Water Quality And Algal Biodiversity
The physico-chemical and algal characteristics of the upper reaches of Ebonyi River were studied in four stations over a four- month period from September to December 2014. The physico-chemical parameters: air and water temperatures, colour, depth, rate of flow, transparency, pH, Total Dissolved Solids (TDS), alkalinity, Biochemical Oxygen Demand (BOD5), Dissolved oxygen (D.O), silica, potassium, phosphate, nitrate, chloride, calcium, lead, iron and mercury were studied using standard methods. Parameters such as colour, calcium, pH, total dissolved solids, alkalinity, chloride, dissolved oxygen, silica, biochemical oxygen demand, phosphate, nitrate, potassium and lead did not significantly differ between the locations (P ≤0.05).
Air temperature, depth, rate of flow and transparency differed significantly between locations. All parameters differed significantly between months except depth and rate of flow which did not significantly differ between the months. Mercury was not detected during the study period. A total of twenty nine (29) taxa of algae were observed in the study. Algal abundance showed the following order: Heterokontophyta > Chlorophyta > Cyanophyta > Euglenophyta > Cryptophyta. Based on Shannon-Wiener diversity index, the water in the four locations studied is moderately polluted. The study revealed that though Ebonyi River is not heavily polluted, the fluctuations of the investigated parameters along the sampling points could be as a result of both anthropogenic and natural activities.
Rivers as water bodies are important by being involved in maintaining a balance in the ecosystem through supporting diverse plankton (phytoplankton and zooplankton) and other organisms in the food chain. In the last decades, there has been a growing necessity for the conservation of our resources, especially water. At the same time, growing populations, progressive industrialization and intensification of agriculture are leading to increased pollution of our surface waters (Mohammad and Saminu, 2012).
Adequate and safe water supply is therefore a pre-requisite for significant socio-economic development of any community. Unfortunately, in many areas of the world, especially developing countries including Nigeria, it is difficult to obtain a steady source of clean water for drinking and for agricultural uses (Akpan-Idiok et al., 2012). Rivers are equally useful in generating electricity, fisheries, irrigation and for domestic animals (Zakariya et al., 2011). Water required for domestic consumption should be free from suspended solids and dissolved impurities etc. (Alexander, 2008). Rivers constitute one of the major sources of water supply in the world (Akpan-Idiok et al., 2012).
The assessment and continuous monitoring of the quality of water sourced from rivers can be used to define existing conditions, detect trend and or establish sources of pollution. The quality of water is often affected by rocks, soil and surface through which it flows and anthropogenic (e.g. industrial, agricultural and mining) activities (WHO, 1996; Ibeto and Onianwa, 2011).
Several studies revealed that these activities coupled with atmospheric factors affect the suitability of water for all purposes (Faniraan et al., 2001; Daghrah, 2009; Hakim et al., 2009; El-Saeid et al., 2011; Al-Tabbal and Al-Zboon, 2012). Maitera et al. (2011) pointed out that sources of water supply are susceptible to pollution due to heavy human dependency on them. Urbanization, domestic and industrial activities thus have greatly contributed to increased scale of pollution of rivers and other bodies of water (Ibeh and Mbah, 2007).
Chemical pollutants include heavy metals, which are elements having specific gravity greater than 4.0 that is, at least 5 times that of water (Akan et al., 2010). The most common heavy metals that humans are exposed to are aluminium, arsenic, cadmium, lead and mercury (Akan et al., 2010). Heavy metals can cause serious health effects with varied symptoms depending on the nature and quantity of the metal ingested (Adepoju-Bello and Alabi, 2005). Excess exposure to these metals can however, be toxic (Akan et al., 2010).
Water physico-chemical parameters are known to affect the biotic component of an aquatic environment in various ways (Ugwumba, 1993). The change in physical characteristics like depth, temperature, transparency and chemical elements of water such as dissolved oxygen, chemical oxygen demand, nitrate and phosphate provide valuable information of the quality of the water, the source(s) of the variation and biodiversity (Mustapha, 2008).
Phytoplankton are microscopic aquatic plants, occurring as unicellular, colonial or filamentous forms, without any resistance to currents and are free-floating or suspended in the open waters (Zakariya et al., 2011). They are important water quality indicators because of their short life cycles, ability to respond to environmental changes and species composition (Dokuli, 2003). Algal abundance can be affected by turbidity levels. High turbidity affects primary productivity,
because turbidity reduces the amount of light penetration which in turn reduces photosynthesis and hence primary productivity (USEPA, 1991; APHA, 1992).
