DISSOLVED AND PARTICULATE NUTRIENT TRANSPORT THROUGH A COASTAL WATERSHED-ESTUARY SYSTEM

Tomales Bay and its adjacent watershed are the location of integrated research on the C-NP-Si biogeochemical coupling between the land and c oastal ocean and cycling of these materials within the bay. In the pre sent paper, budgets have been constructed to describe the rainfall del ivery of dissolved nutrients to the watershed and export of dissolved and particulate nutrients from the watershed, mostly in runoff. The qu antity of dissolved materials, especially dissolved organic materials, delivered to the watershed by rainfall is about the same as the expor t. Suspended load transport represents the major net removal of C, N, and P from the watershed, and this flux shows large interannual variat ion. Runoff-adjusted particle flux from the watershed is small at pres ent in comparison with estimates based on sedimentation rate in the ba y over the past 130 years. This difference apparently cannot be explai ned by natural or managed interannual variation in runoff or by other obvious aspects of water management. We believe that changes in agricu ltural land use have led to recent decreases in erosion and removal of particulate materials from the watershed. Even though the watershed h as been disturbed by agricultural practices over the past 130 years, t he system as a whole appears largely to have recovered to steady-state conditions.