Estuarine Oxygen Resources-Photosynthesis and Reaeration

Photosynthesis and reaeration values are presented for the Sacramento-San Joaquin Estuary from data derived by using field observations of diurnal changes in dissolved oxygen. Observed photosynthetic rates agree favorably with rates calculated from an empirical equation that includes measurements of chlorophyll, solar intensity, light extinction coefficients, water depth and temperature. The equation is presented for calculating photosynthesis for a wide range of environmental conditions. Seasonal maximum photosynthetic rates occur between April and September. Photosynthetic rates generally decrease downstream throughout the estuary. Measured rates vary from 0.04 g/m³/day to about 14 g/m³/day. Independent measurements of atmospheric reaeration and reaeration rates calculated from empirical equations show that the rates are highly variable and difficult to predict. Oxygen contributed by reaeration ranges from a loss of oxygen of 10 g/m³/day when the water is supersaturated, to an increase of over 12 g/m³/day. Reaeration rates vary from 50% of the photosynthetic rate to about 10 times the photosynthetic rate.