UNU-INWEH_Water-Health Course
Case Study: POLLUTION OF LAKEWATER ECOSYSTEM: LAKE NAIVASHA
FLOWER FARMS
SUMMARY
Lake Naivasha is a shallow freshwater lake located in the center of the Rift Valley in Kenya. It is
not only an important ecological site due to its biodiversity, but also a main economic resource
of Kenya for its horticultural production and tourism development. Heavily polluted and
shrinking, Lake Naivasha is in dire trouble. Environmentalists say the cause is clear: flower
farms. The flower farms have taken water from the lake for irrigation and then dumped
pesticide-waste back into the lake. Harmful practices in the basin, such as rampant discharge of
raw sewage into the Lake, result in eutrophication and high demand on available oxygen in the
Lake. This problem has long been ignored by policymakers, but the situation has recently
reached a head due to thousands of fish and other freshwater organisms perishing in the lake.
Flower farms around the lake have adopted constructed wetland technologies to treat their wastes
prior to release into the lake’s ecosystem as a mitigation measure against the degradation of the
Lake ecosystem.
INTRODUCTION AND BACKGROUND
Lake Naivasha is a shallow freshwater tropical lake located at an altitude of about 1885m above
sea level within the Kenyan Rift Valley. The basin measures approximately 3400km2 and
extends 60 North from the equator, lying between 360 07’ and 360 47’ east of Greenwich
Meridian. The lake is located in a semi-arid environment with scarce surface and underground
water resources. It is drained by only two perennial rivers - Malewa and Gilgil. The Lake,
which has an unstable water column, is moderately eutrophic with reduced oxygen levels found
as sampling profiles meet the sediment-water interface (Hubble and Harper 2002).
LAKE NAIVASHA BASIN
Lake Naivasha watershed is a unique ecosystem because Lake Naivasha, which was declared a
Ramsar site in 1995, is the only fresh water lake within the Rift Valley. The Basin plays a very
important role in Kenya’s national development, contributing to about 70% of Kenyan flower
export, 15% of Kenyan electric power and is home to attractive tourist sites. Since independence
in 1963 the area has witnessed rapid land use transformation from commercial ranching to a
mixture of commercial ranching and rapidly growing smallholder (rural and urban) settlements
(Mireri, 2005). At the beginning of 1900s the land use in the watershed changed from pastoral
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economy to large scale white settler farming. The land use changes since independence have led
to rapid growth in population, human settlement, intensive commercial farming, tourism and
geothermal production. These have put intense pressure on natural resources in the watershed,
which threaten the sustainability of Lake Naivasha. Increased demand for scarce environmental
resources such as water and biomass has led to increased abstraction of surface and ground water
resources, depletion of forestry resources, pollution of water bodies and siltation of the lake
(Mireri 2005). The lake is an important source of fresh water in an otherwise water-deficient
zone, but is prone to natural and unpredictable fluctuation of water levels . It supports a thriving
fishery, an extensive flower-growing industry and geothermal power generation. It is home to a
wide range of aquatic and terrestrial flora and fauna, including vegetation, birds, fish and
mammals. The adjacent area is ideal for horticulture, which plays a crucial role in the
development of both the local and national economy, providing employment to more than 30 000
people. The lake and its surrounding areas are fragile ecosystems that face increasing threats
from irrigated agriculture, water abstraction, the fast-growing Naivasha Township, and human
population growth throughout the basin (Otiang'a-Owiti and Oswe 2009).
Lake Naivasha, Kenya, is currently experiencing severe environmental problems as result of
pollution from agricultural effluents and urban water surface runoff, uncontrolled water
abstraction, improper land use practices in the catchment area and proliferation of wetlands’
invasive species. These problems are exacerbated and compounded by changes in climate and
inadequate conservation interventions.
FLOWER FARMS (Fig. 1).
Kenya’s cut-flower industry has been praised as an economic success as it contributed an annual
average of US 141 million foreign exchange, 352 million in 2005 alone (Mekonnen et al. 2012) .
