In This Issue:

The Caliper V15 #1 Cover
CBL™ News
Water-Quality Studies
Science Humor
Innovative Uses
Bits and Bytes
Workshops & Contests
What's New

Go to past issues of
The Caliper

Return to
Vernier Home Page

by Dan Holmquist and Scott Holman

With the introduction of our new Vernier Ion-Selective Electrodes, we decided it was time to do a trial water quality study in the greater Portland, Oregon area. Our choice was the Tualatin River, a medium-sized river that flows about 100 miles from the Coastal Range west of Portland to its eventual confluence with the Willamette River near the center of Portland. We collected water samples at four locations on April 24th at the following locations:

• Site 1: After the river flows from the heavily-forested Coastal Range
• Site 2: After the river meanders through agricultural land for 15 miles
• Site 3: After the river has gone through more agricultural land and residential suburbs
• Site 4: After the river flows several more miles through populated suburbs of Portland

• As expected, temperature increased from site 1-4 (9.5, 12.1, 13.3, and 13.3°C).
• The pH values, measured using a Vernier pH System, hovered very close to a value of 7, which is typical for western Oregon water (7.12, 6.99, 7.01, and 7.04).
• The Conductivity Probe revealed that the level of total dissolved solids (TDS) increased significantly from site 1-4 (32.2, 41.1, 56.0, and 64.6 mg/L TDS, respectively).

The results indicated a gradual increase in the Ca2+ and Cl- ion concentrations throughout the four sites. As is typical for western Oregon water, water hardness is very low; the highest Ca2+ concentration (17.3 mg/L) would correspond to a Calcium Water Hardness value of 44.0 mg/L, a value considered "very soft water." The highest chloride concentration (8.1 mg/L) is far below the EPA chloride drinking water standard of 250 mg/L.

Because the Tualatin River flows through agricultural areas between sites 1 and 3, and flows through populated areas (between sites 3 and 4), we thought it might be interesting to see how nitrate (NO3-) and ammonium (NH4+) levels were affected. Here are the results of each of these tests:

There is a noticeable increase in both nitrate and ammonium ion concentrations. These may be due to runoff of fertilizers from farm fields between sites 1 and 3. Stream flow drops significantly after site 1, so decomposition of biological matter may contribute to the increased levels of nitrate ions. Water with nitrate levels less than 1 mg/L are generally considered to be "unpolluted," while levels higher than 10 mg/L are unsafe for drinking water. The peak nitrate level of 2.53 mg/L at site 4 is moderately high.

We also made dissolved oxygen measurements using the Vernier Dissolved Oxygen Probe. This small decrease in dissolved oxygen concentration shown below may be due to an increase in biological decomposition in the stream.

Dissolved Oxygen Concentration

The purpose of this article is to show how easily data can be collected using a variety of Vernier sensors and portable data acquisition systems. Your students can experience the same kind of excitement we did while investigating a local lake or stream. The following sensors were used in our experiments:

Sensor Order Code Price: