by recommendations from a Laboratory Operations Manager at the University of Maine in Orono (Christopher London), whom I met while doing fieldwork at the nearby Howland Research Forest. Woods Hole locals, such as John Driscoll and Fred Palmer of the Woodwell Climate Facilities department, kite foiler and carpenter Tad Ryan, and employees at Eastman’s Hardware, have also offered transformative recommendations on building materials and techniques to stabilize the floating chambers.
Working hands-on with the floating chambers on the reservoirs, Santarém, Dr. Leonardo Maracahipes-Santos, Tanguro’s Scientific Projects Coordinator, and Sebastião “Seu Bate” Nascimento of Tanguro Field Station have made invaluable improvements to the chamber design and deployments. A few of their contributions include advice on safe deployment locations, monitoring and collecting data from the chambers over time, and constructing aluminum and galvanized steel components for the floating bases. They also designed a new mount for the most recent chamber addition—a bubble trap that uses an inexpensive pressure sensor to autonomously measure the volume of gas released as bubbles.
Freshwater ecosystems worldwide emit nearly half as much carbon dioxide and methane as fossil fuel combustion. On the Amazon-Cerrado frontier, where Tanguro is located, there are hundreds of thousands of small agricultural reservoirs, which are important, yet overlooked, greenhouse gas sources. These artificial ponds—installed to provide drinking water for cattle, facilitate road crossings, or supply energy at the farm scale—can persist for decades, creating low-oxygen conditions that drive methane production. Monthly sampling of six reservoirs over a year by Water Program Director Dr. Marcia Macedo revealed high methane and carbon dioxide emissions, varying with season and reservoir size. But these measurements did not capture the significant variability that can occur on daily, monthly, and annual time scales, including transient “hot spots” and “hot moments” of high greenhouse gas emissions.
This lack of frequent measurements hinders climate scientists’ ability to integrate emissions at the reservoir scale in order to estimate cumulative greenhouse gas emissions at the landscape scale. The autonomous floating chambers will address that gap, enabling comprehensive carbon monitoring and modeling of the reservoirs.
From the tropics to the Arctic
Additionally, these chambers are versatile tools that can be used across different environments. Funded by a subsequent FCS grant, six new floating chambers will accompany me to the Yukon-Kuskokwim Delta, Alaska, this summer to measure greenhouse gas emissions from Arctic ponds. The chambers will supply the frequent data necessary to constrain the LAKE model utilized by Arctic Program scientists Dr. Elchin Jafarov and Andrew Mullen. The model predicts variations in carbon emissions from ponds, providing insight into processes regulating methane and carbon dioxide. By applying the LAKE model to both Arctic ponds and Amazon reservoirs, we can gain a deeper understanding of their impacts on regional greenhouse gas budgets.
“Deploying floating chambers will streamline the process of gathering aquatic data and enhance the temporal resolution of the data, which is vital for modeling and currently absent in existing datasets,” notes Jafarov.
Problem-solving and collaboration
While calibrating the low-cost sensors in our boat one March afternoon, Santarém and I noticed the linear actuator on another nearby chamber wasn’t retracting and extending as it should. Expecting another replacement was in store, we tuned into the radio and popped open the electronics case to check for “symptoms.” Blinking lights and radio silence revealed an entirely new and perplexing issue causing the malfunction.
Building this system from the ground up over the last year, the one constant has been mind-bending electronics puzzles that keep me up at night. As a biogeochemist by training, these problems usually require some tinkering, a dictionary, a lot of Googling, and sometimes bugging electrical engineers down the street at the Woods Hole Oceanographic Institution (Lane Abrams) and Spark Climate Solutions (Bashir Ziady), whose advice and contributions have substantially improved the chambers’ electrical designs. Each problem can usually be traced to a perfectly logical, satisfying solution, leaving me feeling wiser and excited to tackle the next one. I’ve tracked this new problem down to something potentially involving a “memory-leaking variable declaration” in my new bubble trap programming code. I might’ve fixed it with a “watchdog timer.” Both are new words for me, too. If the watchdog timer doesn’t pan out, Santarém and I will try another fix.
Designing, building, and testing these chambers has been an iterative and constantly evolving process. What works well? What doesn’t? How can we do this more simply? Using less energy? For a lower cost? How can we improve the design so that other researchers can easily build these floating chambers as well? Soon we plan to publish open-source instructions detailing how to build and troubleshoot the floating chambers—I have already sent preliminary instructions to three interested research groups. I’m lucky to collaborate with many talented people from Woods Hole to Maine and Brazil, many of whom are as new to chambers and fluxes as I am to engineering. Nevertheless, these floating chambers incorporate a brilliant flourish from each of them.
Arctic wetlands are known emitters of the strong greenhouse gas methane. Well-drained soils, on the other hand, remove methane from the atmosphere. In the Arctic and boreal biomes, well-drained upland soils cover more than 80% of the land area, but their potential importance for drawing methane from the atmosphere—the underlying mechanisms, environmental controls and even the magnitude of methane uptake—have not been well understood.
A recent study led by researchers from the University of Eastern Finland and University of Montreal, in collaboration with Woodwell Climate Research Scientist, Dr. Anna Virkkala, has expanded our understanding of these dynamics, finding that Arctic soil methane uptake may be larger than previously thought. The results show uptake increasing under dry conditions and with availability of a type of soil organic carbon that can be used in microbial uptake processes.
The study was primarily conducted at Trail Valley Creek, a tundra site in the Western Canadian Arctic. The authors used a unique experimental set-up consisting of 18 automated chambers for continuous measurements of methane fluxes. No other automated chamber system exists this far North in the Canadian Arctic, and only few exist above the Arctic circle globally, most of which are installed at methane-emitting sites.
The high-resolution measurements of methane uptake (more than 40,000 flux measurements) revealed previously unknown daily and seasonal dynamics: while methane uptake in early and peak summer was largest during the afternoons, coinciding with maximum soil temperature, uptake during late summer peaked during the night. The study shows that the strongest methane uptake coincided with peaks of ecosystem carbon dioxide respiration—meaning that as methane is removed from the atmosphere, carbon dioxide production in the soil is high. Complementing flux measurements at Trail Valley Creek with measurements at other sites spread across the Canadian and Finnish Arctic showed that the availability of soil organic carbon and other nutrients may promote methane consumption in Arctic soils.
“The methane cycle has previously been primarily studied in wetlands because of their high methane emissions, but this study shows that drier ecosystems are also very important in the methane cycle,” says Dr. Virkkala.
These findings are highly relevant for estimating the current Arctic carbon budget, and for predicting the future response of Arctic soil methane uptake to a changing climate. According to the study, high-latitude warming itself, occurring up to four times faster in the Arctic than the rest of the world, will promote atmospheric methane uptake to a lesser extent than the associated large-scale drying.
“The Arctic methane budget has remained highly uncertain,” remarks the paper’s lead author, Dr. Carolina Voigt. “Our research provides one potential mechanism that might explain those uncertainties, and highlights the importance of methane measurements in drier ecosystems to calculate more accurate methane budgets.”