The industry provides income from tourism (Fig. 2), employment, income and infrastructure
such as schools and hospitals for a large population around Lake Naivasha. On the other hand,
the commercial farms have been blamed for causing a drop in the lake level, polluting the lake
and for possibly affecting the lake’s biodiversity. Some 60 flower farms line the entire lakeside,
growing cut flowers for export largely to the European Union. While the flowers industry is
Kenya's largest horticultural export (405.5 million last year) it may have also produced an
environmental nightmare. Sustainability has become a catchword in the realm of economic
growth, environmental protection and socially just development (Walmsley, 2002). Long term
protection of the environment often requires economic growth in the short term to slow down,
with the anticipated belief that it will be sustainable in the foreseeable future. It is particularly
challenging to curb economic growth in favor of ecological well-being in underemployed
communities. This is why determining how to best manage the cut-flower industry on Lake
Naivasha is extremely complicated. It is understood that a valuable resource such as freshwater
cannot simply be left untapped (Enniskillen, 1999), as an ability to develop and utilize water
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resources is linked to a nation’s ability to develop and prosper (DWAF and WRC 1996 from
Walmsely, 2002) (Cited from Keira Loukes 2008)
CONSTRUCTED WETLANDS. (Fig. 3)
To deal with the pollution problem, flower farms around the lake constructed wetland
technologies have been taunted as the solution to the pollution problems currently facing Lake
Naivasha, and have been adopted to treat their wastes prior to release into the lake’s ecosystem
(Kimani et al. 2012). Data on the efficiency of the increasing application of constructed
wetlands in flower farm wastewater treatment around Lake Naivasha, however remains scanty.
A thorough evaluation of the efficiency of the constructed wetlands in treating the flower farm
waste water effluents would go a long way in establishing National guidelines (Kimani et al
2012).
THE KINGFISHER CONSTRUCTED WETLAND
The Kingfisher constructed wetland was constructed in 2005 at approximately $40,000 and was
designed to receive approximately 45m3 of wastewater per day from pack houses (where cut
flowers are stored, graded and packaged for export), Dudu Tech houses (where production of
bio-control agents for Integrated Pest Management on flowers take place), staff canteen, laundry,
equipment and spray gears washings and septic water from wash rooms. The Kingfisher wetland
is a combined (hybrid) system of a subsurface flow system known as gravel bed hydroponics
(GBH) section and a surface flow system with three sequential treatment cells (Kimani et al
2012).
WATER QUALITY ANALYSIS
A study was conducted between October 2009 and March 2010 to measure water quality
parameters at 9 sampling stations along the Kingfisher constructed wetland system from inlet to
outlet (Kimani et al 2012). Results of this study indicated that constructed wetlands are highly
efficient in wastewater effluent treatment and can be used in amelioration of point sources of
pollution into inland water bodies. Water quality significantly improved from inlet to the outlet:
Conductivity declining from 722 µScm-1 to 514 µScm-1
 Total suspended solids (TSS), BOD, COD, total nitrogen and total phosphorous declined
significantly (P 0.05) from inlet to outlet.
 Heavy metals generally occurred in low concentrations at the inlet, but still declined in
their concentrations though not significantly.
 Water temperature decreased significantly (F8,81=12.78, P<0.05) from 23.1±0.35OC at
the inlet to 18.3±0.38OC at the outlet, except in the dry month of January.
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Mean pH changed significantly (F8,81=5.39, P<0.05) from 6.81±0.17 at the inlet to
6.65±0.10 at the outlet.
A great significant reduction in conductivity (F8,81=6.38, P<0.05) was observed as
wastewater flowed through the wetland system from a high of 722±631.86 μScm-1 to a
low of 514±14.75 μScm.
TDS (Total Dissolved Solids) decreased significantly (F8,81=6.45, P<0.05) from inlet
(357±30.92 mgl-1) to the outlet (260±7.06 mgl-1).
Changes in BOD (Biochemical Oxygen Demand) as the wastewater flowed through the
wetland system closely mirrored that of conductivity, TDS and TSS, and showed high
accumulation of pollutants in the day cell (S5). Overall the mean BOD significantly
declined (F8,81=33.64, P<0.05) from a high of 138±15.09 mgl-1 at the inlet to 72±5.49
mgl-1 at the outlet. Like other parameters, BOD increased at the day cell (S5) reaching a
high of 267±15.09mgl-1 and then decreased continually to the v-channel. Comparison of
BOD variations through time at the inlet and outlet showed the BOD to be consistently
lower than the inlet.
The mean concentration for COD (Chemical Oxygen Demand) varied significantly
(F8,81=2.32, P<0.05) along the wetland system from a high of 569±175 mgl-1 to 186±62
mgl-1 at the outlet.
The mean concentration of TN ( Total Nitrogen)at the outflow was significantly lower
(F8,81=5.02, P<0.05) than the inflows measuring 2.0±0.34 mgl-1 and 5.1±0.65 mgl-1,
respectively.
Total phosphorus concentrations in the flower farm wastewater effluents showed a
similar trend like the TN, initially increasing slightly up to the day cell when the
concentration abruptly decreased from a high of 5.5±0.82 mgl-1 to a low of 2.6±0.24
mgl-1.
