NIGERIAN INSTITUTE FOR OCEANOGRAPHY AND

MARINE RESEARCH/AFRICAN REGIONAL AQUACULTURE CENTRE

P. M. B. 5122, ALUU, PORT HARCOURT.

Water quality and Plankton diversity of effluents receiving lower Awba Stream and reservoir were assessed at four stations; three along the stream and one at the reservoir. Significant spatial variation was observed in dissolved oxygen (DO], Biological Oxygen Demand (BOD), Ammonium Nitrogen (N-NH₃, N-NH₄), Alkalinity and total Hardness (P<0.05) among the physiochemical parameters of the study stations. A posteriori test showed the sewage rich effluents receiving station 2 to account for significant difference in DO, BOD, N-NH₃, N-NH₄, and Alkalinity. The station had least DO level (1.33mg/l± 0.58) and highest BOD (204.0mg/l ± 23.14), NH₃ (3.80mg/l±0.35),NH₄ [4.10±0.35] and Alkalinity [139.17mg/l±4.10]. A posteriori test also revealed that station 3 which receives effluents from chemical laboratory was the cause of significant difference in total hardness. The station had highest total hardness (136.83mg/l±34.15). Station 4 which was at the reservoir and devoid of effluent discharge had the most diversed Phytoplankton and zooplankton. Mehinic Diversity Index (MDI) and Simpson diversity Index, (SDI) values at the station for Phytoplankton were 0.30 and 0.81 while those of zooplankton were 0.66 and 0.88. Station 3 had least diversed phytoplankton, MDI and SDI diversity values for zooplankton; MDI: 0.32; SDI 0.51. This indicates undesirable effects of effluents discharge on physicochemical properties and plankton diversity of the receiving water body.

Key Words: Water quality parameters, phytoplankton, zooplankton, effluents, species diversity.

INTRODUCTION

In Nigeria, especially in Urban areas, surface waters have been used as the most expedient media of disposing wastes particularly effluents. The ecological implications of the effluents discharge include alteration of water quality parameters from environmental background levels which in turn result in upsetting the ecological equilibrium of the water bodies and exerting acute toxic and chronic effects on inhabiting organisms.

Among the water quality changing agents are untreated sewage and other household effluents which principally consist of organic substances (human nitrogenous and other organic matters) and other nutrient rich substances such as soap and detergents (Yakub 1998). Other sources of organics and nutrients are effluents from industrial activities such as breweries (Ogbeibu and Edutie 2002, Saad et al 1994), textiles, paper and pulp mills, and food processing (Saad et al 1994).

Perhaps, a moderate quality of this type of wastes could benefit aquatic environment, but when the rate of discharge outstrips their rate of conversion to inorganic and inert materials problems ensue. These problems include escalation of BOD, and toxic substances such as Ammonnia and hydrogen sulphide, and oxygen depletion. Excessive nutrients input also stimulates massive algal growth that leads to overcrowding and subsequent death of inhabiting organisms (Mason 1992). River Ogupa in Ibadan is devoid of fish as a result of sewage dumping (Sikoki & Kolo, 1993).

The massive algal growth caused by excessive nutrient input is with a marked decline in species diversity. This has been reported to be a serious problem in fresh water, estuaries and enclosed seas (Boaden and Seed 1985). This species diversity is the most commonly used and reliable parameter in biology to determine how healthy an environment is (Ogbeibu & Edute 2002). It is a measure of availability of various ecological niches to be occupied by various species of organisms with in an ecosystem.

Therefore, decline in phytoplankton diversity is expectedly followed by decline in species diversity of organisms of higher trophic levels such as Zooplankton, Macro invertebrates and vertebrates.

Other major contaminants of aquatic environment whose point sources are industrial and laboratory activities are toxic substances such as heavy metals, synthetic organic and inorganic substances. Mason (1992) and Yakub (1998) highlighted common toxins contained in effluents of various industrial and laboratory activities. Surface waters in Nigeria especially in urban areas have been reported to contain considerable levels of these toxins (Ajao 1996; Ajao and Fagade 1991; Ajao et al, 1996; Akueshi 1980, Don-Pedro et al 2004 and Wangboje & Oronsaye 2001).

Apart from toxins which are of direct lethal effect on the organisms, these effluents may also contain substances of indirect impact as obtainable in organic and nutrients rich effluent, especially alteration of the water quality parameters.

