Date of Award
2025
Document Type
Honors Thesis (Open Access)
Department
Colby College. Chemistry Dept.
Advisor(s)
Greg Drozd, Ph.D., Associate Professor of Chemistry, Colby College
Second Advisor
Whitney King, Ph.D., Dr. Frank and Theodora Miselis Professor of Chemistry, Colby College
Abstract
Kelp, or brown algae, is an emerging form of ocean-based biological carbon dioxide removal, converting dissolved CO2 into organic molecules via photosynthesis. The export of detritus and dissolved organic carbon (DOC) from coastal beds to beyond the continental shelf contributes to carbon sequestration, especially through the microbial production of refractory DOC (RDOC). The influence of microbial degradation on kelp-derived DOC is not yet well understood, contributing to inconsistency in carbon sequestration estimates. This study utilizes dark bottle incubations of both blades and holdfasts from two farmed kelp species in the Gulf of Maine — Saccharina latissima and Saccharina angustissima — to examine the microbial processing of kelp-derived DOC over 90 days. The optical properties of chromophoric and fluorescent dissolved organic matter (CDOM and FDOM) were characterized using UV-VIS spectroscopy and excitation-emission matrix (EEMs) fluorescence spectroscopy. DOC and CDOM concentrations increased rapidly early in the experiment. While [DOC] proceeded to rapidly decrease, CDOM concentrations remained elevated through Day 90. Optical proxies for CDOM and FDOM suggest an upward trend in the humification of kelp-derived organic matter through Day 90 across all samples. Trends in average molecular weight and aromaticity varied by species and tissue type. EEMs red-shifts due to increased molecular complexity suggest the production of bio-recalcitrant DOC. Since changes in optical properties did not reach steady state by Day 90, definitive conclusions cannot be made on CDOM and FDOM contributions to carbon sequestration. However, these promising results encourage further work into the contribution of Maine-farmed kelp to biological CDR and carbon sequestration.
Keywords
Carbon sequestration, marine chemistry, kelp, RDOC, CDOM, carbon dioxide removal
Recommended Citation
Riazi-Sekowski, Sophia N., "Microbial Degradation of Kelp-Derived Dissolved Organic Matter in the Context of Carbon Sequestration" (2025). Honors Theses. Paper 1476.https://digitalcommons.colby.edu/honorstheses/1476
Comments
Primary collaboration: with the Bigelow Laboratory for Ocean Sciences and Sarah Douglas, Ph.D., who is credited for experimental design and set up. Analysis was completed by the thesis author. Further details on collaboration are included in the full text.