Each evening we transform a hotel room into a laboratory. First, we move four 19-liter jugs and five 4-liter cubitainers from the backseat of our SUV into the closet. These samples are filtered to collect suspended particles. Next we carry in the portable freezer, which contains water samples from each site. Freezing is the ideal method of preservation for certain samples, because it inhibits outgassing of volatile chemicals (such as ammonia) and degradation of organic matter by microbes. When we return to WHOI, we will thaw frozen water samples and have them analyzed for nutrients, which include phosphate, nitrate, nitrite, ammonium, and silicate. We also collect a suite of other water samples, some of which have specific preservation requirements (more on this later!).
The next step is setting up the filtration station in the bathroom. On top of a garbage can we set a filtration unit that was designed by our colleague Dr. Valier Galy and his PhD advisor, Dr. Christian France-Lanord. We pressurize the unit using a bicycle pump so that we can force a large volume of river water through a membrane (made of polyethersulfone) with openings of 0.2 microns (a micron is 1/1,000 of a millimeter. To understand just how small this is, consider that human hairs measure between 30 and 120 microns). We are most interested in the particulate matter trapped on the membrane, as oppose to the water that passes through the membrane (since we collect all the filtered water we need on station). By collecting the particulate matter at many sites during different flow conditions, we hope to develop a record of the spatial and temporal variability of the sediment load.
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