1.0 INTRODUCTION AND LITERATURE REVIEW
1.1 INTRODUCTION
Agriculture in the early days was generally considered too small an industry to have significant impact on the environment. The remarkable growth of the agriculture industry in many countries over the past decades has increased adverse impact on the environment. (Acketors,2014). The cultivation of organisms in ponds (Tincker, 2012), tanks (Millamena et al., 1991), rivers and coastal areas may have great influence on the environment, in addition to the impacts of all human activities.
According to Hopkins et al., (1995), there are potential and identified environmental impacts of fish farming such as the following. Wetlands, such as mangroves and mud flats, destruction for construction of ponds. Hypernutrification of estuarine ecosystems by fishpond effluent. “Biological pollution” of native fish stocks through escarpment of agriculture stocks.
The last for impacts can be addressed through improved water management methods. The environmental impact of fish culture have been well documented as a result of the explosive growth of such operation in south east Asia and to a lesser extent in Latin America (Aiken, 2015) and it has also caused social impacts (Bailey, 2001).
Chamberlin (2015) discovered, from fishpond effluent management study that dissolved oxygen, pH, ammonia, and nitrite, hydrogen sulfide, redox potential, sediments, phytoplankton, and bacterial counts are fishpond parameters to be monitored. Depending on the stocking density, the concentration of materials, suspended solid and oxygen demanding subsistence may be varied. During the harvest time, the water in ponds is drained and the nutrients, suspended solids and BOD are the highest in discharged water. Solid matter, mainly mixture of uneaten feed, feces, phytoplankton colonizing bacteria and dissolved matter such as ammonia, urea carbon dioxides and phosphorus are the major constituents of the effluents of fish farms (Macintosh, and Philips, 1992)”. A very high nutrient load can be expected in effluents during harvesting, draining and cleaning of ponds, because additional discharge of material previously bound to sediment and particulate in matter. These issues when not monitored and checked could precipitate worrisome environmental problems. It is therefore necessary to embrace on this study.
1.2 OBJECTIVES OF THE STUDY
The objectives of the study are:
1.3 LITERATURE REVIEW
1.3.1 ENVIRONMENTAL IMPACTS OF FISH POND EFFLUENTS
Feed, unconsumed feed and metabolic waste products such as faeces, pseudo-faeces and excreta in intensive culture provide the largest source of nutrients that cause pollution (Seymour and Bergheim, 1992). Bergheim et al., (1994) reported that fishpond exist with suspended solid levels ranging from 1 to 100mg/1 during ‘normal’ operation but between 30 to 5800mg/1 during cleaning of ponds. Tsutsumi et al., (1992) reported that approximately 90% the feed given to fish results in discharge into the environment. In Thialand, it has been reported that 77.5% of nitrogen and 86% of phosphorus added to intensive ponds were lost to the environment (Macintosh and Philips, 1992). However, there is lack of data on the specific amount and quality of effluents loading from fishponds as well as to related ecological effects on receiving water bodies (Barg, 2014). Nevertheless, (Macintosh and Philips 1996), were able to identify the primary and second day effects from waste materials from semi-intensive and intensive fish culture systems.
Eutrophication of coastal water due to the discharge of effluent from fish farm which contains large load of organic matter nitrogen and phosphorus is well documented. Based on 10 current annual fish production of 150,000 ton and feed conversion ratio (FCR) of 1.5, the waste released from fish feed is estimated to be 131,250 tons organic matter, 8,400 tons of nitrogen and 3,150 tones of phosphors (Lin, 2012).
Ecological impact of eutrophication, as a result of excessive primary production may lead to lower biological diversity and highly imbalance trophic structure of biota in the system. Finally, the highly polluted environment resulting from continuous nutrient influx would make the water quality unsuitable as a source of water for fishpond. (Macintosh and Philips, 1992). According to SRAC (2015), the potential environmental effects of water discharged from aquaculture ponds include:
Organic matter in the effluent which may increase the oxygen demand of water downstream from the discharge. Nitrogen and phosphorus in the effluent may stimulate algal blooms in the receiving body of water. Solids in the effluent may settle in downstream from the point of discharge.
The effect on receiving waters will depend largely upon the volume and strength of effluents in relation of the volume of the receiving water body, as well as on the aquatic species present in the receiving water body. (SRAC,2015).
1.3.2 ENVIRONMENTAL IMPACTS FROM CHEMICALS
It has been discovered that the use of chemicals in aquaculture is widespread because no legal registration has been required for their use (Lin, 1998). Because of their importance in fish industry, various drugs and antibiotics were dumped into culture systems. Savas (1992) noted that, in southeast Asia, fish culture indulge in the overuse and abuse of the antibiotics and other drugs, to avoid massive mortality in culture ponds.
