River to reef: Inorganic carbon cycling in the Belizean coastal ocean

Global ocean pH is decreasing due to the uptake of anthropogenically generated CO2, however, in coastal waters pH control is more complex and driven by additional factors such as riverine outflow characteristics and net ecosystem metabolism. Understanding the impact of these factors is rendered critical and timely given that they are likely impacted by the rapid land-use change ongoing in coastal zones around the world. Investigations along the coast by traditional sampling methods, are logistically difficult, which has historically presented a barrier to gaining a comprehensive understanding of coastal carbonate cycling and pCO2 fluxes. In this thesis I present a technologically driven approach to ascertain local drivers of carbonate chemistry at the coast. Traditional discrete water sampling was combined with fixed-point sensor-equipped observatories and sensors mounted on an autonomous surface vehicle to measure relevant parameters over time and space. My study area, located off the coast of Belize City, hosts coral reefs, seagrass beds and mangroves, and is influenced by freshwater from the Belize River, which drains the largest catchment in the country. The study region is determined to be a net-source of CO2 to the atmosphere, however, the potentially corrosive Belize River water did not appear to reach the barrier reef. Mangroves were likely exporting organic matter and dissolved inorganic carbon to the coastal waters, and therefore a source of atmospheric CO2. Seagrasses on the other hand were likely mitigating the atmospheric CO2 flux. On the barrier reef the diel cycles in pH were largely driven by benthic composition. My findings have relevance on a local to global scale, and offer new insight into carbonate system dynamics in tropical coastal waters with riverine inputs.