Assessment Of Eutrophication Level Of Municipal Surface Water
The level of some nutrient elements in Abuja surface water were investigated for six months to determine the eutrophication profile and make logical inference on the fate of surface water system in the nearest future. Samplings were done monthly for a period of six months covering October to March and standard methods were used for the measurement of some nutrients constituting the indices of eutrophication.
The results showed high levels of microbial activities. Biochemical oxygen demand (BOD) showed high levels of pollution which varied with time and velocity of water current. Other parameters investigated were chemical oxygen demand (COD), nitrate concentration, total dissolved solid (TDS), conductivity, algae count, temperature, pH, phosphate and potassium concentrations.
Maximum and minimum values of some eutrophication parameters in the sites were recorded as follows: BOD ( Orozo 38mg/L- 7.37mg/L, Gidan Mangoro 31.2mg/L- 5.08mg/L, Nyanya 32.4mg/L- 10.05mg/L, Wuse 40.30mg/L- 7.007mg/L, Jabi 26.50mg/L- 3.10mg/L). Similarly total dissolved solid maximum and minimum values in the sites were given as Orozo 1222mg/L- 105.1mg/L, Gidan Mangoro 861.0mg/L-148.8mg/L, Nyanya 676.0mg/L- 127.6mg/L, Wuse 200.0mg/L- 86.2mg/L, Jabi 846.0mg/L-151.8mg/L. These results point to eutrophication indicators in Abuja surface water system. The results showed that the concentrations of nitrogen, phosphorus and potassium may be significantly increased beyond their compensation level by the growing human population in Abuja metropolis.
Eutrophication is the natural process whereby a confined water body (e.g. lake or dam) ages with time due to accumulation of silt or organic matter in the lake (Ademoroti, 1996).
A young lake is characterized by low nutrient level and consequently low plant productivity and at this stage is described as oligotrophic (few food) lake. The water body gradually acquires inorganic and organic nutrient from catchment areas and these promote aquatic growth and increased biological productivity causing the lake to become murky with decaying organic matter and phytoplankton. The water body is said to be eutrophic (well fed) and consequently, the decaying organic matter depletes its available oxygen. Increase in the accumulation of silt and organic matter, makes the water body shallower and sunlight penetrate slowly to the bottom, making the water warmer. Plants take roots along the shallow edges and the lake slowly transforms into a marsh or swamp which may eventually lead to dry land (Ademoroti, 1996).
Anthropogenic impact and seasonal climatic changes have aggravated eutrophication in water bodies worldwide. Advancement in science and technological innovation in agricultural practices has resulted in increased usage of natural and synthetic manures rich in phosphorus, potassium, and calcium in farming. These have accelerated the natural process of eutrophication worldwide. Nations of the world are conscious of the famous Malthusian economic theory and hence fight against this detrimental prediction by increasing food production through the construction of dams for irrigation and energy. Nations in arid regions are also making efforts to conserve their existing water resources to meet the increasing food demand through water storage reservoirs to conserve and harness this precious resource more efficiently. Such reservoirs and lakes are subject to several kinds of degradation and losses through evaporation, inefficient storage and consumption waste in addition to the growth of all kinds of aquatic organisms such as plankton, insects, fish and angiosperms. These changes lead to the phenomenon of eutrophication (Rashid and Anjum, 1985).
Eutrophication therefore causes progressive deterioration of water quality especially lakes due to luxuriant growth of plants with the effect that the overall metabolism of the water is affected (Richard, 1970).
A research carried out by Rashid and Anjum (1985) showed that the presence of Euglena, oscillatoria and Anabaena Spp indicate high organic pollution responsible foreutrophication and this affects the species of microinvertebrates and macrovertebrates including the species of fish in the water. It was found that the predatory specie Notopterus hotopterus was gradually increasing causing threat to the survival of some useful fish inthe water body. Eutrophication is therefore detrimental to crop production, fish farming and provision of portable drinking water.
Eutrophic water bodies receive large amount of aquatic plant nutrients relative to their surface area and volume and have high production of aquatic plants (Fred and Ann, 1978). Oligotrophic water bodies tend to be poorly fertilized and have low aquatic plant production, mesotrophic water bodies receive moderate amount of aquatic plants nutrients.
Thermocline is a term used in describing the depth in a water body in which there is rapid change in temperature with depth as a result of the division of the water body into layers with different densities (Fred and Ann 1978). These are the epilimnion the warmer and less dense surface waters and also the hypolimnion which describes the cooler, more dense bottom waters. The thermocline provides a barrier of mixing water between these two layers and is normally present between early June to October in temperate water bodies (Fred and Ann 1978). During this thermal stratification, waters of the hypolimnion are isolated from the atmosphere by the thermocline and cannot replenish their oxygen. Algae which have grown in this area died and decomposed leading to reduction of oxygen at the bottom. In many eutrophic waters, this depletion is sufficient to cause anoxic conditions (Zero dissolved oxygen) in the hypolimnion (Fred and Ann 1978; Muir, 2001).
