OXYGEN SAG CURVE

A graph of the measured concentrations of Dissolved Oxygen in water samples collected (1) upstream from a significant Point Source (PS) of readily degradable organic material (pollution), (2) from the area of the discharge, and (3) from some distance downstream from the discharge, plotted by sample location. The amount of dissolved oxygen is typically high upstream, diminishes at and just downstream from the discharge location (causing a sag in the line graph) and returns to the upstream levels at some distance downstream from the source of pollution or discharge.