9 Lentic-Lotic Water System Response to Anthropogenic …
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by human intervention (ILEC 2007) (Table 1). The rapid rate of societal growth
and change in modern times not only accelerates the types of changes that occur
under natural conditions, but also introduces novel materials and substances that
fundamentally, directly, and adversely impact aquatic ecosystem health and function. Since about the 1960s, Kenyan lakes and rivers have come under increasing and
considerable pressure from a variety of inter-connected human activities on land and
water. Deforested and degraded lands and wetlands are becoming increasingly characteristic features in the region as a consequence of the rapidly growing population
(Waktola 1999; Shepherd et al. 2000; Swallow et al. 2002; Nyingi et al. 2013). Lake,
river, and wetland ecosystems are being degraded by human activities through, for
example, catchment degradation, pollution, siltation, bank encroachment, and overabstraction (Thenya 2001; Moinde-Fockler et al. 2006; Xu 2008; UNEP 2009; SEI
2009; Onywere et al. 2011; Kiema 2013; Schagerl and Renaut 2016). Such stresses
exacerbate vulnerability to current and future climate risks (SEI 2009; IPCC 2014).
Continuously eroded lands are being cultivated, grazed, and/or settled, leading to
rapid depletion of soil nutrients and forest resources.
Increasing deforestation and/or fragmentation of habitats for varied end-uses,
such as settlement and agriculture, compromises the services of many ecosystems
(Mogaka et al. 2005a, b ; Negishi and Nakamura 2006; Thenya 2001; UNEP 2009),
and changes surface and groundwater regimes with resulting impacts on water availability for nature and human societies (Table 1). It also impacts the function and
operation of existing water infrastructure (SEI 2009). For example, 100,000 ha of the
Mau Complex was lost between 2000 and 2009, while on Mt. Elgon large tracts of the
forest were excised for human resettlement in the 1970s (UNEP 2009); both of these
water towers are catchments for rivers that drain into Lake Victoria Nyanza Gulf,
the central rift lakes, and Lake Turkana. Between 1960 and 2000, for example, Lake
Victoria Nyanza Gulf and its catchment underwent enormous ecological changes,
which are linked to a number of inter-related problems, such as rapid population
growth, poverty, land degradation and declining agricultural productivity and water
quality (Odada et al. 2004; UNEP 2006; Odada and Olago 2007). Sedimentation,
nutrient runoff, urban and industrial point source pollution and biomass burning
induced the rapid eutrophication of Lake Victoria that was seen over the latter part of
the twentieth century, resulting in invasion of water hyacinth, loss of endemic biodiversity and interelated and compounded problems for the lake environment and the
welfare of its people (ICRAF 2000). Biomass burning is also a key source of phosphorus in Lake Victoria through atmospheric deposition (Tamatamah et al. 2005).
These are still persistent issues today (Table 1).
Completed and planned development projects such as the construction and filling
in of the Gibe series of dams in Ethiopia have raised concerns about the sustainability of Lake Turkana as a consequence of reduced inflows (Avery 2010, 2012).
These are recently reported, through analysis of satellite data, to have translated to
a lake level drop of approximately 1.5 m during the filling of the Gibe III reservoir
whose construction was completed in December 2016 (Hodbod et al. 2018). Further,
although a minimum of a 10-day flood has been proposed to sustain the ecological
functioning of the lake, it is unknown whether this flood duration and size would
197
by human intervention (ILEC 2007) (Table 1). The rapid rate of societal growth
and change in modern times not only accelerates the types of changes that occur
under natural conditions, but also introduces novel materials and substances that
fundamentally, directly, and adversely impact aquatic ecosystem health and function. Since about the 1960s, Kenyan lakes and rivers have come under increasing and
considerable pressure from a variety of inter-connected human activities on land and
water. Deforested and degraded lands and wetlands are becoming increasingly characteristic features in the region as a consequence of the rapidly growing population
(Waktola 1999; Shepherd et al. 2000; Swallow et al. 2002; Nyingi et al. 2013). Lake,
river, and wetland ecosystems are being degraded by human activities through, for
example, catchment degradation, pollution, siltation, bank encroachment, and overabstraction (Thenya 2001; Moinde-Fockler et al. 2006; Xu 2008; UNEP 2009; SEI
2009; Onywere et al. 2011; Kiema 2013; Schagerl and Renaut 2016). Such stresses
exacerbate vulnerability to current and future climate risks (SEI 2009; IPCC 2014).
Continuously eroded lands are being cultivated, grazed, and/or settled, leading to
rapid depletion of soil nutrients and forest resources.
Increasing deforestation and/or fragmentation of habitats for varied end-uses,
such as settlement and agriculture, compromises the services of many ecosystems
(Mogaka et al. 2005a, b ; Negishi and Nakamura 2006; Thenya 2001; UNEP 2009),
and changes surface and groundwater regimes with resulting impacts on water availability for nature and human societies (Table 1). It also impacts the function and
operation of existing water infrastructure (SEI 2009). For example, 100,000 ha of the
Mau Complex was lost between 2000 and 2009, while on Mt. Elgon large tracts of the
forest were excised for human resettlement in the 1970s (UNEP 2009); both of these
water towers are catchments for rivers that drain into Lake Victoria Nyanza Gulf,
the central rift lakes, and Lake Turkana. Between 1960 and 2000, for example, Lake
Victoria Nyanza Gulf and its catchment underwent enormous ecological changes,
which are linked to a number of inter-related problems, such as rapid population
growth, poverty, land degradation and declining agricultural productivity and water
quality (Odada et al. 2004; UNEP 2006; Odada and Olago 2007). Sedimentation,
nutrient runoff, urban and industrial point source pollution and biomass burning
induced the rapid eutrophication of Lake Victoria that was seen over the latter part of
the twentieth century, resulting in invasion of water hyacinth, loss of endemic biodiversity and interelated and compounded problems for the lake environment and the
welfare of its people (ICRAF 2000). Biomass burning is also a key source of phosphorus in Lake Victoria through atmospheric deposition (Tamatamah et al. 2005).
These are still persistent issues today (Table 1).
Completed and planned development projects such as the construction and filling
in of the Gibe series of dams in Ethiopia have raised concerns about the sustainability of Lake Turkana as a consequence of reduced inflows (Avery 2010, 2012).
These are recently reported, through analysis of satellite data, to have translated to
a lake level drop of approximately 1.5 m during the filling of the Gibe III reservoir
whose construction was completed in December 2016 (Hodbod et al. 2018). Further,
although a minimum of a 10-day flood has been proposed to sustain the ecological
functioning of the lake, it is unknown whether this flood duration and size would