Nutrient limitation is important in the regulation of algal abundance (Hirose et al., 2003). Therefore, evaluating the physico-chemical and algal constituents of surface waters is essential in appraising their quality and suitability for various purposes (Omo-Irabor and Olabanyi, 2007).
1.1 Statement Of Problem
Pollution of our environments has long been identified as a major challenge to the sustainability and stability of our ecosystems, especially the aquatic environments. Pollution is a challenge to the health of both aquatic organisms and humans. Human activities constitute greater percentage of the pollution of the environments including the Ebonyi River. The Ebonyi river passes through the outskirts of the town of Obollo-Afor in Udenu L.G.A. where human activities observed are farming along its’ banks at some locations, laundry, swimming, bathing and collection of alluvial soil for constructions. Due to these activities and other natural activities, the physico-chemical parameters and diversity of algae need to be analysed to determine the quality of water. There is also, the need to identify more of our local algal species, which can be used in preparing a checklist of algae in the future.
1.2 Objectives Of The Study
The objectives of the study are to:
- Assess the physico-chemical parameters of Ebonyi River
- Identify algal biodiversity of the Ebonyi River.
- Correlate the physico-chemical parameters with algal biodiversity
- Determine the trophic status of the Ebonyi River.
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.
The statistically significant variation in the mean rate of flow between locations might be attributed to the topography of Ogbodu-Aba which is the steepest of all the locations. The biological implication of rate of flow is that high rate of flow could wash away some algal biomass, thereby disrupting their growth and subsequent removal from the system (Bellinger and Sigee, 2010).
Transparency was maximum in November and December when there was little or no rain that brought in silt and debris from the catchment areas as transparency was largely determined by suspended solids and tended to be high when suspended solids were low (Mohammad and Saminu, 2012). This result agrees with the result obtained by Khan and Choudhary (1994) on Lake Kaptai, Bangladesh that absence of rain, run-off and flood water as well as gradual settling of suspended particles could lead to higher transparency.
The pH range of 5.7 – 7.8 with mean of 6.85 ± 0.0768 recorded in this study indicated that the water was slightly acidic with occasional slight alkaline condition and this is in consonance with the report by Welcome (1975) that rivers flowing through forest are acidic with pH ranging from 4 to neutrality. The acidic nature of the river could also be attributed to reduced rate of photosynthetic activities which reduces the assimilation of Carbon dioxide and bicarbonates which are ultimately responsible for increase in pH (Simpi et al., 2011). The pH range recorded in this study can be compared to Imoobe and Oboh (2003) observation of a pH range of 5.4 – 7.4 on River Jamieson in Delta state, Nigeria. The significant difference in the monthly mean pH recorded in this study is attributed to low pH in the flood season and high in the dry season (Awachie, 1981; Wright, 1982; Ogbeibu and Victor, 1995) due to runoffs containing acidic ions from the surrounding forest. Rainy season months: September and October had lower pH means than November and December. Anthropogenic impacts involving the use of soaps and detergents may have also contributed to the acidic pH observed (Akubugwo and Duru, 2011). The mean pH of 6.85 ± 0.0768 recorded in this study falls within WHO permissible standard of 6.5 – 9.5. There was no statistically significant difference in the mean pH between locations.
The variations in the mean TDS between months indicated that rainfall might have brought in nutrients that caused high values recorded in September and October. This agrees with the observations of Manjare et al. (2010), Singh et al. (2010) and Simpi et al. (2011). Flood from the rain dissolve solids from lands surrounding the river to increase TDS values during the rainy season (Akubugwo and Duru, 2011). TDS mean value of 177.7 ± 9.307 mg/l recorded in this study is below the WHO maximum permissible limit of 1000 mg/l.
Alkalinity values of between 10 and 90 mg/l with a mean of 38.28 ± 2.88 mg/l are higher than the results of 24.2 and 78.5 mg/l by Mohammad and Saminu (2012) at Salanta River, Kano State, Nigeria. The statistically significant difference in mean alkalinity between the wet and dry months could be attributed to the erosion of the soil with bicarbonate, carbonate or hydroxide compounds during the wet season into the river (APHA, AWWA and WEF, 2005). Low alkalinity recorded in this study during dry season is line with the findings of Offem et al. (2011), who reported that alkalinity of Ikwori Lake, South-Eastern Nigeria was low during the dry season. The mean alkalinity was not beyond WHO standard of 100 mg/l.
