Artificial dams in the KNP are mostly shallow stagnant
water systems subject to considerable evaporation
and sedimentation. Hippo that urinate and defecate
in such dams cause a build-up of phosphate-rich
sediment. High animal densities that develop around
water points may also increase run-off of faecal
material in to the dams. Warm water temperatures,
high hippo densities and stirring up of the sediments
by the hippo result in progressive eutrophication and
cyanobacterial proliferation. Mortalities occurred
when the wind blew algal rafts to areas of preferred
drinking on the dams. That no elephant, buffalo and
hippo deaths were seen may be because these species
tend to drink at any part of the dam and wade into
the water to drink (therefore ingest water away from
the algal raft).
Small dams are important features of the landscape
for both tourists and animals in the KNP. The natural
migration of animals to wetter areas in dry seasons
and years is no longer possible. Preventing further
mortalities, particularly of threatened or endangered
species was a priority, but no easy solutions were
available in this complex habitat.
Possible control measures included reducing faecal
loading of dams, however lethal hippo removal
was not possible and burning of the veld around
(or fencing) a dam would impact large numbers of
animals. Hippo culling or adding spillways to the dams
would not remove the dense layers of hippo dung
already present on dam floors. Removing sediment
in dams by flushing them out in the wet season (in
wet years), emptying and dredging dams, the use
of copper sulphate or phosphate binders were all
considered impractical, ecologically disruptive or
unlikely to be effective. Floating booms would likely
have been disrupted by animals and/or rendered
useless by changing wind direction. In the end,
breaching the dams prevented further major mortality
events by causing the hippo to move away.
eutrophication and harmful algal blooms. Such blooms
continue to occur sporadically in the KNP (as well as
other parks and game farms) so monitoring by wildlife
managers and veterinarians is needed to detect
mortality clusters around affected dams, particularly
in early winter, that could be due to cyanobacterial
intoxication. Borehole-fed concrete troughs are less
likely to have algal blooms. Early testing of water for
the algae and their toxins is needed to confirm the
diagnosis.
Probably the most visible example of
unintended consequences, is what
happens every time humans try and
change the natural ecology of a place
– MJ Wheatley (writer and management consultant)
Roy G Bengis, Danny Govender, Emily Lane, Jan G Myburgh, Paul
J Oberholster, Dewald F Keet, Peter E. Buss and Leon Prozesky
2016 Eco-epidemiological and pathological features of mortal-
ity events related to cyanobacterial bio-intoxication in the Kruger
National Park. Journal of the South African Veterinary Associa-
tion 87(1), a1391. http://dx.doi.org/10.4102/jsava.v87i1.1391
While the recent drought has significantly reduced
hippo numbers, future solutions could include
replacing dams with artificial wetlands or adding
vegetated islands to dams. Increasing the aquatic
biodiversity would make dams less prone to
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