It was discovered that the river Jordan which is currently the largest and longest river that flows into Israel was under threat of extinction following eutrophication. Adequate measures were taken to keep it alive for utility and consumption since major rivers in Israel were contaminated by agriculture and industrial wastes which made the Jordan River the only natural and clean river in the country (Shoshana, 2012). Biodiversity of algal communities in the upper Jordan River formed as a result of natural climatic and anthropogenic impact was used to predict the disastrous outcome.
1.1 Causes Of Eutrophication
1.1.1 Natural Sources
Eutrophication can also be described as the process of fertilization of natural waters (Fred and Ann, 1978). There is no place in Abuja where Eutrophication has been described as an algal bloom. Nevertheless, there is the need to put drastic environmental measures to prevent its occurrence in the near future. Any process which favours the growth of aquatic plants or plant life can lead to eutrophication. Nutrients required for plant growth include sulphur, calcium, magnesium ,sodium ,iron, zinc, copper etc. The major nutrients required by plants are nitrogen, phosphorus and potassium. Nitrate-nitrogen is most often obtained from urea. When urea is excreted by animals it hydrolyses rapidly to ammonia which is then acted upon by the bacteria Nitrosomonas and is oxidized to nitrite. Another bacterium called Nitrobacter oxidizes the nitrite to nitrate which is available as plant nutrient (Ademoroti, 1996). The triple bond of Nitrogen, N≡N present as N2 in the atmosphere can be broken by thunderstorm to make it soluble in water during rain and all these form a natural process for nitrogen fixation into the soil which can be washed along with sand and silt to cause eutrophication in water body (Ababio 1990).
In stabilization ponds, nitrate acts as an algal nutrient thereby reinforcing the symbiotic relationship between algal and bacteria and this is the basis of wastewater purification in facultative ponds (Ademoroti, 1996).
Hydrolysis of urea
NH2CONH2 + H2O → 2NH3 + CO2
Oxidation of ammonia by Nitrosomonas.
55NH3 + 76O2 + 5CO2 → C5H7NO2 + 54NO-2 + 52H2O + 54H+ (bacteria cells)
Oxidation of nitrite by Nitrobacter.
400NO-2 + 195O2 + 5CO2 + NH3 + 2H2O → C5H7NO2 + 400NO-3 (bacteria cells)
Other natural sources leading to eutrophication include rock weathering and erosion. Erosion can transport clay, silt and plant nutrients such as calcium and phosphorus in suspension into water bodies for eutrophication (Lathrop et al 1998). The nutrients available in an environment therefore also depend on the topography (Likens, 1972).
1.1.2 Anthropogenic Sources
Human activities in urban and rural areas have led to an increase in plant nutrients such as nitrogen, phosphorus, and potassium through improper disposal of sewage rich in urea from faeces and urine, food waste and other municipal waste products. The use of detergents with branch chain hydrocarbon cannot be degraded by bacteria and hence lead to the death of aquatic animals and subsequent enrichment of water body with nitrogen. The use of detergents with optical brighteners for aesthetic beauty of clothes has led to the enrichment of water bodies with nitrogen because these optical brighteners and perfumes often contain chromophore structure –N=N- to enhance red shift and desirable colour characteristics (Ababio, 1990).
Human agricultural practices such as the use of organic and inorganic fertilizers have led to increase in plant nutrients and consequently the phenomenon of eutrophication. Agricultural run-off from irrigated farms and leaching of fertilizer to water bodies have enormously increased these nutrients to favour the growth of algae (Lathrop, 1998). Nutrients from agricultural systems can pollute natural waters through drainage water, soil erosion and animal waste and soil water, making these nutrients mobile and enhancing eutrophication (Eckert 1995; Gimba, 2011).
Developing nations of the world are embracing industrialization to improve their economies and standard of living and this trend has led to the production and discharge of various contaminants to the aquatic environment. Fertilizer industries, detergent industries, food industries among others discharge a lot of waste which can find their ways into lakes, streams or rivers or even directly to the municipal sewer system (Weibel, 1970).
1.2 Statement Of Problem
The increasing population density in the Federal Capital Territory (FCT) Abuja, have resulted in increasing discharge of domestic and industrial waste into water bodies. This could trigger eutrophication and hence the need for continuous monitoring for strategic planning in the FCT.
1.4 Aims And Objectives
The aim of this research work is assess eutrophication parameters in surface water bodies in Abuja.
The objectives include among others to;
- Establish the physicochemical parameters of the surface water of the selected sites.
- Determine the nutritional level of the surface water using standard methods.
- Investigate the level of algal bloom in the selected sites.
- Correlate the algal bloom with nutritional level of the water bodies.
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