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Summer Research Project 2023
- Title: Carbon in flux: Measuring and forecasting the heartbeat of the Harvard Forest
- Group Project Leader: Jackie Matthes
- Mentors: Michael Dietze; Jonathan Gewirtzman; Alexis Helgeson; Ashley Keiser; Sparkle Malone; Corey Palmer
- Collaborators:
- Project Description:
Overarching Intellectual Theme
Forest and wetland ecosystems play a critical role in the global carbon cycle that influences the net amount of carbon dioxide and methane in the atmosphere. Trees take up carbon dioxide from the atmosphere through photosynthesis and store complex carbon within their biomass, and they release carbon dioxide through cellular respiration. The metabolism of soil microbes is fueled by the decomposition of biomass and other plant substrates that produce carbon dioxide. Under low oxygen conditions, for example in flooded soils and inside tree trunks, a specialized group of soil microbes can produce methane as the end product of their metabolism instead of carbon dioxide. These complex connections cycle carbon among soils, plants, and the atmosphere within ecosystems at timescales from seconds to centuries.
Understanding how forest and wetland carbon cycling responds to disturbances like invasive insects and extreme climate events (e.g., heatwaves, drought and deluge events) is a major priority for better predicting future impacts on the carbon cycle. At Harvard Forest, we are measuring ecosystem carbon cycling with fast networked sensors and field measurements, and we run experiments in the field and lab to better understand carbon storage and flux. We also investigate patterns in landscape carbon dynamics through satellite data, and we connect these measurements to models that can forecast future changes.
This overarching project has three subprojects that investigate key uncertainties in forest and wetland carbon cycling. Students across all subprojects will work collaboratively to develop conceptual understanding of project themes, assist with field data collection, and structure data analysis and presentation. Subproject 1 (2 students) will investigate the processes and weather conditions that influence methane uptake and methane release within upland soils (typically well-drained and unflooded), wetland soils, and trees at Harvard Forest. Students will analyze existing methane data collected along towers measuring from the soil to above the forest canopy, and they will collect new field data from soils and trees within the tower footprints to assess spatial patterns in methane consumption and production. Subproject 2 (1-2 students) will measure the microbial respiration flux of carbon dioxide to the atmosphere and the movement of carbon from decomposing plant biomass into soil pools within an area of hemlock forest that is experiencing tree stress and mortality caused by the invasive hemlock woolly adelgid insect. Students on this subproject will conduct field and lab measurements to measure the microbial processing of carbon as it moves through the decomposition process at points across the landscape. Subproject 3 (2-3 students) will use a forecasting model to assess key uncertainties in the ecosystem carbon cycle that informs additional field data collection efforts.
In more detail, these three subprojects will investigate:
1) Methane dynamics in upland and wetland systems (2-3 students)
Emissions and uptake of methane (CH4) between ecosystems and the atmosphere is the largest source of uncertainty in the global atmospheric CH4 budget. Increasing atmospheric CH4 concentrations (Nisbet et al., 2019) is of concern because CH4 is 34 times more effective at trapping heat in the atmosphere compared to an equivalent mass of carbon dioxide over a 100-year timeframe and accounts for 42% of warming since the pre-industrial period (IPCC, 2021).
Areas with relatively small CH4 uptake and emission rates, like the forest and wetland ecosystems at Harvard Forest, have been largely understudied but could contribute significantly to regional and global budgets. Microbes near the surface of upland (non-flooded) forest soils typically consume atmospheric CH4, but soils can release CH4 to the atmosphere during periods of flooding and through tree stem transport from deep groundwater and/or within-stem CH4 production. To improve our understanding of ecosystem methane flux at Harvard Forest, this project will use an archive of data (2012-present) measuring gradients of CH4 concentration from soils to above the forest canopy to calculate net CH4 uptake or release between the ecosystem and atmosphere in different seasons and weather conditions.
In addition to analyzing the legacy of data, students in this project will also measure net CH4 fluxes at smaller scales from soils and tree stems within the tower gradient footprints. Students will collaborate to design a field sampling scheme to better understand locations of CH4 uptake and release using field chamber measurements along gradients of soil moisture and within nearby wetlands. The combination of top-down tower CH4 gradient measurements and bottom-up CH4 chamber measurements will help to identify the summer time periods and places on the landscape that are critical for CH4 uptake and release. A typical week on this project will involve 2-3 full days of fieldwork and 2-3 days of computer work.
