Water is one of the most important and most precious natural resources of the ecosystem. It is essential in the life of all living organisms from the simplest plant and microorganisms to the most complex living system known as human body . All living organisms on the earth need water for their survival and growth. But due to increased human population, industrialization, use of fertilizers in agriculture and man-made activity, water is highly polluted with different harmful contaminants. Therefore it is necessary that water quality be checked at regular time intervals to avoid human diseases and biodiversity losses    .
Natural water contains different types of impurities as well as introduced impurities in different ways such as weathering of rocks and runoff of surface soils, atmospheric deposition of aerosol particles and from several human activities  . High levels of pollutants mainly organic matter in river water cause an increase in biological oxygen demand  , chemical oxygen demand, total dissolved solids, total suspended solids and fecal coli form. They make water unsuitable for drinking, irrigation or any other use .
The increased use of heavy metal pollution in agriculture and industry could result in a continued rise of the concentration in freshwater and production of chronic poisoning in aquatic animals and human . Furthermore, fecal pollution of water causes water born disease, which has led to the death of millions of people and can affect also other biodiversities in water bodies . Therefore, water quality concerns are often the most important component for measuring access to improved water sources. To ensure the safety of drinking water, acceptable quality in terms of its physical, chemical and bacteriological parameters should be checked  - .
Lake Edward is a large watershed with varied ecosystems, rich in biodiversities such as a wide variety of fish species and other aquatic resources . However, the excessive use of various agrochemicals in the nearby lands of the rivers, uncontrolled urbanization, lack of well-planned development on the river banks and population growth are increasingly polluted the watershed water ecosystems. The surrounding lands are used for agricultural activities and water of these ecosystems is generally used for irrigation purposes and drinking water for the population as well as animals. People nearby the rivers and Lake use these water ecosystems for washing their clothes, bathing, washing their cattle, etc. These anthropogenic activities may degrade the quality of water in Lake Edward basin. According to Kilham  and Lehman  , despite their ecological, evolutional and geological roles, the real ecology and chemistry of the rivers in the broad south-eastern plain, and others that flow across the western Mitumba escarpment into Lake Edward are essentially unknown and unmeasured.
However, no water quality or water quantity data exists for tributaries rivers and the lake itself, except the work of Talling and Talling  and Bagalwa et al.  , who studied the water quality in some rivers feeding Lake Edward. The results of their studies showed that water quality was suitable for aquatic life and some selected microorganisms consisting of total coliform, fecal coliform (Escherichia coli) and Vibrio cholera were present. Nevertheless, they didn’t consider in their studies heavy metals and anions concentrations, which also play a vital role in assessing water quality along with physicochemical and bacteriological (microorganisms) parameters.
A basic understanding of Lake Eduard watershed is necessary for park managers to preserve the high quality of water resources and the biodiversity using the water . This includes not only Lake Eduard, but the inflows to the lake as well. It is hypothesized that the quality of water in the catchment of the lake Eduard is deteriorated by anthropogenic activity taking place actually. Obtaining knowledge of the entire watershed could lead to a better understanding of the spawning habitat of fish and other unique biodiversities in the Lake but also in the entire Virunga National Park catchment.
The present study was conducted to assess the water quality of the ecosystems in and around Lake Edward watershed with respect to physicochemical parameters and major heavy metals concentrations, bacteriological parameters as well as macroinvertebrates assemblages.
2. Materials and Methods
2.1. Sampling Site
The study area covers Lake Edward and its catchment area in DR Congo side. The catchment of Lake Edward covers 15,840 km2. The lake is fed primarily by rivers draining the surrounding mountains. In addition, the Kazinga Channel, a 30 km-long, 1 km-wide, drowned river valley that flows from Lake George (914 m a.s.l.) to the east, is a major inflow. Lake George is mainly fed by streams draining the Rwenzori Mountains . Currently, Lake Edward overflows into the Semliki River, which runs northwards into Lake Albert and hence to the White Nile like Figure 1 shows.
