Group 5 Research Report

Research Contributors: John Rhee, Brian Rosales, Xi Wang & Ann Lii

In order to investigate the ion composition and concentration in the Olentangy River water as part of the REEL project, Group 5 has set off on a journey to collect water samples. The group’s assigned location for water sample collection and analysis is at the Olentangy River from 5th Ave to Confluence Park. To collect the samples, the group hiked the bike trail up north from Confluence Park and gathered 3 samples (S33-S35) spanning 1.5 miles. Afterwards, the group drove north to 3rd Avenue and collected 1 sample (S36). The remaining two samples (S37-S38) were collected near 5th Avenue in a secluded location. The group’s preferred sites of sample collection were below the bridges near the pillars, due to the ease of accessing the river. Clean plastic bottles were used to collect approximately 300 mL of water samples at the river bank.

For each water sample, the pH and buffer capacity were measured, and Ion Chromatography  was used to investigate the presence of ions in the water sample. The group used Xplorer GLX for the pH and buffer capacity, calibrated through the use of pH 4 and pH 7 buffer solutions. In order to find the ppm concentrations from the water sample, a calibration curve was constructed for each ion from the standard solutions with known ppm, which were prepared by the entire class.

In order to validate the hypothesis that the group’s collected sample results are consistent with the other groups and with the historical data, a t test was used in combination with the F-test.

Results for the PH, buffer capacity, and a summary of ions found in the water sample:

Table 1: pH and Buffer Capacity

Table 2: Concentrations of Ions in Group 5 Samples

The majority of the ion concentrations, pH, and buffer capacity were found to be significantly different from the historical data due to a variety of factors.  A t test was utilized to show this to 95% level of certainty. Calculations were done via Excel, and the results are as follows:

Table 3: The Summary of the t-test Results Comparing Present Measurements with Historical Data in the region from confluence to 5th Ave.

Table 4: t-test for Upper Olentangy and Lower Olentangy

Analysis of the 2009 data revealed that the concentration of calcium at upper and lower Olentangy River was significantly different. Therefore, based on these findings, the Group’s first hypothesis is that the calcium concentration will be significantly different between the Lower Olentangy River, where our samples were collected, and the Upper Olentangy River. Between Confluence Park and 5th Ave, the average concentration of calcium in the Olentangy River was found to be 99.8 ppm, while the average concentration of calcium was 117.3 ppm in the Olentangy River above I-270. The results show that there is a decrease in calcium as the Olentangy River flows from its upper region to its lower region.  By the t-test, the concentration of calcium is significantly different (Table 4). According to Olentangy Watershed Inventory, the Olentangy River flows on a bedrock of Delaware limestone with a thin layer of sediment (loose sand, gravel, and cobble).  Below Home Road in Powell, the Olentangy River flows on an increasing thickness of this layer of sediment. The presence of a limestone bedrock at Delaware with little sediment protection allows a significant amount of Ca²⁺ to be dissolved into the river water, providing an explanation of the high initial concentration of Ca²⁺ in the Upper Olentangy river. One contributing environmental factor to the decrease in Ca²⁺ downstream would be the existence of dams in the proximity of Group 5’s collection sites. The dams provide the means for the river to flow at an increased rate through height difference, giving the river even less time to leech calcium from the limestone, which already has significantly more sediment protection compared to upstream. Finally, it should be noted that the inflow of tributaries (more than 10) into Lower Olentangy, as well as the existence of a bedrock providing a good base for an aquifer (capturing rainfall as groundwater and adding them to the river) serves to dilute the concentration of Ca²⁺ further.

The second of Group 5’s hypotheses is that there will be a significant difference in Ca²⁺ concentration in the region of Confluence Park to 5^th Avenue between the 2009 and 2011 data. The calcium concentration of this region in 2011 was 99.8 ppm, while the Ca²⁺ concentration in 2009 was 137 ppm. This shows that the Ca²⁺ concentration of 2011 was 37.2 ppm lower than that of 2009.  To see if this difference was significant, both an F and t test were performed (Table 3) with a result that the difference between Ca²⁺ concentration in 2009 and 2011 is indeed significant.  What could cause such a decrease?  According to National Oceanic and Atmospheric Administration National Climate Data Center the amount of rainfall for November 2010 to October 2011 was 51.91 inches, compared to the 40.11 inches of rainfall for November 2008 to October 2009. Meanwhile, most of the high-sulfur-emitting power plants are along the Ohio Valley. The 23% increase in rainfall may have brought more SO₂ from the atmosphere (H₂O reacts with SO₂ to form acid rain) into the river, which decreases the ionic concentration of Ca²⁺ (calcium becomes a solid through a reaction with sulfur). The increase in rainfall would have also resulted in an increased volume of groundwater added to the Olentangy River, which, in combination with the rainwater, would have further diluted the Ca²⁺ in a given sample. The increased quantity of SO₂ that was introduced to the river, combined with the diluting effects of the rainwater/groundwater combination, could be a significant factor in the decrease of Ca²⁺ in 2011 compared with 2009.

Through this experiment, Group 5 has learned that a multitude of factors can affect the concentration of ions, in this particular case, calcium. Geological factors, such as the soil composition, type of bedrock formation, amount of rainfall, groundwater, and the condition of the joining tributaries all contribute to the concentration of ions in river water. These concentrations are also further changed by human factors, directly through waste-water generated from industrial, agricultural and urban activities, as well as indirectly through air pollution (introduction of SO₂ through rainfall).

Table 5: 2011 Data vs. 2009 Data in Region from Confluence Park to 5th Ave.

Note: The concentrations are the average concentrations.

References

Olentagy Tributaries:  http://www.olentangywatershed.org/files/Inventory/Inventory_section8.pdf

Acid lakes, acid rain, and nitrogen and sulfur oxides:  http://www.physics.ohio–state.edu/~wilkins/energy/Companion/E14.8.pdf.xpdf

National Oceanic and Atmospheric Administration National Climate Data Center http://www.ncdc.noaa.gov/temp–and–precip/ranks.php?periods%5B%5D=12&parameter=pcp&year=2009&month=10&state=33&div=0

Olentangy Watershed http://www.olentangywatershed.org/files/Inventory/Inventory_section3.pdf