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Although biologist have been studying the effects of human activities on aquatic systems and its effects on fish production for decades, their findings have only relatively recently being translated into methods suitable for monitoring the quality of water bodies. Mostly, bio-indicators such as benthic macro-invertebrates, phytoplankton and zooplankton are among the common bio-indicator organisms used during bio-monitoring of water to determine the suitability for fish production (Tassi, 2009). Artificial (and in some cases natural) changes in the physical and chemical nature of freshwaters can produce diverse biological effect ranging from the severe (such as a total fish kill) to the subtle (for example, changes in enzymes level or sub-cellular components of organisms) (Pagano et.al., 2006), changes like these indicates that the ecosystem and its associated organisms are under stress or that the ecosystem has become unbalanced (Masona, 2007).
Because flora and fauna of various trophic levels can integrate the effects of water quality or habitat changes over time, they become effective pollution indicators (Fernando, 2002). The concentration of a pollutant in an organism is the result of many variables such as the concentration of the pollutant in the water, the physical-chemical form of the pollutant, the membrane permeability of the organism, the type and quantity of food and its degree of contamination, the physiological state of the organism and the characteristics of the physical environment influencing the organism as well as the pollutant (Rose et.al., 2003). The response of biological communities or of the individual organism can be monitored in a variety of ways to indicate effects on the ecosystem. The co-existence and abundance of certain species at a particular location can indicate for example whether that habitat has been adversely altered (Pearl et al., 2003). The reactions of individual organisms such as behavioral, physiological or morphological changes can also be studied as responses to stress or adverse stimuli (for example caused by the presence of contaminants (Bailey et al., 2001).
If an environment receives a foreign pollutant, the organism living in it will start to take up the pollutant, from the water or food, and concentrate it in its body (Straskraba and Tundisi, 2008). Assuming that the pollutant concentration in the environment is constant overtime and the pollutant concentration in the organism body increases, death will occur after a long period. Conversely, a continuous decrease of the pollutant concentration in the medium produces a corresponding release of the pollutant form the organism, with some delay (Anmtage, 2008).
The kinetics of both pollutant uptake and release by the organism has the same pattern for any substance and animal species, whereas the uptake-and loss-rate are dependent on the characteristics of the organism as well as on those of the pollutant and the environmental conditions.
Bio-monitoring is measuring the conditions and integrity of various sources of water to ensure the health and fitness of the water body for the growth and production of fish species. For lotic (running) water systems, analysis of benthic macro-invertebrate communities provides the principal means of achieving this, particularly since macro-invertebrates are more stationary and less temporal than periphytic or attached microscopic communities (Relyea, 2008).
Biological monitoring refers to the collection and analysis of stream macro-invertebrate communities as indicators of water or habitat quality. Macro-invertebrates are larger than microscopic primary benthic (bottom dwelling) fauna, which are generally ubiquitous in fresh water and estuarine environments and play an integral role in the aquatic food web (Bernard et. al., 2003), they are the most commonly used bio-indicator of water quality among the community of indicator organisms because the presence or absence of certain pollution tolerant or intolerant species can be a great determining factor in ascertaining the level of pollution of the water available for fish production.
Total absence of pollution intolerant species, indicates bad water quality which may have adverse effect on fishes inhabiting such water bodies or in most cases, death of the fishes. They are insects and animals without backbone (invertebrates) that can be seen with unaided eye (without a microscope) that live in and on the bottom of streams, lakes, ponds, reservoirs, estuaries and oceans (Downing and Rigler, 2002). Insects (largely immature forms) are especially characteristics of freshwaters; other major groups include worms, mollusk (snails, clams) and crustaceans (scuds, shrimp etc.) (Lathrop and Markowitz, 2001). They are more readily collected and quantified than either fish or periphyton community. Species comprising the upstream communities occupy various niches, based on functional adaptation or feeding mode (e.g. predators, filter or detritus, feeders, scavenger); their presence and relative abundance is governed by environmental conditions (which may determine available food supply) and by pollution tolerance levels of the respective species (Cardoso et.al., 2006).
Benthic macro invertebrates are of great importance in assessing water quality available for fish culture because they have several characteristics that makes them easy to study and show clear responses when faced with adverse environmental conditions (Davis and Simon, 2005).
Aquatic PollutionDegradable wastes are organic materials that can undergo decomposition through bacterial attack. The inputs that can be included under this category are urban sewage, agricultural waste, food processing waste distillery waste, paper-pulp mill waste, and organic discharge from chemical industry and oil spillages (Hutchinson, 2000). In addition, inputs like leaves and grass clippings and run-off from livestock feedlots and pastures also contributes to this. When natural bacteria and other micro-organisms in the water breaks down to organic materials, they use up the oxygen dissolved in water (Edington and Hildrew, 2003). Most of the fishes and bottom dwelling animals cannot survive when levels of dissolved oxygen drops too low. When this occurs, it kills fishes and other aquatic organisms in large numbers, which leads to disruption in food chain.
Fertilizers containing nutrients such as nitrates and phosphates could also have effects similar to those of organic wastes. In excess levels, nutrient over-stimulates the growth of aquatic plants and algae (Moore, 2000). Excessive growth of these clogs waterways, uses up dissolved oxygen as organisms decompose besides and thereby blocking light to deeper waters. The depletion of oxygen in turn, proves very harmful to aquatic organisms as it affects respiration of fish (Campaioli et. al., 2004) and other aquatic organisms that derive oxygen from water.
