SEASONAL-CHANGES OF DISSOLVED-OXYGEN AND PLANT NUTRIENTS IN SEAWATER NEAR SALMONID NET PENS IN THE MACROTIDAL BAY OF FUNDY

Seasonal observations for tidal periods of 12 or 24 h in, or near, Bay of Fundy salmonid mariculture sites were made. Variables measured inc luded dissolved oxygen, salinity, temperature, chlorophyll a, current velocity, dissolved inorganic nitrogen, phosphate, and silicate. Circu mstantial evidence suggests that the following processes were most imp ortant in controlling levels of dissolved oxygen: advection which supp lies oxygen-saturated water and removes dissolved oxygen deficits; pho tosynthetic oxygen production which supersaturates seawater with disso lved oxygen during the spring and summer; and chemical and biological oxidation processes which could be dominant in removing dissolved oxyg en during the night and in the late summer/fall when temperatures rema in high but photosynthetic activity is low. Levels of nitrate, phospha te, and silicate were not increased by the salmonid mariculture indust ry above those typical of the oligotrophic Bay of Fundy, although ammo nia levels were higher near the salmon net pens. During the summer, le vels of silicate and dissolved inorganic nitrogen were diminished coin cident with uptake by the microalgal bloom.