After taking a trip to the University of Pennsylvania to use their ICP-OES, I have phosphorus data for all of my sites! In the coming days, I will plot and interpret this data using ArcGIS and Excel. With a combination of spatial and statistical analysis, I will be looking for a relationship between proximity to WWTPs, land use, and bioavailable sediment-bound phosphorus.
Although we ultimately concluded that it is not the best option for this project, we briefly experimented with using the Sea-Bird Scientific HydroCycle-PO4 Phosphate Sensor for in-lab P analysis while waiting for access to an ICP. It is meant for in-situ data collection, but we were able to analyze bottled samples by cleansing the machine with DI-water in between runs.
Now that I’ve collected and dried my bed sediment samples, I am using a 1M CaCl2 solution to extract the bioavailable sediment-bound P from the sediment itself. Each sample will be left in-solution on a shaker table for 24 hours, at which point I will filter and bottle the solutions. The samples will remain in refrigerated storage until they are ready for P analysis.
Today, I assisted Dr. Toran’s graduate student Liz in analyzing her overland flow samples via ion chromatography. Ion chromatography is used to identify and quantify ionic species within a solution.
Overland flow is the process by which water that does not infiltrate the soil flows down-slope into a body of water. This water can carry nutrient-bearing waste such as fertilizer, fuel, and detergent.
In order to collect storm water that is representative of the overland flow entering the Wissahickon, we have installed Nalgene™ Storm Water Samplers at each of our sites. The samplers are buried near the stream in a PVC pipe and can hold up to one liter of storm water. Because the bottles are buried, we can sample rain events at any time without having to be in the field.
To ready my stream bed sediment samples for ICP-OES (inductively coupled plasma optical emission spectrometry), I am first preparing them via microwave digestion. In this process, I aim to extract the bioavailable phosphorus bound to the sediment by submerging it in sulfuric acid and subjecting it to high temperatures over time. I am trying to replicate the amount of agitation the sediment would undergo in a stream so as to avoid over-extracting phosphorus. For this reason, I used relatively mild time and temperature settings.
During the last two weeks, I’ve been travelling to tributaries of the Wissahickon and collecting stream bed soil samples with Dr. Toran and her graduate student, Liz. In the coming weeks, I will release the sediment-bound phosphorus in the samples via microwave extraction. At this point, any sediment-bound phosphorus will be freed and can be analyzed and quantified by inductively coupled plasmaoptical emission spectrometry (ICP-OES).
I am very excited to begin working with Dr. Laura Toran this summer through the Frances Velay Research Fellowship at Temple University. My focus is on nutrient pollution and eutrophication in urban streams. I will be investigating the concentration and origin of bioavailable, sediment-bound phosphorus in the Wissahickon Creek.