On the pulse

by Britta Voss
Wednesday, April 10th, 2013

If spring is supposed to come in like a lion and go out like a lamb, the Northwest is doing it wrong. The summer-like weather of two weeks ago shifted abruptly back to winter phase, punctuated this morning by incessant heavy rain and wind that reminded me of Cape Cod. Through it all, the Fraser is doing its best to transition to freshet mode. The cooler weather has slowed its initial surge, but the water level, along with turbidity and dissolved organic matter, are still on the rise.

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I want to focus today on the water samples I’m collecting and why I came here in the first place. As alluded to in a previous post, our fantastic time series record, made possible through the hard work of numerous students and their faculty advisors at UFV, has shown some intriguing trends. In particular, we saw a spike in the concentration of dissolved organic carbon (DOC) at the very beginning of the 2011 spring freshet. By spike, I mean in a matter of a few weeks, the concentration increased by about 4x. For comparison, concentrations of inorganic species, like calcium and chloride, decreased during this period. Since this pulse is so rapid, even our time series samples (at about every other week) couldn’t fully capture it. So I came back with the goal of tracking this event at extra-high frequency to see how this DOC lines up with other changes in the river, and possibly changes in the composition of the DOC itself.

So in addition to DOC concentration, I’m also collecting samples for dissolved inorganic carbon, carbon isotopes, DOC incubations, nutrients, major and trace elements, water isotopes, and suspended sediments. Comparing the behavior of all these components will shed light on how this DOC pulse plays out and what drives it. The optical probe (see last post) is critical for evaluating how DOC concentrations are changing, and for making the anticipation of waiting to analyze all the samples tolerable.

In the interest of ensuring that I don’t miss the peak, I’ve decided to extend my time here. Even if it means sleeping in my car—don’t worry, the sampling site has electricity, so I can charge the pump battery!—and hitchhiking back to WHOI, I’m here to see this through!

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