SUSPENDED SOLIDS AND TURBIDITY REQUIREMENTS OF FRESHWATER AQUATIC LIFE AND EXAMPLE RELATIONSHIP BETWEEN TSS (MG/L) AND TURBIDITY (NTUS)

Turbidity is the optical property of a suspension that causes light to be scattered and absorbed rather than transmitted through the water column. The scattering and absorption of light is caused by: 1) water; 2) suspended particulate matter ranging in size from colloidal to coarse dispersions; and 3) dissolved chemicals (Wetzel 1983; Boyd 1990). Suspended materials may include suspended sediments, finely divided organic and inorganic compounds, plankton, and other microscopic organisms (APHA 1985). Because primarily suspended solids cause turbidity, these two parameters are often discussed together. Suspended solids concentration in water is quantified by filtering a known volume of water through a weighed standard glass-fiber filter, and drying the residue retained on the filter to a constant weight at 103-105oC (APHA 1985). The “total suspended solids ” (TSS) concentration within the sample is then reported as milligrams of dried residue per liter of water filtered (mg/l). Although the terms “suspended solids ” and “turbidity ” are sometimes used synonymously, the degree of turbidity is not equal to the suspended solids concentration; rather, turbidity is an expression of only one effect of suspended solids upon the character of water (i.e., the ability of light to penetrate through the water column). Because the particle size and nature (e.g., organic vs. inorganic) of the suspended solids affect the light scattering, different turbidities can be measured for waters having the same TSS concentration (McKee and Wolf 1963). Early researchers used a variety of approaches to quantify turbidity, including the “milliont