River Characterization of the Assonet River

Students conducted a characterization study of the Assonet River above Locust Street in Assonet, MA. They chose three sites in a third order segment of the river. Malbone Street was the most accessible site near the headwaters and was downstream from the confluence of the Cedar Swamp River and the Assonet River. The Cedar Swamp River drains a large area of wetlands (Cedar Swamp). Beechwood Street is downstream from another small wetlands and is close to Malbone Street. Locust is downstream from the Quaker Brook confluence and a section of the Assonet River called Forge Pond. The pH of all sites, at all samplings, was below the optimal range of 6.5 – 8.5. Sections of the Assonet River are highly acidic. This may be due to the acidity associated with surrounding wetlands. DO of Malbone Street was lower than the other sites as expected due to decomposition in the wetlands. The higher DO concentration at Beechwood Street and Locust Street was due to aeration caused by turbulence. Nutrient concentration for both nitrogen/nitrate and reactive phosphorus were below detection limit except in September. Discharge in September was the lowest. Decreased concentration in November and April may be due to the dilution effect of increased discharge. Load calculations were based on BDL values where necessary and show that load for both nutrients was driven by discharge. The higher load for both nutrients in September at Beechwood compared to Locust was probably the presence of duckweed flowing down from Forge Pond. These aquatic plants would absorb nutrients. Overall physical and chemical parameters indicate good water quality. This was substantiated by the Family Biotic Index of macroinvertebrates. Students used the Hilsenhoff 10 Max Family Biotic Index due to the large number of caddishflies. The Beechwood Street FBI was 4.73 (Good water quality) and Locust was 4.44 (Good water quality)