TOMALES BAY METABOLISM - C-N-P STOICHIOMETRY AND ECOSYSTEM HETEROTROPHY AT THE LAND SEA INTERFACE

Bays and estuaries receive inputs from the adjacent land and exchange materials with the coastal ocean. Net system metabolism records the role of such land-sea interface ecosystems in altering the chemical state of essential plant nutrients. Water and salt budgets have been constructed for Tomales Bay, California, in order to estimate water advective and mixing exchange rates between the bay and coastal ocean over 2 years. Net non-conservative fluxes of dissolved P, N and C were calculated. The bay is a net source for dissolved P, C and total alkalinity, and is a net sink for dissolved fixed N. Stoichiometric analysis can be used to interpret the non-conservative nutrient fluxes. The dissolved P source is interpreted to be the result of net oxidation of approximately 10 mmol organic C m-2 day-1. CO2 released by this oxidation largely escapes to the atmosphere. This net respiration is about 12% of the total system respiration. Most dissolved inorganic N liberated during the oxidation is not exported hydrographically; rather, the bay is a net sink of dissolved fixed N. This N is assumed to be lost from the water via denitrification (3·2 mmol m-2 day-1). Sulphate reduction (5·1 mmol m-2 day-1) is also an important component of respiration in this system. Denitrification is a minor component of gross C metabolism, but is the major sink of N in this system. The organic matter driving this net heterotrophy may be of either terrestrial or marine origin. © 1991.