This study was carried out to assess the water quality and plankton diversity of effluents receiving ends of lower Awba stream and Awba reservoir.

Awba stream, a tributary of Ona river has its lower course running through the university of Ibadan campus in Ibadan. Fig. 1 presents map of the University of Ibadan with the four sampling stations along the stream and reservoir.

Station 1 is close to the stream’s entry point into the university campus and free of effluent discharge. Spills of sewage effluents from broken drainage pipes are channelled to the stream at station 2. Station 3 receives effluent from chemistry department in the faculty of science.

Station 4 is at Awba reservoir where the stream drains into the reservoir has an area of six hectares, a depth of 5.5m and about 27 million litres water capacity (official notice board at the reservoir). It is used for experimental demonstration and research purposes. It is free of effluent discharge.

WATER QUALITY TESTS

Tests for water quality parameters were done with the use of "fish farmer water quality kits" box (by HACH company U.S.A.). Tests were made for temperature, DO, CO₂, Alkalinity, Total Hardness and Ammonium Nitrogen (HN₃: NH₄) at each station following procedures outlined in the manual contained in the box.

For BOD, water sample was collected, oxygen was fixed with wrinkler solutions and brought to the environmental biology laboratory of zoology department University of Ibadan. Titrometric method was used to determine initial DO and final DO (after days incubation).

Plankton net of 60um mesh size was used to collect plankton samples. The samples were immediately fixed and preserved with 4% formalin after which analyses for abundance and species composition were conducted in the laboratory. Tests for water quality parameters and plankton samplings and analyses were done in triplicate.

Water Quality Tests: Mean value and standard deviation for each parameter at each station were computed. The Microsoft excel statistical analysis tool pack was used for all measures of central tendency and dispersion and analysis of variance.

Plankton: Overall total abundance of each plankton species collected in the three samples for the four station was computed. Percentage of the over all total in each station and mean of the value of the three samplings as well as the standard deviation were also computed.

Species diversity in each station was determine using two species diversity indices:

i. Mechanic Diversity Index (MDI) = S/N

S = Number of species

N – Total number of organisms.

ii. Simpson Diversity Index (SDI) which also measures evenness of distribution or equitability.

SDI = I -

ni = Number of Individuals in each species

N = total number of individuals.

RESULTS

The result of the water quality measurements were summarised and presented in Table 1. Station 2 had significantly lower DO and higher BOD, N-NH₃, N-NH₄, and Alkalinity than stations 1,3, and 4 (P<0.05). Station 2 also had significantly higher CO₂ than station 4 (P <0.0.05). Total Hardness was highest at station 3, but only significantly higher than that of station 4 (P< 0.05). NH₃, NH₄ and BOD were significantly lower in station 1 than in station 2,3, and 4. Although spatial variation was observed in temperature, there was no significant difference.

The abundances and species diversities of phytoplankton and zooplankton are summarised in Tables 2 and 3 respectively. Station 3 had the least phytoplankton species diversity values. MDI 0.1, SDI: 050, while station 4 had the highest values, MDI: 030: SDI: 081.

Station 4 also had highest zooplankton diversity indices values: MDI: 066; SDI: 0.88, followed by station 3, MDI: 0.44; SDI: 0.79, then station 1, MDI: 0.38; SDI: 0.77 while station 2 had the least values, MDI: 0.32; SDI: 0.51.

Station 1: The relatively low levels of BOD, NH₃, and NH₄ at this station is indicative to the fact that low DO concentration (4.67mg/l + 3.05) here might not be as a result of high organic matter in the water at this station.

Phytoplankton species richness at this station was low (MDI:0.155). Only three species were encountered; Oscillatoria, Microcysts and Anabaena but with relatively high abundance and even distribution or equitability (SDI:0.67).

Meanwhile, these phytoplankton belong to cyanophycea family (Blue green algae) which have been reported to dominate water bodies where there is "Eutrophication caused by excessive release of nutrients into the water body (Mason, 1992).

The station had higher species richness and equitability for zooplankton than for phytoplankton (MDI:0.38; SDI: 0.77). The low DO level at this station and monopoly of phytoplankton group by these blue greens is indicative to the likelihood of the water to have been contaminated upstream before the University of Ibadan campus entry.

