ABSTRACT
Lake Baringo waters and sediments are being impacted negatively by metal contaminants sourced from the lake’s watershed posing a human and environmental health concern. The main objective was to determine the concentration of heavy metals cadmium (Cd), copper (Cu), mercury (Hg) and lead (Pb) in water and sediments, and to characterize sediments in terms of grain size and total organic carbon and relate them to the heavy metal levels encountered at the sampled sites. 5 sites were selected and samples collected over a period of six months. Water samples were collected in polypropylene bottles and acidified with ultra-pure HNO3 to pH < 2 and stored at 4oC prior to analyses. Sediments were collected using a grab sampler and analyzed for total extractable metals using the multi-acid digestion method. Particle size classification was done by standard method of analysis by sieving and organic carbon (OC) was estimated using the Loss on Ignition (L.O.I) method. Data obtained was tested for normality and homogeneity of variance. Heavy metal concentrations were compared using analysis of variance (ANOVA) to test for differences among sites (α = 0.05). Pearson correlation was used to establish inter metallic relationships. Mean values of the physico-chemical parameters studied for all sites (pooled data) were as follows: E.C. 374.19±0.5μScm-1, pH 7.62±0.03, temperature 28.4±0.15°C, T.D.S. 373.6±0.5 and salinity 0.12±0.05%. There were significant differences between the sites for all parameters measured (p<0.05) except for percent salinity (p=0.739). The range mean concentrations of heavy metals in water were as follows Cu (0.4–0.7), Cd (0.6– 0.8) and Hg (0.003-0.005) ppb. The range of mean sediment concentrations (in mg/kg) were as follows: Cu (6.95-17.0), Cd (1.04–1.21), and Hg (0.18–0.27). Sites with higher percentages of silt and clay recorded a higher concentration of Cd and Cu same as to the percentage of TOC. Mean concentrations of heavy metals in water and sediments columns showed that a greater percentage of Cu (90.2 %) was retained in sediments while Cd and Hg released a greater percentage to the water column compared to what was in the sediment (36.8 % and 29.8%). Over 95% of the concentrations of Cd and Hg in water and sediments were significantly lower than those recommended by the WHO and USEPA as drinking water guideline values. The findings can be useful in policymaking with regard to environmental management and conservation of regional lakes facing similar challenges. Information on metal concentrations in the lake’s freshwater can also be used in protecting human health. Further research on metal partitioning in water and sediments is recommended.
CHAPTER ONE
INTRODUCTION
Background information
Management of natural resources such as water, soils and vegetation in semi-arid regions is an issue of concern in many countries. This is the case for Kenya where most of the population lives in the crowded areas of the country with moderate to high rainfall (Johansson and Svensson, 2002). In Kenya, arid and semi-arid land (ASAL) covers 80% of the country and around 30% of the population lives in those harsh ASAL areas (Johansson and Svensson, 2002). The rapidly growing human population has lead to the expansion of the agricultural activities to the semi-arid regions that are fragile and vulnerable to anthropogenic activities. The growing population, combined with limited land scarcity in the agriculturally productive highlands has led to increasing immigration to marginal areas in spite of their ecological limitations. But since those marginal and moisture deficit regions are vulnerable, to the increased population, the exerted pressure has often resulted in severe degraded land, soil erosion and sedimentation of open water bodies including lakes and rivers.
Lake Baringo is centred at 00°32'N 036°05'E and is Kenya’s third largest freshwater lake in Kenya. It is internationally recognized for its biodiversity Ramsar Site no. 1159 (www.ramsar.org). The larger part of Lake Baringo watershed is characteristic of semi- arid environment and faces many challenges among which soil erosion (Onywere et al., 2014) and water pollution is also high. These have deteriorating effects not only on the land resources, the soil productivity and the size of available agricultural land but also on open waters, as streams and lakes, through its detachment, transportation and deposition of sediments. The sediments and runoff by extension then become sources of contamination to most water bodies that serve as drinking water sources for many people living in the surrounding areas.
More recently there have been environmental impacts of far reaching dimension on both human and livestock health, brought about by an invasive plant species Prosopis spp. (Mathenge plant) introduced to the area to control erosion and provide fodder for livestock, the basis of livelihood in the area. The concerns on prosopis spp. are on lowered water table and a threat to the lake shoreline plants. In addition the area is a highly fragile ecosystem with impacts on water quality from geothermal manifestation. The drainage into Lake Baringo is via Molo River which collects water from the Mau Escarpment as far south as Elburgon Forest, and is structurally controlled, following the troughs between the fault scarps or the base of the fault scarps in its flow northward. It flows through the Loboi plain into the lake. Ndoloita hot springs are also controlled by the Ndoloita fault scarp, and take its waters into the Loboi Swamp on the northern end of Lake Bogoria. From the swamp the river flows north into Ngarua swamp where it joins the Molo, into Lake Baringo, 23 km north of Lake Bogoria. Perkerra River also provides significant recharge into the lake (Onywere et al., 2014).
