INVESTIGATING THE EFFECT OF OIL SPILL ON FISH

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1 International Journal of Innovative Environmental Studies Research 3(2):13-26, April-Jun SEAHI PUBLICATIONS, ISSN: INVESTIGATING THE EFFECT OF OIL SPILL ON FISH ADIOTOMRE, K.O. Department of Chemical Engineering, Delta State University, Abraka, Nigeria ABSTRACT This project work developed and solved an advection-diffusion model which was used as a tool for investigating the effect of oil spill on fishes in water. The model predicted the concentration and spread of oil spill at given time periods. The model was simulated using MATLAB 7.5 at given initial and boundary conditions. The concentrations where plotted against x-direction (gill) at given time periods also against wind velocity using MICROSOFT EXCEL. The gill was taking into consideration because oil spill in water reduces the free oxygen in that area required by the fish for respiration. The result showed that at different wind velocities concentration decreased with increase in time at various distances. And concentration increased when varied with wind velocity. This shows that there will be increase in death of fishes close to the source of spill, than those other places further from it. Keywords: Oil Spill, Free Oxygen, Fish Deaths. INTRODUCTION Industrial growth has been accompanied by imposed environmental risks all around the world Because of the growing industrialization, the need for oil exploration and transportation has increased, so the risks of oil spill accidents are high. A major oil spill can cause long term and irrecoverable damages to the aquatic environment. The environment has been recognized as an important contributor to the attainment of good health or ill health. The environment includes living and non living components. The quality of the environment affects man, influencing his actions while man s actions and inactions influence his environment (Roche, 2003). Insightful epidemiological studies have linked specific health conditions with exposures to hazardous substances in the environment. A growing concern in the field of environmental health is the impact of oil spillage on the well-being of individuals, residing close to the affected areas, as well as the degradation of the environment resulting from such spills. Oil spills have been reported over several decades in many parts of the world, from Africa to North America. The Niger Delta region of Nigeria has been greatly affected by oil spillage in recent years, with its devastating effects on the environment and the populace. Oil spillage is the release of liquid petroleum hydrocarbon into the environment due to human activity. Oil Spill is a form of pollution and the term is also applied to marine oil spills (release of oil into the ocean/coastal waters). Oil spills include releases of crude oil from tankers, offshore platforms, drilling rigs and wells as well as spills of refined petroleum products (such as gasoline, diesel) and their byproducts, including heavier fuels used by large ships such as bunker fuel, or the spill of any oily white substance refuse or waste oil (Adelana, et al. 2011). As at June 2010 it was estimated that about 546 million gallons of oil or the equivalent of an Exxon Valdez spill per year, have poured into the ecosystems of the Niger Delta over 50 years of oil production (Nossiter, 2010; National Oil Spills and Detection and Response Agency (NOSDRA), and Francis, et al 2011). Between 1976 and 2001 a total of 6,817 oil spills were recorded, with only 70% recovered (UNDP 2006). The NOSDRA recorded another 2,405 spills between 2006 and mid-2010, with an increasing trend year-on-year: 252 in 2006, 598 in 2007, 927 in 2008 and 628 in It rose again in 2010 (Ezigbo, 2010a) partly because the over 7,000 square km of pipelines linking 606 oil wells are old and begging for 13

2 replacement in the region (Francis, et al 2011). The major international oil companies operating in the Niger Delta include Shell Petroleum Development Company Ltd; Chevron (Chevron Nigeria, Ltd.); ExxonMobil; Eni (Nigerian Agip Oil Company); Total (Elf) (Total E&P Nigeria Limited) (Francis, et al 2011). Since 2000, the following major spills have occurred as presented in Table 1. Table 1: Major Oil spills in Nigeria since 2000 Date Location Quantity (Gallons Vessel/Oil Company 21/12/2011 Bonga Field 1,694,000 Shell 01/05/2010 Niger Delta 29,414,000 Exxon Mobile 2009 Bodo 4,310,040 Shell 25/08/2001 Ogbodo 2,926,000 Shell May 2001 Ogoniland Unknown (but Shell significant) Many of the previous spills, arising from a number of causes, were not completely accounted for and were not properly cleaned up (Achebe, 2012) and often take many months to stop the spills. This made the UNDP claim that it would take upwards of thirty years to clean up the Niger Delta s oil spills and associated environmental degradations. The fishing industry is an essential part of Nigeria s sustainability because it provides much needed protein and nutrients for people, but with the higher demand on fishing, fish populations are declining as they are being depleted faster than they are able to restore their number. Overfishing is not the only impact on marine communities. Climate change, habitat loss, and pollution are all added pressures to these important ecosystems. The banks of the Niger River are desirable and ideal locations for people to settle. The river provides water for drinking, bathing, cleaning, and fishing for both the dinner table and trading to make a profit. As the people have settled along the shores of the rivers and coasts, marine and terrestrial habitats are being lost and ecosystems are being drastically changed. The shoreline along the Niger River is important in maintaining the temperature of the water because the slightest change in water temperature can be fatal to certain marine species. The federal government set up agencies to supervise the efforts of various stakeholders in combating the problems arising from oil spillage. While success has been recorded in a few quarters, a lot still needs to be done, in order to achieve a healthy environment. In this work we study a mathematical model of oil spill processes in seas (arising from tanker or offshore accidents, liquid waste, etc.), such as advection, turbulent diffusion, surface spreading, evaporation, dissolution and emulsification. These processes may influence the transport of oil spill. There exist a wide range of research articles focused on the surface movement of oil spills and describing the numerical simulation of oil spills in accidents occurred in some seas However, a large part of mathematical investigations of the used computational schemes is still almost open. Therefore, the first goal of this paper is the analysis of numerical schemes for simulating oil spills in order to obtain accurate predictions of the movement and the fate of the spilled oil. This forecast gives an idea of the oil spill impact and is crucial for properly designed clean-up recovery operations and the protection of ecologically sensitive zones. Aims and Objectives This project work developed and solved an advection-diffusion model which was used as a tool for investigating the effect of oil spill on fishes in water. The model predicted the concentration and spread of oil spill at given time. This study was designed to estimate the rate of diffusion, extent of contamination and the adverse effects of the oil spill on fishes in water in the study area. This information will be helpful to the rural dwellers of the community having spill problems. The project work focuses on how mathematical models are used to predict pollutant concentration in water due to spill. Attention is given to the fact that the pollutant is harmful to aquatic lives and also to human lives. 14

