By guest bloggers Natalie Wamester and Kalaria Okali, April 2018
Having lived in Milton for our entire lives, we thought we knew it well, but this year, in our Advanced Environmental Science at Milton Academy, we were able to study Milton through a new lens. We knew of Neponset River, mostly the estuary section; however, neither of us had ever heard of Pine Tree Brook–a tributary stream of the Neponset which flows from headwaters in the Blue Hills through Milton and joins the Neponset River near the Central Ave. trolley stop.
In many areas of Milton the Brook is hidden away, being visible to those who walk the adjacent path in the Pine Tree Brook neighborhood near Milton High or as parents, students, and teachers crossing the footbridges over the Brook to enter Glover School. At the start of the school year in September, we met with NepRWA’s Chris Hirsch and Annie O’Connell to explore research ideas in the watershed. They told us of a population of wild brook trout in the headwaters of Pine Tree Brook and presented us with the idea of studying the habitat of Pine Tree Brook and determining which sections, other than the headwaters, would be suitable for native brook trout.
Pine Tree Brook originates in the Blue Hills, flows through both forested and urbanized regions of Milton, and empties into the Neponset. It can be broken into three distinct sections: the trout population’s current habitat, or the headwaters, (pink), the restoration area (green), and downstream (yellow) (Figure 1). These sections are divided by four dams (black squares on Figure 1) that were added to the stream at various times in the past. NepRWA recently modified and partially removed the second dam (see arrow in figure 1) with the hope of granting the trout population a larger habitat (hence this section’s name, the “restoration area”). Before continuing to alter the dams, NepRWA was interested in determining whether the habitats of the restoration area and downstream section are suitable for brook trout. That is the task we took on in our class this fall.
To assess each section, we calculated a Habitat Suitability Index (HSI) for each section of the stream. The components of the HSI consist of six variables: pH, dissolved oxygen, average maximum temperature, base flow (the average flow level without the influence of short term runoff from a precipitation event), percent riffle fines (the percentage of stream bed sediment that is smaller than 3 mm), and dominant substrate type (the type of sediment that makes up the stream bed). We gathered these data from October of 2017 to January 2018 with frequent visits to multiple sites along Pine Tree Brook. After completing data collection, the HSI is calculated using a formula. HSI ranges from 0-1 with the target value being 1, for ideal trout habitat, and 0 being unfavorable for trout.
Based on these calculations, we determined that the headwaters and the restoration areas had similar enough habitats for the trout to be able to survive in each section (Figure 2).
While the downstream section also had a high HSI, we believe that a certain amount of uncertainty plays into that high score, as the section is noticeably different than the headwaters (the trout’s current habitat) and the restoration area. The downstream area extends from the outlet of Pope’s Pond, along the Pine Tree Brook neighborhood, past Pierce and Glover, under School Street, and finally in the the Neponset Near Central Ave. This portion of the stream is much more urbanized and therefore subject to more direct runoff from impervious surfaces (roads, driveways, roofs, etc). Many stormwater drains on the adjacent streets also empty directly into the stream. We hope that with future testing, additional data may show any differences between the upper two sections and the lower section. Given that the HSI accounts only for the physical state of the brook and excludes other important factors, such as water chemistry, our continued study of the conductivity and chemical makeup of the brook’s water should allow us to develop a deeper understanding of the habitat suitability.
Through this project, we developed a deeper understanding of how our actions impact both our environment and the populations within this environment. Many of the issues that surfaced in this project often go undiscussed, and with this experience behind us we hope to continue the conversation next year in college. Additionally, we set the stage for future Milton Academy environmental students to continue studying Milton’s evolving environment and its inhabitants.