Water Quality and Algal Biodiversity
Chapter One
OBJECTIVES OF THE STUDY
The objectives of the study are to:
(i) Assess the physico-chemical parameters of Ebonyi River
(ii) Identify algal biodiversity of the Ebonyi River.
(iii) Correlate the physico-chemical parameters with algal biodiversity
(iv) determine the trophic status of the Ebonyi River.
CHAPTER TWO
LITERATURE REVIEW
Some studies on physico- chemical and algal biodiversity of water bodies in Nigeria have been carried out. They include Tiseer et al. (2008) on seasonal occurrence of algae and physico-chemical parameters of Samaru Stream, Zaria, Nweze (2009a) on algal diversity of Adada River, Zakariya et al. (2011) on physico-chemical characteristics and phytoplankton diversity of the lower Niger River, Mohammad and Saminu (2012) on water quality and phytoplankton of Salanta River, Kano, Nigeria and Akpan-Idiok et al. (2012) on water quality assessment of Okpauku River, Yala, Cross-River State.
ABIOTIC FACTORS (PHYSICO-CHEMICAL PARAMETERS)
The physico-chemical parameters consist of physical components of the environment affecting the water bodies like temperature, total suspended solids, transparency, colour and rate of flow and chemical components like total dissolved solids, alkalinity, heavy metals (USEPA, 1991). Some heavy metals are lead, copper, cadmium, mercury, zinc, chromium and arsenic.
Aquatic organisms (from micro-organisms to fish) depend on certain temperature ranges for optimal growth (APHA, 1992). The normal range to which fish is adapted in the tropics is between 8⁰ C and 30⁰ C (Alabaster and Lloyd, 1980). Increase in temperature augments the productivity of a body of water by increasing algal growth, bacterial metabolism and nutrient cycling rates (Klapper, 2001). Biologically, one of the most important effects of temperature is the decrease in oxygen solubility as the temperature increases. As a result, the increase in temperature can also increase the oxygen demand of biological organisms such as aquatic plants and fish (Wetzel, 2001).
Transparency is largely determined by suspended solids and tend to be low when suspended solids are high and vice versa (Mohammad and Saminu, 2012). Khan and Choudhary (1994) reported that higher transparency occurred during winter and summer due to absence of rain, runoff and flood water as well as gradual settling of suspended particles.
Total Dissolved Solids (TDS) depend on various factors such as geological character of watershed, rainfall and amount of surface runoffs and gives an indication of the degree of dissolved substances (Singh et al., 2010). Manjare et al. (2010) reported that high TDS is due to heavy rainfall.
The pH value is governed largely by the carbon (iv) oxide/bicarbonate/carbonate equilibrium (AWWA, 2001). A pH value of higher than 8.5 indicates that a significant amount of sodium bicarbonate may be present in the water (Ibrahim and Ajibade, 2012). The pH values have been observed to vary according to seasons. As noted by Serano and Toja (1995) a gradual increase in pH towards the end of a hydrological cycle coincided with high primary productivity. Also Awachie (1981), Wright (1982), and Ogbeibu and Victor (1995) reported that the pH of rivers is low in the flood season and high in the dry season. Generally, rivers flowing through forests are acidic with pH ranging from 4 to neutrality (Welcome, 1975).
Flow rate is the volume of water that flows past a fixed point in a river or stream over time (Kucera and Grafman, 2014). The build up of phytoplankton populations in rivers requires a low rate of flow; otherwise, they are flushed out of the system. Phytobenthos can tolerate high rates of water flow and as such predominate over phytoplankton population in fast flowing rivers and streams (Bellinger and Sigee, 2010).
Dissolved oxygen provides a broad indicator of water quality and dissolved oxygen concentrations in unpolluted waters are normally about 8-10 mg/l (at 25⁰ C) (DFID, 1999). Dissolved oxygen is important as a respiratory gas and it is used in biological and chemical reactions (Mustapha, 2008). Different organisms have different oxygen requirements and as such, dissolved oxygen concentration is an important factor which determines their behavior, growth and distribution (Adakole, 1995). Mohammad and Saminu (2012) reported that dissolved oxygen has significant negative correlation with temperature, hence, when the temperature is high, dissolved oxygen is low and vice versa. A drop in dissolved oxygen value may also be as a result of high deposit of organic matter from agricultural run-off into the river, decomposition of organic matter by micro-organisms, respiration by zooplankton, fish and other benthic organisms (APHA, 1992). High dissolved oxygen value might be due to abundant oxygen contributed by plants during photosynthetic activity, which contribute in oxygenating the water column and at the same time reducing respiration by aquatic organisms and decomposition process at the bottom (Olele and Ekelemu, 2008).
CHAPTER THREE
MATERIALS AND METHODS
METEOROLOGICAL DATA
Rainfall, relative humidity and solar radiation data for Nsukka zone for the study period were collected from the Centre for Basic Space Science (CBSS), University of Nigeria, Nsukka meteorological station located at Eburimiri village, Nsukka which is about 5 km away from the study location.
STUDY LOCATION
Ebonyi River originates in Udenu Local Government Area precisely in Obollo-Afor which is one of the major towns in Enugu State and flows through Ebonyi State to Cross-River State where it finally joined the Cross River which flows into the Atlantic Ocean. Ebonyi River has many tributaries along its course some of which are Vava stream at Obollo-Etiti, Amanyi River at Orba and Oshenyi River at Ogbodu-Aba.