The mean concentration of lead was unexpectedly low in the flower farm wastewater
effluents, ranging from undetectable levels to a high of 0.15±0.13 mgl-1. Mean
concentrations did not vary significantly between the inflow and outflow effluents
although increases were observed at sites S5 and S6 though not significant.
Like lead, copper mean concentrations were also unexpectedly low, rarely exceeding
0.08mgl-1. Mean concentrations ranged from undetectable levels to a high of 0.08±0.06
mgl-1 with an average concentrations 0.06±0.03mgl-1. The concentrations of copper at
the inflow did not differ significantly from the outflows, although a general decrease in
concentration was observed. Outflow mean concentrations for manganese were much
lower than the inflow with an average value of 0.07±0.01 mgl-1. The concentrations of
manganese at the inflow did not differ significantly from the outflows, although a general
decrease in concentration was observed.
CONCLUSION
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The Kingfisher constructed wetland in Naivasha showed high efficiency in wastewater treatment
by significantly reducing the levels of most physical-chemical constituents, nutrients and heavy
metals from the wastewater effluents. The effectiveness of the constructed wetland in waste
water treatment became most visible when temporal variation in concentration of most
parameters was compared. Most parameters showed wide temporal variations in their
concentrations at inlet but stabilized at the outlet throughout the study period. Temporal
variations of pollutants at the inlet were attributed to heightened farm activities and prevailing
weather conditions. A key function of constructed wetlands is to lower the levels of nutrients in
the wastewater effluents, which would otherwise result in eutrophication of the recipient water
bodies. This study shows that constructed wetlands are an important intervention strategy in
dealing with the pollution threats of Lake Naivasha from the surrounding farmlands. Therefore,
there is need to encourage other flower farms to adopt the Kingfisher constructed wetland
technology to deal with their wastewater effluents (Kimani et al 2012).
REFERENCES
Enniskillen (1999): The Ramsar Convention on Wetlands: The Lake Naivasha Riparian
Association (LNRA), Kenya. Interview with Chairman Andrew lord Enniskillen, by Catherine
Mgendi and Susan Matindi. http://www.ramsar.org/award/key_awards99_interview_lnra.htm
Hubble, David S. and Harper David M. 2002. Nutrient control of phytoplankton production
in Lake Naivasha, Kenya Lake Naivasha, Kenya Developments in Hydrobiology Volume
168, 2002, pp 99-105.
K. Loukes. 2008. Kenya’s Cut-flowers: An Unsustainable Industry on Lake Naivasha.
http://www.queensu.ca/ensc/undergraduate/courses/ensc501/pastprojects/Loukes.pdf
Mireri, Caleb. 2005. Challenges Facing the Conservation of Lake Naivasha, Kenya. FWU,
Vol. 3, Topics of Integrated Watershed Management – Proceedings 89. https://www.unisiegen.de/zew/.../mireri.pdf
Kimani, R.W., Mwangi B.M. and Gichuki C.M. Jan 2012. Treatment of flower farm wastewater
effluents using constructed wetlands in lake Naivasha, Kenya. Indian Journal of Science and
Technology. Vol. 5 No. 1 (Jan 2012) ISSN: 0974- 6846
Mekonnen, M.M. and Hoekstra, A.Y. and Becht, R. (2012) Mitigating the water footprint of
export cut flowers from the Lake Naivasha Basin, Kenya. Water resources management, 26 (13).
3725 - 3742. ISSN 0920-4741
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Otiang'a-Owiti, G.E and Oswe, Ignatius Abiya. 2007. Human impact on lake ecosystems: the
case of Lake Naivasha, Kenya. African Journal of Aquatic Science Volume 32, Issue 1.pages
79-88. DOI:10.2989/AJAS.2007.32.1.11.148
Walmsley, J (2002). Framework for Measuring Sustainable Development in Catchment Systems.
Environmental management. Vol. 29 (2).
IMAGES
Fig 1. Lake Naivasha Flower Farms. http://www.nigelsecostore.com/blog/wpcontent/uploads/2014/03/flower-farms-lake-naivasha.jpg
Fig. 2. Lake Naivasha is now a booming industry for international flower-growers, growing and
sending roses to the supermarkets of Europe.
http://blogs.exeter.ac.uk/fieldcourses/files/2015/01/students-in-the-flower-farm.jpg
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Fig. 3. Wetland system for recycling wastewater. http://www.green-water.org/gallery/sher2.jpg
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