2) Soil carbon microtopography in hemlock forests (1-2 students)
Eastern hemlock is a foundation tree species that plays a unique role in structuring ecosystem processes. At Harvard Forest, the eastern hemlock species has been in decline since about 2013 due to stress and mortality from the invasive insect hemlock woolly adelgid. The impact of the hemlock woolly adelgid represents a major forest disturbance, which is likely to become more common with climate change, that has increased the rate of tree death and inputs of tree biomass to the forest floor as dead limbs and trees (called coarse woody debris; CWD) fall to the forest floor. As these forests transition to new species (like birch), the hemlocks may leave a historical footprint in the soil influencing future decomposition and the turnover of carbon. A major goal of this subproject is to better understand decomposition directly around hemlock CWD and its influence on the movement of carbon from plant to soil ecosystem pools.
This project will use micro-transects moving away from hemlock CWD to measure the turnover of organic matter as related to a potential hemlock historical footprint. Students will collaborate to design a project to better understand the interaction between historical footprints and carbon turnover. Measurements could include production of greenhouse gases by the soil microbial community, and mass loss of fresh organic matter. Paired lab measurements from soils collected along these microtransects will be used to assess variation in microbial biomass and labile carbon pools. A typical week will involve 3-4 full days in the field or lab and 1-2 days of computer work.
3) Forecasting to inform data collection (2-3 students)
Iterative forecasting is an exciting new research area aimed at making ecology more predictive while also better responding to the needs of decision makers. Building on an existing effort that has developed a daily forecast of the terrestrial carbon cycle at Harvard Forest, this summer’s REU project aims to explore the ways that forecasts can be used to optimize field data collection. Specifically we will focus on two data streams, soil respiration and tree growth (as measured by dendrometer bands), that exhibit significant within-season variability that are our most direct measures of how soil and plant carbon pools are changing over time.
This project will involve a mix of computational work and field work, with students alternating between three tasks: 1) researching and implementing protocols for how to use the existing forecasts to decide what and when to make measurements (e.g. make measurements when the predicted uncertainty exceeds some threshold); 2) making measurements in the field; 3) using these observations to validate the forecasts and update predictions. New observations (2) will also be used to evaluate and refine the proposed sampling protocols (1). In addition to the goals of validating and improving predictions for how growth and respiration will vary across different environmental conditions and at different times in the growing season, a major goal of this project is to prototype the effectiveness of “adaptive” monitoring over traditional measurement protocols based on a fixed measurement frequency (e.g. every other week). Such protocols have the potential to reduce monitoring costs while simultaneously increasing the power and utility of the data that is collected. More broadly, terrestrial carbon forecasts play an essential part of carbon monitoring requirements (e.g. UN Framework Convention on Climate Change), accrediting commercial carbon sequestration efforts, and improving long-term projections of ecosystem responses to climate change and increased climate variability.
General requirements for all overall project:
1. Participate in field data collection, including ~8 hours per field day with biting insects and hot, humid conditions. Field data collection days will often require early morning departures (meeting to leave at ~8 am).
2. Hike with scientific gear (20-30 lb. pack) in forested off-trail terrain.
3. Willingness to work in a collaborative team of students and mentors. Practice clear daily communication with students and mentors. Be willing to ask questions about everything from procedures and logistics to the theoretical background of our research. Make and help to identify mistakes, which are expected, respected, inspected, and corrected, and be willing to learn together as a project team.
4. Willingness to be flexible with day-to-day tasks that range from field research to computer analysis of data, and pitching in to help students and mentors across subprojects. - Readings:
Nisbet et al., Science 2014, DOI: 10.1126/science.124782
Delwiche et. al ESSD 2021, doi:10.5194/essd-13-3607-2021
Crowther et al. Science 2019, DOI: 10.1126/science.aav0550
Orwig and Foster, The Journal of the Torrey Botanical Society 1998, 125(1): 60-73.
Ellison et al. Frontiers in Ecology and the Environment 2005, doi: 10.1890/1540-9295(2005)003[0479:LOFSCF]2.0.CO;2
Dietze et al. PNAS 2018, doi:10.1073/pnas.1710231115 - Research Category: Watershed Ecology, Soil Carbon and Nitrogen Dynamics, Physiological Ecology, Population Dynamics, and Species Interactions, Large Experiments and Permanent Plot Studies, Invasive Plants, Pests & Pathogens, Group Projects, Forest-Atmosphere Exchange, Ecological Informatics and Modelling
