Lake Kyoga, one of the great African lakes in Uganda is facing an increasing pressure from human activities yet there is limited information on water quality of the lake. Therefore this study determined selected physico-chemical parameters of Lake Kyoga at some landing sites (Kayei, Acholi inn, Waitumba, Masindi port) and anthropogenic activities (boat dock, waste site, garden, fishing). The parameters included temperature, pH, water flow rate, dissolved oxygen (DO), nitrite (NO 2 -) and phosphate (PO 4-P). The American Public Health Association (APHA) and Water Watch Australia protocols, standard meters, Merck’s rapid test kits and timing of a float were used to measure the parameters. The results showed that the mean temperature, pH, DO, and PO 4-P significantly (p < 0.05) varied across the anthropogenic activities. On the other hand, only temperature, pH and flow rate varied significantly (p < 0.05) across the landing sites. Lake Kyoga water flow rates were the fastest at Masindi port (0.031 m/s) and the least in Waitumba (0.021 m/s) governed by river inflow and surface vegetation cover. The mean pH (6.73 - 7.15) and DO (10.15 - 13.50 mg/l) of the lake at all the study sites were within the Environmental Protection Agency (EPA) standard values of 5.5 - 8.5 and ≥9.0 mg/l respectively. These mean pH and DO values reflect more or less neutral waters which are equally well saturated with oxygen at all the landing sites. However, areas close to the waste sites had the least oxygen levels (10.15 mg/l) followed by gardens (11.82 mg/l) while fishing areas were the most saturated with oxygen (13.50 mg/l). On the other hand, temperature (25.06°C - 25.76°C) and (0.13 - 0.49 mg/l) levels in the study sites were above EPA standards of 25°C and ≤0.03 mg/l respectively signifying warmer waters and sewage pollution at the sites. Fortunately, the NO 2 - levels were within the EPA drinking water guideline of 0.5 mg/l. The orthophosphates (PO 4-P) were highest in the waste sites (0.35 mg/l), followed by gardens (0.24 mg/l) and least in the fishing areas (0.12 mg/l). However, phosphates in the form of P 2O 5 were higher than the EPA standard value (0.5 mg/l) at Kayei (0.55 mg/l) and Acholi inn (0.55 mg/l) landing sites as well as at waste sites (0.80 mg/l) and gardens (0.55 mg/l) pointing to high nutrient (phosphorus) input at these sites. The high concentrations of nitrites in Lake Kyoga at the investigated anthropogenic activities and landing sites plus phosphate amounts close to waste sites and gardens including Kayei and Acholi inn landing sites call for vigilance in protection of Lake Kyoga through optimized planning. Hence, National Environment Management Authority should ensure proper sewage management in Lake Kyoga catchment to avoid discharge of untreated sewage into the lake. The authority should also regulate waste dumping and cultivation around the lake so as to reduce nutrient (phosphorus) enrichment.
Lake Kyoga is one of the African Great Lakes situated in Uganda, East Africa [
Unfortunately, Lake Kyoga is very vulnerable to the impacts of pollution [
Lake Kyoga (
Lake Kyoga basin experiences a bi-modal rainfall distribution pattern with two peak rainfall periods in April/May and October/November while the rest of the months (March-November) have well-spread distribution of rainfall [
Four landing sites (
At each of the landing sites (Kayei, Acholi inn, Waitumba and Masindi port), water samples and on-site measurements were taken at every established anthropogenic activity (boat dock, waste site, garden and fishing areas). For temperature, pH and DO, 6 on-site measurements were each taken during the mid morning, afternoon and evening, totalling to 18 measurements for every parameter at each anthropogenic activity. On the other hand, only 6 water samples were obtained to determine nitrite and phosphate concentrations and 6 on-site flow rate measurements taken at each anthropogenic activity, all during the mid morning period. The water samples and measurements were taken at a distance of 10 m from one another in an area of about 2500 m2. All the water sampling and measurements were done in the months of December, 2015 and January, 2016.
Dissolved Oxygen and temperature were determined using a simple DO meter [
The pH of the water samples was determined using a pH meter [
The water current (flow rate) was determined by timing a float [
Nitrite ( NO 2 − ) concentrations were determined colorimetrically using Merck’s rapid test kits [
Phosphate (PO4-P) concentrations were also determined colorimetrically using Merck’s rapid test kits [
The data were summarized in form of descriptive statistics (minimum, maximum, standard deviation, mean, standard error of the mean) and presented in tables and bar graphs. Comparisons of the physico-chemical parameters across the various landing sites and anthropogenic activities were carried out using one way ANOVA (F test) and Kruskal Wallis (H) test while relationships between the parameters explored using spearman’s correlation coefficient (rs). The above tests were done after verifications of the assumptions of normality of data and homogeneity of variance using Kolmogorov Smirnov (KS) and Levene (L) tests respectively. All the inferences were made at 5% level of significance with the analyses done using Microsoft Excel 2007 and SPSS 20 Computer packages.
