Seasonal Changes of Dissolved Oxygen and Plant Nutrients in Seawater near Salmonid Net Pens in the Macrotidal Bay of Fundy

Abstract

Seasonal observations for tidal periods of 12 or 24 h in, or near, Bay of Fundy salmonid mariculture sites were made. Variables measured included dissolved oxygen, salinity, temperature, chlorophyll a, current velocity, dissolved inorganic nitrogen, phosphate, and silicate. Circumstantial evidence suggests that the following processes were most important in controlling levels of dissolved oxygen: advection which supplies oxygen-saturated water and removes dissolved oxygen deficits; photosynthetic oxygen production which supersaturates seawater with dissolved oxygen during the spring and summer; and chemical and biological oxidation processes which could be dominant in removing dissolved oxygen during the night and in the late summer/fall when temperatures remain high but photosynthetic activity is low. Levels of nitrate, phosphate, and silicate were not increased by the salmonid mariculture industry above those typical of the oligotrophic Bay of Fundy, although ammonia levels were higher near the salmon net pens. During the summer, levels of silicate and dissolved inorganic nitrogen were diminished coincident with uptake by the microalgal bloom.