Research Document - 2005/038
A Preliminary Perspective on Dissolved Oxygen Standards and Models in the Marine Coastal Zone with Particular Consideration of Finfish Aquaculture in the southwest New Brunswick portion of the Bay of Fundy
By Page, F.H.
The trend toward setting standards pertaining to the concentration of dissolved oxygen in coastal marine and estuarine areas is increasing around the world. Most of the standards are aimed at protecting the production and ecosystem processes of the coastal zone and limiting the anthropogenic perturbation to natural levels of dissolved oxygen to only a few percent (5-10%). In Canada, the CCME has developed preliminary national dissolved oxygen standards for the coastal zone but these have not been fully adopted by the various coastal jurisdictions throughout the country.
Marine aquaculture requires oxygen for the respiration needs of the cultured organisms and the breakdown of its organic waste products or effluents. Historical experience with marine aquaculture around the world has shown that aquaculture has the potential to significantly reduce oxygen concentrations and in some cases the reductions can be severe. Although localized and moderate reductions can take place almost immediately upon the implementation of an aquaculture operation, severe reductions seem to take many years if not decades. In Canada, the Canadian Federal and Provincial governments also hope to enhance aquaculture development in the country and in the southwestern New Brunswick area the industry and governments, both provincial and federal, are working toward adopting a performance based approach to aquaculture environmental impacts. In some of Canadian areas aquaculture already is the major anthropogenic driving force influencing coastal zone concentrations of dissolved oxygen. A few Canadian marine aquaculture operations are already, periodically reducing dissolved oxygen concentrations on relatively small spatial and temporal scales to levels below accepted international guidelines and recommended national guidelines.
On a global basis models simulating and predicting the impact of fish farming on the concentration of dissolved oxygen are beginning to include consideration of both near-field and far-field processes. In some cases oxygen is being used as the model currency and oxygen standards are being used to estimate holding capacity limits for aquaculture. All of the modeling experience indicates that the major controlling factor for environmental impact and oxygen concentration in particular, is water circulation. In well flushed areas with sufficient minimum water velocities, oxygen supply rates can be balanced with farm production so that the demand of farming activities and the oxygen demands for degradation of organic waste products can be met and environmental standards achieved. In poorly flushed areas and areas with weak currents this balance is difficult to achieve and it is in such areas that water quality degradation has generally occurred.
The time has therefore arrived for Canada to proceed seriously and rapidly toward the development and implementation of adequate dissolved oxygen standards and management protocols for the marine coastal zone and aquaculture. Such an effort will enable us to avoid the serious eco-socio-economic consequences associated with poor water quality. From a risk analyses perspective the dissolved oxygen issue might be classified as manageable. Aquaculture takes place in a relatively small proportion of the Canadian coastline and it is only within some of these areas that aquaculture is intense enough to pose potential problems. Hence, the likelihood of a major aquaculture induced depletion of dissolved oxygen is probably low to moderate and the impact of reductions is also probably low to moderate.
It is suggested that the existing CCME guidelines and approaches for water quality guidelines can be used to guide the development of appropriate standards. It is also suggested that aquaculture development may be potentially accommodated through the adoption of the use-protection approach and the Initial Dilution Zone concept. This accommodation will require the development and implementation of jurisdictionally specific monitoring and water quality modeling capabilities and the passing of jurisdictionally appropriate regulations. To be successful, and consistent with the principles underlying Canada’s desire for more holistic and integrated coastal zone planning and management, this process should engage all the appropriate stakeholders and levels of expertise. The process should begin with an intense oxygen monitoring program to determine natural variations in key aquaculture areas as well as variations within and around existing farms. The process should also include the development of high spatial and temporal resolution three dimensional water circulation models, relatively simple and empirically driven water quality models, the coupling or linking of these with each other and with GIS integrated management planning and management initiatives and calibration and validation with field data.
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