The study was carried out in the Gbondapi community, which is in the Southern Province of Sierra Leone, Pujehun District. Pujehun District is bordered by the Atlantic Ocean to the southwest and the Republic of Liberia to the southeast. Gbondapi is in Kpanga-kabonde Chiefdom, and it is situated 19.3 km away from the district headquarter town Pujehun. The study area is on the Wanjei River, which is an important local center for fish landing, informal trade, and river transport in the area. The climate in Pujehun District is tropical and humid. There is a clear rainy season from May to October and a dry season from November to April which is typical of Sierra Leone’s southern coastal zone [23][24]. Along the River Wange area in Pujehun, Sierra Leone, the key economic activities involve agriculture (especially large-scale palm oil plantations and cassava farming for value chains) and mining (diamonds, gold, construction minerals), alongside local fishing, with increasing focus on developing the agricultural value chain to boost local economies. Pujehun is one of Sierra Leone’s poorest districts, relying heavily on these natural resources, with international investment in plantations and mining being major employers of the indigenes. The Wanjei River is one of the many lowland rivers that flow from the southern Sierra Leone coastal plains. These rivers have a lot of seasonal changes. During the rainy season, the flow is higher and the surface is more connected. During the dry season, the flow is lower. This is attributed to tidal exchange and freshwater coming in from upland catchments (based on field observations and river discharge characteristics).

The samples for analysis were collected in sterilized bottles carefully taken so that no bubbling was observed during sampling to avoid influencing the dissolved oxygen result. The water temperature, Dissolved Oxygen, and pH were recorded in situ using 3-in-1 HANNAH portable water quality parameter analyzer. The pH of water samples of the water would be measured with the help of a pH Meter with a glass electrode. All other parameters were collected and analyzed by adopting the procedures that were followed by Sharma and Walia [25]. Water samples collected from the stations or selected sample sites using PETS bottles were corked, stored in the cool box with ice cubes, and transported to the laboratory immediately and stored at a temperature of below 4˚C American Public Health Association [26] to prevent vaporization and biodegradation of the analytes that are awaiting the Physico-chemical analysis [27].

The following items Motorized boat, water Quality Parameter testing kits, Global Positioning System (GPS) Device, Digital Camera, Plastic bucket/cool man, PET bottles, Masking tapes, and Markers were some of the field equipment used to conduct the experiment. Data collection design was employed and accompanied by laboratory tests to determine the levels of Physico-chemical parameters of River Wanjei and assess the effects of seasonal variation on the levels of the Physico-chemical parameters of the water body.

Sampling sites or locations within the study area were mapped out on transect (with a specified distance) and located using GPS. All coordinates and elevation were recorded (Table 1). Four sites (entrance, upper, middle, and lower) parts of river Wanjei were sampled. The sites were designated as Entrance (Site 1); Upper (Site 2); Middle (Site 3); and Lower (Site 4). During each sampling occasion, samples were taken twice a day (A for morning and B for evening) which corresponds to the highest and lowest water level. To determine the possible sources of pollution, a thorough one-day preliminary survey of sampling stations was conducted, and the proportional sources of pollution to the river were taken into consideration when choosing these sampling sites. Sampling was done in both rainy and dry seasons (October 2021-July 2022) to cover the varying activity periods and to determine the effects of seasonal variation on the levels of Physico-chemical parameters of the river under study. The sampling frequency was two days in a month. During each sampling occasion, samples were taken twice a day corresponding to the highest and lowest water level. Selected parameters of both physical (temperature, electrical conductivity, turbidity, and TDS), and chemical (pH, as well as concentrations of PO 4 3 − , NH 4 + , DO, BOD5, COD, chloride, total alkalinity, total hardness, biological properties.

Table 1. Sampling location and coordinates.

Water Samples for the analysis of water parameters temperature, pH, dissolved oxygen (DO), chemical oxygen demand (COD), biological oxygen demand (BOD), chloride, total alkalinity, total hardness, carbon dioxide, total dissolved solids, lead, copper, iron, chromium, cadmium, nickel, and manganese will be preserved and transported to a reputable research laboratory. For the preservation and the analysis of water samples of the water understudy, the standard methods of Trivedy & Goel [28]; and then APHA, 2005 will be followed. Also, the results obtained will be analyzed, compared with the WHO (World Health Organization) (Table 2) and other international standards, and discussed in brief, which has to play a conclusive role in deciding the status of water quality of the river under study. These are the health-based targets for safe drinking water quality, which are often applied when assessing surface water used for human consumption:

Table 2. WHO (World Health Organization)—Drinking Water Guidelines.

