This acronym stands for Nephelometric Turbidity Unit. The meter reading cannot be used to compare the turbidity of different water samples unless the instrument is calibrated. The aquatic science instructors will calibrate the meter regularly. Calibration consists of adjusting the meter reading to a known value when a standard sample is placed in the light beam. A standard suspension is often made from a polymer called Formazin for greater reproducibility.
Turbidity relates to the effect that suspended particles have on water clarity.
Rainfall and runoff can increase the suspended solid load in a river and make the river appear cloudy or muddy. High biological productivity related to increases in nutrients and temperature can result in increases of diatoms and other algae that contribute to turbidity. Turbidity meters can be used to estimate plankton density. River plumes that are rich in organic matter and suspended solids are clearly differentiated from the Lake Michigan water as they enter they lake. Elevated turbidity can cause an increase in temperature since suspended particles absorb heat.