Simplified Diurnal Curve Analysis

Simplified equations have been developed for analysis of river diurnal curves, or graphs of dissolved oygen (DO) concentration versus time covering day-long periods, to produce estimates of gross photosynthesis and respiration rates. Reaches with long time of flow between stations can be analyzed because rate of DO change is calculated by Stokes total time derivative. Application to the Charles River, Mass., demonstrates usefulness of the calculated rates in water quality analysis. The simplified equations produced photosynthesis and respiration rates in good agreement with previously reported rates derived by computerized systematic analysis. Calculated photosynthesis rates correlated with the product of algae times phosphorus concentrations. In the Charles River, photosynthesis dominated over atmospheric reaeration as a source of DO replenishment in late June.