productivity. The Yaquina Bay estuary has high primary productivity throughout the year due to high dissolved oxygen concentrations and cool water temperature from tidal flushing. Nutrients Silicon Sediment input from the Yaquina River contributes to the Yaquina Bay estuary chemistry, varying with seasonal rainfall. In the winter when there is higher rainfall and therefore more input from the River, siliceous diatoms are more abundant and have higher species diversity. This is contrasted with fewer diatom species in seasons when there is less rainfall. Rocks are mostly made of silica and when land weathering takes place, rocks are broken down into their smaller silica components. With increased rainfall and sediment transport, this weathering provides a source of silica for diatoms in Yaquina Bay. In general, the upstream Yaquina River source material is more quartz dominated (more silica) than downstream source material. Some of the heavy minerals upstream include micas (biotite and muscovite made of potassium, aluminum, and silica), hematite (iron), and limonite (iron oxides). Near the coastal shoreline and mouth of the Yaquina Bay estuary, the sand grains are mostly feldspars and chert (silica), and volcanic fragments (most likely high in silica, potassium, aluminum, sodium, and calcium). In nearshore marine deposit sediment, the source material is less quartz (less silica) compared to upriver sources; heavy minerals include pyroxene (a group of silicate minerals), hypersthene (magnesium iron silica), and diopside (magnesium calcium silica). Carbon Organic carbon concentrations of the Yaquina Bay estuary vary depending on depth. Concentrations are lowest in the channel (<0.2%) and highest in shallower sediments, particularly from samples collected at tidal flats (2.7%). About 1-7% of sand in the Yaquina Bay estuary is made of carbonates like mollusk shell fragments and foraminifera. Carbonate concentrations are higher in the bay channel (5%) and decrease towards the bay margin (3%). Nitrogen Major nitrogen sources for the Yaquina Bay estuary change with season. During drier seasons, the ocean is the major nitrogen source while the river is the major source in wetter seasons, where river discharge can be up to five times higher than drier seasons. Samples taken at the surface with varying salinities showed dissolved inorganic nitrogen is found mostly at the two salinity extremes; the mouth of the estuary and up the Yaquina River. The input at the mouth of Yaquina Bay indicates input from upwelled waters during the summer season. The nutrient flux into the estuary is enough to