The annual rainfall varies from 650 - 900 mm . The monthly mean maxima of temperature vary from 26.3˚C in January to 30˚C in September, while the minima vary from 15.5˚C to 17.8˚C. The absolute maximum temperature is of 32˚C generally in February, and the absolute minimum temperature is of 14˚C generally recorded in January, February, June and July  .
2.2. Physicochemical Analysis
Two methods were used to determine the quantity of water at the sampling sources. Discharge from rivers was measured by determining the velocity of a floating object and the total cross-sectional area of the river following the Floating Method procedure  . For source and borehole bucket and stopwatch method was used. Very easy method to estimate discharge by simply measuring the time it takes to fill a container of a known volume. This method only works for systems with fairly low flow volume. A bucket of 10 liters was placed
Figure 1. Study area and sampling sites, Lake Edward Basin Congo side.
underneath in order to capture all the discharge and a stopwatch was used to estimate the time necessary to fill the bucket .
Surface water temperature, pH, Conductivity, Transparency, Dissolved Oxygen (DO), five-day Biological Oxygen Demand (BOD5), Chemical Oxygen Demand (COD), Total Hardness, Calcium, Magnesium, Chloride, Sulphate, Fluoride, Hydro-carbonate, Free CO2, Total phosphorus, soluble reactive phosphorus, Total nitrogen, Ammonium, Nitrate and Total Suspended Solide (TSS) were measured in different sites and analyzed following the procedures described in Golterman et al.  , APHA  , Wetzel and Liken .
Samples were collected during different times of the day. At each sampling point, two water samples were collected in prewashed glass bottles. Water was collected at a depth of 30 cm, near midstream in plastic bottles at the same time, for other chemical analyses (heavy metals). The plastic bottles were rinsed before overnight with 1 M HCl and then with distilled water. At the site, bottles were also rinsed thrice with sample water before final collection. The samples were placed in a cooler box with ice for transportation at Goma Volcano Observatory laboratory. Analyses were not done immediately upon arrival at the laboratories; samples were stored in a refrigerator at 4˚C with preservation as appropriate. In situ, temperature was measured using an YSI PROFESSIONAL PLUS. The meter sensor was dipped into the water and the temperature reading was recorded after the meter had stabilized. The pH was determined using the same YSI PROFESSIONAL PLUS, which was first standardized with two buffers (4 and 10). The conductivity was also measured in situ with the same equipment. Transparency of the water was determined with the aid of Secchi disc. The calibrated disc was lowered into the water and the depth at which it disappeared observed and recorded. The level of DO in the water was determined after fixation in the field, following the iodometric Winkler’s method  . BOD5 was measured as the decrease in DO after incubation in the dark at 20˚C for five days. The BOD5 in mg/L of DO was calculated by subtracting the mg/L of DO in incubated sample bottles from the DO in initial bottles . Hydro-carbonate ( ) was estimated titrimetrically using 0.1 N HCl with phenolphtalein and bromocresol as indicators (5%). Total hardness determined by complexometric method using EDTA after added a tampon and Eriochrome T indicator. Calcium hardness also was determined by complexometric method using mirixid indicators. Magnesium was determined by subtracting the Total hardness and calcium hardness. The Chloride was determined by titration with silver nitrate and potassium chromate indicator . The sulfate was determined using gravimetrical method. TSS (mg∙l–1) was estimated by filtration of water samples through analytical filter paper (Whatman 589, 185 μm pore size), which was dried at 105˚C and pre-weighed . The nutrients (TN, , , TP and ) were determined using a spectrophotometer (UNICO 1200 at 630 nm for nitrogen and 850 nm for phosphorus). All measurements were made in duplicate. Data were compared with UNECE  ; FEPA,  and WHO  standards.
