Tuesday, July 23, 2013

Natasha Christman: Rest and Respiration

Part of my research this summer is to analyze the respiration of phytoplankton at particular sites in Bellingham Bay and to apply this data to better illustrate the biological processes and characteristics of the region. Phytoplankton are part of a delicate balance of photosynthesis and respiration; while they can fix carbon dioxide and emit oxygen through photosynthesis, without light they also respirate, which means they actually consume oxygen and produce more carbon dioxide. The reduced oxygen levels resulting from this process contribute to the overall drop in dissolved oxygen and the pattern of hypoxic increase. Our goal is to better link and understand these relationships.

So how might one go about measuring the metabolic output of tiny marine microscopic organisms? On our research cruise on July 17th, we collected additional water samples from a point just outside the bay, called Eliza, and the known and regular center point of the hypoxic zone in Bellingham Bay, referred to as BB6. Samples from about a meter off the site bottoms were taken for a "deep" sample, in addition to surface sample collection. These bottles were brought back to the lab and then transferred to air-tight BOD bottles so no transfer of additional oxygen would skew the samples' own dissolved oxygen levels. Using a chemical reaction, half of the samples were "fixed", essentially freezing the respiration of the plankton for an initial value. Then, after 36 hours, the second set of bottles were fixed, showing how the respiration of the plankton changes the chemical composition of the seawater.

The bottles were stored during this period in a cooler much bigger than this
and with cool seawater flowing through it to keep the samples incubated.
Additionally, the cooler provided a nice dark environment.

After the incubation of the samples, I was ready to analyze the final levels of oxygen present in the samples. To accomplish this, I used a Winkler titrator to invoke a chemical reaction and find a subsequent equivalence point. This equivalence point indicates a specific amount of oxygen that was present in the sample at the time it was fixed. Then, through a series of calculations, the respiration rate of the plankton is able to be found, giving us more data on the plankton community and relationship with the hypoxia present in the bay.

The titrator and a sample during the chemical reaction.
Upon reaching equivalence, the yellow color of the sample turns clear.

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