Significant variations (p < 0.05) exist among water samples and sampling regimes for the physical parameters (pH, temperature, TDS and electrical conductivity) assessed at four different sites (Table 3). The highest mean value (pH = 8.57) of pH was found at Upper stream during February 2022 sampling, while the lowest mean value of 6.70 at same location was exhibited during October 2021 sampling regime. The pH values of the four locations and the sampling regimes were within the standard level of pH for rivers (pH = 6.5 - 8.5), except for the pH value of 8.57 obtained at the upper stream for sampling in February 2022. These values are within the permissible limit of WHO and FAO set for drinking and irrigation purposes, respectively. These findings are similar to those of Shamsur etal. [29], who noted the highest mean pH value of 6.68 in Tatholia Union and lowest mean pH value of 6.52 in Gaglajur Union, Bangladesh. Jesmin [30], also found pH values of groundwater in Gaibandha aquifers ranging from 6.73 - 8.66 indicating slightly acidic to alkaline water. Temperatures across sites and sampling regimes ranged from 26.5˚C (ST-2 during February 2022) to 32.3˚C (ST-1 during December 2021) sampling regime and were found within the permissible limit of WHO standards (WHO, 2021). This result falls below the limit of other studies, that was reported to be within the range of 19.0 to 23.9˚C [31]. Thus, the average temperature of the river is favorable for aquatic ecosystem. Since it influences both the physical and chemical properties of the water as well as the organisms, temperature is a crucial component for the aquatic ecosystem. Total Dissolved Solid (TDS) values across sites and sampling regimes ranged from 28.06 (ST-4 during October 2021) to 52.74 (ST-3 and ST-2 during December 2021 and April 2022) sampling regimes. These values are far below the WHO and FAO standards level of TDS for rivers (500 and 2000 mg/L) respectively. These findings are also below the figures 120.190 mg/L reported by Alam [32]. Total dissolved solids indicate the salinity behavior of water [33]. Water containing more than 500 mg/L of TDS is not considered as desirable for drinking water supplies and water with high TDS may taste bitter, salty, or metallic and may have unpleasant odors which are undesirable or harmful to human and aquatic life [31].

Electrical conductivity (EC) values across sites and sampling regimes ranged from 124.00 µs/cm (ST-4 during July 2022) to 145.20 µs/cm (ST-3 during December 2021) sampling regime that was within the standard level of EC for river (EC = 50 - 1000 µs/cm). The ability of water to transmit electric current is referred to electrical conductivity and it is a method for determining the purity of water (Sakthivadivel etal. [34]. The presence of ions, their overall concentration, mobility, valence, relative concentrations, and measuring temperature are all known to be affected by this ability. Findings of this study indicate low mineralization. The definitions of mineralization levels vary from country to country [35]. For this study, low mineralization indicates less than 200 µS/cm, moderate mineralization indicates between 200 to 700 µS/cm, high mineralization indicates between 700 to 2500 µS/cm and super high mineralization (medicinal water) indicates more than 2500 µS/cm. The EC values of the present study exhibited low salinity compared to the EC values (255 to 497 µS/cm) found by Halim [36] that signified medium salinity of their water sampled across seasons.

Table 3. Physical parameters for water samples collected from selected sites.

MCL = maximum contaminant level accepted, LSD = least significant difference, s = site, sreg = sampling regime.

3.2.1. Major Ions and Minerals Assessed

Sodium (Na⁺) values across sites and sampling regimes ranged between 26.16 mg/L (ST-3 during June 2022) and 31.14 mg/L (ST-1 during December 2021) sampling regimes (Table 4). These values are within the standard level of sodium for both general use of water and for drinking purposes (Na⁺ = 200 mg/L). Potassium (K⁺) values across sites and sampling regimes ranged between 28.60 mg/L (ST-1 during June 2022) and 31.83 mg/L (ST-3 during October 2021) sampling regimes (Table 4). These values are above the standard level of potassium for drinking (K⁺ =< 6.0 mg/L). Magnesium (Mg²⁺) values across sites and sampling regimes ranged between 15.58 mg/L (ST-4 during December 2021) and 22.45 mg/L (ST-4 during April 2022) sampling regimes (Table 4). These values are within the standard level of magnesium for drinking (Mg²⁺ = 80 mg/L). Calcium (Ca²⁺) values across sites and sampling regimes ranged from 47.86 mg/L (ST-3 during June 2022) to 63.78 mg/L (ST-1 during February 2022) sampling regimes (Table 4). These values are within the FAO and WHO permissible level (800 mg/L and 100 mg/L respectively) for drinking water and irrigation purposes. The highest amount of calcium recorded in water samples during dry season was 63.78 mg/L in February at site-1 could possibly be as a result of the close proximity of the site to the Wharf or jetty, hence addition of waste water and introduction of sewage water along with rain could be responsible for the increase in amount of calcium [37]. The lowest amount of calcium in water was recorded during raining season, possibly due to calcium absorbed by many organisms for shell construction, bone building and flora precipitation of lime [38].

Table 4. Chemical ions and minerals in water samples collected from selected sites.

MCL = maximum contaminant level accepted, LSD = least significant difference, s = site, sreg = sampling regime.

Calcium carbonate ( CaCO 3 + ) values across sites and sampling regimes ranged between 28.21 mg/L (ST-4 during October 2021) and 33.52 mg/L (ST-1 during April 2022) sampling regimes (Table 3). These values are within the standard level of calcium carbonate for drinking ( CaCO 3 + ≤ 300 mg/L).