Udenu is located in the Derived Guinea Savannah vegetation zone which has humid tropical climate with marked dry (November – April) and wet (May – October) seasons. Mean monthly temperature ranges between 27⁰C and 29⁰C. Chima et al. (2009) observed that mean annual rainfall in the State ranges between 1600 mm and 2500 mm with the least rainfall (29 mm) in the driest month of the year.
CHAPTER FOUR
RESULTS
METEOROLOGICAL DATA
Meteorological data for the period of study (four months) showed temporal variations (Figure 2). Rainfall ranged between 2.3 mm to 247.4 mm with peak in September (247.4 mm) while the least monthly rainfall (2.3 mm) was observed in December. The mean monthly rainfall was 111. Relative humidity values ranged from 81.57% to 87.87% with the highest value in September (87.87%) while the lowest was in December (81.57%). The mean monthly relative humidity was 84.94 ± 1.34.
Solar radiation ranged from 103.4 w/m² to 110.2 w/m² with the peak in November (110.2 w/m²) while the least was observed in October (103.4 w/m²). The mean monthly solar radiation was 108.23 ± 1.62 w/m².
CHAPTER FIVE
DISCUSSION
The results showed that the quality of water varied among the months. Changes in air temperature and water temperature as in most physical and chemical parameters are primarily governed by the local climatic conditions (Imoobe and Oboh, 2003). Air temperature levels obtained in this study showed a declining trend from the rainy season months to December which is a harmattan month. The statistical significant variation in the mean air temperature might be attributed to cold weather conditions of harmattan and more cloud cover in December. Water temperature differed significantly between months. The minimum and maximum temperature of 20 – 26oC observed in this study is line with the observations of Okayi (2003) that minimum and maximum temperature of 24.5 – 29.5oC is normal for tropical waters for optimal growth of organisms. Air temperatures were generally lower than water temperatures at all stations and at all sampling times, which contradicted the work of Imoobe and Oboh (2003) that noted higher air temperature than the water temperature.
The significant variation in the mean colour between months showed that run-offs into the river in the rainy months brought in debris, sediments or silts which increased the colour value. There was no statistical significant difference in the mean colour between locations; this might be as a result of uniform soil properties along the investigated stretch on the river.
Depth values of between 15.5 and 91 cm recorded in this study are lower than those recorded by Aghoghovwia (2011) of 780 – 1500 cm on Warri River, Nigeria. Higher depth during the wet period also agrees with the results obtained in other regions by Aghoghovwia (2011) and Singh et al. (2010). Depth values tend to increase as a result of influx of flood which consequently increases the volume of water in the basin.
CHAPTER SIX
CONCLUSION
This present study concluded that physico-chemical and algal characteristics of Ebonyi River showed monthly variations. Based on the results of the physico-chemical parameters, the water quality in Ebonyi River was slightly acidic and not highly polluted. Mean colour obtained in this study is higher than the WHO recommended standard for natural unpolluted waters, hence unfit for drinking unless purified. High value for colour leads to reduction in sunlight penetration into the river resulting in low productivity of the algal population especially in rainy season. The concentration of phosphate observed is higher than the WHO limit and this could have been caused by rain, surface run-offs, agriculture run-off and laundry activities (Manjare et al., 2010). Lead content is beyond the WHO guideline for drinking water and the concentration was observed to have increased along the months as rain declined, with the highest recorded in December. The water of Ebonyi River has lead content higher than maximum permissible limit and therefore unfit for drinking especially in the dry season.
However, the composition, abundance and distribution of the algal species indicated that the Ebonyi River is moderately polluted. Heterokontophyta represented by diatoms had the highest species number, followed by Chlorophyta, Cyanophyta, Euglenophyta and Cryptophyta in decreasing order. Diatoms seemed to have wider tolerance range for pH fluctuations. Ebonyi River is slightly acidic, hence the dominance of the diatoms (DeNicola, 2000).
Cyanophyta and Euglenophyta are eutrophic species (Zakariya et al., 2011) and since in Ebonyi River the former ranked third in abundance and euglenoids (indicator species for organic pollution) were observed, the river is moderately polluted as revealed also by diversity indices results.
There are members of the Chlorophyta that serve as indicator organisms, such as desmids e. g. Cosmarium sp. and Ankistrodesmus sp., these desmids are found especially in oligotrophic environments (Yasmin et al., 2011). The presence of certain desmids, even in low numbers is considered to be a good indicator of mildly acidic, oligotrophic conditions (Wehr and Sheath, 2003).
T-test analyses results showed that the mean values for algal populations for the late wet season differed significantly from the mean values of the early dry season, with late wet season having more algal population.
The results of the diversity indices showed also that the Ebonyi River is moderately polluted. Cyanophyta have detrimental effects on various uses of water (Zakariya et al., 2011), hence there is the need to prevent our natural water supplies from being taken over by the Cyanophyta. The use of inorganic fertilizers within the river’s catchment areas should be limited. Further work needs to be carried out on the lower Ebonyi River, since it passes through Ebonyi and Cross-River States where it could be open to heavy discharges of contaminants.
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