Sixth grade students at the Pierce Middle School in Milton, MA conducted a study of the macroinvertebrate community in Pine Tree Brook. Pine Tree Brook is located in the Neponset River Watershed and is a tributary of the Neponset River, which flows into Boston Harbor. Pine Tree Brook flows through the northwest part of Milton and was identified as an "impaired river" by the state of Massachusetts. The students at Pierce Middle School planned to use macroinvertebrates to assess the water quality of this brook. The students measured flow, calculated discharge, conducted a physical habitat survey, and sampled macroinvertebrates to better understand the dynamics of Pine Tree Brook.
A sampling site, located off Thurston Street, was chosen where students could easily access the river. Upon conducting the physical habitat survey, students noticed that the velocity and height of the brook fluctuated rapidly. They contribute this fluctuation to the impervious surfaces in the immediate area and the storm drains that they observed emptying directly into the brook during rain and snow events while sampling. They also recognized that this drainage system could also contribute to an increased amount of pollutants, such as oil, fertilizer, sand, salt, and litter to be dumped into the brook. Students noticed large amounts of sand covering the bottom of the brook and the riparian zone was almost non-existent in some areas or lined with concrete.
The macroinvertebrate community was scarce. Only 33 macroinvertebrates were collected, sorted, and identified in the samples. Based on the macroinvertebrates found, more than 50% of the population consisted of Coleoptera. The three most dominant groups of macroinvertebrates were Coleoptera, Amphipoda, and Trichoptera. Coleoptera and Amphipoda are shredders, indicating these aquatic insects are able to obtain their food by shredding leave, sticks, and other large organic matter that have fallen into the brook. The MBGI index was calculated and confirmed the students suspicions that Pine Tree Brook's water quality could be classified as very poor (MBGI = 14.8). In conclusion, the physical habitat and flow are affecting the number and type of macroinvertebrates present in Pine Tree Brook.
Students plan to work with local Pine Tree Brook Neighborhood association to begin putting an action plan together to improve the water quality of the brook.