CONSULTANCY AND RESEARCH IN AQUACULTURE AND THE AQUATIC ENVIRONMENT

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• CONSULTANCY AND RESEARCH IN AQUACULTURE AND THE
  AQUATIC ENVIRONMENT

A Company in the NIVA-group
Modelling of environmental impact of aquaculture
hydrographical models
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Modelling objectives

• Reach a better understanding of
• aquacultures impact.
• Find causes of perceived problems.
• Give recommendations on remedial actions to be
  taken.
• Identify areas with less risk.
• Give indications of total carrying capacity of
  the areas.

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What is a model ?...we mean a mathematical model.
One or more expressions or equations. Example 1
A familiar expression Fish length A (1 e-kt)
is a model. Importance of data To determine
coefficients A and k for a particular species of
fish, you must have data. Without data you have a
theoretical model but you can not apply it to any
fish species. Similarly
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Example 2 Effect of freshwater source on the
coastal sea
Equations for conservation of momentum, mass,
propagation of turbulence, transport of heat and
salinity make a hydro dynamical model.
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Bathymetric map
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Another view to the bay
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Numerical mesh
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Residual current in the future - current now
change in the future. Colour coded is the
change in the absolute values. Vectors denote
directional change.
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Temperature
Salinity
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Vertical slices in temperature and salinity
lt Vertical slice Temperature
Vertical slice gt Salinity
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Effect of an aquaculture on P conc. in the water
column
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Effect of an aquaculture to the bottom
deposition of Carbon
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How to compute carrying capacity ?
There have been various approaches. All focus to
the description of the most limiting factor
likely to affect fish health and
mortality first. For Bolinao Bay, this factor
seems to be oxygen availability. Clearly, when
dissolved oxygen drops below 2 mg/l fish
mortality will occur. But dissolved oxygen
content in water is the result of several
processes. There are organisms that produce
oxygen and those that consume it. Fish and
shellfish are those that consume it. They play a
direct and an indirect role.
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How to compute carrying capacity ?
Available nutrients are taken by phytoplankton
which grows in number very quickly, thereby
depleting nutrient content in water. A huge
number of phytoplankton cells in water are now
hungry and can not find enough nutrients any
more. This is the start of the phytoplankton
crash. When it crushes, it does so in phase.
Suddenly a huge mass of phytoplankton leftover
is found in water. Decomposition of this mass
will cause deadly hypoxia.
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Effect of nutrient inflow on PHYTOPLANKTON
concentration
Let N-nutrient concentration, P- phytoplankton
density, I- total nutrient inflow. Concentration
of N and P will change according to dN/dt (I -
N) D e N P dP/dt e N P - D P where D is the
flushing rate of the lake, e is the efficiency
of phytoplankton uptake. Flushing rate D Q/V.
In steady state N D/e, P I - D/e.
Look N P I If we measure eutrophication as
an increase in phytoplankton concentration, the
concentration will increase linearly with the
nutrient inflow. So we see that carrying
capacity is linearly related to the nutrient
inflow because when P reaches a critical
concentration, DO will drop to the value where
fishkill is imminent.
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Assumptions of Model

• HYDRODYNAMIC TRANSPORT
• 2D Model
• Grid size 75m x 75 m (160 x 301 grid points)
• 3 open boundaries Guigiwanen, Cangaluyan, Tambac
  Bay
• Tidal forcing obtained from pressure gauges
• PARTICLE DISPERSION (RESIDENCE TIME)
• Each grid has a particle
• Bottom friction varied depending on type of
  structure
• cf0.001 (no structure)
• cf0.25 ( fish cage, fish aggregating device
  (FAD),fyke net)
• cf0.5 (fish pen and bivalve culture)

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Residence Time of Control
Assuming no mariculture structure
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Residence Time With Varying Mariculture Structures

• Vulnerability of Channel
• (Caquiputan)
• Residence Time Based on actual distribution of
  structures (2003)

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I. CAQUIPUTAN
CONTROL
Residual (Blocked control)
Blocked Caquiputan
Residence Time
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II. YEAR 2003
CONTROL
Residual (2003control)
Distribution of Structure (2003)
Residence Time
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CRITICAL SITE
2003 Distribution
Residence Time (B)
Residual (D-B)
W/o Caquiputan
Residence Time (D)
Removing the structures in Caquiputan will
significantly improve the residence time