Apponequet Regional High School, Lakeville, Massachusetts
Kelsey Walker, Caitlin Young, Tim Emery, Ricky Garant, Nick Marangi, Pete Gauraldi
What is the effect of the waste water treatment plant on the water quality of the Nemasket River? Students chose three sites to study. These were located at the headwaters near Assawompset Pond, Route 105 (reference site), and Murdock Street (impact site). Murdock Street had a greater expanse of aquatic vegetation than the Route 105 site. The treatment plant is located between these two sites and deposits nitrates and phosphates into the river with its effluent. Phosphates are more readily removed from effluent via chemical reactions, while nitrates are more difficult to remove. Nitrates can be removed using BNR (biological nitrogen removal) technology. This, however, is expensive as it requires the use of retention ponds where aquatic vegetation absorbs nitrates from the effluent.
Students collected data on dissolved oxygen, temperature, pH, nutrients, and macroinvertebrates. Temperature fluctuations were normal for the time frame investigated. In November, 2006 the pH was consistent at all three sites (6.4). In April, 2007 pH varied among the sites. Rte. 105 had lowest pH (5.9) and Murdock Street the highest (7.8). In Nov, 2006 DO was the highest at the headwaters as was expected due to aeration as water passed over the dam and hit rocks. Data for Rte 105 was unreliable because the hydrosonde was moved to an area of low flow. Murdock St was lower than the other sites and showed a gradual increase in DO throughout the day most likely caused by photosynthesis of aquatic vegetation.
Discharge increased from the headwaters to Murdock St as expected. Also, discharge was much higher in April due to winter storms and spring run off. Reactive phosphorus concentration was below detection limit for most samples except at Rte 105 in September and November, 2006 and at the headwaters in November, 2006. Lower concentrations in April were most likely due to the dilution effect of increased discharge. Load for RP reflected discharge since load for all BDL values was calculated using 0.008 mg/L. The concentration for nitrogen/nitrate was within normal range but always higher at Murdock Street. Again, note the lower concentration in April was likely due to dilution. Nitrate load was always higher at Murdock reaching a maximum of 120 kg/day in April, 2007.
Students collected a variety of macroinvertebrates at Rte 105 and Murdock St. The FBI was 3.69 (excellent water quality) at Rte 105. The calculated FBI was 5.31 at Murdock St. (fair water quality). Also the % intolerant organisms were 51.9 % at Rte 105 and 30.7 % at Murdock St.
Students concluded that the data supported their hypothesis that the waste treatment plant was placing stress on the aquatic ecosystem downstream from the plant. This conclusion is supported by the load for each site (in particular nitrate load), as well as the FBI and % intolerant macroinvertebrates.
Apponequet Regional High School, Lakeville, Massachusetts (2007). Is the Nemasket River Stressed Out?. In Watershed Access Lab Projects. Project 59.
Available at: https://vc.bridgew.edu/wal_projects/59
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