05
Sep

Interns collecting and identifying macroinvertebrates at our Commercial Avenue stream site.

This summer, NMRWA lead a water quality monitoring internship program. Through this program, high school students with an interest in environmental science were able to gain field experience by assisting in stream monitoring.

As you may already know, NMRWA monitors four stream sites each month as a way to assess the health of our watershed. Stream monitoring involves water quality parameters such as temperature, pH, and conductivity, among others.

Our interns assisted in monitoring two of our four stream sites throughout June, July, and August. In addition to measuring classic water quality parameters, our interns sampled for aquatic macroinvertebrates.

In freshwater streams such as Nine Mile Run, macroinvertebrates serve as indicators of water quality. For example, mayfly larvae are highly sensitive to pollution. For this reason, finding mayfly larvae in a stream is an indicator of high water quality. Midge fly larvae, on the other hand, are not sensitive to pollution. Finding only midge fly larvae in a stream may be an indicator of low water quality.

Mayfly larva (Field Studies Council, 2015).

Midge fly larva (DIY Fly Fishing, 2009).

At NMRWA, we use macroinvertebrate data to calculate water quality “grades” for our stream sites. Our grades are an average of four values: the percent of EPT macroinvertebrates collected (% EPT), the percent of pollution sensitive macroinvertebrates collected (% intolerant), the total taxa richness score, and the dominance index. You can learn more about these values here.

Our interns assisted in the grading process by hand-calculating % EPT, % intolerant, and the total taxa richness score. We later calculated the dominance index and the overall score for each of the two sites sampled by our interns. The results are given below.

Water quality grades based on macroinvertebrate data collected by our interns.

While these may not seem like impressive scores, we are seeing an improvement from previous years. In 2016, Commercial Avenue received a D (34.3) and Duck Hollow recieved a C- (44.2). In 2013, Commercial Avenue received an F (11.5) and Duck Hollow received a D (27.3). Our results support the trend that we have been seeing throughout the past several years: gradual improvement in the quality of our stream sites.

We thank our interns for their role in monitoring the health of our watershed this summer and wish them a happy school year!

Group photo of our interns.

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