THE EFFECT OF ELEVATED CO2 DRIVEN BY GROUNDWATER AND OIL RESERVOIR ON THE PORE WATER CHEMISTRY AND SEDIMENT QUALITY OF TIDAL MUD FLAT OF SAN PEDRO MARSH, CALIFORNIA

In this research study, we examined the effects of elevated CO₂, nitrogen (N), and carbon (C) inputs on sediment and water’s microbial community. We measured carbon (C), nitrogen (N) (C:N ratio), and carbon dioxide (CO₂) in the Salinas de San Pedro tidal marsh in southern California. The results from the current and previous studies showed high CO2 flux to the atmosphere. This could be explained by excessive CO₂ discharge from underlying fault line either from groundwater aquifer near the surface or from an existed oil field reservoir. Sediment core samples from 0-5 cm (surface or top) and 5-10 cm (below the surface or bottom) were collected from the Salinas de San Pedro study site to assess the C:N ratio. We measured the C:N ratio for the surface (top) and below the surface (bottom) samples in various locations of the salt marsh. The results showed that C:N ratios varied greatly from surface to depth of 10 cm below surface. The sample analysis has revealed higher concentration in the carbon and nitrogen signatures in surface samples. The C:N ratios ranged from 11.1:0.11 to 1.07:0.07 in bottom samples and from 0.79:0.09 to 0.76:0.05 in the top samples. The C:N ratios tend to decrease with depth, which may be a result of the increased clay content with depth. Higher clay content is often associated with more decomposed organic matter with a lower C:N ratio. As a result, increase decomposition leads to increased CO2 production and thus higher CO₂. In turn, an increase in CO₂ leads to increased net primary production, which in some ways leads to increased decomposition either through recruiting decomposers or by priming the decomposition of more recalcitrant organic matter. Thus, we suggest that the major processes contributing to CO₂ enrichments within aquatic systems are in-situ respiration driven by natural and anthropogenic organic matter inputs, groundwater, and gas discharge from the local fault zone. The links between the latter sources and CO₂ super saturation in salt marsh waters and sediments provide insight into the complex dynamics between terrestrial and aquatic carbon cycling.