Assessment of water quality and quantity of Lake Nakuru, Kenya

Assessment of water quality and quantity of Lake Nakuru, KenyaMr. Jackson Raini , FlamingoNet, Moi Road, P.O Box 13493-20100, Nakuru, Kenya.Tel: +254733349620, +254722427222.Email: jackson@flamingonet.orgAbstract:Owing to its strongly sodic nature, Lake Nakuru haslimited uses for man. Its waters render it unsuitable forirrigation, contact sport, fishing or domestic consumption.Yet it is a highly valued national park and a majorgenerator of revenue for the local and national economy.The monitoring programme is aimed to provide concreteevidence of the nature and scale of detrimental changearising from anthropogenic activity and also serve toguide, direct and evaluate the success of conservationmeasures undertaken in the catchment.Parameters monitored in situ are; dissolved oxygen(DO mg/l and DO % saturation), electrical conductivity(Ec), salinity, pH, water temperature, oxidation-reductionpotential. Total phosphorus, soluble reactive phosphorus,and nitrogen were analyzed in the lab.The water balance model was developed throughanalysis of lake conditions - water level, salinity, as wellas climate and surface inflows, calibration, validation,test simulations. The data generated so far hasdemonstrated the high degree of natural variation thatcan occur in the lake under different environmentalconditions. Marked changes in water levels occur in thelake due to high levels of evaporative loss. This results indramatic changes in salinity and hence in theconductivity of its waters. Algal blooms occur frequentlycausing extraordinary elevations in day time dissolvedoxygen levels. Following algal crashes anddecomposition, dissolved oxygen levels plummet tocreate anoxic conditions over extensive areas in the lake.The only water quality parameter, which remainsremarkably constant in the lake, is pH. This is due to thehigh buffering capacity of the lake. By understandingthe natural variability that occurs, we are betterpositioned to recognize and evaluate impacts on the lakecaused by human activity in its catchment. Themonitoring has also enabled us to establish theconditions, which are optimal for maintaining high levelsof primary productivity, and conversely it has helpeddefine conditions that suppress normal primaryproductivity and favour the proliferation of undesirablealgal species. It has further enabled the us to consider thedirection of water environmental management of theLake Nakuru catchment in the future by analyzing waterpollution loads and water discharges reaching the lake.The water quality and quantity trends are discussed.Keywords: biodiversity, phytoplankton, water quality,1. IntroductionThe study was carried out in Lake Nakuru, a shallowalkaline-saline lake located in the eastern arm of the RiftValley Province, Kenya. The lake has a mean surfacearea of 44 km 2 , mean depth of 2.5 meters, volume of 92x 10 6 m 3 and a maximum depth of 4.5meters. The park,which occupies an area of 188 km2, has a very highconcentration of wildlife consisting of 70 mammalspecies, 400 bird species and over 200 plant species.Lake Nakuru catchment basin is a closed drainagesystem of 1800 km 2 . The Mau Forest ComplexEcosystem is presently the most threatened in Kenya byencroachment, illegal logging; charcoal burning,overgrazing, population pressure, poverty, and forestburning.The forest cover in the basin has declined from 47%in 1970 to only 7% currently. Since the lake lies at thelowest point of the catchment basin, it is the finalrepository of the sediment and nutrient loads carried byits feeder rivers. Sedimentation compromises the waterbalance of the lake and also acts as a mechanism forintroducing soil bound contaminants into the system.Soil loss from subsistence farms in the catchment hasbeen calculated to be as high as 50 ton/hectare/perannum or five times higher than would have occurredunder natural vegetative cover.The