Sulphate ( SO 4 2 + ) values across sites and sampling regimes ranged between 6.55 mg/L (ST-1 during June 2022) and 8.85 mg/L (ST-4 during February 2022) sampling regimes (Table 3). These values are within the standard level of sulphate for drinking ( SO 4 2 + = 250 mg/L).

Chloride (Cl⁻) values across sites and sampling regimes ranged between 4.40 mg/L (ST-2 during June 2022) and 7.53 mg/L (ST-1 during April 2022) sampling regimes (Table 3). These values are within the standard level of chloride for drinking (Cl⁻ = <250 mg/L). These findings are similar to those range reported by Jindal and Sharma (2011). Fluoride (Fl⁻) values across sites and sampling regimes ranged between 1.09 mg/L (ST-4 during June 2022) and 2.01 mg/L (ST-3 during February 2022) sampling regimes (Table 3). At site ST-1, sampling regimes in December 2021 (1.43 mg/l), February 2022 (1.25 mg/l), April 2022 (1.18 mg/l), and June 2022 (1.43 mg/l) are within the standard level of fluoride for drinking (Fl⁻ < 1.5 mg/L). Similarly, at ST-2, sampling regimes Oct.-2021 (1.45 mg/l), Dec.-2021 (1.47 mg/l), Apr.-2022 (1.18 mg/l), Jun.-2022 (1.15 mg/l), and Jul.-2022 (1.38 mg/l); and at ST-3, Jun.-2022 (1.09 mg/l) and Jul.-2022 (1.21 mg/l) are within the standard level of fluoride for drinking and irrigation purposes.

3.2.2. Chemical Nutrients Assessed

Phosphate ( PO 4 3 − ) values across sites and sampling regimes ranged between 0.40 mg/L (ST-1 during June 2022) and 4.43 mg/L (ST-1 during February 2022) sampling regimes (Table 5). These values are above the standard level of phosphate for drinking ( PO 4 3 − = 2 mg/L), which may be considered to indicate pollution or increased risk of eutrophication. Site ST-2 had consistently phosphate values within the standard level of phosphate for drinking ( PO 4 3 − = 2 mg/L). Sampling at Feb.-2022 for sites ST-1 (4.43 mg/l), ST-3 (2.53 mg/l) and ST-4 (2.57 mg/l) exhibited higher values above the accepted standard level of phosphate for drinking.

Nitrate ( NO 3 − ) values across sites and sampling regimes ranged between 21.90 mg/L (ST-1 during June 2022) and 27.93 mg/L (ST-4 during December 2021) sampling regimes (Table 5). These values are above the standard level of nitrate for drinking ( NO 3 − = <10 mg/L). Ammonia ( NH 3 2 + ) values across sites and sampling regimes ranged from 0.13 mg/L (ST-3 during June 2022) to 2.63 mg/L (ST-4 during December 2021) sampling regimes (Table 5). In this present study, the measured value of ammonia is similar to that done by Mezgebe etal. [39] who obtained a range of 0.16 ± 0.01 to 0.43 ± 0.19 mg/L. The statistical analysis showed least significance differences among the studied sites. Thus, our experimental findings showed that the amount of ammonia was within the permissible limit of FAO (5 mg/L) for drinking and irrigation purposes.

Table 5. Chemical Nutrients in water samples collected from selected sites.

MCL = maximum contaminant level accepted, LSD = least significant difference, s = site, sreg = sampling regime.

3.2.3. Dissolved Gases Assessed

Important variations exist in the chemical content of water sampled across sites and various sampling regimes. Dissolved oxygen (DO) and biological oxygen demand (BOD) significantly (p < 0.05) differed among water samples assessed across sites and sampling regimes. The DO values across sites and sampling regimes ranged from 6.54 mg/L (ST-3 during June 2022) to 8.72 mg/L (ST-4 during October 2021) sampling regime that was above the standard level of DO for rivers and drinking water (WHO, 2008) (Table 6). The maximum value recorded in ST-4 may be due to the self-purification of the water along the course of the river. This is similar to study done by Mezgebe etal. [39] who recorded 10.2 mg/L in Tsaeda Agam River in Mekelle City, Tigray, Ethiopia

The oxygen necessary for the microorganism to undertake the biological breakdown of dissolved solids or organic materials in the wastewater under aerobic circumstances is known as the biochemical oxygen demand [40][41]. The biochemical oxygen demand reported from water samples from Wanjei River ranged between 1.21 mg/L to 2.18 mg/L. The highest demand for oxygen in the water was recorded during the dry season (at ST-3 in February 2022) due to the possible addition of high amount of waste from the surrounding and the addition of organic waste in river by certain human activities including are not limited to farming and pepper garden which also be responsible for the increase in BOD [42].

Table 6. Dissolved gases in water samples collected from selected sites.

MCL = maximum contaminant level accepted, LSD = least significant difference, s = site, sreg = sampling regime.