The composition of greenhouse gases in Earth’s atmosphere and the ecological dynamics of the biosphere are inextricably linked, as carbon dioxide (CO2) and methane (CH4) are primarily cycled through plant and microbial metabolisms. Due to this close coupling, ecosystem disturbances – e.g., land-use transformations, floods and droughts, and insect and pathogen outbreaks – can create disruptive feedbacks with the climate system. I work at the intersection of ecosystem ecology and atmospheric science to understand how disturbances impact ecological dynamics and whether they trigger climatic feedbacks in wetlands, forests, and novel anthropogenic ecosystems. To conduct this research, I measure ecosystem-atmosphere carbon fluxes and synthesize large global datasets, analyze remotely sensed imagery, and conduct ecosystem-climate modeling.
Impacts of forest insects and pathogens under climatic change
Insects and pathogens are ubiquitous forces of disturbance in global forests, where in the U.S. they impact 45 times the area of wildfire, create billions of dollars of damages annually, and trigger major shifts in ecosystem dynamics. Despite these widespread impacts, forest insects and pathogens (FIPs) are unrepresented in most global ecosystem-climate models, until recent work proposed a generalized ecophysiological scheme for modeling these impacts (Dietze & Matthes, 2014). Building upon my previous work that synthesized remotely sensed imagery with long-term field surveys to investigate the impacts of FIPs (Hatala et al. 2010, 2011), my lab is working to develop an ecoinformatic model-data synthesis framework to forecast the future impacts of FIPs on temperate forests (NSF-1638406). Through this work, we will investigate the impacts of forest insect and pathogen characteristics – e.g., intensity of activity, host specificity, and temporal dynamics of irruption cycles – on tree functional diversity, carbon, water, and energy fluxes, and the potential for these disturbances to initiate state changes within forest ecosystems.
Understanding carbon fluxes in novel anthropogenic ecosystems
One of the most visible symbols of global change is the creation of novel anthropogenic environments. In my research, I work to understand how we can apply ecological principles to understand changes in these constructed ecosystems, including landscapes used for fossil fuel extraction. Hydrofracking for shale gas in the United States is predicted to grow steadily over the next twenty years because natural gas is the most efficient fossil fuel for combustion. The construction of ecosystems for natural gas extraction most often occurs as land-use conversion from agricultural ecosystems. However, there is large uncertainty surrounding the quantity and mechanisms of fugitive methane emissions released to the atmosphere from these activities compared to agricultural baseline greenhouse gas emissions. In collaboration with researchers at the Ohio State University, we are investigating ecosystem-atmosphere CH4 flux before, during, and after land-use conversion from cattle agriculture to natural gas extraction (NSF CBET grant 1508994, Aug 2015-Aug 2018). To attribute CH4 flux to biological or geological sources and understand spatiotemporal variability in these processes, we are measuring ecosystem-scale fluxes of isotopic 13CH4 from ecosystems to the atmosphere.
Global change feedbacks in wetlands
Global wetlands play an important role in the carbon cycle, as they sustain some of the highest rates of CO2 uptake and sequestration and are also a significant source of CH4 from microbial methanogenesis. For my PhD research, I measured four years of continuous biosphere-atmosphere CO2 and CH4 fluxes from ecosystems experiencing land-use change in California’s Sacramento-San Joaquin Delta. The Delta was drained for agriculture in the mid-19th century, but land managers have recently begun restoring wetlands to prevent the further loss of soil carbon. To evaluate the impact of land-use change on the ecosystem carbon balance, I established a small network of eddy covariance towers to directly measure CO2 and CH4 fluxes from Delta ecosystems with three levels of inundation: a drained pasture, a rice paddy, and a flooded restored wetland. This research concluded that flooding transformed ecosystems from net carbon sources to net carbon sinks, but approximately doubled CH4 emissions (Hatala et al., 2012a). My research also measured rapid coupling between plant and methanogenic microbial metabolisms for the first time at the ecosystem-scale, as recently fixed plant photosynthates were converted to CH4 by microbes within hours (Hatala et al., 2012b). Furthermore, this work found that the landscape complexity of wetland plant patches produced nonlinear feedbacks to the magnitude of microbial CH4 emissions (Matthes et al., 2014), providing a potential mechanism for more robust scaling of global wetland CH4 emissions from satellite data. I continue to work with researchers in the Delta, including collaboration with the California Department of Water Resources to develop accounting programs for wetland ecosystem carbon capture credits.
In addition to the impacts of land-use change, wetland ecosystems are also vulnerable to future climatic disturbances including sea level rise, droughts, and more intense storms, all of which are expected to directly impact ecosystem carbon exchange. During the next few years, I will develop a research program to address questions regarding the response of wetlands to hydrologic disturbances: 1) Do ecosystems newly flooded from sea level rise capture carbon like restored wetlands? 2) How do extremes in fluctuating redox conditions due to droughts or floods impact ecosystem carbon cycling and biosphere-atmosphere CO2 and CH4 fluxes?