9 Lentic-Lotic Water System Response to Anthropogenic …
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be sufficient to do so (Avery 2012). Following the commissioning of the dam, the
lake has undergone fluctuations affecting the productivity of fisheries (Gownaris
et al. 2017). Changes in the lake littoral habitat could lead to a reduction of over
two-thirds in fishery yields (Gownaris et al. 2017), and the analysis of fisheries data
from Kolding (1995), MoLFD (2008), (KNBS 2012; 2013; 2014) comports with
fishermen reports that the diversity of fish species catch has declined over the past
five years due to littoral habitat changes.
Box 1: Ecological Impacts on Lake Nakuru
(a) The bad—In Lake Nakuru, dense suspensions of Arthrospira fusiformis
are the main and preferred food for Lesser Flamingos (Jenkin 1957;
Vareschi 1978; Kaggwa et al. 2013). This alkaliphilic cyanobacterium,
which grows well even at pH 10 (Grant et al. 1990), is the key primary
producer in soda lakes (Melack and Kilham 1974; Schagerl et al. 2016),
forming the base of the food chain and supporting large concentrations
of Lesser Flamingos (Phoeniconaias minor). Recently, cyanobacterial
toxins, mainly from Microcystis flos-aquae and Anabaena flos-aquae,
have been suggested as potentially lethal agents for Lake Nakuru Lesser
Flamingos (Nelson et al. 1998; Raini 2009; Krienitz et al. 2003; Codd et al.
2003; Metcalf et al. 2006). These changes have had significant negative
impacts on Lake Nakuru Park tourism, as flamingos are one of its major
attractions.
(b) The good—The only fish species in Lake Nakuru is the filter feeding
cichlid, Sarotherodon alcalicum grahami, introduced from Lake Magadi
in 1953 to combat mosquitos. The introduction of fish substantially
increased the diversity of the lake ecosystem by extending the food chain
to over 30 species of fish-eating birds.
Evidence suggests that lakes are warming in response to anthropogenically-driven
global warming; Lake Victoria, for example, was noted in the 1990s to be one-half
of a degree (°C) warmer than it was in the 1960s (Hecky et al. 1994; Bugenyi
and Magumba 1996), and is estimated to have warmed by >1°C between 1927 and
2009 (Sitoki et al. 2010), consistent with changes in surface temperature at tropical
elevations above 1000 m worldwide. There appear not to be any new published
data on long-term lake water temperature trends for other lakes in Kenya since the
1990s, except for the global analysis of nighttime surface (sometimes referred to as «
skin ») temperatures of lakes, including Lake Turkana, over the period 1985–2009 by
Schneider and Hook (2010). Their results show an average warming of 0.025 °C yr
−1
for lakes in the tropics, with greater warming occurring in the mid- and high latitudes
of the northern hemisphere than in low latitudes and the southern hemisphere. One
consequence of the warming could be increased lake stratification that affects fishery
productivity, as was observed in Lake Turkana in the 1980s (Kallqvist et al. 1988).
201
be sufficient to do so (Avery 2012). Following the commissioning of the dam, the
lake has undergone fluctuations affecting the productivity of fisheries (Gownaris
et al. 2017). Changes in the lake littoral habitat could lead to a reduction of over
two-thirds in fishery yields (Gownaris et al. 2017), and the analysis of fisheries data
from Kolding (1995), MoLFD (2008), (KNBS 2012; 2013; 2014) comports with
fishermen reports that the diversity of fish species catch has declined over the past
five years due to littoral habitat changes.
Box 1: Ecological Impacts on Lake Nakuru
(a) The bad—In Lake Nakuru, dense suspensions of Arthrospira fusiformis
are the main and preferred food for Lesser Flamingos (Jenkin 1957;
Vareschi 1978; Kaggwa et al. 2013). This alkaliphilic cyanobacterium,
which grows well even at pH 10 (Grant et al. 1990), is the key primary
producer in soda lakes (Melack and Kilham 1974; Schagerl et al. 2016),
forming the base of the food chain and supporting large concentrations
of Lesser Flamingos (Phoeniconaias minor). Recently, cyanobacterial
toxins, mainly from Microcystis flos-aquae and Anabaena flos-aquae,
have been suggested as potentially lethal agents for Lake Nakuru Lesser
Flamingos (Nelson et al. 1998; Raini 2009; Krienitz et al. 2003; Codd et al.
2003; Metcalf et al. 2006). These changes have had significant negative
impacts on Lake Nakuru Park tourism, as flamingos are one of its major
attractions.
(b) The good—The only fish species in Lake Nakuru is the filter feeding
cichlid, Sarotherodon alcalicum grahami, introduced from Lake Magadi
in 1953 to combat mosquitos. The introduction of fish substantially
increased the diversity of the lake ecosystem by extending the food chain
to over 30 species of fish-eating birds.
Evidence suggests that lakes are warming in response to anthropogenically-driven
global warming; Lake Victoria, for example, was noted in the 1990s to be one-half
of a degree (°C) warmer than it was in the 1960s (Hecky et al. 1994; Bugenyi
and Magumba 1996), and is estimated to have warmed by >1°C between 1927 and
2009 (Sitoki et al. 2010), consistent with changes in surface temperature at tropical
elevations above 1000 m worldwide. There appear not to be any new published
data on long-term lake water temperature trends for other lakes in Kenya since the
1990s, except for the global analysis of nighttime surface (sometimes referred to as «
skin ») temperatures of lakes, including Lake Turkana, over the period 1985–2009 by
Schneider and Hook (2010). Their results show an average warming of 0.025 °C yr
−1
for lakes in the tropics, with greater warming occurring in the mid- and high latitudes
of the northern hemisphere than in low latitudes and the southern hemisphere. One
consequence of the warming could be increased lake stratification that affects fishery
productivity, as was observed in Lake Turkana in the 1980s (Kallqvist et al. 1988).