Biochemical oxygen demand (BOD5) levels of 0.1 – 9.9 mg/l are high compared to 0.74 – 2.96 mg/l recorded at Otamiri River, Imo State by Akubugwo and Duru (2011) and 2.47 – 3.53 mg/l recorded at Guma River, Benue State by Okayi et al. (2013) all in Nigeria. The statistically significant difference in the means of BOD was observed between months, but not between locations. The high BOD might be attributed to organic, inorganic and oxygen demanding pollutants present in the water sources (Mohammad and Saminu, 2012). These oxygen-demanding pollutants might have been introduced by washing off decaying organic materials during rainfall from the surrounding forest floors. Compared with the scale reported by Maria (1983) and Adakole et al. (2002), Ebonyi River with BOD mean value of 1.9983 ± 0.261 mg/l is moderately polluted. This might be associated with waste water contamination as noted by UNESCO/WHO/UNEP (1996). The mean BOD of Ebonyi River was within the range provided by the WHO.
The dissolved oxygen values recorded in this study (5.76 – 16.8 mg/l with a mean of 8.33 ± 0.249) is comparable to the values recorded by Mohammad and Saminu (2012) on Salanta River, Kano, Nigeria, with 5.9 – 16.9 mg/l with a mean of 8.8 ± 1.02, but high compared with 3.4 – 7.0 mg/l recorded for Calabar River by Akpan and Offem (1993) and 0.5 – 1.6 mg/l recorded for Asa River, Kwara state, by Eletta and Adekola (2005) all in Nigeria. DFID (1999) noted that as indicator of water quality, the dissolved oxygen concentrations in unpolluted waters are normally about 8 – 10 mg/l at 25oC. The dissolved oxygen values of 5.76 – 16.8 mg/l recorded in this study is above the range of 5 – 9.5 mg/l provided by WHO as standard range. Statistical significant difference for dissolved oxygen mean was observed between months, but not between locations. This high dissolved oxygen in Ebonyi River may likely be as a result of turbulence caused by water movement (Mohammad and Saminu, 2012).
There was spatio-temporal variation in the level of percentage dissolved oxygen saturation in the locations sampled. Dissolved oxygen was supersaturated in September in Obollo-Afor; September and November in Obollo-Etiti; and September and October in Ogbodu-Aba. It was undersaturated in October, November and December in Obollo-Afor; October and December in Obollo-Etiti; November and December in Ogbodu-Aba and in all the months in Obollo-Eke. Supersaturation occurs due to high photosynthetic activity (Nweze, 2003). Supersaturation observed in the months in Obollo-Afor, Obollo-Etiti and Ogbodu-Aba coincided with the months of high photosynthetic activity while undersaturation in all the months in Obollo-Eke may be attributed to low photosynthetic activity.
The range of silica recorded in Ebonyi River was 0.05 – 0.8 mg/l with a mean of 0.33 ± 0.04. There was statistically significant difference in the means of silica between months, but not between locations. December mean was statistically higher than the other months. This might be attributed to an increase in concentration in the nutrient level due to concentration effect by evaporation of the river water which is more in the harmattan months.
The range of values reported for potassium (0.6 – 5.8 mg/l) is high compared to 0 – 0.35 mg/l in Jamieson River, Niger Delta, Nigeria by Imoobe and Oboh (2003) and 1.216 – 3.425 mg/l in Ganga River, India by Joshi et al. (2009), but lower than 2.00 – 9.00 mg/l in Manipur River, India recorded by Singh et al. (2010). The mean potassium recorded in December is significantly higher than the means in other months. This might be attributed to high evaporation (Vlok and Engelbrecht, 2000). The mean of potassium (3.20 ± 0.24 mg/l) is below the maximum limit provided by the WHO.
The mean phosphate value recorded in this work (11.72 ± 0.682 mg/l) is higher than 1.49 ± 0.76 mg/l recorded on the lower Niger River by Zakariya et al. (2011), 9.23 ± 0.56 mg/l on Salanta River by Mohammad and Saminu (2012) and 0.09 mg/l on Ganga River recorded by Joshi et al. (2009). Moreover, it is higher than the WHO standard for drinking water. The lowest mean phosphate value was recorded in September and it was significantly different from other months. The increase in the means of the other months might be attributed to concentration effect caused by evaporation (Zakariya et al., 2011).
The values of nitrate recorded in this work (0.18 – 67.2mg/l) is high compared to 0.05 ± 0.01 – 0.32 ± 0.02 mg/L on Otamiri River by Akubugwo and Duru (2011). The observed mean value (Table 20) of 24.46 ± 2.892 mg/l is higher than 11.9 ± 1.98 mg/l on Salanta River by Mohammad and Saminu (2012) and 5.14 ± 4.71 mg/l on the lower Niger River by Zakariya et al. (2011) all in Nigeria. Statistically significant difference in the means of nitrate was observed with September having lower value than the means of other months. There was an increase in the level of nitrate as rainfall declined and this agreed with the findings of Wolfhard and Reinhard (1998) that nitrates are usually built up during dry seasons. As noted by Johnson et al. (2000) high nitrate levels (> 1 mg/l) are not good for aquatic life, hence the Ebonyi River may not likely support a rich biota. The maximum value for nitrate was observed to be beyond the maximum permissible limit of 50 mg/l for drinking water by the WHO (2006).