impacts of this soil loss on farm productivityand economic security are obvious. The impacts on thewater quality of streams from which the farmingcommunity draws its water are less obvious and thedanger to life arising from exposure of human andanimal populations to pesticide residues and otherpotentially dangerous leachates are least noticeable, untilthey reach epidemic proportions.Deforestation in vital watersheds, cultivation andurbanisation, individually and collectively exert effectswhich alter the hydrological regimen of an area. In theNakuru basin, this has resulted in higher run-off rates,higher and more destructive peak discharges in rivers andother water courses, marked seasonality in stream flowand significant declines in the stable yields of wells andboreholes. As the demand for water grows andabstraction rates increase, the capability of the catchmentto harvest and hold rain water appears to be diminishing.This may account for the lake uncharacteristically dryingout each year, for 5 consecutive years between 1993 to1997 and intermittently between 2003 to 2004.1

Urban discharges into the environment of Nakurupose a threat to human and wildlife. The practices ofdumping urban waste in a geologically porous andfissured areas and discharging poorly or untreatedsewage and storm water into the lake are questionable interms of environmental safety.Contamination of the lake with pesticide residues,heavy metals and other associated contaminants hasalready occurred and appears to be growing problem.Enrichment of the lake with nutrients from agriculturaland urban sources is also occurring giving rise to bloomsof toxic algae which out-compete the natural biota of thelake.Lake Nakuru can be seen as "the canary in the cage".As the focal point for the interaction of a multiplicity ofenvironmental effects brought about by natural eventsand anthropogenic activity in its catchment area, itprovides measure of the state of the environment. Thedegradation of the lake should serve as a warning that theenvironment is losing its vitality. The extinction of life inthe lake as we know it will be forewarning of the fatethat awaits the human occupants of the catchment basin.2. Methodology2.1 Data collectionIn situ measurements of basic water qualityparameters were carried out from 1992, fortnightly at 8sampling sites in Lake Nakuru and at 5 sites alonginfluent streams and sewage channels. The sites are asfollows: (a) Lake shore gauges, (b) Mouth of RiverNjoro, (c) Lakeshore drums, (d) Presidents pavilion, (e)Mouth of River Makalia, (f) Between Makalia & Nderit,(g) Mouth of River Nderit, (h) Kampi ya Nyati, and (i)Kampi ya Nyuki. River sampling sites were as follows (j)Baharini springs (k) Town sewage channel (l) RiverNjoro downstream (m) River Makalia downstream (n)River Nderit downstream. Pelagic sampling sites were asfollows: (1) Njoro River Mouth to Kambi Nyati transect(2) Drums to Sarova transect (3) PresidentPavilion to Point E transect, (4) Lake Shore gauges-Kampi ya Nyuki transect and (5) Makalia to Nderittransect.The lakeshore sites were accessed by wading. Arubber dingy or a fiber glass boat and a 15/40 hp Endurooutboard engine were used for sampling 10 mid lakesites located along 5 established transects. In the pelagiczone, water samples for vertical limnological profileswere collected at different depths (0-4m) using a plasticvan dorn-type messenger closed sample bottle with acapacity of 1.25lts. The physico-chemical parameterswere measured in situ using a WTW multiline p4portable meter. The meter is fitted with drift-controlledcombined electrodes, and has an accuracy level of ±1 ofmeasured value. Water transparency was measured usinga calibrated 20cm black and white Secchi disc.Parameters monitored were; dissolved oxygen (DO mg/land DO % saturation), electrical conductivity (Ec),salinity, pH, water temperature, oxidation-reductionpotential (ORP).2.2 Laboratory