CONSULTANCY AND RESEARCH IN AQUACULTURE AND THE AQUATIC ENVIRONMENT
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Page 1 CONSULTANCY AND RESEARCH IN AQUACULTURE AND THE AQUATIC ENVIRONMENT A Company in the NIVA-group Modelling of environmental impact of aquaculture – hydrographical models
description
A Company in the NIVA-group. Modelling of environmental impact of aquaculture – hydrographical models. CONSULTANCY AND RESEARCH IN AQUACULTURE AND THE AQUATIC ENVIRONMENT. Modelling objectives. Reach a better understanding of aquacultures impact. Find causes of perceived problems. - PowerPoint PPT Presentation
Transcript of 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 butyou 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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Residualcurrent in the future - current now = change in the future.
Colour coded is the changein the absolute values.
Vectors denote directional change.
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Temperature Salinity
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Vertical slices in temperature and salinity
<= Vertical slice: Temperature
Vertical slice: => 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 mortalityfirst.
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 andan 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 PdP/dt = e N P - D Pwhere 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* = IIf 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 TRANSPORT2D ModelGrid size: 75m x 75 m (160 x 301 grid points)3 open boundaries: Guigiwanen, Cangaluyan, Tambac BayTidal forcing obtained from pressure gauges
PARTICLE DISPERSION (RESIDENCE TIME)Each grid has a particleBottom friction varied depending on type of structure:
cf=0.001 (no structure)cf=0.25 ( fish cage, fish aggregating device (FAD),fyke net)cf=0.5 (fish pen and bivalve culture)
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Residence Time of Control
Guigiwanen
Luciente
Luna
CaquiputanStrait
Tambac Bay
Pilar
Sta.R ita
0.001
5
10
15
20
25
30
Tim
e (d
)
Assuming no mariculture structure
High residence time,low flushing Low residence time, high flushing
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Residence Time With Varying Mariculture Structures
I. Vulnerability of Channel
(Caquiputan)
II. Residence Time Based on actual distribution of structures (2003)
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I. CAQUIPUTAN
- 3 0
- 2 0
- 1 0
0
1 0
2 0
3 0
Tim
e (
d)
b
0
5
1 0
1 5
2 0
2 5
3 0
Tim
e (
d)
Blocked
c d
a
G uig iw a ne n
L uc ie nte
Lu na
C a qu ipu tanS tr a it
T a m b ac B a y
P ila r
S ta .R i ta
CONTROL Blocked Caquiputan Residence Time Residual(Blocked & control)
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II. YEAR 2003
0 .001
5
10
15
20
25
30
-3 0
-2 5
-2 0
-1 5
-1 0
-5
0
5
10
15
20
25
30
P e nB iv a lv eCa g e
F y k e n e t
F A D
Legend
Tim
e (
d)
Tim
e (
d)
b c d
a
Guigiw anen
Luc iente
Luna
C aquiputanStrait
Tambac Bay
Pi lar
Sta.R ita
CONTROL Distribution of Structure(2003)
Residence Time Residual(2003&control)
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CRITICAL SITE
2003 Distribution Residence Time (B)
Residual(D-B)
W/o Caquiputan Residence Time (D)
0
5
10
15
20
25
30
Tim
e (d
)
Tim
e (d
)
b c d e
PenBivalveC age
Fyke net
FAD
Legend
a
G uigiw anen
Luciente
Luna
C aquiputanS tra it
Tam bac Bay
P ilar
S ta.R ita
-30
-20
-10
0
10
20
30
Removing the structures in Caquiputan will significantly improve the residence time