3 Adiotomre.. Int. J. Innovative Environ. Studies Res. 3(2):13-26, 2015 DEVELOPMENT OF MODEL Accumulation rate = introduced by source strength - + net rate of amount of mass Accumulation = V Applying Fick s law, flux = D C= concentration of pollutant (oil spill) x= direction of the gills of the fish K= diffusion co-efficient due to diffusion and turbulence Total flux= D + u*c U=velocity Flux leaving at x+ Net flow = ( = D ) + u*c + ( ) ( ( 15 ) )=( ( ) )

4 Net flow in z direction =( ) Accumulation rate = ( ( ) ) Assuming 0 is constant in x directions q Is source strength = + q + = + q X direction is the gills of the fish, because fish get their oxygen from the water, and oil diffusion in water affects the oxygen in the water, by reducing the amount of oxygen in water, other directions are negligible. + = + q Equation is the final model equation. Boundary conditions = 0 = Analytical Solution of the Model + ( ) + q = 0 At q=0 This equation consists of three terms, representing respectively the local accumulation or depletion, the movement by the carrying fluid, and the effect of diffusion (movement by random motions in the fluid). In one dimension, the advection-diffusion equation simplifies to: + = C(x,t)= F( with ŋ= Where (with the dimensionless exponent expected to be positive) is a size factor to represent the temporal decay of the maximum concentration value (At x = 0), and where the function F ( is the shape factor giving the similar curve profile. This function has a stretched coordinate so that the same value F ( is obtained for increasing values of x as time goes on (constant ). This is to take into account the spreading of the pollutant patch. The exponent 2 of x is an educated guess, to render the functional dependency compatible with the equation at hand. [The choice is rooted in the fact that t appears in the equation as a first-order derivative, while x enters the equation as a second- order derivative.] The factor D in the denominator of is there to make 16

5 the ratio dimensionless; therefore has no units, and its function F ( takes on a universal character. Finally, the factor 4 is introduced for pure mathematical convenience. From (2.10), we calculate the derivatives of c needed to solve Equation (2.4): = F ( + = F ( = = = + = + Then, substitution of, and in the diffusion equation yields: F ( = + + The time factors cancel out (thanks to the careful definition of ), and the Partial-differential equation is reduced to an ordinary differential equation, with Variable : ( ) + + x + = 0 Since the exponent is still free, we will now choose it so that the two groups in the parentheses are identical, i.e. = 1/2, x=0. A solution is one that obeys = 0 This is: = A Where A is an arbitrary constant of integration. Putting all the pieces together, we arrive at the following solution: C(x,t)= A exp( ) We note that this solution already meets the boundary conditions (vanishing concentrations far away on both sides). The remaining, initial condition determines the constant of integration. Conservation of the total amount of the substance requires that = = M At all times. Calculations yield A = = exp( ) Taking M =1, and the final solution is therefore: = exp( ) 17

6 Parameter Estimation The diffusion coefficient of oil in water D, in units of cm 2 per hour, was provided as a function of temperature T in Celsius: D = T According to data present on the US National Oceanographic Data Center website, the average water temperature of the Gulf of Mexico was calculated to be 22. Using this value, the diffusion coefficient of oil in water was calculated to be D = 0.47cm 2 /hr. The diffusion coefficient was then converted to units of m 2 per day, resulting in the final value of D = m 2 /day. RESULTS AND DISCUSSION The model was solved and developed using MATLAB 7.5 and EXCEL. The model on simulation was able to predict the contribution of the concentration of levels of pollutants in water and its effect on fish at different time duration. Being a one dimensional model it also predicted the spread of pollutants on dispersion due to wind velocity. Variation of Concentration with Distance at Different Times This showed the effect distance from the source of oil spill will have on the fish. The model solution results indicated that there was a variation of pollutant concentration with distance in x-direction at a given time duration for a constant wind velocity of m/s, and at various distances i.e. 0, , , , , and the various concentrations at the respective distances at different times from the results table showed that as the distance increased the concentration decreased, as could also be seen from figures 1-4.This showed that the concentration is higher at source point, so fishes closest to the source of spill are most affected Table 2: Variation of concentration with distance at time 20hrs and wind velocity m/hr Distance (m) Adiotomre.. Int. J. Innovative Environ. Studies Res. 3(2):13-26, 2015 Concentration (g/m 3 ) at 20hrs Table 3: Variation of concentration with distance at time 40hrs and wind velocity m/hr Distance (m) Concentration (g/m 3 ) at 40hrs

