Algae are photosynthetic organisms that grow in a range of aquatic habitats, including lakes, pounds, rivers, oceans, and even wastewater. They can tolerate a wide range of temperatures, salinities, and pH values; different light intensities; and conditions in reservoirs or deserts, and they can grow alone or in symbiosis with other organisms [1]. Algae are broadly classified as Rhodophyta (red algae), Phaeophyta (brown algae), and Chlorophyta (green algae) and classified by size as macroalgae or microalgae. Macroalgae (seaweed) are multicellular, large-size algae, visible with the naked eye, while microalgae are microscopic single cells and may be prokaryotic, similar to cyanobacteria (Chloroxybacteria), or eukaryotic, similar to green algae [2]. They are a diverse group of prokaryotes with varying morphological and physiological properties and have attracted increasing interest because of their immense potential [3-5]. Their common feature is their oxygenic photosynthesis, similar to that in higher plants, and they make large contributions to the equilibrium of the earth’s atmosphere by producing oxygen and removing carbon (IV) oxide [6]. Vast interest in microorganisms obtained from extreme environments has grown considerably because they represent an innovative approach to obtaining new, underexplored resources [7].

Furthermore, microalgae can also be described as minute photosynthetic organisms that are found mostly in aquatic systems such as marine, fresh, or brackish waters, as well as in the soil and air [8]. Aquatic microalgae (phytoplankton) can be found living suspended close to the lighted surface, growing above the high tide in deep oceans (supralittorial), within the waves (intertidal), or at an at an extreme low and clear water level of about 200 m in depth (sublittorial). Microalgae can also be found living within sediments (benthonic), which includes those growing on sand (epipelic), attached to stones (epilithic), on other algae or plants (epiphytic), or on animals (epizoic) [9]. They can be a rich source of carbon compounds, which can be utilized in biofuels, health supplements, pharmaceuticals, and cosmetics. They also have applications in wastewater treatment and atmospheric CO₂ mitigation. Microalgae produce a wide range of bioproducts, including polysaccharides, lipids, pigments, proteins, vitamins, bioactive compounds, and antioxidants [10]. The interest in microalgae as a renewable and sustainable feedstock for biofuel production has inspired a new focus in biorefinery. Growth enhancement techniques and genetic engineering may be used to improve their potential as a future source of renewable bioproducts [11].

Fresh water bodies need to be constantly monitored from time to time; these include rivers, lakes, streams, wells, and springs. The river system is the most complex and one of the oldest of the freshwater bodies in the world [12,13]. Rivers are prone to pollution due to the huge anthropogenic activities that are suspected to be related to a large number of epidemics and chronic diseases suffered by humans [14,15] and the quality of water can be determined by its physical, chemical, and microbiological properties [16]. The physicochemical parameters, including pH, turbidity, dissolved salts, and hardness, can affect the biological activities of the river, and the presence of nutrients such as nitrates, sulfates, and phosphates is equally crucial for primary productivity in the aquatic environment [17].

The pollution of rivers and streams with chemical contaminants has become one of the most critical environmental problems of the century. Water pollution can cause harm to living resources, hazard to human health, hindrance to aquatic activities, and impairment of water quality with respect to its use in agriculture, industry, and other economic activities [18]. The major sources of pollution include domestic and industrial wastewater discharges, mining, surface runoff, and agrochemicals [19]. Water quality analysis is important to protect the natural ecosystem [20]. It involves the process of evaluating the physical, chemical, and biological nature in relation to natural quality, human effects, and intended uses, particularly those that may affect human health, industrial use, and the aquatic system. The most common standards used to assess water quality relate to the health of ecosystems, the safety of human contact, and drinking water. The physico-chemical parameters are very essential and important to test the water before it is used for drinking, domestic, agricultural, or industrial purposes [21]. Water quality standards have been established to regulate substances that potentially affect human health, the environment, and the aesthetic qualities of water.

Several studies have previously identified and characterized microalgae in water collected from some rivers in Nigeria [22-24]. However, there is a paucity of data on microalgae from streams in UNIZIK. Therefore, this study was designed to assess the physicochemical characteristics and green microalgae composition of UNIZIK Stream, Awka, in Anambra State, Nigeria. The stream that runs through Nnamdi Azikiwe University plays an important role in the drainage system pattern in Unizik, which is designed in a way to collect run-off water from the rain. These water sources serve as fishing sites for fishermen during the rainy season and also as a source of water for farmers for irrigation. In recent times, there has been a need to construct a dam at the University for the Development of Aquaculture. However, the background information on the quality of the water was lacking. The aim of the study is to determine the physiochemical characteristics and microalgal composition of UNIZIK Stream, Awka, and Anambra State, Nigeria.

