sustain primary productivity during the summer months. Phosphorus Phosphorus is generally a limiting nutrient in the ocean. In Pacific Northwest estuaries, an important source of phosphorus comes from ocean upwelling in the summer (see below). Samples taken at the surface with varying salinities showed dissolved inorganic phosphorus more prevalent in areas with higher salinities compared to lower, thus indicating the ocean as the source for this system. Oxygen Dissolved oxygen (DO) concentration is an important water quality parameter because of its close relationship with biological activity. In the Yaquina Bay estuary, DO levels may be lower and almost hypoxic due to low DO levels with coastal upwelled water imported into the estuary. DO levels of imported ocean water are dependent on physical factors (wind stress and cool water temperature) and biological factors (association with chlorophyll a and respiration). Ocean influence of DO levels in the estuary extends to about 10 km (6.2 mi) upriver. In the upper estuary beyond ocean influence, DO levels decrease with increasing temperature. Chlorophyll a Chlorophyll a (Chl a) concentrations vary seasonally with ocean water import, particularly during summer upwelling. Variation of Chl a also depends on the timing of summer upwelling each year, where upwelling could occur earlier or be delayed. Oregon estuaries typically have low median Chl a levels, about less than 5 micrograms per liter of water. When high concentrations of Chl a are advected into the estuary, there is also an increase in flood tide DO levels. Upwelling Summer upwelling along the Oregon coast brings nutrients from deep waters up into the Yaquina Bay estuary. This event, along with decreased rain and river input, and increased light, all contribute to the seasonal chemistry variability in the Bay. Environmental concerns Coastal hazards of Yaquina Bay As with any coastal zone, there are inherent hazards present. Especially in the Pacific Northwest, coastlines are impacted by large waves, storm surge, strong currents, wind, and rain. Yaquina Bay is seasonally affected by these impacts, with winter typically the most intense period. Storms and rain increase, which leads to more land runoff and also causes waves and currents to reshape the coastline. Erosion is a problem not only for the Yaquina Bay, but for the entire Oregon Coast. Yaquina Bay's sediments are made up of sandstone, siltstone and clay-containing mudstone and these soft sediments contribute to the annual erosion rates. Waves, however, are the main proponent of