PhD, Massachusetts Institute of Technology, Environmental Engineering (2018)
MS, Cornell University, Biological and Environmental Engineering (2012)
BS, UC Berkeley, Civil and Environmental Engineering (2007)
Rob Jackson, Postdoctoral Faculty Sponsor
Current Research and Scholarly Interests
I completed my PhD at the Massachusetts Institute of Technology where I was studying the role of methane bubbles in chemical cycling within Upper Mystic Lake, MA. As part of this work I designed, built, and deployed custom sensors to measure bubble volume and release timing in-situ. I also led a study looking at the potential for particle transport via rising bubbles, and we found bubble-facilitated transport of both heavy metals and cyanobacteria from lake sediment. I recently completed a postdoc in the Sunderland Lab at Harvard where I built a mechanistic model to estimate methane emissions from hydropower reservoirs, with the ultimate goal of proposing mitigation strategies to reduce emissions.
I am now working as a postdoc in the Jackson lab here at Stanford where I study methane emissions from wetland systems. I am coordinating a USGS Powell Center for Synthesis and Analysis group to use eddy covariance data from flux towers in wetlands throughout the world to better understand flux drivers, improve biogeochemical models of methane emissions, and increase certainty of global wetland emissions estimates.
In addition to exploring the world of global methane modeling, I continue to design and build new bubble catching devices for deployment in lakes and flooded wetlands.
Rob Jackson, (8/5/2019)
Vertical transport of sediment-associated metals and cyanobacteria by ebullition in a stratified lake
View details for DOI 10.5194/bg-2019-243
Dynamics of microbial populations mediating biogeochemical cycling in a freshwater lake
2018; 6: 165
Microbial processes are intricately linked to the depletion of oxygen in in-land and coastal water bodies, with devastating economic and ecological consequences. Microorganisms deplete oxygen during biomass decomposition, degrading the habitat of many economically important aquatic animals. Microbes then turn to alternative electron acceptors, which alter nutrient cycling and generate potent greenhouse gases. As oxygen depletion is expected to worsen with altered land use and climate change, understanding how chemical and microbial dynamics impact dead zones will aid modeling efforts to guide remediation strategies. More work is needed to understand the complex interplay between microbial genes, populations, and biogeochemistry during oxygen depletion.Here, we used 16S rRNA gene surveys, shotgun metagenomic sequencing, and a previously developed biogeochemical model to identify genes and microbial populations implicated in major biogeochemical transformations in a model lake ecosystem. Shotgun metagenomic sequencing was done for one time point in Aug., 2013, and 16S rRNA gene sequencing was done for a 5-month time series (Mar.-Aug., 2013) to capture the spatiotemporal dynamics of genes and microorganisms mediating the modeled processes. Metagenomic binning analysis resulted in many metagenome-assembled genomes (MAGs) that are implicated in the modeled processes through gene content similarity to cultured organism and the presence of key genes involved in these pathways. The MAGs suggested some populations are capable of methane and sulfide oxidation coupled to nitrate reduction. Using the model, we observe that modulating these processes has a substantial impact on overall lake biogeochemistry. Additionally, 16S rRNA gene sequences from the metagenomic and amplicon libraries were linked to processes through the MAGs. We compared the dynamics of microbial populations in the water column to the model predictions. Many microbial populations involved in primary carbon oxidation had dynamics similar to the model, while those associated with secondary oxidation processes deviated substantially.This work demonstrates that the unique capabilities of resident microbial populations will substantially impact the concentration and speciation of chemicals in the water column, unless other microbial processes adjust to compensate for these differences. It further highlights the importance of the biological aspects of biogeochemical processes, such as fluctuations in microbial population dynamics. Integrating gene and population dynamics into biogeochemical models has the potential to improve predictions of the community response under altered scenarios to guide remediation efforts.
