All of our sampling finally behind us, our expedition draws to a close. Yesterday was in some ways the simplest day, and in others the most ambitious. Most importantly, as you can see from the first photo, the skies graced us with an entire day of beautiful sunshine. Had it been pouring down rain, like the previous three days, our afternoon on the harbor patrol boat would have been less idyllic. But by some meteorological marvel, we were treated to lovely views of Vancouver and the surrounding Coast Range as we steamed around the Fraser delta.
Our sole objective at this station was to collect large volumes of water, 100 liters, at each of three different depths in the main channel. We had hoped to do this last year, but our plan to pump the water immediately through filters on site turned out to be completely ineffective because the very fine particles in the Fraser immediately clogged our filters. Our approach this year was to simply pump the water on board the boat and transport it back to our “lab” to filter at our leisure (with our new and improved filtration units).
With the help of our boat captain Felix and mate Jeffrey, we spent the morning scouting out the best location (a stretch with a stable bottom and light enough ship traffic that we could drift while pumping). We waited until the afternoon to begin collecting water because we wanted a point in the day when the tide was not flooding (to maximize the outflow of the river against the inflow of the tide and because low current speeds during slackwater allow particles to settle!). Once we were on station, the pumping went brilliantly and in less than two hours, we had 380 liters of water on board. The extra 80 liters were a replicate to conduct an experiment with a precipitating agent (aluminum sulfate or “alum”) to see if this method could be used in the future to expedite the filtration process.
Now the real work begins! We spent Wednesday evening and all day Thursday filtering the depth samples. We are still working through the alum water in a race against the clock to pack up all our gear and samples for shipping tomorrow. Then we must bid farewell to our friends at UFV and return to WHOI, where we will have more samples in our hands than we’ll know what to do with! A huge thanks to everyone who made this campaign possible, in particular the folks at Port Metro Vancouver for generously offering the services of the P/V Port Fraser for our delta sampling, and our colleagues at UFV and their students, who will be continuing the time series sampling for another exciting year. See you next spring for the freshet!