August 16, 2005
Today I got to spend the day with Dave in his office. I got a close look at the Acrobat and the sensors on it.
I had my chance to ask a lot of questions. I wondered, for example, why we were collecting all the samples that we had if the machine has all the sensors to check them in real time. He explained that sometimes the machine gives readings that are obviously incorrect. Kelly's test calibrates the findings and provides validity.
I also wanted to know how the sampling sites had been chosen. That was an easy one, since they were chosen based on previous testing. He then showed me graphs from previous tows and noted a dramatic change in conditions near Station five, which is the little lighthouse at Conimicutt. A possible reason for this is the narrowing of the channel there. Water below the lighthouse has a greater salinity. It's almost like the waters don't mix much up river.
Environmental conditions have an impact on the mixing of waters in the estuary. Two factors are winds and tides. Dave's tows are timed to coincide with the Neap Tides because that means the currents from the tides will be stronger. The stronger the currents, the stronger the mixing effect is expected to be. Certain areas of the Bay have higher levels of dissolved oxygen. The amount of bacteria in the sediment can impact this because they will use oxygen at depth. When an area has less than 3mg/liter of oxygen it is hypoxic and fish kills can occur.
The main sources of oxygen are from the atmosphere and photosynthesis of aquatic plants. Yet, a proliferation of surface phytoplankton doesn't necessarily mean more oxygen for plants at depth. Phytoplankton also respires using up much oxygen before it can get to the benthic organisms.
Before I left, Dave told me we'd meet at the dock at 8:30 tomorrow morning to load up and be on our way by 10:00.