USC Dana and David Dornsife College of Letters, Arts & Sciences > Blog

August 17, 2012

Water Sampling in Big Fisherman’s Cove

Filed under: Uncategorized — justinbo @ 5:55 am

In our last week interning here on Catalina Island, I started to realize that soon I would have to go back to Los Angeles and begin the school year. While I’m extremely excited to be surrounded by people I haven’t seen for almost three months now, I have to say that I’m definitely going to miss the sheer amount of space and endless beauty that this place provides.

This week, I have been working extensively with Professor Ginsburg’s Environmental Studies 320a course, working as the student’s teaching assistant. We have been working in the lab each day this week, testing for different nutrients in the water column of Big Fisherman’s Cove.

On Monday, students collected water samples from the cove using a Niskin bottle. To compare data at different depths, the students collected water at 2, 4, 6, 8, and 10 meters. From this, they looked at dissolved oxygen content, as well as ammonia and iron levels.

For the analysis of ammonia and iron, we used a serial dilution of two different standard solutions. Using an acid base reaction with the standards, we created a color change reaction, which we then used a spectrophotometer to measure the specific absorbance of each solution at different wavelengths. With our samples, we added the same reagents and catalysts that we added to the various dilutions of the standard solution, and measured the absorbance of the samples as well.

Standard solution, catalyst, and reagent for the ammonia analysis.  Photo by Justin Bogda

Top: standard solution assay for ammonia analysis.  Bottom: seawater samples from 2, 4, 6, 8, and 10 meters in Big Fisherman’s Cove.  Solutions are in cuvettes, ready to be analyzed by the spectrophotometer.  Photo by Justin Bogda

Sample in spectrophotometer before analysis.  Photo by Justin Bogda

Receiving a standard curve from our standards, each at a different concentration covering the ranges that we expected to see in our samples, we were able to make a curve correlating the concentrations with absorbance, and compare our samples to that curve to determine what the specific concentrations of our samples were.

The first day that the class tried the assay for ammonia, results were less than ideal. I performed the assay as well, and struggled to make a standard curve from which I could get meaningful data. The following day, I tried to perform the assay again, this time using more precise instruments such as volumetric flasks to perform the dilutions, and I obtained much better results. Ammonia levels were in the range, between .5 and 4 µM, that we expected. Iron, for which we tested today, was seen in concentrations between .5 and 2 µM, a bit less than the 10 µM concentration that we expected.

Measuring nutrients such as ammonia in the water provides a baseline measurement that, according to our records, has not been done in some time. If concentrations were greater than we expected, it would be an indication of pollution from the land, as natural levels ammonia from excretions from organisms should be negligible. It is helpful to measure indicators of water health, especially in a protected area like Big Fisherman’s Cove, so that if there were potential threats to it such as sewage runoff, we could detect it.

When I look back on this summer, I feel a definite sense of accomplishment. While a great deal of the work we did this summer was immediately beneficial to my practical skills and knowledge, I feel even better that my fellow interns and I set up projects and potential research that can be built at the Wrigley campus by the Environmental Studies department and other collaborators. I will be coming back throughout the fall to continue with the restoration project and seeding, so while I leave Catalina nostalgic, I’ll get to continue work here soon.

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