The levels of chloride recorded in the river (3 – 25.49 mg/l) were comparatively lower than the results by Akubugwo and Duru (2011) of 48.39 – 145.17 mg/l on Otamiri River, Imo State, Nigeria and Manjare et al. (2010) of 31.06 – 57.61 mg/l on Tamdalge tank, India. The chloride values observed by Joshi et al. (2009) on Ganga River, India with the range of 1.97 – 13.48 mg/l are lower than the range observed in this study. The statistically significant difference in the mean value of chloride in September and October from the other months might be attributed to run-offs into the river from the catchment areas where potash fertilizer must have been applied to soil to increase fertility. The mean chloride of 9.850 ± 0.832 mg/l recorded in this study is not beyond the WHO standard of 250 mg/l.
Calcium values of 0.08 – 2.72 mg/l with a mean of 0.938 ±0.0916 mg/l recorded in this study were much lower than the values recorded by Kadiri (2000) on Ikpoba River Reservoir with values between 5.5 -14.8 mg/l , Singh et al. (2010) on Manipur River, India with values between 6.01 -17 .63 mg/l; Kadhim (2014) on Euphrates River, Iraq with values between 72.1 – 240 mg/l and Joshi et al. (2009) on Ganga River with values between 10.9 – 27.4 mg/l. Maximum mean calcium was recorded in September which is a wet month. This trend is supported by the findings of Joshi et al. (2009) and, Imoobe and Oboh (2003), but contradicts the findings of Singh et al. (2010) who reported minimum calcium level during wet season. The calcium peak in the wet season might be explained in terms of influx of floodwaters that brings in calcareous materials (Imoobe and Oboh, 2003). The mean calcium recorded was within WHO (2006) limit of between 100 – 300 mg/l.
The observed lead values in Ebonyi River (0.011 – 0.19 mg/l with a mean of 0.0872 ± 0.00617 mg/l) contrasts with undetected levels by Akubugwo and Duru (2011) on Otamiri River, Imo State, Nigeria. The presence of lead in water is associated with changes in water chemistry (e.g., reduced pH or ionic composition) which can cause sediment lead to become re-mobilized and potentially bioavailable to aquatic organisms (Weber, 1993). The primary form of lead in freshwater at low pH ( ≥ 6.5) is predominantly Pb2+ and less abundant inorganic forms include Pb(HCO)3, Pb(SO4)2, PbCl, PbCO3 and Pb2(OH)2CO3 (UNEP, 2010). At high pH, lead precipitates as Pb(OH)+ and PbHCO3+ into bed sediments (Weber, 1993). Conversely, at low pH, lead is negatively sorbed, that is, repelled from the adsorbent surface (Gao et al., 2003). Low pH values in Ebonyi River may have favoured release of lead from sediments. High levels of lead recorded in Ebonyi River could have been derived from four different sources: biogenic materials, Aeolian particles, fluvial particles and erosion (Ritson et al., 1994). The mean lead recorded in this study is higher than the WHO (2006) maximum permissible limit of 0.01 mg/l.
The range of iron levels of 0.05 – 1.2 mg/l recorded in this study were comparatively higher than 0.004 – 0.07 mg/l in Otamiri River, Imo State, Nigeria, recorded by Akubugwo and Duru (2011) and 0.2 – 0.8 mg/l in Ganga River, India, recorded by Trivedi et al. (2009). The mean iron (0.44 ± 0.44 mg/l) recorded in this study is beyond the WHO (2006) standard (0.3 mg/l) for drinking water. The high Iron level could be associated with runoffs from the surrounding land carrying loose earth laden with iron (Nweze, 2003). Mercury was not detected in Ebonyi River during the period of the study conforming to report from Otamiri River, Imo State, Nigeria recorded by Akubugwo and Duru (2011).
The algal population of Ebonyi River was dominated by the diatoms (Bacillariophyceae) with 49.62% followed by Chlorophyta (30.93 %), Cyanophyta (8.59%), Euglenophyta (8.56%) and Cryptophyta (2.28%) in decreasing order. A total algal density of 8765 individuals/ml were encountered during the period of the study in all the locations. Obollo-Afor had the third highest mean algal density of 465.5 individuals/ml dominated by diatoms, followed by Chlorophyta, Euglenophyta and Cyanophyta. Diatoms are noted for their high tolerance of environmental stress caused by anthropogenic activities, hence the dominance at the site as observed by Ayoade et al. (2009).
