Apponequet Regional High School, Lakeville, Massachusetts
Amanda Eloma, Jen Frazier, Caitlyn Coelho, Hannah Harkey, Lizzy Iolli, Vicky Gavin, and Hillary Locke
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 both upstream and downstream 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. The plant removes phosphates using ferric chloride and is allowed by permit to deposit 0.2 mgL into the NMK. Ammonia in the effluent is removed using nitrifying bacteria which add oxygen to for nitrate. This remains in the effluent.
Students collected data on dissolved oxygen, temperature, pH, nutrients, and macroinvertebrates. Temperature fluctuations were normal for the time frames investigated. In October, 2008 and April, 2009 pH remained in the lower range of normal with little diurnal fluctuation at Vaughan St and Murdock St. At each sampling Rte. 105 had lowest pH6.0 – 5.1) and Murdock Street the highest (6.3 – 6.9). In October, 2008 DO at Vaugnan St. showed the greatest diurnal change possibly due to the plant photosynthesis and cellular respiration in the wetlands. Rte 105 and Murdock St. were steady (avg 8.1 ppm) . DO in April 2009 was much higher at both of these sites(12.5 – 13.5) with a distinct diurnal change at Murdock St. Aquatic vegetation was covered with water at this time and discharge was the highest at this site.
Discharge increased from the headwaters to Murdock St as expected. Also, discharge was much higher in April due to winter storms, snow melt and spring run off.
Reactive phosphorus concentration was below detection limit for most samples except at Vaughan St. and Rte 105 in October, 2008. 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 or BDL but always higher at Vaughn St. 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 6.31 (fairly poor water quality) at Rte 105. The calculated FBI was 5.69 (fair water quality). Also the % intolerant organisms was 8.0 % at Rte 105 and 24 % at Murdock St.
This did not correspond with any of the previous years. In 2006 – 2007 Rte. 105 had excellent water quality and Murdock had fair quality. The difference can be attributed to the 4 inch rainstorm prior to sampling. More tolerant species (ex. Amphipoda) were washed down from the wetlands above Vaughan 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) and increased presence of aquatic vegetation downstream. Macroinvertebrate data was inconclusive.
Apponequet Regional High School, Lakeville, Massachusetts (2009). The Effect of the Waste Water Treatment Plant on the Nemasket River. In Watershed Access Lab Projects. Project 76.
Available at: http://vc.bridgew.edu/wal_projects/76
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