One of the main objectives of hydrology is to quantify the fluxes of water and associated materials into and out of a watershed. To achieve this, measurements have to be made in a boundary zone between the watershed and an adjacent body, where that body could be the atmosphere, the groundwater system, the coastal zone, or even another watershed. However, each boundary zone is subject to a unique set of processes that have to be understood before accurate watershed flux estimates can be determined. Also, different processes may play a role in watershed-estuary interactions at different time scales. During my career I have investigated such processes over a range of time scales in different types of coastal boundary zones, but primarily in estuaries. Prior to 1993 I did some work on coastal salt marshes in Long Island Sound. During 1993-2001 I performed research about Chesapeake Bay in Maryland. Since 1999 I have been doing research in a variety of coastal and estuarine boundaries in California, including in the Sacramento-San Joaquin delta as well as the deltaic/estuarine zones of the Salinas, Navarro, and Eel Rivers. I also have been working on the Umpquah River estuary in Oregon.