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Sun Simulation and Particle Aggregates

This week began with a shift in focus from last week.  While last week I was measuring the particle size of standardized latex beads, this week I was able to take measurements on water samples from local streams and ponds.  On Monday an ASE high school intern began working in Dr. Tratnyek's lab as well.  She has been very helpful in assisting me with data collection and analysis of the data.

On Tuesday we went to two local streams and a duck pond to collect water samples.  We began analysis by taking particle size measurements on each sample.  Once we had a good idea of the particle size characteristics of the samples we decided to test the effects of sunlight on the particles.  We used both a solar simulator and natural sunlight, exposing the samples to the direct light.  At specified time intervals measurements were taken on the DLS.  After plotting the results it was clear that in two of the samples, the duck pond sample and one of the stream samples, particle size was changing in response to the sunlight.

The results were interesting and further exploration was needed in order to determine exactly what was causing the change in particle size.  At this point we decided that sonication of the samples may be able to tell us if the increasess and decreases in particle size were simply due to particles aggregating and aggregations breaking apart.  In some samples this seems to be the case, however the results are still not conlusive.  It's possible that it is a mixture of both particle aggregation and small cells reacting to the presence of sunlight.

At first, when one of the samples did not demonstrate particle size change in response to sunlight we were a little discouraged.  However, upon further thought it turned out to be a great opportunity to determine what the particles are since it seems as though they are not easily disturbed.  Our current theory is that this particular sample contains clay particles that are of fairly uniform diameter.  Fortunately our lab has a small collection well characterized clay samples.  We are currently in the process of using this clay to make solutions with a known mass percentage of clay and compare DLS measurements of the standard to the water sample.  Replicating the results obtained from the water sample with those from a labaroatory created sample would be a big step towards being able to characterize particles in water.

I took a little bit of time this week to think about how my project relates to other projects going on at CMOP.  While the title of the project, Environmental Particleomics, seems to indicate that the main focus is particles, there is a much broader story that these particles will tell.  Bridging the gap between aquatic biogeochemistry and particle assemblages will allow scientists to characterize particles and determine the link between particles properties and the environmental factors that affect communities of aquatic organisms.  This has great implications for predicting fishery populations and obtaining a "snapshot" of general aquatic organism health in the aquatic habitat of corncern.