Nitrogen fixation and nitrification at the San Pedro Ocean Time-series (SPOT)
Collaborator: Doug Capone (USC)
Coastal marine ecosystems are seasonally dynamic and highly productive. Phytoplankton populations shift from nutrient replete conditions in spring to nutrient limited conditions in other seasons. The San Pedro Ocean Time-series (SPOT), located 17 km offshore of Los Angeles, is a representative and accessible model coastal system with an existing framework for routine sampling and a substantial database of relevant observations, including the dynamics and diversity of microbial populations since 2000. However, apart from a few sporadic and opportunistic studies, systematic efforts to detail carbon and nitrogen cycling at SPOT have been lacking. It is critically important to understand the nutrient controls on primary production in coastal waters and the capacity of coastal ecosystems to sequester carbon dioxide. We are examining rates of primary production, inorganic nitrogen uptake, and nitrification in the upper water column of SPOT over two seasonal cycles. Our specific goal is to understand the roles of biological nitrogen fixation and nitrification to supporting the nitrogen necessary for primary production at this site, and how these processes may be linked to biological production of the greenhouse gas nitrous oxide.