Oxygen measurements

I have another photo-op here. Today I'm working on oxygen measurements with a membrane inlet mass spectrometer (MIMS) in Todd Kana's lab at the University of Maryland. Dissolved gasses (oxygen and nitrogen) come out of solution and cross a membrane into a vacuum chamber where they flow into the mass spectrometer. The mass spectrometer separates the molecules using magnets and so figure out if a molecule of oxygen or nitrogen is hitting a detector.

We are using this instrument to investigate the amount of oxygen used and produced in photosynthesis in Prochlorococcus (Prochlorococcus is our organism of interest - see page on the Astrobiology project for more info). While there is a great deal of literature on what molecules are upregulated in high light for Prochlorococcus, we are interested in photosynthetic behavior of this organism in different light conditions. This kind of work, along with carbon fixation and fluorescence measurements, is important for predicting how an organism will behave (photosynthesize) in a variety of light conditions.


The MIMS instrument uses oxygen isotope ratios to look at both the amount of oxygen used and the amount produced in photosynthesis, so we add an isotope of oxygen not found in air (18-O2). I'm not going to explain how this works in detail, but just want to put up a picture of the screen output. The green and white dots below are isotope ratios of importance (16-O2:nitrogen and 18-O2:nitrogen respectively). This screen shows that 18-O2 is decreasing rapidly (white) while 16-O2 is beginning to decline (green) relative to the flux of nitrogen through the membrane (which should be mostly constant). (Yellow is nitrogen, blue and red are 18-O2 and 16-O2).

Inside the PAM fluorometer

Today we had to replace the halogen lamp in the diving PAM fluorometer, since ours burnt out. Photo-op!

Long term data

Opinion: The importance of long term data on ecosystem function

This post is actually quite appropriate to the SERC Solar Radiation Laboratory (connected to the Photobiology Lab where I work), in which long term data on solar UV is collected...

I recently attended a DC science cafe meeting, entitled "A tale of two bays: Uncovering the story in long term ecological data." The two scientists speaking had the same message to the public; long term ecological data is an important tool for understanding both human-driven and natural environmental changes in our landscapes.

Shifting Baselines

Why, you might ask, should the public care? As a member of a civilization that runs at such a fast pace and large scale, is is only through information collected a while back that we have a baseline with which to compare the current state. We need to know what bays and other ecological systems were like in the past to know how they are changing. The problem with just taking a baseline now is that it could have already shifted from human influence. This phenomenon is called 'shifting baselines,' and the classic example is of the change in size and number in cod population. 

"[Shifting baseline syndrome] has arisen because each generation of fisheries scientists accepts as a baseline the stock size and species composition that occurred at the beginning of their careers, and uses this to evaluate changes. When the next generation starts its career, the stocks have further declined, but it is the stocks at that time that serve as a new baseline. The result obviously is a gradual shift of baseline, a gradual accommodation of the creeping disappearance of resource species, and inappropriate reference points for evaluating economic losses resulting from overfishing, or for identifying targets for rehabilitation measures."

-Pauly 1995

Nutrients in Bays: A big problem in the Chesapeake but not in the San Fransisco Bay

These particular scientists have found strikingly different consequences for high nutrient loads in bays in two different parts of the country. In San Fransisco, shellfish do an amazing job of filtering phytoplankton out of the water, and nutrient levels are actually higher than in the Chesapeake. Over the last 10-20 years, there has been a shift in which animals are dominant, BUT this can be attributed to a natural oceanographic phenomenon (Pacific decadal oscillation). In the Chesapeake, however, nutrients from farming, and other human activities, leak out into the Chesapeake and cause low oxygen 'dead zones' that can kill fish and other organisms.

In the Chesapeake there are fewer shellfish these days than 100 years ago (I heard over 90% loss?), so likely there is now a lowered capacity to deal with high nutrient and resulting phytoplankton loads. Also, the West Coast experiences upwellings of cold nutrient-rich (and low oxygen) deeper ocean water from time to time, so maybe the San Fransisco Bay has had to adapt to this kind of situation regardless of human impact.

Anyway, the point of the story is that management of factors such as high nutrient loads cannot be done using blanket generalizations. High nutrient amounts in the Chesapeake are a problem even though they are lower than levels experienced in the San Fransisco Bay.

What can you do?

These scientists urged us after the lecture to contact our politicians. One of the scientists was involved in a zonation hearings committee.

See the South River Federation Website to volunteer and help out with work in the Chesapeake. They do oyster reef restoration and other projects...