The increase in human population in the drainage basin of Lake Baringo has exerted pressure on the available water resources which has led to a decline in the quality and quantity of water and other resources within the lake. The number and population of urban centres in the lake’s drainage basin have been on the rise over the years posing a threat to the lake’s survival. It is subject to direct deposits mainly from sources such as anthropogenic activities, runoff, the atmosphere and erosion due to its exposure. Studies have shown that water quality can be negatively impacted by such activities and thus rendered unsafe for aquatic life and human use (Oduor, 2003; Ogendi et al., 2007; Ogendi et al., 2014).
Previously published records of the lake Baringo levels show significant rise and flooding of the mudflats and the ring of acacia forest around the lakes in 1901 and 1963. The flooding being witnessed during this study suggested a return of a 50 year cyclic climatic event (Onywere et al., 2014). The increase in water volume has been significantly high and the input from the rivers recharging the lakes has been consistent, indicating that the flooded situation will not cease soon. The flooding has had immense and detrimental effects on the ecosystem, the settlements, the infrastructure and the biodiversity. Despite the recent rise in lake levels, some studies have shown that during the last decades both the depth and the area of Lake Baringo have decreased dramatically. For instance, a study by Johansson and Svensson (2002) reported that the shrinkage of the lake was due to both siltation and inadequate inflow of water volumes to the lake creating a negative water balance. The change in land-cover (for example deforestation) around the catchment area causes an increase erosion and sediment transport to the lake and changes in hydrologic pattern but that could be amplified by changed rainfall conditions. Deforestation in the catchment area is on the rise mainly as result of extensive overgrazing, charcoal burning and expansion of human settlements. The changed land cover is in many respects an effect of the increased population combined with the large social importance of livestock.
The main town near the lake is Marigat, other smaller settlements include Kampi ya Samaki and Loruk. All these urban centres have contributed increased population density and enlarged spatial expansion over the last few decades. Lake Baringo contributes to the economy of the country as well as community livelihoods through tourism which is the major activity in this area and boating. The lake is threatened by irrigation activities through the abstraction of large volumes of water from both the lake and the inflowing rivers. For instance, Perkerra Irrigation Scheme utilizes over 70% of the Perkerra River water leaving 30% to flow into the lake (Oduor, 2003). Pastoralism and agro-pastoralism are also the major activities practiced by the residents including the Ilchamus, Rendille, Turkana and Kalenjin, threatening further the lake through sedimentation and increase in erosion. Lately the lake’s water level has steadily increased leading to submergence of some of the infrastructure on its shores, crop failure and mass displacement of people and livestock (Lake Baringo, 2012).
Studies by Johansson and Svensson (2002), report that anthropogenic activities on the shores as well as on the drainage basin of Lake Baringo have led to the degradation of the lake and the land-water ecotone in the recent past. The lake basin is shallow and has no known surface outlet. The waters are assumed to seep through lake sediments into the faulted volcanic bedrock therefore serving as a sink for the contaminants emanating from anthropogenic activities. Heavy metals constitute some of the contaminants that are of major concern to human health workers, tourist entrepreneurs, wildlife, fisheries managers, and conservationists owing to their ability to accumulate in the lake sediments. Pollutants in the surrounding and/or underlying environments enter into water bodies and have been shown to affect aquatic life depending on their chemical speciation, toxicity, bioavailability, rate of uptake and metabolic regulation by specific organisms.
Studies on basic physico-chemical characteristics carried out in various rivers and lakes have focused on the water quality parameters with little or no consideration given to the bottom or sediment characteristics. Sediment analyses are carried out to evaluate qualities of the total ecosystem of a water body (Nnaji et al., 2010). Studies point out that soils and sediments are repositories for physical and biological debris, and they are considered to be the ultimate sink for a variety of toxicants because pollutants may persist in sediments long after the original sources of contamination are eliminated. In the hydrologic systems, sediments serve as an indicator of contamination since it is a media for metal uptake and also due to their high sensitivity compared to water. Soares et al., (1999), reported that sediments have the capacity to accumulate and integrate low concentrations of trace elements in water over time allowing the possibility for metal determination even when levels in overlying waters are extremely low and undetectable.
Increased metal loads in lake water and sediments are a human health concern due to bio-magnification of metals along the aquatic and terrestrial food chains and food webs. Human health risks are primarily due to the elevated concentrations of copper, cadmium, lead and mercury in water and fisheries that are part of the local people’s diet. For instance, Cadmium has been linked to kidney and liver damage as well as osteoporosis and pulmonary emphysema as was the case in Japan where people consumed rice cultivated using cadmium-contaminated irrigation water (Dipankar et al., 1999). The goal of this study was to determine the physicochemical parameters of water and the characteristics of sediments. Additionally, the study sought to assess the sources and the concentration of heavy metals in water and sediments on a spatial scale on Lake Baringo.
