End of summer research at Jamestown

The end of summer is upon us, and I have had much time to reflect on the work I have done this summer. Sampling days at Jamestown were hot, humid and mosquito friendly but were often immediately followed up with respite in the traditionally and characteristically frigid geochemistry lab. During the last few weeks of July and the beginning of August, a new facet of my research was finally introduced: UV Digestion of organic matter. Simply put, the goal of analysing drinking water at Jamestown was to determine whether colonists ingested debilitating or even lethal doses of arsenic and iron. Levels of iron are extremely high, but if the colonists allowed the water to sit in open air essentially all the iron in the water would be oxidized and fall out of solution as a solid. Arsenic does not behave this way and any arsenic in the water will be directly ingested. But, what if there is more arsenic in the water that we aren’t detecting because it is attached to organic matter? This is the new question I have started to pick apart by a method involving UV Digestion of organic material. In the lab I allow a UV light to pass through the water samples which destroys organic material, therby liberating any arsenic attached to these molcules. I can then re-analyze water samples to see if there is any increase in arsenic concentration, and whether this increase is lethal. I found a doubling of arsenic in one well located between the banks of the James River and the wall of the fort, and a slight increase of arsenic in the swamp surface waters. UV Digestion has been performed on a few samples, but not enough to draw any sort of pattern (let alone conclusion) regarding this new facet of my research.

For the remainder of my senior year I will be collecting water samples once per month, and will continue to analyze for arsenic, iron and dissolved organic carbon. Thus far I have found that precipitation may control the distribution of species rather than the groundwater chemistry itself. After large storm events, there is an increase in hydraulic gradient between the swamp and the fort. This increase in hydraulic gradient (essentially slope) causes water to flow more quickly, and typically in higher volumes. The more quickly the water flows out from the swamp, the more concentrated the receiving groundwater will become. This is a trend we have observed. Between June 12 and 15 there was heavy rain which caused an increase in iron and arsenic for almost every well sampled. Thus, physical rather than chemical processes may be controlling the speciation of metals and organic matter in the Jamestown groundwater system. But, more work must be done to see how changing seasons affects groundwater chemistry at Jamestown. Stay tuned for more details!