2.3. Heavy Metal Analysis
Collected sub-samples were sent to INES regional laboratory for heavy metal testing. Lead, Cadmium, Zinc, Nikel, Chronium, Selenium, Iron, and Mercurywater content were determined. For analysis of Cd, Pb, Ni, Zn and Cu direct determination by flame atomic absorption spectrometry as described in ISO 8288  was used. The test sample was acidified by adding nitric acid in order to obtain a pH of 1 to 2. An acidified sample portion of 100 ml was used for analysis. Calibration solutions were also prepared using standard solutions of 1000 ppm (Sigma Aldrich Inc.) for each element. Absorptions of calibration solutions were measured and standard curves were plotted. Test solutions were also tested and absorptions obtained were projected on the standard curves to get the corresponding concentrations. Results were reported in mg/l.
Mercury was determined using AAS method after tin(II) chloride reduction without enrichment as described in ISO 12,846  and Iron as described in ISO 6332 . Calibration curve were prepared by measuring the absorbance standard solution of respectively mercury and iron at different concentrations. Results were reported in mg/l.
2.4. Bacteriological Analysis
Samples were collected in clean, sterile polypropylene 200 mL bottles. Before the bottles were washed with deionized water and sterilized in the oven at 60˚C overnight. At the field, bottles were washed thrice before collecting sample. All samples were kept in refrigerated cool box and transported to the laboratory. All analyses were completed at the Laboratory of Bacteriology at Goma Volcano Observatory. Analyses for total coliform, fecal coliform and fecal streptococci were made in accordance with standard methods . Nutrient agars (NA), Salmonella-shigella agar, Thiosulphate citrate bile salt sucrose agar were used to determine heterotrophic bacterial, Salmonella and Shigella, Vibrio cholera respectively .
Due to insecurity reasons in the region, we were not able for streams and rivers to follow an upstream to downstream gradient. Sampling was done both for the wet season (September to May) and the dry season (June to August).
2.5. Macroinvertebrate Sampling and Analysis
The benthic macro-invertebrates were collected using a standard form hand-net of 30 cm wide, 20 cm high and 50 cm long with mesh size of 500 mm. They were collected along the river stretch in a stream direction with an effective sampling effort of 10 minutes per person . The presence of stones in the river bed and water plants were taken in the hand-net and washed in a bucket to collect macro-invertebrate attached. The collected organisms were stored and preserved in formalin 4 % on the field. Identification was made at the malacology laboratory of up to the species level when possible using the keys of determination of Needhan and Needham  and Micha and Noiset . If the species were not fund in the key, the identification was restricted to the family or genus level.
3. Results and Discussion
The highest temperature in the watershed was recorded at Vitshumbi fountain (28.6˚C) and the lowest was recorded at Muwe River (19.2˚C). This temperature is higher than the temperature recorded in Mikeno sector (16˚C to 20˚C) by Karume et al., . Temperature is an important water factor because the rate of chemical reactions increases at higher temperatures, which in turn affects biological activities and growth of aquatic organisms . The temperature was conform to the WHO recommended range of 20˚C - 32˚C and will not constitute any problem to the residents . pH varied from 9.39 in Semuliki river to 3.23 in Biondi ground water. This range is out of range of the WHO standards for drinking water . Ground water sustainability is a major challenge because the ground water is a widely distributed resource that is affected by local users and contamination . Electrical conductibility is high in Rutshuru River (1882 µS/cm) and low EC was recorded in river sans nom (38 µS/cm). These highest values in Rutshuru River show the influence of human activities on the physical quality of water in the living place where river crosses. The variation of EC is observed in all the sampling sites as also observed in other studies in