Station 2: The very low level of DO (1.33mg/l ±0.58) and high BOD (204mg/l ±23.14), NH₃ (3.80mg/l ±0.35) and N-NH₄ (4.10mg/l± 0.35) levels are manifestations of the effect of organic rich sewage effluents being discharged at this station. This conforms with the reports of Saad et al (1994) and Yakub (1998), that point of organic effluent discharge experiences marked decline in DO level as well as elevation of BOD and reduced compounds such as NH₃ and NH₄.

The station possessed Chlorella, a green algae, and three blue green algae (Microcysts, Aphanizomenon, Oscillatoria.] Therefore, the station had higher species richness than station 1 (MDI:0.2) but with less equitability (SDI: 0.64). Microcysts and chlorella were much higher in abundance than others.

The three zooplankton species at this station were of very low abundances. The station had the least diversity indices values for zooplankton (MDI:0.32; SDI: 0.51).

The decline in plankton diversity due to the alteration of water quality parameters by organic effluents discharge will with no doubt affect species composition and distribution of higher trophic biotic components of the ecosystem. This has been a major problem in Nigerian bigger water bodies especially in urban areas such as river Ogunpa in Ibadan (Sikoki & Kolo 1993), and Lagos lagoon (Adeniyi 1980; Ajao 1996; Ajao & Fagade 1991; Ajao et al 1996).

Station 3: The significantly higher DO level at this station (10.00mg/l + 2.00) than at station 2 (P<0.05) is attributed to self purification of the water down to this station from station 2. photosynthetic activities of the relatively abundant phytoplankton (Microcysts and Oscillatoria) could have also boosted DO level at this station. The station had the lowest Alkalinity (85.50 mg/l±0.50) and highest total hardness (136.83 mg/l±34.15) levels. This is indicative to highly acidic and high contents of calcium and magnesium ions in the effluents from the chemistry laboratory being discharged at this station.

The relatively high BOD and NH₃; NH₄ at this station could be as a result of presence of organic mater at this station.

Microcysts and Oscillatoria (blue green algae) were the only phytoplankton encountered at this station although with equal and relatively high abundance. Thus the station had the least diversed phytoplankton (MDI:0.10; SDI:0.5).

However, the station is only next to station 4 in term of zooplankton diversity. Five species of zooplankton were encountered at this station with a relatively high equitability (MDI 0.44; SDI; 0.79). This is attributable to high DO level and tolerance of the zooplankton to high total hardness and organic mater at this station.

The improvement of zooplankton diversity at station 3 over what was observed in station 2 showed the evidence of biological self purification down stream organic pollution point. This is typical of all organic pollution in lotic waters (Hart & Fuller, 1974, Mason 1981, Ogbeibu & Edutie 2002).

Station 4: There was a tremendous improvement on the water quality parameters tested for at this station. For instance DO concentration about the optimum level required for aquatic life (7.67mg/l±2.08). The station had the least C0₂ level (23.33 mg/l±9.87). N-NH₃, N-NH₄ and BOD were significantly lower than those of stations 2 and 3. This suggests reduction in organic load at this station.

The improvement in water quality at this station over others could explain the highest plankton diversity recorded at this station. Except Anabaena, Chlorella, and Aphanizomenon, all phytoplankton recorded in the entire sample collections (for all the stations) were present at this station with relatively high equitability (MDI: 0.30; SDI: 0.81).

The zooplankton group was of higher species richness and equitability than the phytoplankton (MDI: 0.66; SDI:0.88). This was also observed in other stations except at station 2 where the phytoplankton had higher equitability than the zooplankton.

Perhaps, relatively high plankton diversity recorded at station 4, which could be attributed to relatively optimal levels of the water quality parameters could be as a result of absence of effluent discharge at this station. More so, down stream location of station 4 at the reservoir could have allowed for self-purification of the water body coupled with dilution effect, which the large expanse body of water at this station could have exerted on contaminants that might have come from stations 2 and 3.

What was observed in stations 2, and 3 are some of the undesirable impact of untreated waste effluent discharge into water bodies. In order to maintain optimum environmental background level of water quality in aquatic environment so as to preserve the biodiversity there in, discharge of waste effluent should be after proper treatment. Expansion and improvement of sewage treatment works around 1960 in London within ten years resulted in dramatic increase in entire biodiversity of the water bodies in the areas (Clark 1992).