Biogeochemical observations and baseline CO2 conditions in the Agua Hedionda Lagoon

Estuarine environments are uniquely diverse coastal subsystems located at the land-river-ocean interface. Across different systems, carbon dioxide (CO₂) parameters and anthropogenic inputs can vary greatly given the heterogeneity between individual estuarine systems, which makes it difficult to characterize coastal ocean systems as a whole. The Agua Hedionda Lagoon (AHL) is a local estuary located in Carlsbad, CA comprising three interconnected basins, which make up a total of about 400 acres off the Pacific coast. This lagoon is highly impacted by the surrounding urbanization, land use, and densely populated community, making it susceptible to anthropogenic impacts. One of the primary features operating at the lagoon is the Carlsbad Aquafarm (CAF), which raises over one million pounds of Mediterranean Blue Mussels (Mytilus edulis) and Pacific oysters (Crassostrea gigas) every year. Understanding the baseline chemical distribution and variability will provide critical information needed by the stakeholders to manage the CAF and lagoon ecosystem. To assess the variable conditions in the AHL, an autonomous shore station system was employed at the CAF to collect continuous measurements for total dissolved CO₂ (TCO₂) every hour, and the partial pressure of CO₂ (pCO₂), pH, temperature, and salinity taken every 15 seconds. Additional sensors deployed in the adjacent lagoon basins and outside of the lagoon collected in situ data for salinity, temperature, dissolved oxygen, pH, and pressure, every 30 minutes. Data collected during 2018 has been analyzed specifically to capture the changing estuarine CO₂ conditions during the year and examines several rain events that occurred in this time frame.