the same watershed  and inrivers in Cote d’Ivoire  . Two rivers were dry during this dry season in the watershed and the discharge varied from river to river and springs during the period of study. Turbidity also varied from sampling points, but it is low in spring and fountain except in Vitshumbi fountain where turbidity is high (180 NTU). The highest value was recorded at Lubiriya River sampling site (743 NTU). Chloride varied from 156 mg/L (Katiri fountain) to 24 mg/L (Ancien Muramba). Concentrations of chloride in all the sampling sites were in the range of the WHO standards for drinking water . Dissolved Oxygen (DO) and Chemical Oxygen Demand (COD) varied in sampling sites during the dry season. Water from sampling sites was very well oxygenated. Generally the DO concentration is higher than 5 mg/L. COD and BOD5 show generally an inverse curve. When BOD5 is high COD is low. Alkalinity varied from 508 mg/L (Rutshuru River) to 4 mg/L (4 mg/L). The highest value of Total hardness was recorded in the river Lubiriya (12.32 mg/L) and the lowest in the river Kisaka and Ikanga 1 River (1.15 mg/L) but for Calcium Hardness the highest value was recorded in Ikanga 2 River (5.44 mg/L) and at Ancien Muramba (0.29 mg/L). Magnesium Hardness varied all from site to site with the highest value recorded in Lubiriya River (6.36 mg/L) and the lowest value in Kyavinyonge 800 m large (0 mg/L). The highest concentration of Sulfate was recorded in Ancien Muramba River (364.8 mg/L) and the lowest concentration in Muwe River (3.84 mg/L). Except Ancien Muramba, all other sampling sites are in the range of standards for drinking water  as indicated in Table 1. Total Phosphorus concentration is high in Lubiriya River (2.16 µmole/L) while Soluble Reactive Phosphorus concentration is high in Kisaka spring (1.63 µmole/L). Total Nitrogen and Nitrate concentration are high in Lubiriya River (29.89 µmole/L and 26.68 µmole/L). Total Suspend Solid varied also from sampling sites. The highest concentration of TSS is recorded in Lubiriya River (0.29 g/L).
There were significant occurrences in some physicochemical parameters which call for caution on discharge untreated waste into Lake Eduard. The sampling sites near populated villageson the lake shore were found to have high concentrations of pollutants. It is a common practice for people living along the lake watershed to discharge their domestic waste as well as human excreta into rivers, which transport them in the Lake. Wild and Domestic animals using the same drinking water can also contaminate the water through direct defecation and urination   and caused increase of physicochemical parameters. The high loads of pollutants were more prominent in rainy season as compared to dry seasons. Comparative results of physics parameters during the dry and wet seasons in 2015-2016 for rivers, surface lake water, springs, ground water and fountains in Lake Eduard watershed are present in Table 2.
There were in general no significant differences in the values between the wet season and the dry season (P < 0.05) in Lake Eduard watershed. But some physical parameters values increased and others decreased. Some rivers discharges could not be taken over the two period and others disappear in dry season.
Table 2. Physics parameters of rivers, ground water, lake water, springs and fountains in Lake Eduard watershed in dry and wet seasons (2015-2016).
Legend: *Discharge in L/sec, T: Torrent, ND: No data, D: Disappeared.
Heavy metal characteristics of water in and around Lake Eduard ecosystem are presented in Table 3 below.
Results reveal that the concentration of heavy metal is low in water in and around Lake Eduard to standards for natural potable water WHO . That situation is probably due to the nature of the bedrock in the watershed and localization of rivers in a forest where human activities are not common. But with the population increase in the region in search for food this situation may change and water became polluted. Then a regular checking of water quality in the region is recommended to keep the Lake Eduard pristine to diver’s heavy metal contamination.
Bacteriological analysis of water in different sampling sites is present in Table 4 below.