analysisLab. analysis was done on replicate samples ofwater stored in a cool box and later transferred to a fridge.Total phosphorus, soluble reactive phosphorus, andnitrogen were analyzed, in the lab using a HACHDR/2010 Spectrophotometer. Algal biomass wasestimated by using Chl a. Chlorophyll a (µg/l) wascalculated after reading the absorbance at 665 nm and750 nm. This was done after leaving the samples in arefrigerator for 23 hours in an extraction process using94.1 methanol. The Chl a represents 1.5 % of the dryweight of organic matter (ash-free weight) of algae. TheChl a content was multiplied by a factor of 67 (Standardmethods, 1998). Algae identification was done using anOlympus compound microscope.Weather data was recorded from 1993 to 2002 at theLake Nakuru National Park Weather Station No.9036359, located about 500 meters from the northernlakeshore (0o17’S, 36o04’E). River discharge volumewas measured using a Bargo calibrated OTT C 2 SmallCurrent Meter (Ref: # 10.150.005.B.E at the Baharinisprings (2FC17), R. Njoro (2FC15), R. Nderit (2FC16),R. Makalia (2FC18), R. Ngosur (2FC27). Lake levelswere measured at Lake Nakuru RGS 2FC14.The waterbalance model was developed through analysis of lakeconditions - water level, salinity, as well as climate andsurface inflows, calibration, validation, test simulations.Calibration is done by using Excel's "goal seek" tool onRMSE value, adjusting the calibration terms to minimizethat value.3. Results3.1. Water & sediment quality monitoring3.1.1 Dissolved oxygenThe dissolved oxygen trends display spatial andtemporal variations. During the study period, monthlymean DO levels in the lake were 8.7±7.7 mg/l with amedian of 7.7 mg/l (Fig 1&2). The highest levels wererecorded at theFig. 1. Mean monthly DO levels (mg/l).2

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The results showed that during the early morningsampling events the lake exhibited a slight thermalstratification. Due to the lakes' shallow depth thepersistence of the thermocline was limited to onlyseveral hours.The lake water pH was fairly constant, showingvery small fluctuations (Fig 7). The mean pH in L.Nakuru as measured at 8 sites was 10.2±0.7 with acorresponding median of 10.24. The lake wascharacterized by high phytoplankton or suspended solidscontent which inhibited water transparency. Seasonalvariations were quite distinct, with values of lower than5cm being recorded during the 1993-1997 periodcharacterized by very low lake levels. Annual meanSecchi disc transparency increased between 10cm to over25 cm in from 1997, showing much higher values duringrainfall seasons.Fig 7. Mean monthly pH at L. NakuruFig 5. Mean monthly water temperature (oC)3.2. Hydro-meteorological monitoringWater flows in perennial streams draining thebasin have become erratic and highly seasonal. The meanannual temperature ( o C) was 18.2 ±0.9, total evaporation(mm) 4,158,597; total rainfall (mm) 2,908,567, surfaceinflow from all inlets (m 3 ) was 1,033,968; ground waterinflow (m 3 ) 464,013. The lake levels fluctuated, with arecorded mean depth of 1.9 meters.Fig. 5. Mean Temperature (Vertical profile)Fig.8. Mean monthly weather parameters (Rainfall,Humidity and Evaporation)4

Fig.9. Average water balance.Fig.10. Mean monthly lake level vs. rain- evap. (mm)3.3. DiscussionThe long-term mean dissolved oxygen level ishigh (9.2±7.4mg/l). The DO levels vary from supersaturation to near anoxia as a function of stratificationand high biological activity of the productive, naturalcommunity living the lake. Super saturation of dissolvedoxygen in the upper waters during the day often resultsfrom the high rates of photosynthesis (Melack & Kilham1974, Vareschi 1982). The fish in L. Nakuru,Sarotherodon alcalicus grahami is known to tolerate DOlevels as low as 3 mg/ l. Similarly, Arthrospira fusiformisproductivity is lowered significantly at DO levels ofbelow 2 mg/l (Vareschi, 1982).The rate of change in