In situ and remote monitoring of water quality in Puget Sound: The ORCA time-series

High frequency hydrological and meteorological measurements have been made in Puget Sound from 2001 to the present using remote profiling moorings. The moorings consists of a toroidal float upon which is mounted an electric winch that is powered by solar panels. Meteorological variables include, wind velocity and direction, air temperature, barometric pressure, and incident solar radiation while hydrographic variables include water temperature, salinity, dissolved oxygen, chlorophyll fluorescence and nitrate. Currently three moorings are operating in Puget Sound. All hydrographic variables displayed high frequency variability at all locations in Puget Sound, likely due to tidally advecting, patchy distributions. In the main basin of Puget Sound, the water column was well mixed during the winter months and water temperature was warmer than air temperature. With the onset of spring conditions plankton (fluorescence) bloomed and oxygen became supersaturated. However, there were numerous and frequent periods of destratification that could be correlated with wind events which mixed chlorophyll-containing surface waters downwards and nutrient-rich, oxygen-undersaturated water upwards. This process enhanced export production and injected oxygen into the deep waters. The chlorophyll maximum was found in the surface waters during the spring and fall bloom periods, but was located in the pycnocline during the summer months. By pooling all the oxygen data by hour of the day a diurnal oxygen curve was determined. The diurnal oxygen cycle was approximately sinusoidal with the minimum slightly before dawn and the maximum about at about 1800h and the amplitude was 17m moles of oxygen per liter. Primary production estimates derived from the oxygen cycle agreed with those determined from classical 14-C incubation methods. Statistical analysis of the data revealed that, at a minimum, daily sampling is necessary to assess the true values of the many measured variables. Without this sampling frequency resolving interannual differences or climate related changes would be difficult. However, given daily or greater sampling it should be possible to determine these types of changes as well as overall trends and cycles.