Executive Summary
A Macroinvertebrate Investigation of Furnace Brook

Marshfield High School
James Merritt

Located across the street from the High school is Furnace Brook. Mike Gilbert and I are conducting an independent Study to determine the relative health of the Furnace Brook. This small stream is a tributary of the South River in Marshfield, Ma. To access the health will we be using a macro-invertebrate biological index as our primary tool? We will also be conducting a riparian survey as well as both a stream profile and flow. To start with we scouted the watershed using both aerial photos and Google earth. After driving to several potential areas we designated three sample sites: Old Maine Street, Furnace Street and Veterans Park.

Each of these sites is with in 2 miles of the school and offered easy access to the brook and a safe place to park. Old Maine Street is the furthest upstream from the mouth of the South River at 9.84 mile, Furnace Street is 8.58 miles and Veterans Park is 7.28 miles. The length of stream we will be investigating is 3.72 miles.

These sites are rich in biological life as well as history. Furnace Brook has donated its name to several land marks in Marshfield. Furnace Brook Middle School and Furnace Street are just some examples. As for the final site, Veterans Park, we found that the site was once an iron mine. This information provides an excellent explanation for the rusty tint to the water flowing through Veterans Park.

On our primary scouting expeditions we observed and sampled from our sites. During this time we created some hypothesis about our sites. At first we believed that the sites would be healthier further upstream and slowly degrade in purity further down stream, due to a higher populated, industrialized area. However our conclusions were proven incorrect. In fact it was quite the opposite the sites were worse off and higher polluted closer to the head waters and slowly corrected itself further down stream.

After collecting, examining, counting and sorting the macro invertebrates we were able to piece the puzzle together. We discovered that our hypothesis was mostly true. The stream flowed in such a way that the further down stream, the water became exponentially healthier. The MGI of the northernmost site old Main, peaked at a 7.2 (very poor quality), however at the final site the pollution was assuaged and the MGI fell to a 5.4 which is decent and far improved from is polluted lineage upstream.

The data we collected was the key to our understanding of our sites. The manner in which we determined water quality was to gather our macro invertebrates and calculate the percent of insects that were tolerant to pollution versus those that were not tolerant. For example May flies and Stone flies are not tolerant to pollution, making them good indicators. On the other end of the scale are such insects as leeches and midges which can tolerate pollution, incidentally making them poor indicators? The percentages are as follows; first is Old Maine, which had 79% of its gathered insects tolerant to pollution and 21% not tolerant. Further downstream at Furnace street we found 84% of the macro invertebrates were tolerant and 16% not tolerant; making Furnace the worst quality overall. Topping it off was Veterans Park with 69% of the life found being tolerant and 31% was not tolerant making; it by far the healthiest site of the three.

In conclusion we learned that our hypothesis was fairly accurate and that water quality improved with the flow of the stream. The information gained from the macro invertebrates lent valuable tokens in our pursuit to find just how healthy furnace brook is.

Please see the PowerPoint Presentation for details.