conductivity that alsoinfluences Arthrospira growth was low, rarely exceeding2 mS/cm per week. Sampling sites located at Rivermouths recorded wide ranges due to dilution. Theconductivity of water increased from 20.38mS/cm (Sep.1973) to 23.28mS/cm (Jan. 1974) and then 25.18mS/cmby March 1974. This was accompanied by a decline ofChl a from 910-200 Chl a m-3. Detailed descriptions ofthe biotic responses are provided in (Melack 1979, 1981,1988, Vareschi 1982, Vareschi & Vareschi, 1984). Theconductivity tolerance threshold for copepod Lovenulaafricana range between 6 to 24 mS/cm (Vareschi 1982).The only water quality parameter, whichremains remarkably constant in the lake, is pH. This isdue to the high buffering capacity of the lake. The meanlong-term pH of the lake at the 8 lake sampling sites is10.2. Tuite (1978) reported a declined of pH from about10.45 in early 1974 to between 10-10.15 during most ofthe period 1974-1976. These pH changes or differencesmay among other factors be as a result of alterations inphotosynthetic activity by algae (Talling et al, cited byTuite 1978). The mean of 10.5 is that recorded by5between 1972-1979 Vareschi (1978, 1979, 1982) and isreported as the only environmental factor which remains“exceptionally constant” and unsusceptible to alkalinityand conductivity.Surface water temperature are typically 25-27oC (Vareschi, 1982) and have not changed much in thelast decade (10 year median=27.3 o C).As is typical of shallow, saline lakes, worldwide,climatic variations have caused large changes in depthand salinity on annual, decadal and longer time scalesand have had major consequences for the ecology of thelake. Daily fluctuations in heating and cooling result instrong diel cycles of stratification and mixing (Melack &Kilham 1974). High insolation and adequate supply ofnutrients usually support abundant phytoplankton (Peters& MacIntyre 1976, Melack et al. 1982, Vareschi 1982).The long term mean electrical conductivity(44.7±39.8mS/cm) is higher, compared to historicalvalues, Tuite, 1978 (mean = 23.8mS -1 ; Range: 15.3-39.28mS -1 ) Vareschi (1978, 1979, 1982) recorded a rangeof 8.5-165.5mS -1 . The lower and upper ranges have beenexceed in the last 10 years (5-222µS -1 ). The lower valueswere recorded during floods while upper ones duringdry-outs (1961 and between 1993-1997).During the study it was evident that somesamples were dominated by blue green algae formingblooms. These are Arthrospira fusiformis (=Spirulinaplatensis), Anabaenopsis magna, Anabaenopsis abijatae,Anabaena arnoldii, Anabaena flos aquae var. circinalis,Synechococcus elongates and Rhabdoderma linearis.Recently, cyanobacterial toxins were suggested aspotentially lethal agents for Lake Nakuru lesserflamingos (WWF, 1998, Krienitz et al 2003, 2005., Codeet al, 2003., Metcalf et al., 2006).The lesser flamingo and tilapia fish both sharethe same food base, which is formed by the cyanophyteArthrospira fusiformis. There have been a number ofunexplained lesser flamingo and fish die-offs in the pastin Lake Nakuru. Mass flamingo die offs in 1993, 1995,100, 2002, 2004, (Beasley et al 2005), and 2006 (Raini,2009), raised concerns regarding populationsustainability. The lake experienced high populationfluctuation. The flamingo breeding attempt at LakeNakuru in 2001 flopped and over 3000 nests abandoneddue to rapid water level recession. A fish kill occurred in1992 and fish stock failed to recover until 1998 due thepersistently low lake levels (Fig.10). As a result of thisdecline in fish population, the fish eating birds were verydifficult to find in the lake, a negative change inbiodiversity. The recent fish kill occurred in August 2004and was attributed to extreme oxygen depletion.The mean lake level has declined from 2.5 m to

