CHARACTERIZING ORGANIC CARBON IN SEDIMENTARY CORES FROM ZOSTERA MARINA BEDS, MAQUOIT BAY, GULF OF MAINE

Seagrass beds are important ecosystems in nearshore environments. They provide nutrients and habitat for commercially important fish species, buffer against storm erosion, and are effective at sequestering carbon. Globally, seagrass beds are in a general state of decline due to human activities such as pollution, climate change, and dredging in the nearshore zone. Little is known about natural fluctuations in seagrass distribution through geologic time because long and unequivocal records of paleo-seagrass have yet to be produced. The purpose of this study is to use organic geochemical techniques (lipid biomarker concentrations and isotope composition) to determine if seagrass organic matter can be detected in sediment cores from Maquoit Bay, Casco Bay, Maine.

Maquoit Bay has extensive beds of the seagrass Zostera marina (hereafter referred to as eelgrass) and is located off of Casco Bay in the Gulf of Maine. Seven sediment cores (ranging between 20-50 cm in depth) were taken from Maquoit Bay using a livingstone corer. These cores were subsampled for organic geochemistry (bulk and higher plant leaf wax lipid carbon isotope composition), lead-210 chronology, and grain size determinations. Within all of the analyzed cores, the δ13C of the bulk sediments ranged from -17‰ at the coretop to -22‰ deeper in the core. Given the multiple sources of carbon with varying δ13C values in the system, it is impossible to determine, with certainty, the degree to which eelgrass contributes to the total organic pool. Preliminary analysis of the lipid biomarker data indicates that eelgrass does contain some higher plant leaf wax lipids (C24, C26, C28 fatty acids), as do the sediments in the core. Isotopic analyses of the higher plant leaf wax lipids are currently underway and may provide an important proxy for eelgrass in other nearshore environments.