Water Quality on the Santa Cruz

For the past two weeks, we’ve been working on water quality with Ms. Berryhill’s class of Earth Science students at McCurdy High School. McCurdy is located close to the Santa Cruz River, and it also has an acequia running through the campus, giving us two fantastic water sources in need of water quality testing!

While our River Classroom students are pros at water quality testing, this was the first time our McCurdy students have used our Vernier water quality sensors. In order to give the students some practice, we did a little experiment.

Students divided into five groups. Each was given a quart-sized mason jar. Students filled their jar about 3/4 of the way full using tap water. Each group used NMWC’s sensors (as well as LaMotte test kits for nitrates and phosphates) to evaluate the quality of their initial sample. We tested temperature, pH, dissolved oxygen, conductivity, turbidity, nitrates, and phosphates. Fortunately, the numbers were reasonable.

Students testing their original water sample

Next each group polluted their water, using chemicals that are generally poured down the drain or that run off into waterways. Each group used a different combination of plants, fertilizer, coffee grounds, oven cleaner, dish soap, shampoo, toothpaste, etc. Some of these products were “green”, while others made no claims to be healthy for the environment.

That's some pretty polluted water!
That’s some pretty polluted water!

After creating some of the most foul-smelling water samples I’ve ever seen, students took more water quality readings (all recorded on a data sheet). Then they were given a daunting task- clean the water! Possible tools included 2 L bottles, coffee filters, socks, sand, rocks, and charcoal. As usual, students were given next to no direction from us. They had to figure it out. They also had to continue water quality testing along the way so that they could determine which filtering methods had the most impact.

Socks are actually pretty good at filtering out the bigger stuff.
It turns out that coffee filters only do so much…

While turbidity decreased as students continued to try to filter their samples, nobody ended up with water they wanted to drink. Conclusion: It’s much easier to keep water clean that it is to try to clean it. Filtering water takes time, energy, and resources, so let’s take care of the water we’ve got!

After we had plenty of practice with the water quality sensors, we moved on to measuring water from the Santa Cruz River and the McCurdy Acequia. During lunch, Ms. Berryhill and I took two grab samples from the Santa Cruz River. These field replicates were further divided into four total samples, one per group. Each group measured each parameter (including temperature and DO, although the official numbers were those that we recorded at the river).

A student tests a sample of water from the Santa Cruz River.

After the Santa Cruz samples had been processed, students went outside to sample the acequia. Because we were running out of time, we only took one sample. Each group recorded their numbers on the board, leading to an excellent discussion of uncertainty in our measurements. If all four samples came from the same place at the same time, why did each group get slightly different numbers? Our uncertainty comes from sample handling, instrument sensitivity, and several other sources.

Comparing data from multiple samples and locations.

The comparison between the river and the acequia turned out to be much more interesting than we had suspected. Not surprisingly, the ditch had a much lower level of dissolved oxygen, a much higher pH, very high conductivity, and a higher temperature. The entire class agreed that the Santa Cruz River is a much healthier body of water!


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