Organic Carbon Oxidation State and Decomposition During Burial in Intertidal Microbial Mat Ecosystems

Baylor University, Waco TX

Investigators

Abstract

Photosynthetic microscopic organisms play a major role in producing oxygen and removing carbon dioxide from our planet's atmosphere. The communities of photosynthetic microbes living near sea level on coastal bay sediments form cohesive mat structures. Microbial mats are considered the oldest ecosystem, and they include microbes that are producers and consumers of organic carbon. These mats act as nature's storage units, locking away carbon and helping to regulate Earth's climate. Since microbial mats are found on nearly 128,000 square kilometers of Earth’s coastline, they are likely important contributors to the global carbon cycle. However, the chemical, geological, and biological factors that determine how effective mats are at storing carbon are not well understood. This project will investigate how well microbial mats store carbon on timescales of tens to thousands of years. To address this question, the team of scientist will conduct research on the tidal flats around Corpus Christi Bay in Texas. They will use a suite of field- and lab-based analytical methods to study mats at multiple sites. Results from this project will help improve predictions of how sea-level rise affects carbon cycling in coastal systems. The research conducted will benefit the scientific community by providing new data on carbon storage, which is a critical component of climate change research. The project will support a new collaboration between research groups at two universities, including one designated as a Hispanic Serving Institution and a Minority-Serving Institution. These groups will share resources and expertise and provide student research opportunities that will help train new scientists from diverse backgrounds. The project includes outreach activities that engage local high school and middle school students, a high proportion of whom are economically disadvantaged and from minoritized populations. The fate of organic carbon in sediments is a function of the intrinsic chemical structures in organic matter and extrinsic factors related to the burial environment. The high organic carbon content of intertidal microbial mats makes them potentially important carbon sinks when mat-derived organic matter is buried, especially during periods of sea level rise when sediment accommodation space increases. The goal of this study is to quantify spatial and temporal differences in the burial rates and preservation of organic carbon in intertidal microbial mat ecosystems. This will be accomplished by assessing the effects of physiochemical parameters in the tidal flat environment on (1) the composition of bulk organic matter produced in microbial mats, (2) the controls on organic matter oxidation and decomposition in tidal flats through diel and seasonal variability of redox and light conditions, and (3) the down-core early degradation of buried mat-derived organic matter during late Holocene/anthropogenic sea level rise. The science team will make field measurements, collect sediment and pore water samples for chemical analysis, and conduct laboratory analyses of pore water chemistry, reactive oxygen species, low molecular weight organic acids, pigments, lipids, bulk organic matter characterization, 16S-rRNA metagenomic analysis, and geoluminescence dating. The project will focus on the factors that affect the oxidation state of carbon in bulk organic matter and specific molecules and how the carbon oxidation state affects organic matter decomposition. Variation in the balance between aerobic and anaerobic heterotrophy is hypothesized to affect the decomposition of specific chemical structures in organic matter. By advancing knowledge of the chemical composition of mat-derived organic matter and the factors affecting its decomposition, this work will help define the roles of microbial mat ecosystems in the global carbon cycle. This project is funded by the Chemical Oceanography and Marine Geology and Geophysics Programs in the Division of Ocean Sciences. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.