The physico-chemical parameters across the various anthropogenic activities in the landing sites are presented in
Temperature as a physico-chemical parameter influences the overall quality of water through its effects on the physicochemical and biological characteristics of the water body including the rate of chemical reactions, solubility of gases e.g. oxygen etc. [
On the other hand, the low temperatures at the garden site may be due to increased mixing of the water near the garden despite the decomposition of organic matter from the garden. However, the temperature values in the study sites
Parameters | Location | Site/Activity | Min. | Max. | SD | CV (%) | Mean ± SE | Fa or Hb | p | Standard [ |
---|---|---|---|---|---|---|---|---|---|---|
Temperature (˚C) (n = 72) | Landing Site | Kayei | 24.8 | 27.0 | 0.48 | 1.87 | 25.54 ± 0.06 | 23.25b* | 0.00 | 25 |
Acholi inn | 24.5 | 26.8 | 0.57 | 2.26 | 25.39 ± 0.07 | |||||
Waitumba | 24.5 | 26.5 | 0.53 | 2.11 | 25.36 ± 0.06 | |||||
Masindi port | 24.5 | 26.7 | 0.49 | 1.94 | 25.12 ± 0.06 | |||||
Human Activity | Boat dock | 24.5 | 26.3 | 0.45 | 1.77 | 25.30 ± 0.05 | 63.19b* | 0.00 | ||
Waste site | 25.0 | 27.0 | 0.44 | 1.70 | 25.76 ± 0.05 | |||||
Garden | 24.5 | 26.5 | 0.47 | 1.90 | 25.06 ± 0.06 | |||||
Fishing | 24.5 | 26.5 | 0.55 | 2.16 | 25.30 ± 0.06 | |||||
pH (n = 72) | Landing Site | Kayei | 5.7 | 7.5 | 0.34 | 4.98 | 6.88 ± 0.04 | 21.80b* | 0.00 | 5.5 - 8.5 |
Acholi inn | 6.1 | 7.5 | 0.30 | 4.37 | 6.90 ± 0.04 | |||||
Waitumba | 6.2 | 7.5 | 0.29 | 4.26 | 6.90 ± 0.03 | |||||
Masindi port | 6.4 | 8.5 | 0.36 | 5.03 | 7.15 ± 0.04 | |||||
Human Activity | Boat dock | 6.6 | 8.0 | 0.26 | 3.77 | 7.01 ± 0.03 | 58.95b* | 0.00 | ||
Waste site | 5.7 | 8.5 | 0.52 | 7.78 | 6.73 ± 0.06 | |||||
Garden | 6.4 | 7.5 | 0.17 | 2.44 | 6.99 ± 0.02 | |||||
Fishing | 6.8 | 7.5 | 0.14 | 2.00 | 7.11 ± 0.02 | |||||
Flow rate (m/s) | Landing Site (n = 6) (F3,20) | Kayei | 0.000 | 0.024 | 0.009 | 54.39 | 0.016 ± 0.004 | 3.07a* | 0.05 | - |
Acholi inn | 0.019 | 0.037 | 0.007 | 27.58 | 0.025 ± 0.003 | |||||
Waitumba | 0.000 | 0.027 | 0.011 | 82.66 | 0.013 ± 0.004 | |||||
Masindi port | 0.015 | 0.061 | 0.017 | 54.13 | 0.031 ± 0.007 | |||||
Human Activity | Garden (n = 24) | 0.000 | 0.061 | 0.013 | 60.841 | 0.021 ± 0.003 | - | - | ||
