1 Fish Farm Wastes in the Ecosystem
11
Environmental Quality Standards (EQS) have been used to set limits to pressures.
The Water Framework Directive, which we will come to later, defines a standard as:
the concentration of a particular pollutant or group of pollutants in water, sediment or
biota which should not be exceeded in order to protect human health and the
environment.
As an example, the current Scottish EQS for azamethiphos is 40 ng/L (SEPA 1997,
1998). In laboratory studies, 50% of lobster larvae exposed to an azamethiphos
concentration of 500 ng/L died within 4 days. The EQS was set below this value in
order to avoid any harm to free-living marine animals, taking into account the natural
decay of the chemical when released into the water.
In the case of such toxic pollutants there is an obvious relationship between
pressure and impact, and the aim is to avoid any such impact. In the case of pollutants
such as nutrients, which cause problems only when in excess, the setting of EQS is
more difficult. The aim, of course, is to avoid the undesirable disturbances associated
with eutrophication or the smothering of seabed communities by particulate waste
from fish farms. The European Urban Waste Water Treatment Directive (UWWTD)
of 1991 concerns the prevention of pollution by discharges of sewage, but the causes
of such pollution are the same wastes as those from fish farms: organic waste, biological oxygen demand, and compounds of nitrogen and phosphorus; and some
aspects of the UK response to the UWWTD can be applied just as well to fish farms
as to urban waste water outflows. (There are differences, of course: human waste
is treated before discharge; fish waste is not.) The United Kingdom set up a
“Comprehensive Studies Task Team” to define standards and evaluative procedures
for UK estuaries and coastal waters. The team (CSTT 1997) suggested that:
Hypernutrification exists when winter values of nutrient concentrations, outwith any area
of local effect, significantly exceed 12 mmol DAIN m
−3 in the presence of at least 0.2 mmol
DAIP m
−3 … Hypernutrification should not, however, be seen as a problem in itself. It
causes harmful effects only if a substantial proportion of these nutrients is converted into
planktonic algae or seaweed.
A region is potentially eutrophic only if the relative rate of light-controlled phytoplankton
growth is greater than the relative water exchange rate plus the relative loss rate of phytoplankton by grazing; and the predicted summer maximum chlorophyll is greater than
10 mg chl m
−3
… A region is eutrophic is observed chlorophyll concentrations regularly
exceed 10 mg m
−3 during summer.
The acronym DAIN refers to “dissolved available inorganic nitrogen”, a useful and
precise way of mentioning those compounds of the element that are useful to
phytoplankton and seaweeds – what I have named earlier as nitrate and ammonia.
DAIP refers to “dissolved available inorganic phosphorus”, for which the shorter
abbreviation DIP or “dissolved inorganic phosphate” will do as well.
These CSTT proposals suggest that, in the case of nutrients, it is difficult to set
simple EQS, because the impact resulting from a given pressure depends on conditions
in the water body receiving the discharge. Sensitivity to pressure is the topic of the
next section.
11
Environmental Quality Standards (EQS) have been used to set limits to pressures.
The Water Framework Directive, which we will come to later, defines a standard as:
the concentration of a particular pollutant or group of pollutants in water, sediment or
biota which should not be exceeded in order to protect human health and the
environment.
As an example, the current Scottish EQS for azamethiphos is 40 ng/L (SEPA 1997,
1998). In laboratory studies, 50% of lobster larvae exposed to an azamethiphos
concentration of 500 ng/L died within 4 days. The EQS was set below this value in
order to avoid any harm to free-living marine animals, taking into account the natural
decay of the chemical when released into the water.
In the case of such toxic pollutants there is an obvious relationship between
pressure and impact, and the aim is to avoid any such impact. In the case of pollutants
such as nutrients, which cause problems only when in excess, the setting of EQS is
more difficult. The aim, of course, is to avoid the undesirable disturbances associated
with eutrophication or the smothering of seabed communities by particulate waste
from fish farms. The European Urban Waste Water Treatment Directive (UWWTD)
of 1991 concerns the prevention of pollution by discharges of sewage, but the causes
of such pollution are the same wastes as those from fish farms: organic waste, biological oxygen demand, and compounds of nitrogen and phosphorus; and some
aspects of the UK response to the UWWTD can be applied just as well to fish farms
as to urban waste water outflows. (There are differences, of course: human waste
is treated before discharge; fish waste is not.) The United Kingdom set up a
“Comprehensive Studies Task Team” to define standards and evaluative procedures
for UK estuaries and coastal waters. The team (CSTT 1997) suggested that:
Hypernutrification exists when winter values of nutrient concentrations, outwith any area
of local effect, significantly exceed 12 mmol DAIN m
−3 in the presence of at least 0.2 mmol
DAIP m
−3 … Hypernutrification should not, however, be seen as a problem in itself. It
causes harmful effects only if a substantial proportion of these nutrients is converted into
planktonic algae or seaweed.
A region is potentially eutrophic only if the relative rate of light-controlled phytoplankton
growth is greater than the relative water exchange rate plus the relative loss rate of phytoplankton by grazing; and the predicted summer maximum chlorophyll is greater than
10 mg chl m
−3
… A region is eutrophic is observed chlorophyll concentrations regularly
exceed 10 mg m
−3 during summer.
The acronym DAIN refers to “dissolved available inorganic nitrogen”, a useful and
precise way of mentioning those compounds of the element that are useful to
phytoplankton and seaweeds – what I have named earlier as nitrate and ammonia.
DAIP refers to “dissolved available inorganic phosphorus”, for which the shorter
abbreviation DIP or “dissolved inorganic phosphate” will do as well.
These CSTT proposals suggest that, in the case of nutrients, it is difficult to set
simple EQS, because the impact resulting from a given pressure depends on conditions
in the water body receiving the discharge. Sensitivity to pressure is the topic of the
next section.