Obollo-Etiti experienced no anthropogenic activities during the period of study and it was well exposed to sunlight. It had the highest mean number of algae with 958.25 individuals/ml, with diatoms dominating followed by the Cyanophyta, Chlorophyta, Cryptophyta and Euglenophyta. Obollo-Eke was not exposed to sunlight, but shaded with dense growth of Bambusa vulgaris (Bamboo) and it also has a tributary. This location recorded the least number of algal density of 210.75 individuals/ml having diatoms dominating, followed by Chlorophyta and Cyanophyta. This could be attributed to low light intensity and absence of other physical and chemical factors which promote algal growth (Zakariya et al., 2011). Ogbodu-Aba was the second highest in the mean algal density. It had 592 individuals/ml with the diatoms dominating, followed by Chlorophyta, Euglenophyta and Cyanophyta. This location had farmlands within its catchment areas.
Diatoms have been reported to be the dominant algae in rivers as reported in this present study, followed by Chlorophyta and Cyanophyta in decreasing order. These results agreed with Zakariya et al. (2011) on the Lower Niger River, Kogi State, Nigeria; Kadhim (2014) on Euphrates River, Iraq; and Tanimu et al. (2012) on wetlands of Hadejia-Nguru, Nigeria. Euglenophyta was the next division in abundance and least represented division was the Cryptophyta which also agreed to the findings of Kadhim (2014).
The result of Shannon-Wiener index showed that all the locations except Obollo-Eke had almost equal number of species. The evenness index is 1 for complete evenness in any community (Begon et al., 1996). None of the locations recorded 1, so there was no complete evenness in the river. The locations with the highest evenness were Obollo-Afor (0.3741) and Ogbodu-Aba (0.3683) showing that species were more evenly distributed there than the rest of the locations. Obollo-Eke was lowest in both Shannon-Wiener index and evenness index of 2.006 and 0.2655 respectively meaning that the location had fewer species number and distribution than the rest, this might be attributed to lack of exposure to sunlight at the location. Moreover, as noted by Al-Jizani (2005) slight pollution may be responsible. Shannon-Wiener index values of ˂ 1 are interpreted as heavily polluted, values between 1 – 3 as moderately polluted and more than 3 as clean water (Whitton, 1975). The water of Ebonyi River based on this classification is moderately polluted.
The significant negative correlation between water temperature and total Heterokontophyta population could be attributed to tolerance of the algae to low temperatures or fluctuations in the water temperature (Bellinger and Sigee, 2010). The positive correlation of water temperature with total Cyanophyta (Blue-green algae) and Euglenophyta populations could be that the algal populations were affected by changes in the water temperature such as blue-greens have optimum growth at higher temperatures (Bellinger and Sigee, 2010). Significant positive correlations between colour and iron, rainfall and total Cyanophyta population could be that they may have affected the water. Total dissolved solids positive correlations with alkalinity, calcium, iron, rainfall and total Euglenophyta population could be that with increase or decrease in TDS values may result in increase or decrease of the variables. The significant negative correlation between transparency and rainfall could be attributed to rain, run-off and flood water which make the water turbid, hence reducing transparency (Khan and Choudhary, 1994). Alkalinity correlated negatively with total Heterokontophyta population and this could be attributed to tolerance of the algal population to changes in alkalinity. The significant negative correlations between chloride and lead, potassium, total Heterokontophyta population and total Chlorophyta population, could be that lead chloride (PbCl) and potassium chloride (KCl) were absent in the water sample and little or no quantity of chloride was needed by the algal populations. Silica had positive correlations with total Heterokontophyta population, because with an increase or decrease in silica value there was a corresponding increase or decrease in the algal population as silica is used by the algae to build their frustules (Bellinger and Sigee, 2010). Silica had negative correlation with rainfall probably because silica values decrease with increase in rainfall as a result of dilution. Phosphate and nitrate had positive correlations with total Heterokontophyta and Chlorophyta populations possibly because they are nutrients for the algal groups and needed for various biological activities and growth (Kadhim, 2014). Positive correlations of the algal populations could be as a result of being supported by the same nutrients. Total Heterokontophyta (Bacillariophyceae) population had negative correlations with rainfall and relative humidity which is in consonance with reports by Hulyal and Kaliwal (2008) on Almathi Reservoir that diatoms had negative correlations with rainfall and relative humidity.
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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