Results

This is the first year that the San Juan Channel has be sampled by this course. As such, this results and discussion section will compare results with historical data retreived from the Department of Ecology. It will also provide a historical background for subsequent courses sampling this area. The master cruise log, CTD data and nutrient data from the San Juan Channel can be accessed by linking to the data repository. This section will discuss results from the CTD profile, water sample analysis, secchi depth, as well as plankton and grainsize analysis. All graphs are oriented as seen in the map below.

CTD Profile

Temperature, salinity and density profiles show strong stratification occurring in the Strait of Juan de Fuca at station one. At approximately eighty meters deep temperature rapidly decreases while salinity and density show a sharp increase, indicating a deep saltwater layer entering the strait from the Pacific Ocean (station 1). However, very little stratification was observed in the San Juan Channel. The Northern most station (2) displayed the lowest top layer salinity, suggesting inputs from the Fraser River were not completely mixed at this point in the channel. However, station 4 at the South end of the channel displayed a homogeneous depth profile of temperature, salinity and density.

Dissolved oxygen profiles show a well-mixed layer at stations 2-4. However, the profile at station one displays low dissolved oxygen at a depth of eighty meters. This is consistent with the temperature and salinity profiles suggesting inputs of colder ocean water, which is lower in dissolved oxygen. CTD data is supported by dissolved oxygen numbers from titrated samples.

Station 2, in North San Juan Channel, had the highest fluorescence of all the stations. This can be attributed to low salinity Fraser River inlows. Stations 3 and 4 exhibited high levels as well indicating high levels of biologic productivity within the entire channel. Fluorescence levels peak at all sites at a depth of 10 meters. While plankton need light to photosynthesize, a depth of 10 meters is optimal for recieving enough light for growth without causing harm.

Nutrients

Nitrate concentrations in Juan de Fuca Strait are within normal ranges for this time of year, which fluxuate seasonally between 10 mM and 30 mM. However, comparison between salinity and nitrate levels suggests that high concentrations of nitrates are flushed into the system from the outer coast, rather than inland sources (Mackas 1997). Department of Ecology data were analyzed and nitrate concentrations displayed similar trends and seasonal variation. In the winter months overall high nitrate concentrations were observed at surface and at depth and salinities indicate a well-mixed layer. Any nitrates entering the system from the coast would have been mixed into the surface layer. Also, biological productivity is typically lower in the winter months, concurring with high overall nitrate levels, as nutrients are not being used for biological processes. The role of biological activity can be observed throughout this data as overall nitrate concentrations are lowest in the summer months when biologic activity is the highest, only to increase in November as biologic activity decreases (Department of Ecology 2005).

Our data displays similar positive correlation between an increase in salinity and an increase in nitrate levels seen for data in May, July, August and November 2000. This again indicates that higher nitrate levels are entering Juan de Fuca Strait from the Pacific. In 2000 coastal upwelling is not observed in the months were data was collected. However, in 1999, coastal upwelling is seen in September monitoring through an increase in both salinity and nitrate levels (Department of Ecology 2005).

Secchi Disk

Secchi depth readings showed slightly higher clarity at station three, with station four having the lowest clarity levels. However, as secchi disk readings changed very little throughout the San Juan Channel, it is unlikely that sediment inputs from the Fraser River are being flushed through the channel (figure 6). However, studies have indicated that the time of year and wind patterns greatly influences the direction and distance of the Fraser River sediment plume; so further studies are needed to clarify these findings (Zhong 2005).

The density of zooplankton at station one was 28.8 organisms/ liter. Qualitative and quantitative assessments of zooplankton densities showed high biologic productivity and diversity in the Strait of Juan de Fuca. Large numbers of copepods, nauplii and zoea were observed in a one ml sample. A comparision of phytoplankton densities can be observed in the figure below. Station four showed the highest densities of phytoplankton, while the lowest densities were seen in the Strait of Juan de Fuca. The high phytoplankton count at station four could be attributed to input from the Fraser River carrying excess nutrients into this system. While excess nutrients entering the Strait of Juan de Fuca are flushed out of the system due to strong tidal influences. It should be noted that the pier sample was taken at night.

An analysis of grain size at station one indicates that very little fine grain sediments settle in the straits. Over 50% of the sample contained grainsize greater than 500 micrometers (figure 8). As rivers are the largest contributors of fine sediments into this system, this indicates that input from the Fraser River is flushing through the Juan de Fuca Strait due to strong tidal currents (Carpenter et al 1985).

Literature Cited

Mackas, D.L. and P.J. Harrison. 1997. Nitrogenous nutrient sources adn sinks in the Juan de Fuca Strati/Strait of Georgia/Puget Sound Estuarine System: Assessing the potential for Eutrophication. Estuarine, Coastal and Shelf Science 44: 1-21.

Department of Ecology. Long term marine quality data. Retrieved May 2005 from the Department of Ecology website: http://www.ecy.wa.gov/apps/eap/marinewq/mwdataset.asp?staID=121

Zhong, L. Modeling estuarine/coastal circulations. Retrieved May 2005: http://www.hpl.umces.edu/~lzhong/estuary_coastal/estuary.htm

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