View details for DOI 10.1186/s40168-018-0556-7
View details for Web of Science ID 000444924800001
View details for PubMedID 30227897
View details for PubMedCentralID PMC6145348
Methane Bubble Size Distributions, Flux, and Dissolution in a Freshwater Lake
ENVIRONMENTAL SCIENCE & TECHNOLOGY
2017; 51 (23): 13733–39
The majority of methane produced in many anoxic sediments is released via ebullition. These bubbles are subject to dissolution as they rise, and dissolution rates are strongly influenced by bubble size. Current understanding of natural methane bubble size distributions is limited by the difficulty in measuring bubble sizes over wide spatial or temporal scales. Our custom optical bubble size sensors recorded bubble sizes and release timing at 8 locations in Upper Mystic Lake, MA continuously for 3 months. Bubble size distributions were spatially heterogeneous even over relatively small areas experiencing similar flux, suggesting that localized sediment conditions are important to controlling bubble size. There was no change in bubble size distributions over the 3 month sampling period, but mean bubble size was positively correlated with daily ebullition flux. Bubble data was used to verify the performance of a widely used bubble dissolution model, and the model was then used to estimate that bubble dissolution accounts for approximately 10% of methane accumulated in the hypolimnion during summer stratification, and at most 15% of the diffusive air-water-methane flux from the epilimnion.
View details for DOI 10.1021/acs.est.7b04243
View details for Web of Science ID 000417549500022
View details for PubMedID 29116771
- An enhanced bubble size sensor for long-term ebullition studies LIMNOLOGY AND OCEANOGRAPHY-METHODS 2017; 15 (10): 821–35
- Persistence of bubble outlets in soft, methane-generating sediments JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES 2017; 122 (6): 1298–1320
- A novel optical sensor designed to measure methane bubble sizes in situ LIMNOLOGY AND OCEANOGRAPHY-METHODS 2015; 13 (12): 712–21
Nonequilibrium clumped isotope signals in microbial methane
2015; 348 (6233): 428–31
Methane is a key component in the global carbon cycle, with a wide range of anthropogenic and natural sources. Although isotopic compositions of methane have traditionally aided source identification, the abundance of its multiply substituted "clumped" isotopologues (for example, (13)CH3D) has recently emerged as a proxy for determining methane-formation temperatures. However, the effect of biological processes on methane's clumped isotopologue signature is poorly constrained. We show that methanogenesis proceeding at relatively high rates in cattle, surface environments, and laboratory cultures exerts kinetic control on (13)CH3D abundances and results in anomalously elevated formation-temperature estimates. We demonstrate quantitatively that H2 availability accounts for this effect. Clumped methane thermometry can therefore provide constraints on the generation of methane in diverse settings, including continental serpentinization sites and ancient, deep groundwaters.
View details for DOI 10.1126/science.aaa4326
View details for Web of Science ID 000353338000032
View details for PubMedID 25745067
Atrazine leaching from biochar-amended soils
2014; 95: 346–52
The herbicide atrazine is used extensively throughout the United States, and is a widespread groundwater and surface water contaminant. Biochar has been shown to strongly sorb organic compounds and could be used to reduce atrazine leaching. We used lab and field experiments to determine biochar impacts on atrazine leaching under increasingly heterogeneous soil conditions. Application of pine chip biochar (commercially pyrolyzed between 300 and 550 °C) reduced cumulative atrazine leaching by 52% in homogenized (packed) soil columns (p=0.0298). Biochar additions in undisturbed soil columns did not significantly (p>0.05) reduce atrazine leaching. Mean peak groundwater atrazine concentrations were 53% lower in a field experiment after additions of 10 t ha(-1) acidified biochar (p=0.0056) relative to no biochar additions. Equivalent peat applications by dry mass had no effect on atrazine leaching. Plots receiving a peat-biochar mixture showed no reduction, suggesting that the peat organic matter may compete with atrazine for biochar sorption sites. Several individual measurement values outside the 99% confidence interval in perched groundwater concentrations indicate that macropore structure could contribute to rare, large leaching events that are not effectively reduced by biochar. We conclude that biochar application has the potential to decrease peak atrazine leaching, but heterogeneous soil conditions, especially preferential flow paths, may reduce this impact. Long-term atrazine leaching reductions are also uncertain.
View details for DOI 10.1016/j.chemosphere.2013.09.043
View details for Web of Science ID 000328868400049
View details for PubMedID 24129000