DO (mg/l) (n = 72) | Landing Site | Kayei | 1.3 | 15.0 | 2.61 | 21.33 | 12.23 ± 0.31 | 4.48b | 0.21 | ≥9 |
Acholi inn | 5.0 | 14.6 | 2.11 | 17.67 | 11.94 ± 0.25 | |||||
Waitumba | 5.2 | 15.0 | 2.55 | 21.06 | 12.09 ± 0.30 | |||||
Masindi port | 5.3 | 14.8 | 1.89 | 15.71 | 12.06 ± 0.22 | |||||
Human Activity | Boat dock | 10.3 | 14.8 | 1.17 | 9.15 | 12.84 ± 0.14 | 79.28b* | 0.00 | ||
Waste site | 5.0 | 14.1 | 2.94 | 28.96 | 10.15 ± 0.35 | |||||
Garden | 1.3 | 14.7 | 2.03 | 17.21 | 11.82 ± 0.24 | |||||
Fishing | 11.3 | 15.0 | 0.86 | 6.36 | 13.50 ± 0.10 | |||||
Nitrite, NO 2 − (mg/l) (n = 24) | Landing Site | Kayei | 0.1 | 0.8 | 0.22 | 78.35 | 0.28 ± 0.05 | 0.45b | 0.93 | ≤0.03 |
Acholi inn | 0.0 | 0.8 | 0.26 | 83.88 | 0.31 ± 0.05 | |||||
Waitumba | 0.0 | 0.8 | 0.22 | 86.81 | 0.25 ± 0.05 | |||||
Masindi port | 0.0 | 0.8 | 0.25 | 90.85 | 0.28 ± 0.05 |
Human Activity | Boat dock | 0.0 | 0.4 | 0.13 | 69.49 | 0.18 ± 0.03 | 26.80b* | 0.00 | ||
---|---|---|---|---|---|---|---|---|---|---|
Waste site | 0.1 | 0.8 | 0.28 | 56.84 | 0.49 ± 0.06 | |||||
Garden | 0.0 | 0.7 | 0.22 | 69.99 | 0.32 ± 0.05 | |||||
Fishing | 0.0 | 0.3 | 0.09 | 68.76 | 0.13 ± 0.02 | |||||
Phosphate, PO4∙P (P2O5), mg/l, (n = 24) 1 mg/l PO4∙P = 2.29 mg/l P2O5 [ | Landing Site | Kayei | 0.0 (0.0) | 0.7 (1.6) | 0.21 (0.48) | 89.37 | 0.24 ± 0.04 (0.55 ± 0.09) | 3.99b | 0.26 | 0.5 (P2O5) |
Acholi inn | 0.0 (0.0) | 0.7 (1.6) | 0.18 (0.41) | 75.33 | 0.24 ± 0.04 (0.55 ± 0.09) | |||||
Waitumba | 0.0 (0.0) | 0.6 (1.4) | 0.16 (0.37) | 79.40 | 0.20 ± 0.03 (0.46 ± 0.07) | |||||
Masindi port | 0.0 (0.0) | 0.5 (1.1) | 0.12 (0.27) | 76.59 | 0.16 ± 0.03 (0.37 ± 0.07) | |||||
Human Activity | Boat dock | 0.0 (0.0) | 0.3 (0.7) | 0.09 (0.21) | 68.76 | 0.13 ± 0.02 (0.30 ± 0.05) | 24.22b* | 0.00 | ||
Waste site | 0.1 (0.2) | 0.7 (1.6) | 0.20 (0.46) | 59.06 | 0.35 ± 0.04 (0.80 ± 0.09) | |||||
Garden | 0.0 (0.0) | 0.7 (1.6) | 0.17 (0.39) | 70.01 | 0.24 ± 0.03 (0.55 ± 0.07) | |||||
Fishing | 0.0 (0.0) | 0.3 (0.7) | 0.09 (0.21) | 74.41 | 0.12 ± 0.02 (0.27 ± 0.05) |
*Significant (p ≤ 0.05); Min.―minimum; Max.―maximum; SD―standard deviation; SE―Standard error of the mean; CV.―coefficient of variation; F―data normally distributed and same variances; H―data not normally distributed and variances are different; Kolmogorov-Smirnov p > 0.05, normally distributed; Lp―Levene p > 0.05, same variances.