The Study Area

The study was carried out on the streams that meandered through some parts of Nnamdi Azikiwe University in Awka South Local Government Area, Anambra State’ The study area lies along the longitude 070 06’ (E) and latitude 060 10’ (N). The stream is located at an altitude between 150 and 155 feet above sea level. The stream is a freshwater stream that flows through the school premises, then through Amansea Town, and finally drains into the Ezu River, a tributary of the River Niger. The stream has good vegetation consisting of tall bamboo trees, oil palm trees, and other rain forest trees forming a canopy along its channel, which provides shade and a favorable temperature condition suitable for aquatic organisms. The stream is also surrounded by farmlands. The analysis was carried out at the Department of Fisheries and Aquaculture Management laboratories in the same university.

Study Period

The study was conducted for a period of three months, March–May 2023, which marks the onset of the rainy season in the area.

Sampling Locations

Four sampling stations were identified on the stream. The stations were chosen based on their proximity and accessibility. Station 1 is adjacent to the Faculty of Agriculture; Station 2 is after the school hostel before the Emelola hostel; Station 3 is after the Emelola hoste; and Station 4 is before the Agric Annex. 

Collection of Water Samples

Water samples were collected randomly from the sampling stations during the sampling period. The collection of water samples was done once a week between the hours of 10.00 and 13.00.  The water samples were collected in 500-ml plastic bottles with lids by submerging the container at a depth of about 0.3m below the water surface. Prior to sampling, the bottles were cleaned with 10% nitric acid and rinsed with distilled water. Then, the bottles were rinsed three times with the stream water at the time of sampling before collection, and caution was taken not to allow any air bubbles inside the bottles. Sample bottles were appropriately labeled to indicate the date of sampling and the sampling station before they were transported to the laboratory and stored at 40 °C awaiting analysis.

Analysis of Physicochemical Parameters in the Water Samples:

The water samples were analyzed for physicochemical parameters such as temperature, pH, turbidity, dissolved oxygen (DO), electrical conductivity (EC), and total dissolved solids (TDS) using standard methods [25].

Temperature

The thermometer was inserted into the water for two (2) minutes. A temperature reading was taken once the displaced value was stable for a few seconds.

pH

The pH was measured using the pH meter, and the electrode of the pH meter was inserted into the water point for two (2) minutes, after which the value was taken once it was stable.

Dissolved oxygen (DO₂)

Samples for dissolved oxygen were taken using the BOD glass bottles (70 ml) (Boyd, 1981; Dubey and Maheshwari, 2004). The dissolved oxygen was fixed using 5 drops each of Winkler's solutions A (manganese sulfate solution) and B (alkaline iodine-azide solution).

DO₂ samples were analyzed by the titrimeteric method [26]. The DO₂ was calculated by using the following:

Where,

V = Volume of water sample used for titration

v = volume of sodium thiosulfate (titrant)

N = Normality of titrant

8 – It is a constant since 1 ml of 0.025N sodium thiosulfate solution is equivalent to 0.2 mg oxygen. (Dubey and   Maheshwari (2004)

D₂ = Dissolved oxygen (mg/l) in the second sample after 5 days of incubation [26].

Nitrite and Ammonia

Nitrite, Nitrate, and Ammonia were conducted by using LaMotte fresh water kits following the manufacturer's instructions.

Collection of Plankton Samples

The samples were filtered and collected through a plankton net. A container was attached to the plankton net, and the samples from the net were filtered and put into a container. The samples were removed from the container and stored in a plastic container. Three drops (3 ml) of formalin solution (10.0%) were added to the samples to preserve the plankton in the samples, and they were taken to the laboratory for analysis and identification.

Evaluation of Microalgae

Samples were allowed to stand for a minimum of 24 hours before decanting the supernatant. The supernatant was removed carefully until a 50-ml concentrated sample was taken. One (1) ml of subsample was collected from it and transferred into a Sedgwick-Rafter counting chamber using a stamped pipette. Identification and enumeration were done under a binocular compound microscope with a magnification 40 x 400. Three replicates of the subsamples were analyzed. Identification and characteristics of planktonic species were made by the descriptive keys by Prescot [27] and Patrick and Reimer [28]. Results were expressed as the number of organisms per mL.

Statistical Analysis

Data collected for physico-chemical parameters and microalgae were collated and subjected to statistical analysis using Analysis of Variance (ANOVA) with SPSS version 20 to determine the differences between stations and months. A one-way ANOVA was applied to determine the level of significance at p≤0.05.

