Deciphering the cryptic cycling of methane in sediments of a coastal Wetland
Dr. Hari Vaidehi Narayanan, Dr. Koushik Roy, Mark Xiang
Principal Investigator: Dr. Alexander Hoffmann
2021.1 - Now
Objectives: Recent studies have provided the first evidence for the simultaneous microbial production and consumption of methane in the sulfate reduction zone of organic-rich sediments, a process named the "cryptic methane cycle." In this process, methane is proposed to be passed directly from methylotrophic methanogenesis to anaerobic oxidation of methane (AOM). However, little is known about the identity of the organisms involved, the trail of carbon from one metabolism to the other, or the environmental net result of the two processes. Our study will focus on sediments from the Carpinteria Salt Marsh Reserve, a productive coastal wetland in Southern California. We will apply radioisotope and stable isotope labeling of collected sediments and combine these methods with molecular probing and nanoscale secondary iron mass spectrometry to investigate cryptic methane cycling on the microbial level. Field measurements of methane emission rates and biogeochemical profiles of sediments along the salinity gradient of the salt marsh will provide information on factors that control cryptic methane cycling and methane release into the atmosphere. As a research assistant, I am involved in collecting sample from the field, slicing sediment cores, preparing media, culturing bacteria and archaea, running ion chromatography, etc.
Detecting solid ferric oxide by liquid scintillation counting
Mentor: Sebastian Krause
Principal Investigator: Dr. Tina Treude
2019.2 - 2020.4
Objectives: Iron oxides have substantial effects on biochemical processes when coupled to organic matter degradation, due to their redox reactivity and ubiquitous presence in aquatic sediments. The oxidized form of iron, Fe (III) or ferric oxide, can be used to detect the anaerobic respiration and metabolic rate of prokaryotes in the iron reduction zone. Therefore, it is important to quantify oxidized iron in aquatic sediments, which usually exists as Fe2O3 in solid form. However, ferric oxide is insoluble in water due to its +3 oxidation state, because water molecules are not strong enough to dissociate the bonds between the Fe3+ and O2- ions. It is thus difficult to determine Fe(III) using traditional techniques like spectrophotometry. The fact that ferric oxide exists in various mineral species with different compositions, including hematite, maghemite, etc., further complicates the pretreatment procedure. This study is inspired by a suspicious result in a monthly radiation survey by liquid scintillation counting (LSC), and aims to test a potential method that quantitatively measures solid ferric oxide and to establish a corresponding standard curve consistent through most mineral species.