with an overall average of 25.35˚C (
pH is the negative logarithm of the hydrogen ion concentration of a solution and is a measure of whether the liquid is acidic or alkaline. It ranges from 1 (very acidic) to 14 (very alkaline) [
The least pH at the waste sites followed by garden is associated with the production of organic acids during the decomposition of organic wastes [
Fishing areas are relatively deeper portions of the lake with less organic matter hence low decomposition compared to the shallower shoreline areas used as boat dock with a lot of organic matter hence increased decomposition thus justifying the high pH in the fishing areas and the relatively low pH at the boat docks. However, the pH values in the study sites (6.73 - 7.15) with an overall average of 6.96 (
Measuring the flow rate of water is the first step to good water management [
The difference in the rate of water flow at the selected landing sites is due to their relative proximity to river Kafu that pours its waters into the lake and causes a drag of water increasing its flow. According to NEMA [
Dissolved oxygen (DO) is a useful water quality parameter and an index of physical and biological processes in water which favor solubility of oxygen [
On the other hand, DO varied significantly (p < 0.05) across the various human activities. Fishing areas had the highest DO (13.5 mg/l) and the waste sites the least (10.15 mg/l). DO values significant (p < 0.05) varied across anthropogenic activities in most of the landing sites except in Acholi inn where there was no significant difference (p > 0.05). However in all the landing sites, the fishing areas had the highest DO followed by boat dock, garden and lastly the waste sites (
The high DO in the fishing areas may be attributed to either low decomposition of little organic matter in the fishing areas or low coverage of the water surface by any vegetation mat which hinders the dissolution of oxygen. Fishermen also usually clear any surface vegetation covering to create way for fishing. The least recorded minimum DO was at the garden site in Kayei (1.3 mg/l) also attributable to decomposition of organic matter from the garden. The least minimum DO was below the minimum DO (3.8 mg/l) recorded in some of the small lakes in Kyoga basin [
The decomposition of organic matter by aerobic bacteria (which uses oxygen) forms humic acid thus lowering pH. This justifies the significant positive correlation between pH and DO (rs = 0.38, p = 0.00, n = 96). The significant positive correlation between pH and DO could also be attributed to increased photosynthesis in the lake. According to Lukubye and Andama [
Nitrite ( NO 2 − ) is one of the forms of nitrogen which usually occurs in minute concentrations with even relatively low levels in the waste treatment plant effluents since nitrogen tends to exist in the more reduced (ammonia; NH3) or more oxidised (nitrate; NO3) forms. Unpolluted waters have low nitrite (<0.03 mg/l) and values above 0.03 mg/l may indicate sewage pollution [
The high NO 2 − in the waste sites followed by garden and boat dock is due to the decomposition of organic matter (animal wastes and plant remains) from the waste sites and gardens. At low oxygen concentrations, the organic compounds (carbohydrates, proteins and lipids) in the organic matter from the waste sites and gardens usually undergo anaerobic fermentation processes forming ammonia [
The generated H+ from the oxidation of ammonia or from the production of organic acids during the decomposition of organic matter (e.g. humic acids) creates some acid conditions thus the significant negative correlation of pH with NO 2 − (rs = −0.43, p = 0.00, n = 96). Furthermore, as the decomposition of organic matter (forming NO 2 − as one of the intermediate products) generates heat, there is increase in temperature hence the significant positive correlation of temperature with NO 2 − (rs = 0.40, p = 0.00, n = 96). Fishing areas with the least NO 2 − levels are relatively deeper portions of the lake which receive less animal and human wastes hence low NO 2 − . There was also a significant negative correlation between flow rate and NO 2 − (rs = −0.52, p = 0.01, n = 24). According to Vega et al. [
The insignificant variation of NO 2 − levels in the different landing sites on Lake Kyoga may be attributed to uniform disposal of sewage (animal and human wastes) and agricultural wastes in the landing sites from the increased numbers of animals and people in the catchment. Furthermore NO 2 − levels in all the study sites were above the standard value of 0.03 mg/l [
The importance of phosphorus is mainly in regard to the phenomenon of eutrophication of lakes. Phosphorus and nitrogen promote the growth of algae leading to blooms. Orthophosphate (PO4-P) is the most readily used form of phosphates for the growth of algae [
The high PO4-P in the waste sites followed by garden and boat dock is due to the potential source of PO4-P from the wastes and plant remains from the gardens. According to Lavelle and Spain [
Aerobic decomposition of the organic matter (with the production of humic acid) to release phosphates also utilizes oxygen thus a significant negative correlation of DO with PO4-P (rs = −0.66, p = 0.00, n = 96). Furthermore, Vega et al. [
The insignificant variation of PO4-P concentrations in the different landing sites on Lake Kyoga concurs with the report by NaFIRRI [
The high concentrations of nitrites in Lake Kyoga at the investigated anthropogenic activities and landing sites plus phosphate amounts close to waste sites and gardens including Kayei and Acholi inn landing sites call for vigilance in protection of Lake Kyoga through optimized planning.
Hence, National Environment Management Authority should ensure proper sewage management in Lake Kyoga catchment to avoid discharge of untreated sewage into the lake. The authority should also regulate waste dumping and cultivation around the lake so as to reduce nutrient (phosphorus) enrichment.
The authors wish to acknowledge the technical support of National Water and Sewerage Corporation, Masindi especially during sampling and analysis of the water parameters. The authors also extend appreciation to the Department of Biology, Mbarara University of Science and Technology for the guidance and support during the entire research period and preparation of this paper.
Ongom, R., Andama, M. and Lukubye, B. (2017) Physico-Chemical Quality of Lake Kyoga at Selected Landing Sites and Anthropogenic Activities. Journal of Water Resource and Protection, 9, 1225-1243. https://doi.org/10.4236/jwarp.2017.911080