Water Quality Parameters

Water quality parameters are chemical, physical, and biological properties that can be tested or monitored to measure water quality. OARS tests the water quality of the SuAsCo rivers using the following interrelated parameters.

Temperature has a significant impact on the ecosystem in several ways. Many organisms, particularly cool-water fish, are sensitive to high temperatures. Warmer water has lower oxygen solubility, leading to a reduced supply of dissolved oxygen. Additionally, algae, weeds, and pathogenic microorganisms can thrive and grow faster in warmer water.

Excess nutrients in the waterways come from wastewater treatment plant effluent (in the Assabet River) and non-point sources such as fertilizer runoff from lawns and golf courses, and sediments eroded at disturbed sites. Total suspended solids (TSS; the amount of silt, clay, organic material, and algae in the water) gives us a measure of the inputs from erosion and the solids in effluent.

Conductivity (the ability of the water to conduct a charge) increases with increasing concentrations of charged ions in the water and is a rough indicator of pollutants, such as untreated waste, entering the stream. In New England, water’s dominant conductivity driver is salt from road salts. OARS testing has shown almost a perfect correlation between conductivity and chloride (a component of salt) in river water. We have noticed conductivity levels increasing over time, and we can use conductivity measurements to identify local sources of salt pollution.

The other major nutrient supporting plant growth, nitrogen, is measured in its various forms as nitrate (NO₃), ammonia (NH₃), and total Kjeldahl nitrogen (TKN). Nitrate and ammonia are readily absorbed by plants and incorporated into proteins, amino acids, nucleic acids, and other molecules. Although most aquatic plant growth in rivers is limited by the availability of phosphorus, increased nitrogen availability can also lead to algal blooms. While ammonia can be readily utilized by plants, high concentrations of ammonia are toxic to fish and other aquatic life. A second effect of increased ammonia occurs when bacteria oxidize the NH₃ to NO₃, a process called nitrification, consuming four atoms of oxygen for every atom of nitrogen converted. This process can dramatically lower dissolved oxygen in the water.

Plants need a balance of two nutrients, phosphorus (P) and nitrogen (N), to grow. Phosphorus is measured as total phosphorus (TP) and ortho-phosphate (ortho-P; soluble inorganic phosphate, the form required by plants). In most fresh waters, the phosphorus concentration available to plants is low enough that they cannot grow at their maximum rate. However, in water bodies where human activities add phosphorus, much greater growth of aquatic plants can occur. In the past, large blooms of duckweed and algae resulted from excess added nutrients (especially in the Assabet). Algal blooms can significantly disrupt the water’s pH (the balance between alkalinity and acidity). Extreme pHs are harmful to aquatic life; pH also affects how other pollutants, such as heavy metals, behave in the environment.

DO concentration in the water column indicates the river’s ability to support aquatic life, such as fish and macroinvertebrates. Aquatic plants and bacteria in the sediments remove DO from the water when they respire. Because plants respire mainly at night, the lowest DO concentrations of the day occur in the early morning. During the day, plants add oxygen to the water column through photosynthesis. Both low morning DO concentrations and large changes in DO concentrations over the day (diurnal variation) damage habitat.

Once in the water column, suspended solids are transported downstream and settle gradually, along with decaying plant matter, to form thick organic-rich sediments in the slower sections of the river. Biological Oxygen Demand (BOD) gives us a direct measure of the decomposition or oxidation processes in the water column. The more difficult-to-perform Sediment Oxygen Demand (SOD) (also considered a biological parameter) test measures the decomposition processes in the sediments. (This has been part of our testing in the past, but OARS does not currently test for BOD or SOD.)

E. coli (Escherichia coli) is a type of bacteria that lives in the intestines of people and animals. e. Coli is commonly found in human and animal feces. Most strains of e. Coli are harmless, but some can make people sick. Water samples are collected to measure e. Coli (Figure 1) to ensure water is safe for public recreation, such as swimming, fishing, or canoeing. E. coli is an indicator organism used to identify fecal contamination in freshwater and indicate the possible presence of disease-causing bacteria and viruses (pathogens).