During the sampling period in Lake Eduard watershed, 6 types of bacteria contaminated water in and around Lake Eduard watershed. The results show that, six sampling sites were contaminated with Escherichia coli, 8 with Klesbiella, 3 with Citrobacter, 13 with Enterobacter, 1 with Salmonella and 2 with Vibrion cholera. Among the sampling points, 27 were found with one or two contaminating bacteria and 14 were found exempts with bacterial contamination. In Dry season two sampling points were contaminated with the Vibrion cholera contrary to the sampling in wet season. Vibrio cholera and Salmonella were reported in samples in Lake Eduard and its tributaries before in the study conducted by Bagalwa et al.  , their presence in the samples confirms that these bacteria are present in Lake Eduard watershed and these occur in dry season. Bagalwa et al.  carried out their study in the same watershed (Lake Eduard) collecting water from sites different from the present study, and at different time of the year, but the presence of these bacteria was also indicated. This confirms that these bacteria are present in the watershed. It was reported diarrhea diseases in some villages as Lunyansenge caused by consumption of contaminated water and
Table 3. Heavy metal characteristics (means in mg/L) of rivers, ground water, lake water, springs and fountains in Lake Eduard watershed (2015-2016).
*in brackets is the maximum value required by standards for natural potable water, in mg/l; N.D.: Not Detected.
Table 4. Bacteriological analyze of water in Lake Eduard and around the watershed (col/mL).
poor hygiene practices. This is also observed in sites where water was contaminated with Enterobacteria. This contamination of water with pathogens is reported at the source but may also occur during handling in households or other working places as reported in other studies . Inadequate protection of water collection and storage containers and unhygienic conditions contribute to contamination at home.
The results also revealed that population living in Lake Eduard watershed who consumes water from shallow wells, Lake, rivers and some fountains without treatment stands the risk of bacteria diseases as the concentration of bacteria exceeds the WHO recommended limit. However, education and awareness on health risk associated with the consumption of untreated water is necessary.
Macroinvertebrate fauna different rivers in the watershed are presented in Table 5 below during the sampling period.
Macroinvertebrate varied from river to river in Lake Eduard watershed. The highest specific richness was found in Semuliki, Musenda and Lubiriyarivers. The orders of Ephemeroptera and Diptera are largely represented in the collection. Some species are rarely found in the rivers. The Order of Tricoptera is represented with only 2 families. The presence of Bellamya contracta was reported in astudy by Brown . Snails, the intermediate host of schistosomiasis, were also found in the rivers and can contribute to the expansion of schistosomiasis in the watershed. These snails are Biomphalaria pfeifferi, Biomphalaria sudanica, Bulinus truncatus and Ferrissia burnipi .
The comparison of specific richness for dry and wet season in the Lake Eduard watershed is presented in Figure 2.
Figure 2 shows that specific richness varied in rivers from 0 to 7. The high value was recorded in the river Lubiriya in dry season while the lowest (0 taxa) was found in wet season in Karukumba and Kisaka after rivers and also in dry season in Kalibuta River. In wet season the high runoff in rivers are pointed as the source of disappearance of many taxa while in dry season Kalibuta river forms a delta distroying the habitat of macroinvertebrate. The number of individual taxa varied also from river to river during the two sampling seasons (Figure 3).
The highest number of taxa was recorded in Karukumba River with 44 individuals in wet season. In general in wet season the number of indivudual taxa was high than in dry season. But comparatively to other tropical region, this number is low .
Variation in all the physicochemical parameters, bacteriological parasites and the macroinvertebrate assemblage were recorded around Lake Eduard watershed. Although some of the parameters of rivers conform to the WHO standard for drinking water, it still needs to be treated since parameters have values that are above the WHO standard for drinking water. Some species of macroinvertebrates
Figure 2. Seasonal variation of specific richness in Lake Eduard watershed.
Figure 3. Seasonal variation of number of indivual taxa in Lake Eduard watershed.
are the intermediate host of many diseases including schistosomiasis and fasciolosis. Regular monitoring of water bodies with required number of parameters in relation to water quality to prevent the outbreak of diseases and occurrence of hazards should be considered. Bacteriological water quality should be carried out for a longer period of time to get a more clear idea about the water quality in the watershed. To understand variations of water quality in the Lake Eduard watershed, more sampling time in the watershed is needed.
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