Journal of Student Research 2018

78 Journal Student Research sampler was programed to draw a 100 mL water sample when the water level threshold was exceeded. The peristaltic pump first flushed the hose by pumping in the reverse direction then drew 100 mL into a 1-L sample bottle housed within the sampler carousel (Fig. 5).

Figure 5. ISCO® 6700 sampler carousel with 24 1 L bottles.

The sampler contained 24 1-L sample bottles, and therefore collected up to 24 discrete samples. After a storm, the bottles were collected and replaced with empty sample bottles. Depth, flow, and sample event data were also downloaded from the samplers. Discrete time interval samples were composited into one sample that represented the entire storm using a flow integration technique. The software program Flowlink 5.1® and Microsoft Excel® were used to flow-composite the time-interval storm samples. Graphs generated from Flowlink 5.1® were created to examine water depth (ft), velocity (ft/s), and flow (ft 3 /s), sampling events over the duration of the sampling period. Data from these graphs were then exported to Microsoft Excel®. The volume of sample from each time interval was weighted by flow for compositing. Thus, a sample collected during a higher flow had a greater volume. Appropriate portions from each discrete sample were combined into a beaker and homogenized with a stir bar and magnetic stirrer to create a flow-weighted composite sample for each storm. Samples for soluble reactive phosphorus (SRP) were filtered through a 0.45 μ syringe filter prior to analysis. Total P samples were predigested with potassium persulfate in an autoclave. P was determined colorimetrically using the ascorbic acid method (APHA 2015). Absorbance was measured on a UV VIS spectrophotometer (Perkin-Elmer Lambda 25). Chemical analyses