Original report written by Frank Wang.
CSMR under high tides Winter 2015
An example of the single most dominant source of global methane emissions can be found just 12 kilometers east of Santa Barbara at the Carpinteria Salt Marsh Reserve, according to graduate student Frank Wang. The reserve, home to numerous plant and animal species and tidal wetlands, is the subject of Wang’s research effort, supported by an Earth Research Institute (ERI) fellowship that provided funding for two consecutive summers. With the help of his advisor, Jennifer King, and numerous student researchers, Wang investigated patterns of gaseous carbon emissions from this local tidal wetland.
Adjacent to kelp beds, a rocky reef, and “The World’s Safest Beach,” the Carpinteria Salt Marsh Reserve provides a habitat for several wetland-native birds and is a nursery for marine and estuarine fish, according to the reserve’s website. The unique nature of the reserve’s mild, moist winters and warm, rainless summers inspired Wang to conceptualize the notion that our estimate of the magnitudes of greenhouse gas fluxes needs to be constrained. “Since both plants and microbes prefer warmer (or suitable) temperatures and enough water supplies,” Wang said, “it would be very interesting to see what would happen when ideal conditions of these two could be met at the same time, which makes Santa Barbara a good place to test out.”
Salt marshes sequester carbon from the atmosphere and contribute to the mitigation of climate change. Even though salt marshes naturally remove carbon, they also emit carbon dioxide and methane, which is why Wang believes his project is so important. He said, “Studying their greenhouse gas dynamics may help us better understand and manage wetlands by maximizing their carbon sequestration (storage) capacity and minimizing the side effects of releasing greenhouse gases.”
As an undergraduate in Hong Kong, Wang became fascinated by the functions of the wetland ecosystem “I decided to conduct this research as it is highly relevant to my past experience,” he said. “The pocket wetlands in California are special as they exist in this dry Mediterranean climate and we do not know about their [greenhouse gas] dynamics that well.”
Wang’s research focused on two primary components. He first looked into the spatial and temporal patterns of carbon dioxide and methane fluxes—that is, the process of carbon dioxide and methane flowing out of the soil and into the atmosphere—from this tidal wetland. Secondly, Wang questioned how these greenhouse gas fluxes related to local environmental characteristics, such as air temperature and soil carbon content.
Soil organic matter differed significantly between the lower marsh zones and the mudflat/transition zone
To better represent the salt marsh’s environmental factors, Wang and his team divided it into four zones: surface elevation, salinity, vegetation cover and tidal regime (the range of elevation experiencing the rising and falling of the tide). The team performed approximately 20 rounds of gas sampling and two rounds of soil sampling. With each entrance into the site, air and soil temperatures were measured, and gas samples were collected and transported back to the lab to be analyzed for their greenhouse gas concentration. Gas samples were taken regularly. Soil samples were only taken twice—in August 2015 and June 2016—from the same sites where gas samples had previously been collected. Back at the lab, these new samples were analyzed for their organic matter content, pH balance, particle size distribution, and total carbon and nitrogen content.
Wang found that the gaseous carbon fluxes showed significant spatiotemporal variability, differences of carbon dioxide and methane fluxes from the wetland soils in different seasons and from different zones of the wetland. “My research suggests that instead of treating any wetland as a homogeneous entity, we need to consider the internal variability of a wetland,” Wang explained. “Not each part of a wetland was formed equally. Some areas are less inundated, and thus will be drier with a different set of vegetation and perhaps soil microbial community. It is still part of the wetland, but the greenhouse gases that come out from the soils of this part of the wetland will be different from another part.”
Wang and his team also found that soils from lower-elevated marsh zones were more acidic, had higher electrical conductivity, and greater soil carbon content than those from the salt flat or the marsh-upland transition zones, which were at a higher elevation. “One of the most surprising results we found was how diverse the seemingly homogeneous Carpinteria Salt Marsh is in terms of soil greenhouse gas fluxes,” Wang said. “Just within a few hundred meters, there are significant changes in hydrology from the ocean to more upland areas, accompanied by changes in tidal reach, soil properties, and plant communities. These different conditions would influence the microbial communities within the soils, and thus the greenhouse gases they produce and release into the atmosphere.”
For Wang, the most rewarding aspect of this project was the opportunity to confirm and further develop his academic knowledge by conducting research in person outside the classroom. With the help of ERI and his team, Wang’s research revealed intriguing patterns in nature providing a foundation for further discovery.
“This project is my first serious scientific project in some sense, and was my second attempt to conduct research on wetland biogeochemistry,” Wang said. “It was very valuable to experience the nitty-gritty and trivia in conducting field research, to figure out not only the scientific questions...but also project planning, logistics, and facility maintenance...I'm lucky to have a supportive advisor and dedicated research assistants.”