I have begun my experiment. To tell the truth, it is not a glamorous affair. It wasn’t even my idea, though I wish it was. It consists of nothing more than 5 gallon plastic jugs, black plastic, duct tape, and several HOBO U26 dissolved oxygen data loggers. The idea came out of a planning meeting where the desire to get more precise measurements of microbial production in the rivers flowing into Tillamook Bay was one of many topics discussed. The method proposed was to incubate samples of water in the dark for a period of time, and measure the change in dissolved oxygen from start to finish. Any decrease in the oxygen level should be the result of organisms in the water respiring, eating or decomposing organic material in the water. <\/p>\n
It is important to know how bacteria change the conditions of the water, changing the amount of nutrients that flow into the bay and the concentrations of both oxygen and carbon dioxide. The ocean is warming and becoming more acidic, bringing increasingly acidic water into the bay with every incoming tide. The nutrients that flow into the bay from the surrounding watersheds lead to increased bacterial growth that close the oyster beds in the bay to harvesting, as well as further acidifying the waters, as dissolved carbon dioxide increases in the water as bacteria release it as a waste product of their metabolic processes and it reacts with water to form carbonate, bicarbonate or carbonic acid. The relationship between higher nutrient inputs into marine waters from terrestrial systems and increased acidification is not just a bay or estuary problem, but a coastal problem as well. The EPA, along with the Navy and many other players, hope to assemble the big picture of how Tillamook Bay works with respect to all of these issues so that the people of the region can better plan for climate change and mitigate potential problems, as well as improve the health of the ecosystem and the lives that depend on it.<\/p>\n
There was a considerable debate about how best to go about incubating the water and how to measure oxygen changes in a scientifically valid manner. The issue with the incubation lies in the transporting of the water to the lab. Changes to the temperature of the water will effect the solubility of oxygen in the water, as well as the rate of production of bacteria, affecting the results. Maintaining water samples at a constant temperature remains impractical and a concern, but a greater concern is with the Winkler method. The Winkler method is a method of analysis that allows for measuring the dissolved oxygen at a single point in time, but not continuously, but the measurement can be more precise than that of a datalogger. It was proposed that only initial and final oxygen measurements would be used to determine the total change in a sample, and the incubation period would be short, a few hours at most. As the experiment was discussed, it became apparent that such a short period of incubation may not adequately capture microbial growth, and that a time series of measurements would be the only valid method of determining a rate of microbial production. Thus, the 5 gallon jug trials, to gather a time series, determine a proper incubation period, and as a basic proof of concept.<\/p>\n
Friday we drove to Tillamook and collected samples, though not as many as we had planned to. We are also evaluating an alternate incubation method using 2 gallon ziplock freezer bags kept dark in a cooler. The samples have been incubating all weekend. On Monday I will download the data from the loggers and see what there is to see. I may even have a graph or two to share next time!<\/p>\n","protected":false},"excerpt":{"rendered":"
I have begun my experiment. To tell the truth, it is not a glamorous affair. It wasn’t even my idea, though I wish it was. It consists of nothing more than 5 gallon plastic jugs, black plastic, duct tape, and … Continue reading