Carbon is an important macronutrient in soils, sediments, and aquatic systems that serves many purposes, ranging from feeding the microorganisms responsible for turning over nutrients for plant growth to outgassing to the atmosphere and driving global climate change. Thus, the quality and availability of carbon is a key limiting factor on ecosystem productivity and nutrient cycling. A key theme in our group is to track how the source of organic carbon in temperate forest soils and inorganic and organic carbon in waterways determines its likelihood to feed the microbial and macrofauna that make these ecosystems fertile, as well as what this transport means for global carbon cycling. We are curious about how terrestrial versus aquatic formation of organic matter drives its turnover and favorability in aquatic systems and how vegetation source (e.g., wood versus leaf and variations in lignin and nitrogen content) drives its turnover and favorability in soils.
In the process of feeding soil (micro)fauna, organic carbon breaks down. Sometimes, it is completely metabolized to gases such as methane or carbon dioxide that drive global climate dynamics. Our group studies not just how appealing organic carbon is for soil fauna, but also ecosystem implications: does organic carbon quality translate to the extent of its decomposition and release of gaseous metabolic products? We also track the movement of methane and carbon dioxide gases through the forested landscape and into rivers and streams. These gases can be consumed by microbes, moved with water downstream, or released directly to the atmosphere where they contribute to global climate change.
Bottom line: how does the fate of dead, post-plant organic carbon influence the fertility and environmental role of temperate forest watersheds (soils plus waterways)? What does this mean for global carbon cycling?
Our projects integrate field and laboratory methods to get a full picture of the biogeochemical cycling of carbon across the Harvard Forest watershed. Our team is skilled in taking wetland, stream, and groundwater samples for greenhouse gas, organic carbon, and microbial analyses. We also excel at measuring soil organic carbon content and type, gas fluxes, and the turnover of related nutrients and elements. Read on to learn about our specific projects this summer!
SUBPROJECT 1 - From Land to Stream: Exploring Aquatic Carbon Cycling and Fluxes in Harvard Forest’s Arthur Brook
One student will work with Dr. Kelly Aho and Abby Beilman this summer to study lateral (land-water) carbon fluxes in Arthur Brook and stream productivity in Arthur and Nelson Brook, two streams in Harvard Forest. Rivers and streams are often supersaturated with greenhouse gases (GHGs), such as carbon dioxide (CO2) and methane (CH4), which can originate from terrestrial or in-situ sources, leading to interesting opportunities for considering the influence of these processes on aquatic biogeochemistry. Despite their relatively small size, these systems are often referred to as biogeochemical hotspots, due to the large amount of nutrient transformation and transport that occurs within them, and are integral to a complete understanding of global carbon cycling and budgets.
We installed three high frequency semi-permanent systems in summer 2025 that measure dissolved CO2, as well as dissolved oxygen, temperature, pH, and conductivity, at two locations in Arthur Brook (upstream and downstream of a wetland), and one in Nelson Brook. Weekly grab samples for dissolved organic and inorganic carbon are also taken. This summer, we plan to expand measurements to include CH4, chlorophyll, and organic matter as well. Preliminary results from the past year show higher CO2 concentrations downstream of the wetland area, indicative of notable lateral flux from wetlands into stream networks. Further work this summer will include characterizing CH4 dynamics in addition to CO2, comparing stream GHG measurements with wetland GHG measurements, calculating flux terms, and exploring how stream productivity (through GHG and oxygen, chlorophyll, organic matter, and organic carbon measurements) correlates with GHG saturation and emissions.
Both Arthur and Nelson Brook are within walking distance from the main campus of Harvard Forest, and Arthur Brook is accessible by car as well. As a part of this group, the student will develop field skills such as gas and water sampling, as well as instrument maintenance, calibration, and troubleshooting, with 2-3 full field days per week. Laboratory analyses will be completed in the Aho Lab at Boston University, and the student will have the opportunity to visit to learn methods for gas and nutrient sample processing and analyses. Using the data collected, the student will learn how to complete visualizations and statistical analyses in R. The students will receive ongoing guidance and mentorship in field, lab, and analytical work, ensuring they feel fully supported and confident in their tasks. The student can expect to focus their independent project on greenhouse gases or stream productivity, depending on interests.
SUBPROJECT 2 - After the Storm: Exploring Hurricanes' Impact on Soil Biogeochemistry
Two students will work with Dr. Hannah Naughton, Marissa Hanley, and Halina Saydam this summer to study the impact of a hurricane simulation on an oak-maple dominated temperate forest ecosystem. Temperate forests are often considered carbon sinks, but the belowground processes that release greenhouse gasses (GHG)—such as carbon dioxide, methane, and nitrous oxide—are shifting with changing nitrogen (N) and carbon (C) inputs, moisture, and temperature. A nuanced understanding of how soil processes cycle C, N, and GHG is crucial for accurately predicting ecosystem functioning and contribution to global warming.
We started this project summer 2024 by collecting weekly soil and gas samples to analyze soil moisture, nutrient profiles, redox chemistry, and GHG emissions. Our research takes place in a 60 m x 120 m hurricane simulation plot with uprooted tree stems and pit-mound structures covering about 20% of the forest floor. Immediate effects of the hurricane-like event had little impact on soil nutrient cycling. Now, more than 35 years later and with a largely regrown canopy, we expect to see significant shifts in nutrient cycling, likely due to the decomposition of increased inputs of woody debris from the event. This summer, we are continuing to explore how pit and mound microtopography created by uprooted trees might create anoxic microsites in the soil that influence biological activity and GHG emissions. With the increasing frequency of storm events and human-caused disturbances, understanding these processes is more important than ever.
The sampling site for this study is located at Harvard Forest, just a 5-minute drive plus 10-minute walk from the main campus. Throughout the project, students will develop both field and laboratory skills, including soil sampling, gas sampling, and nutrient analysis. Fieldwork will require 2-3 full days per week and involves sampling soils and transporting equipment and samples to and from the forest. In the lab, students will learn soil and litter measurements and perform data analysis, including statistics in R. Students will receive ongoing guidance and mentorship in field, lab, and analytical work, ensuring they feel fully supported and confident in their tasks. Our team is piloting projects related to macroinvertebrates’ role in decomposition and chemical composition of leaf litter as it relates to nutrient cycling in forest systems. Students interested in exploring these subtopics further will have the opportunity to develop and refine their own hypotheses throughout the summer, promoting independent thinking within the research framework.
TBD