1.9 meters. The preliminary water balance model is afirst attempt at understanding the lakes water budget.Better data (ground water recharge, rainfall and riverflow) should be used to re-calibrate the Water Balancemodel before a final water balance model can bedeveloped.3.2 Abbreviation and acronymsWTW-Wisesens-chaftlich Technische WerkstättenWeiheim, (Germany).DO-Dissolved OxygenWWF-World Wide Fund for Nature3.3. AcknowledgmentI wish to thank the management of the WWF and theDarwin Initiative for financing the study.3.4. ConclusionTo improve and maintain surface flows and water qualityin the catchment, more information needs to be generatedon the status of water resources, with particular emphasison the current rates of utilization and the rate ofreplenishment and other changes that may affect theavailability and quality of water. . There is also need toestablish a framework for integration of sound andsustainable practices in resource management anddevelopment with regard to initiating programmesaimed at improving and maintaining water quality andbalance in the catchment basin. A GIS database Manualfor Water Pollution & Hydrological Analysis Modulesdeveloped recently by JICA, if properly used, will helpin the calculation of pollution load, water quality, riverdischarge and lake levels.3.5 References1) Beasley Val, Aiyasami S.S, Motelin G., Pesier A.P.,Codd, G.A., Nelson M,N., Maddox C.W.,Carmichael W.W., Anderson M.D., Sileo L., KockR.A., Cooper J.E., Franson, J.C., Cooper W.E.,Kilewo, M.K., Mlengeya, T.K., Manyibe, T., RuizM.O(2006). Mass Die-offs of Lesser Flamingo(Phoeniconaias minor) in East and Southern Africa.Current Knowledge and Priorities for Research.Manuscript No. 7017 submitted to the Journal ofWildlife Diseases.2) Tuite, C.H. (1978). The lesser flamingo (P. minorGeoffroy) Aspects of its ecology and Behaviour inthe Eastern Rift Valley Lake of Kenya and NorthernTanzania, a Ph.D. thesis submitted to the Univ.Bristol.3) Harper D.M, R. Brooks Childress, Mauren, M.Harper, Rosalind R. Boar, Phil Hickley, Susanne C.Mills, Nickson Otieno, Tony Drane, EkkehardVareschi, Oliver Nasirwa, Wanjiru E. Mwatha,Joanna P.E.C. Darlington & Xiavier Escute’-Gasulla ( 2003). Aquatic biodiversity and salinelakes: Lake Bogoria national Reserve, Kenya. K.Martens (ed.) Aquatic Biodiversity. KluwerAcademic Publishers, Netherlands.4) Childress B., Harper D., Hughes B., Bossche W.,Berthold P., Querner U. (2004). Satellite trackingLesser Flamingo movements in the Rift Valley, EastAfrica: pilot study report. Ostrich, 2004, 75(1&2):57-65.5) Ballot A., Krienitz, L., Kotut, K., Wiegand, C.,Metcalf, S. J., Codd, G.A., Pflugmacher, S. (2004).Cyanobacteria and cyanobacterial toxins in threealkaline Rift Valley lakes of Kenya-Lakes Bogoria,Nakuru and Elementeita.6) Japan Bank for International Cooperation (JBIC)(2002b) Final report for special assistance forproject sustainability (SAPS II) for Greater Nakuruwater supply project in the republic of Kenya. JapanBank for International Cooperation, Tokyo, Japan.7) Ballot, A.,L., Krienitz, Kotut, C. Wiegand, J.S.Metcalf, G.A. Codd, and S. Pflugmacher,2004.Cyanobacteria and cyanobacterial toxins in threealkaline Rift Valley lakes of Kenya-Lakes Bogoria,Nakuru and Elmenteita. Journal of PlanktonResearch 26:925-935.8) ILEC (2005). Managing Lakes and their Basins forSustainable Use. A Report for Lake Basin Managersand Stakeholders. International Lake EnvironmentCommittee Foundation: Kusatsu, Japan.9) JICA (1994). Nakuru Sewage Works Rehabilitationand Expansion Project Feasibility Study FinalReport.10) JICA (2002). Final Report for Special Assistance forProject Sustainability II.11) Kenya Wildlife Service (2002). Lake NakuruIntegrated Ecosystem Management plan 2002- 2012.Plan developed in collaboration with NetherlandsGovernment, KWS, MCN, WWF, Moi University,and University of Nairobi.12) American Public Health Association, AmericanWater Works Association, and Water PollutionControl Federation.1995. Standard Methods for theExamination of Water and Wastewater, 19 th ed.American Public Health Association, Washington,DC.6