The physico-chemical parameters of UNIZIK Streams, Awka, in the month of March are presented in Table 1. The results revealed a significant reduction (p<, 0.05) in the values of dissolved oxygen and pH I at Station 1, while other stations (2, 3, and 4) were within the same range. In addition to this, a significant increase (p<0.05) was observed in the values of nitrite, nitrate, and ammonia in Station 1, while other stations (2, 3, and 4) were within the same range with no significant difference (p > 0.05). Nevertheless, the values of temperature were within the same range (30.22–30.92) in all four stations under consideration. The same trends were equally observed during the sampling months of April and May (Tables 2 and 3). However, all the values of the physico-chemical parameters in UNIZIK streams obtained in this study in all stations were all below the WHO standard for a typical stream except in Station 1, where higher values of ammonia (0.07±0.01) and 0.06±0.01 were recorded in the months of April and May, respectively.

Comparative values of dissolved oxygen in the UNIZIK stream during the sampling period are shown in Figure 1. The results indicated that the values of dissolved oxygen were elevated across the sampling months, with the highest value (8.99) recorded in Station 2 in the month of May, while the lowest (4.11) was observed in Station 1 in the month of March (Figure 1). Comparatively, the values of pH during the sampling period are presented in Figure 2.The pH values were within the same range in all the stations, except in station 1, which consistently recorded lower values in all the sampling months. The values of temperature in the surface water rose in the month of March, peaked in April, and later declined in the month of May in all the sampling stations (Figure 3).

Comparatively, the values of nitrite presented in Figure 4.4 revealed that the values of nitrite in the stream declined from March to May in all the sampling stations. In the case of nitrate and ammonia (Figures 4.5 and 4.6), the values of these parameters declined from the month of March to May in Station 1, while other stations were within the same range in all the sampling months.

The microalgal species identified in the UNIZIK stream during the sampling months are presented in Table 4.4. A total of eight species of microalgae belonging to seven classes, orders, and families were identified during the study. The percentage of microalgae in all the sampling sites across the stream in the month of March is shown in Table 4.5. From the results, Closterium sp. recorded the highest percentage (60.97%) in station 2, while Bryococcus sp. recorded the lowest value (12.19) in station 2. In the month of April (Table 4.6), Bryococcus sp. recorded the highest percenyage of 58.3%, while Closterium sp. recorded the lowest (4.20%) in station 1. The percentage of microalgae in all the sampling sites across the stream in the month of May is shown in Table 4.7. Closterium sp. recorded the highest percentage (47.52%) in station 4. And Spirulina sp. had the lowest percentage of 1.24% at Station 2.

The comparative total number of microalgae in the UNIZIK stream is shown in Figure 4.7. The highest total number of all species (144) was recorded in Station 3 in the month of May. While the lowest (55) was observed in station 1 in the month of March, However, the number of algae increased from March to May. However, station 3 consistently recorded the highest number of microalgae in all the sampling months. The number of individual species of microalgae in the studied stream during this trial is shown in Figure 4.8. The highest number (8) was recorded in station 3 in the month of May, and the lowest (2) was recorded in station 1 in the month of March. However, stations 2 and 3 consistently recorded the highest number in all sampling months (Figure 4.8).

Table 1: Physico-Chemical Parameters of UNIZIK Streams, Awka in the Month of March (Mean ±SD).

Means within the same row with different superscripts are significantly different (P<0.05)

Table 2: Physico-Chemical Parameters of UNIZIK Streams, Awka in the Month of April (Mean ±SD).

Means within the same row with different superscripts are significantly different (P<0.05)

Table 3: Physico-Chemical Parameters of UNIZIK Streams, Awka in the Month of May (Mean ±SD).

Means within the same row with different superscripts are significantly different (P<0.05)

Figure 1: Comparative values of Dissolved oxygen in UNIZIK Stream during the sampling period.

Figure 2: Comparative values of Temperature in UNIZIK Stream during the sampling period.

Figure 3: Comparative values of pH in UNIZIK Stream during the sampling period.

Figure 4: Comparative values of Nitrite in UNIZIK Stream during the sampling period.

Figure 5: Comparative values of Nitrate in UNIZIK Stream during the sampling period.

Figure 6: Comparative values of Ammonia in UNIZIK Stream during the sampling period.

Table 4: Micro algae Species identified in the UNIZIK Stream during the Sampling Period.

Table 5: Percentages of Micro algae Composition in UNIZIK Stream during the Month of March.

Table 6: Percentages of Micro algae Composition in UNIZIK Stream during the Month of April.

Table 7: Percentages of Micro algae Composition in UNIZIK Stream during the Month of May.

Figure 7: Number of Microalgae in UNIZIK Stream during the sampling period.

Figure 8: Number of Species Microalgae in UNIZIK Stream during the sampling period.

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