Statement of the problem
The presence of inorganic and organic pollutants including heavy metals in Lake Baringo is an issue of concern as their presence impairs the water quality. This in turn affects the health of human who consume the metal contaminated water and fish. Communities that live within the basin of the Lake Baringo (Tugens, Pokots and Illchamus) depend on the lake as a source of water for various purposes (drinking, cooking and agriculture). Local regulations aimed at improving the quality of freshwater ecosystems have been important steps in achieving improved ambient water quality conditions. The area has been experiencing high rates of sedimentation caused by the increased soil erosion impairing sediment quality. However, the sediments of aquatic ecosystems have not received this same attention. This is surprising and unfortunate, as sediments and the associated benthic organisms are critically important in maintaining the health and productivity of aquatic ecosystems. In a healthy aquatic community, sediments provide a habitat for many organisms but with increased sedimentation, the interstices of gravel and cobble stream bottoms, greatly decreasing the spawning areas for many fish species and the habitat for macroinvertebrates, which serve as food for many fish species. Sediments carry along with them organic matter, animal or industrial wastes, nutrients, and chemicals. Due to the different land use activities carried out in the area, the sediments transported also may contain some toxic substances such as pesticides which may contain heavy metals and depending on their properties, such as toxicity, solubility and chemical breakdown rate they may pose a greater danger to aquatic plants and animals and eventually to human health. Presence of heavy metals in a water body affects the quality of water and sediments which therefore impact the aquatic organisms from the macroinverterbrates to fish of which through biomagnifications, the health of humans especially those who consume fish (food fish) are at risk.
Objectives
Broad Objective
The overall objective was to investigate the influence of anthropogenic activities and sediment characteristics on water and sediment quality in Lake Baringo.
Specific Objectives
1. To determine the physico-chemical characteristics of water at selected sites of Lake Baringo.
2. To characterize the sediments (grain sizes) of lake Baringo study sites and total organic matter.
3. To quantify the concentration of selected heavy metals in lake water and sediments from selected sites of Lake Baringo (Pb, Cu, Cd and Hg) and compare with the recommended WHO/EPA values.
Hypotheses
1. There is no significant difference in physico-chemical variables of lake water irrespective of anthropogenic disturbance levels.
2. Sediment characteristics (grain size) and organic matter is the same among the selected sites.
3. There is no significant difference in the concentration of heavy metals in lake water and sediments collected from the different sampling points and their concentrations are within the range recommended by WHO/EPA.
Justification
Pollution in aquatic ecosystems by inorganic chemicals is a major threat to the aquatic organisms including fishes. Runoff water containing pesticides and fertilizers and effluents of industrial activities and sewage effluents have been cited as the main sources of heavy metals (Saeed and Shaker, 2008). The most common anthropogenic sources of metals are industrial, petroleum contamination and sewage disposal. As mentioned earlier, Lake Baringo is a fresh water lake which is important to the population of its drainage basin as a source of water for domestic use and for watering livestock, a source of fish (food fish) for the local community, a source of vegetation products which are used in boat construction and also of great economic value through tourism and the conservation of biodiversity. The high dependence on the water body has led to decline in the water levels as well as deterioration in water quality. Pollution in this lake is attributed to agricultural and horticultural as well as domestic and industrial activities in the lake’s catchment. The heavy metal pollution is exacerbated by the haphazard solid and liquid waste disposal practices from the surrounding urban centres.
Pastoralists in the area also keep large herds of cattle which overgraze the catchment vegetation leading to enhanced runoff, soil erosion and sedimentation in streams and the lake. The sediments are considered to be the ultimate sink for a variety of heavy metals and other toxicants which can affect the survival of aquatic organisms.
Elevated heavy metal levels can cause adverse effects not only to aquatic organisms but also terrestrial organisms like humans that utilize water and food items from the lake. Heavy metals from the sediments make their way into the food chain, accumulating in fish, water birds and other wildlife. The fact that human and environmental health is likely to be negatively affected through consumption of heavy metal-contaminated fish justifies this study. We need to have adequate information on the levels, sources and likely effects of heavy metals in the lake. The study specifically identified the potentially toxic metals; quantified their concentrations in the water and sediments at some selected sites in the lake and related them to the WHO/EPA guidelines.
The information obtained can be used by relevant institutions such as NEMA, KMFRI, WRMA, MoH and managers of the lake among others in the management and conservation of such water bodies, and in issuing fish and water consumption advisories and therefore preventing humans from the adverse effects of consuming heavy metal-contaminated water and fish. Such information can also greatly contribute to a comprehensive environmental policy for water bodies receiving metal pollutants from adjacent areas.
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Item Type: Kenyan Topic | Size: 67 pages | Chapters: 1-5
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