Antibiotics are usually administered in fish feed. There are evidences that only 20-30% of the antibiotics in the fish feed are actually ingested by fish while the remaining 80-70% are flushed into environment as unconsumed medicated food, (Samuelson, 2001). Several studies on Salmon farms, by Aoki, (2004) revealed that antibiotic residues can be extremely persistent in marine sediments and may lead to development of bacterial antibiotic resistance.
According to NACA (2005), the commonly used chemicals in grow-out ponds are formalin, malachite green, potassium permanganate, copper sulfate, medicated feed and local herbs. These component medicaments when constantly deposited in the environment unmonitored, may pose serious environmental problems requiring some level of micro-biochemical and biochemical investigation and intervention.
1.3.3 ENVIRONMENTAL IMPACTS OF SEDIMENTS
Another source of pollution, generally not accounted for, is sediment, collection and disposal of accumulated sediment deposits between production cycles is considered to be essential in promotion good water quality for successive fish production cycle. Based on the 40,000 have of fishponds operated in Thailand in (1996), the total production of sediments is approximately 16.2 million metric tons dry sediments per year (Briggs and Funge-Smith, 1994) illegal disposal of waste into drainage by flushing ponds with water will increase the nutrients, oxygen demand, and solid loading.
The illegal disposal is exacerbated by its lack of utility because pond sediment is not suitable for agricultural and horticultural use as fertilizer due to its low organic content and high salinity. Sediments affect the growth, and survival of fish and, water quality in ponds. For intensive fish culture, a major disadvantage associated with natural bottom ponds is the deterioration of the pond bottom with time. Development of anoxic condition in sediments may adversely affect the quality of overlying water (Sanarath, 1998).
1.3.4 MANAGEMENT OF FISH POND EFFLUENT
According to SRAC (2015) several pond management practices showed great potential for reducing the impact of effluents on the environment. Reusing channel catfish pond water for multiple crops by harvesting without draining the pond greatly reduced the volume of effluent discharged and also made full use of the natural waste assimilation capacity of the pond ecosystem. Effluent volume can significantly be reduced by keeping the pond water level below the level of the pond overflow device so that rain fall was captured rather than allowed. A model of pond overflow for an average climatologically year showed that capturing rain fall, rather than letting it leave the pond as overflow, reduced the discharge of nitrogen by more than 91%, phosphorus by more than 88%, and biochemical oxygen demand by more than 92% compared to ponds managed without water storage potential.
A study of marine fishponds showed that water exchange which is a common practice in fish farming-can be drastically reduced, or eliminated entirely, without sacrificing growth or survival of fish. Reduced water exchange decreases the total amount of nutrients, solids, and organic matter discharged into adjacent water bodies. Water exchange is less often used in the culture of fresh water fish, but another study showed that if water exchange is practiced to improve water quality in freshwater ponds, the resulting effluent could be used to irrigate agronomic crops production; use of effluent for crop irrigation reduces the overall volume of effluent discharges. Two studies were conducted to assess the effectiveness of treating effluents before they are discharged into environment. Passing pond effluents through constructed wetlands was a highly effective technique for reducing the concentrations of nutrients and organic matter in the water ultimately discharged to the environment.
According to SRAC (2015), A second study showed that suspended solids from catfish pond effluent can be significantly reduced and concentrations of organic matter and nitrogen covered by applying the effluent as an overland run of to well-established strips of either Bahia or Bermuda grass. This filtering technique is relatively easy and inexpensive, although relatively large lands areas also may be required to use this technique commercially.
1.3.5 USE OF AQUATIC PLANT
According to Silva and Camargo (2006), treating effluents using aquatic macropytes may be an alterative approach to fish farming management. Macrophyte-based wastewater treatment systems are relatively inexpensive to construct and operate, easy to maintain and provide effective and reliable wastewater treatment (Farahbakh shazad et al., 2000; Lin et al., 2005; Greenway, 2005; Hadad et al., 2006). The resulting gains in vegetative biomass can also provide economic reforms when harvested (El-Sayed, 1999; Sinnghal and Rain, 2003). Some floating aquatic macrophyte reused in constructed wetlands, mainly in tropical countries due to their capacity to absorb and store large quantities of nutrients, and their rapid growth rate (Ran et al., 2004; Costa-pierce, 1998).
From studies carried out in Brazil by Thomas and Bim (1998); Silva and Camargo (2003 and 2005), it was discovered that floating aquatic macrophyte species are abundantly and widely distributed occurring both in polluted and non-polluted aquatic eco-systems.