Results and Discussion

Temperatures ranged widely at the two inner (55 and 56) and, to a lesser degree, the three middle harbor stations (53, 54 and Dockton). Each station showed a very noticeable thermocline between approximately 8 and 12 meters. This is likely due to a relatively slow flushing rate of the water in Quartermaster Harbor (DNR 2004). Closure of an opening between Maury and Vashon Island restricted the exchange of water solely to southern harbor mouth. Conversely, the outer harbor stations (50, 51 and 52) were well mixed throughout the water column, showing only a slight thermocline between approximately 5 and 10 meters. Overall, stratification increased with distance from the entrance into Quartermaster Harbor.

All inner and middle harbor stations showed a very noticeable halocline between approximately 5 and 7 meters in depth. During the week prior to sampling, 3.0 in of precipitation was recorded at the nearby Tacoma Narrows Airport. This likely increased the input of the many small fresh water streams that empty into Quartermaster Harbor. Being less dense, this water then overlays the denser, saltier water entering from Puget Sound. Outer harbor stations showed a much higher degree of mixing with a much less noticeable halocline at approximately 5 meters.

Very noticeable pycnoclines were noted at all inner and middle harbor stations, mirroring the depths of the thermoclines and haloclines. This makes sense as density is a function of temperature and salinity. Once again, this could be attributed to the relatively slow flushing rate of Quartermaster Harbor and fresh water input from local streams. The geography of Quartmaster Harbor makes the harbor sheltered which means it is less susceptible to winds.

Comparison of CTD DO and discrete DO water samples

Correlation of CTD DO levels with discrete DO water samples showed a high correlation of determination of 0.9156.

All stations showed supersaturated DO levels above approximately 8 meters of depth, with levels increasing with distance from the harbor entrance. This corresponds to the levels of highest chlorophyll, an indicator of phytoplankton concentration, in the discrete water samples. Due to the much higher level of mixing in the outer harbor stations, DO saturation levels decreased much slower with depth than at the middle and inner harbor stations.

The CTD fluorescence data did not represent what was actually occurring in the harbor on this date. The highest level of fluorescence, 3.13 mg/m³, was measured at 4 meters of depth at station 50. The above comparisons of the CTD fluorescence data with fluorometer data for the discrete water samples show very low coefficients of determination of 0.321 and 0.247. But comparison of the two fluorometers used to analyze the water samples show a high coefficient of determination of 0.9315. Because of this, the descrete water fluorometer data was averaged for each depth and used in place of the CTD data to generate the above UWT fluorometer contour plot.

Transmissivity showed a decreasing trend with increasing distance from the harbor entrance. Outer harbor stations showed much lower variability, 84.2%-95.8%, than the inner and middle harbor stations, 62.5%-87.8. In general, transmissivity decreased with distance from the entrance into Quartermaster Harbor. The relatively low transmissivity in the inner and middle harbor stations corresponds with the high fluorescence and DO data, both indicators of phytoplankton concentration.

At the entrance to Quartermaster Harbor, pH showed little variability below 8 meters of depth. Below this depth, pH was approximately 7.7 to 7.8. This corresponds with values from previous research for this area and time of year (Feely et. al 2010). Inside the harbor, pH increases corresponded to high levels of chlorophyll, an indicator of phytoplankton concentration. As shown below, two genera of diatoms (Chaetoceros spp. & Thalassiosira spp.) were in high concentration on the sampling date. Diatom concentration in fresh water has been linked to increases in pH (Dixit et. al 1992).

Secchi disk measurements ranged between 3 and 5.5 meters with an average of 4.7 meters. Depths generally increased with distance from the harbor entrance. This does not correspond to the CTD transmissivity data which showed the opposite trend. This could be due to the suspended load in the plume from the Puyallup River which empties into Commencement Bay to the south of Quartermaster Harbor.

Twenty unique genera of phytoplankton were identified in the water samples. While concentration and diversity of phytoplankton varied greatly between the eight stations, Chaetoceros spp. and Thalassiosira spp. were consistently most abundant. The higher concentrations at the inner and middle harbor stations, except for dockton, correspond with the higher chlorophyll levels.

A zooplankton net capture was conducted at station 50 between 50 and 150 meters of depth with a 150μm mesh. Four separate organisms were identified in the sample.

Grains ranging in size from 0.4 to 250 μm were present in each sediment sample. Grains above 500μm were present in five samples and above 1000 μm only in four. Sediment collected at the inner stations showed a tendency toward smaller grain size, silts and clays. Stations 51 and 52, which see a greater turbulence due to being in the harbor entrance, showed a much higher percentage of sands. Greater turbulence typically keeps smaller grains suspended and out of the sediments. Sediments at the outer harbor stations were classified as loamy sand. The middle harbor stations were silt loam. The inner harbor stations were silt.

Dissolved inorganic nitrogen (DIN), PO₄, and Si(OH)₄ are used by the phytoplankton which causes concentration levels to drop. Our data is consistent in the respect that when phytoplankton cell counts are high, there is a decrease in nutrients as well. The only exception to this is Dockton Dock which we believe to be an anomaly.

Feely RA, Alin SR, Newton J, Sabine CL, Warner W, Devol A, Krembs C, Maloy C. 2010. The combined effects of ocean acidification, mixing, and respiration on pH and carbonate saturation in an urbanized estuary. Estuarine Coastal and Shelf Science 88(4): 442-449.