ORGANIC GEOCHEMISTRY AND ENVIRONMENTAL IMPACTS OF OIL SEEPS IN COASTAL WATERSHEDS

The ecological and geochemical impacts of naturally occurring oil seeps within marine environments are well studied, however, terrestrial oil seeps and their effects on proximal watersheds, ecosystems and water quality remains unexamined. Among the contaminants present in crude oil are polycyclic aromatic hydrocarbons (PAHs), which are recognized as carcinogens and can negatively impact ecosystem health. Santa Paula Creek, located in Southern California, contains natural oil seeps within and adjacent to the stream channel. The impacts of crude oil within Santa Paula Creek are especially concerning as the stream flows through a local park and ultimately feeds into the Santa Clara River watershed. Towsley Canyon, also located in Southern California, contains crude oil seeps as well as improperly sealed wells. Both sites represent different hydrological conditions, Santa Paula Creek is a year-round stream while Towsley Canyon is subject to ephemeral stream conditions. To investigate the transport and fate of organic contaminants associated with crude oil located within Santa Paula Creek and Towsley Canyon, water and sediment samples were collected at various locations within each stream, including downstream of crude oil seeps and PAH concentrations were quantified by gas chromatography-mass spectrometry (GC-MS). Characterization of crude oil components, such as PAHs, alkylated PAHs and alkanes were conducted on crude oil found at each respective site. Crude oil analysis involved deasphaltenation and fractionation, followed by quantification of PAHs and n-alkanes by GC-MS. Petroleum components were detected downstream for each study area, but significant impacts were primarily limited to the immediate areas around the seeps during the relatively low flow condition. However, evidence of oil was observed further downstream such as tar staining on rocks and trees. This suggests the potential for greater oil transport during high flow conditions.