7 Table 4: Variation of concentration with distance at time 60hrs and wind velocity m/hr Distance (m) Concentration (g/m 3 ) at 60hrs Table 5: Variation of concentration with distance at time 100hrs and wind velocity m/hr Distance (m) Concentration (g/m 3 ) at 100hrs Table 6: Concentration and Time variation at wind velocity m/s Time (hrs) Concentration (g/m 3 ) at 0.02m Concentration (g/m 3 ) at 0.04m Table 7: Concentration and Time variation at wind velocity m/s Time Concentration Concentration (g/m 3 ) at 0.04m (hr)s (g/m 3 ) at 0.02m Adiotomre.. Int. J. Innovative Environ. Studies Res. 3(2):13-26, 2015 Table 8: Concentration and Time variation at wind velocity m/s Time (hrs) Concentration (g/m 3 ) at 0.02m Concentration (g/m 3 ) at 0.04m

8 Table 9: Concentration and Wind velocity variation at distance 0.02 and 0.04m and time 20hrs Wind velocity (m/hr) Concentration (g/m 3 ) at 0.02m Concentration (g/m 3 ) at 0.04m Table 10: Concentration and Wind velocity variation at distance 0.02m and 0.04m and time 40hrs Wind velocity (m/hr) Concentration (g/m 3 ) at 0.02m Concentration (g/m 3 ) at 0.04m

9 Figure 1: Variation of Concentration (g/m 3 ) with Distance (m) at time 20hrs Figure 2: Variation of Concentration (g/m 3 ) with Distance (m) at time 40 hrs 21

10 Figure 3: Variation of Concentration (g/m 3 ) with Distance (m) at time 60hrs Figure 4: Variation of Concentration (g/m3) with Distance (m) at time 100 hrs 22

11 Concentration (g/m3) Concentration (g/m3) Adiotomre.. Int. J. Innovative Environ. Studies Res. 3(2):13-26, 2015 Variation of Concentration with Time at a Particular Distance The model also tested for the variation of concentration with different time intervals of dispersion monitored at a particular distance. From the results and plots it was observed that at constant wind velocity the concentration decreased at increase in time, showing that there was a greater effect of oil spill on fish at the source. The concentration was also observed to decrease as wind velocity increased. This shows that there is better dispersion pollution as wind velocity increases thus diluting pollutant Time (hrs) Figure 5: Variation of Concentration (g/m 3 ) with Time (hrs) at wind velocity m/hr and distances 0.02m and 0.04m Time 3(hrs) 4 5 Figure 6: Variation of Concentration (g/m 3 ) with Time (hrs) at wind velocity m/hr and distances 0.02m and 0.04 m. 23

12 Concentration (g/m3) Adiotomre.. Int. J. Innovative Environ. Studies Res. 3(2):13-26, Time (hrs) Figure 6: Variation of Concentration (g/m 3 ) with Time (hrs) at wind velocity m/hr and distances 0.02m and 0.04m. Variation of Concentration with Wind Velocity The concentration of pollutant increases as wind velocity increases, the model is tested at various distance, and at various time. Here there is lower dispersion at higher velocities. Also at higher wind velocity there is high effect on fishes in water as observed in figures 8 and 9. Figure 8: Variation of Concentration (g/m 3 ) with Wind velocity (m/hr) at 20hrs 24

13 Figure 9: Variation of Concentration (g/m3) with Wind velocity (m/hr) at 40 hrs CONCLUSION In conclusion this project work developed and solved a mathematical model that is able to predict the concentration levels of oil spill diffusion in water affect in fishes. The model being a one dimensional (xdirection) was able to predict the diffusion within a time duration. This work was to show how the effect of oil spill on fishes in rural areas looks like. From the model solution results could be inferred; 1) The effect of oil spill diffusion near the source is higher than away from the source, since concentration point is always at maximum at source point and decreases as we go away from the source due to wind effect. 2) As time increases the concentration level tends to decrease away from the source. 3) The effect of wind velocities is more at low velocities than higher wind velocities, since the increase in wind velocity decreases concentration. This is due to higher dispersion at higher velocities which leads to dilution. This shows that there will be increase in death of fishes close to the source of spill, those other places further from it RECOMMENDATION This work was only limited to the gills of the fish because diffusion of oil in water reduces the oxygen required for the fish for respiration. For a more explanatory method the two and three dimensional model should be done, because it will give a broader knowledge about oil spill effect in other parts of the fish, like the mouth etc. 25

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