Heat, acids and alkalis and some chemicals such as cyanides can be considered as dissipating wastes as they lose damaging effects soon after they enter water bodies. Particulates like dredging spoil, fly-ash, China clay-waste, colliery waste and a variety of man-made materials like plastics are inert but they may clog feeding and respiratory structures of animals and may also reduce photosynthesis by reducing light penetration or may smother benthos (Simons, 2009). Conservative wastes like heavy metal, halogenated hydrocarbons and radioactive material are not subject to microbial attack and therefore, exist over a long duration and cause harm to plants and animal (Lampert and Sommer, 2004).
Sources of Pollution
The sources of pollution of a given water body, can be categorized as point and non-point. Point source of pollution occurs when polluting substances are emitted directly into water ways. A pipe channeling toxic chemicals directly into a river is an example. A non-point source occurs, when there is run-off of pollutants into a water way, for instance, when fertilizers for agricultural fields are carried into a stream by surface run-off. The common point sources of pollution are municipal and industrial waste effluent, run-off fields; discharge from vessels, storage tanks and piles of chemical, run-off from construction sites; and by passes from Sewers and sanitary pipes (Pollard, 2000).
The non-point sources include flow from agricultural field, and orchards, run-off from logging operations, urban run-off from logging operations, urban run-off from unsewed areas and septic tanks leachates, atmospheric deposition and rural runoff from roads, when toxic substances enter lakes, stream, rivers, oceans and other water-bodies, these get dissolved, i.e. suspended in water or get deposited on bed (Hynes, 2002). This results in water pollution thereby quality of water deteriorates, affecting aquatic eco-systems, pollutants can also seep down and affect ground water deposits. The most important sources of pollution are city sewage and industrial waste discharged into rivers by virtue of the quantities in which these are discharged. According to Lenat (2004), only about 10 percent of the waste water generated at present, is being treated, allowing about 90 percent of it to directly enter receiving water. Due to this, pollutants enter ground water, rivers and other water bodies and may even harbor pathogens. Agricultural run-off or the water from fields that drain into rivers is another major source of water pollution as it could be rich in the major nutrients like nitrogen, phosphorous and pesticides (Mecan, 2004).
Testing for chemical pollution in our nation’s water bodies, have traditionally meant using analytical chemistry. In recent years, environmental agencies have endorsed biological monitoring to enhance or replace chemical monitoring. The theory behind biological monitoring (bio-monitoring) is to use the organisms living in the aquatic system as a measure of water quality. These concepts have being applied to the study of so many water bodies and have proven effective in the determination of the water quality for fish production (Homing and Pollard, 2008).
Bio-monitoring an aquatic system uses the same theoretical approach. Aquatic organisms are subject to pollutants in the stream as if flows by day and night. Consequently, the health of organisms reflects the quality of water they live in. If the pollution levels reach a critical concentration, certain organisms will migrate; fail to reproduce or die, eventually leading to the disappearance of these species at the polluted site (Parker and Salansky, 2007). Normally, these organisms will return if conditions improve in the system.
Bio-monitoring involves the use of organisms to assess the health of the environment and is based on our understanding of how organisms interact with their environment. Bio-monitoring focuses on changes in community structure (distribution and abundance) (Cao et. al., 2007). The biological monitoring commonly used are based on the presence or absence of taxa indicators of environmental wellbeing (e.g. biotic indices) or on the complexity of the community identified with the level of environmental well-being (e.g. Diversity indices).
Biological monitoring (biotic and diversity indices) is not a direct measure of the biological effect produced by pollution, because the observed alterations may be due, in addition to the pollution, to other stress (e.g. natural or anthropogenic stress not caused by pollutants). Nevertheless, biological monitoring, when applied to the same community over time, may reflect some biological modifications, showing that the community, and then the physical environment have been stressed. As a consequence, biological monitoring may be considered a useful “warning signal” (Rundle et. al., 2002).
1.1Justification of this Study
Ikpoba River in Benin City, Edo state, Nigeria, is surrounded by residential areas and it is commercially a hot spot for sellers and buyers that hang around the bank of the river to perform various transactions. It is subject to human pressures which has exerted great pollution effects in the water body. Factory effluents, agricultural waste, domestic waste and industrial waste, have been continually disposed off in this river. The proximity of this river with urban communities, have also facilitated the discharge of toxic waste in this river.
This study provides data mainly about the benthic macro-invertebrate population level as indicators of water quality for fish production and growth in Ikpoba River. Benthic macro-invertebrate community has been analyzed by measuring the taxa density and tolerance values which is the Ephemeroptera, Plecoptera and Trichoptera values.
1.2Objectives of the Study
The objectives of this study are to analyze the composition, abundance, diversity and distribution of macro-benthic fauna in the Ikpoba river water body;establish changes in distribution patterns associated with ecological alteration due to human activities;assess the water quality of the river through the evaluation of richness of benthic macro-invertebrates populations and through the measurement of physiochemical parameters;provide baseline information for the long-term assessment of pollution and its effect on fish production in future research.