INVESTIGATING HUMAN INFLUENCE ON NUTRIENT LEVELS IN THE MACHIAS RIVER ESTUARY IN MACHIAS, ME

Estuaries are biologically diverse habitats, supporting numerous fisheries important to the economy of Maine. Pollution caused by water treatment plants can threaten the water quality in estuaries. A municipal waste water treatment plant dumps into the mouth of the Machias River estuary. This study investigates whether this plant is affecting the growth of biota downstream. One component was to measure soft-shell clam (Mya arenaria) growth rates over time, tidal height, and exposure to predation. The second component was to determine water quality, and in particular nutrients levels to which the clams are exposed.

To determine the water quality, one-liter samples were collected at three sites down stream from the plant May through December of 2008. Samples were also collected at two sites in a control estuary from the Pleasant River in Addison, Maine. The samples were vacuum filtered, and total suspended solids (mg/L) were determined. Salinity was measured for each sample using a hand refractometer. The samples were then analyzed for phosphates, nitrates, and nitrites using a Lachat Quick Chem 8500.

Our results show very low levels of phosphates, nitrites, and nitrates for all sampling. The recommended level of nutrients in estuaries and coastal ecosystems is below 0.01 mg/L of phosphorous and below 0.1 mg/L of nitrogen (a 10:1 ratio of N:P). (NOAA/EPA, 1988). Our concentrations never exceeded these levels, but were below them for several samples. Samples at varying tidal heights were analyzed, however no significant difference was detected.

Early salinity measurements were lower than expected for an estuarine system. Our initial working hypothesis was that a lateral separation between fresh and salt water existed in these estuaries so we just collected surface samples. Based on salinity data during the summer, this hypothesis was questioned. Depth samples were collected and analyzed.