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.

Spatial distribution of suspended particulate wastes at open-water Atlantic salmon and sablefish aquaculture farms in Canada

“…Elevated levels of particulate matter in surface waters around fish net-pens may reflect farmderived enhancement and/or natural detrital and inorganic matter variability. Previous studies investigating fish culture-phytoplankton interactions and the time-scales involved for phytoplankton turnover indicate that enhanced primary production in the vicinity of an open-water fish farm is an unlikely cause of seston enhancement (Gowen et al 1988, Wildish et al 1993, Stirling & Okumus 1995, Cheshuk et al 2003. Relatively high TPM levels in surface waters at the study sites were not associated with relatively high chl a levels (Fig.…”

Seasonal changes in benthic fluxes of dissolved oxygen and ammonium associated with marine cultured Atlantic salmon

“…Small vertical y radients in physical chemical properties existed in the water column due to tidal exchange and wind/wave action. Salinity varied from 27 to 32 %o, ammonium concentrations ranged from 3 to 10 pM in surface water and from l to 6 P M at 10 m d u r~n g August 1990 (Wildish et al 1993). Dissolved oxygen at depths to 1 m above bottom \was never below 75 O/o of saturation values.…”

“…Water depth at the site varied from 12 to 14 m at mean low water with a neap-spring tidal amplitude of 5 to 8 m. Maximum tidal currents of 16 cm S -' were measured a t 7 m depth outside of fish cages (Wildish et al 1993). Small vertical y radients in physical chemical properties existed in the water column due to tidal exchange and wind/wave action.…”

“…Hydrographic characteristics of Bliss Harbour and the aquaculture area are described in detall in Wildish et al (1990) and Wildish et al (1993). Water depth at the site varied from 12 to 14 m at mean low water with a neap-spring tidal amplitude of 5 to 8 m. Maximum tidal currents of 16 cm S -' were measured a t 7 m depth outside of fish cages (Wildish et al 1993).…”

“…This work is part of a larger col.laborative study to determine the environmental impacts of a n expanding salmon mariculture industry on a macrotidal estuary (Wildish et al 1993).…”