Environmental Engineering Reference
In-Depth Information
the inter-trophic effects in the food chain cascade down
the food chain:
12.3.4 Lake biomanipulation
Lake biomanipulation or foodweb manipulation has
become a routine technique for improving water
quality of lakes and reservoirs (Kasprzak et al. 2002).
The technique has an ecological basis (Reynolds 1994)
and therefore complements the methods involving
nutrient reduction for lake restoration. If applied in
conjunction, biomanipulation and nutrient reduction
measures can speed up the process of lake rehabil-
itation. Conceptual works culminating in two import-
ant hypotheses have greatly enhanced our insights
into foodweb relationships: (i) the size-efficiency
hypothesis (Brooks & Dodson 1965, Hall et al. 1976)
and (ii) the cascading trophic interactions hypo-
thesis (Carpenter et al. 1985). The hypotheses together
elucidate ecosystem functioning and structure, and
inter-trophic feedback effects. The size-efficiency
hypothesis enhances our insight into the fish-
zooplankton dynamics, in that fish will tend to prey
most heavily on the largest zooplankton taxon,
Daphnia . According to the trophic cascade hypothesis
Piscivorous fish
planktivorous fish
zooplankton
algae
In short, the lake foodweb is influenced by nutrient
inputs (bottom-up control) on one hand and zoo-
plankton grazers and predatory fish (top-down) on the
other (Fig. 12.8). Intensifying predation by carnivor-
ous or piscivorous fish will trigger changes that will
lead to a decrease in the biomass of planktivorous
fish and an increase in that of zooplankton, especially
that of larger-bodied Daphnia spp. These changes
will culminate in a reduction of phytoplankton biomass
and lead to improvements in water clarity and the
promotion of diverse biological communities (Perrow
et al. 1997, Perrow & Davy 2002a, 2002b). Among
Reduction,
removal
Restocking
PLANKTIVORES:
FISH
Predation
Predation
Inoculation?
Piscivores
Bioturbation
S
Refuges
Limitations
Zooplankton
LIGHT
Macrophytes
Shading
Uptake
Reduction
in inflows
Grazing
Competition
Interference,
toxicity
ALGAE
Nutrients
N, P
Uptake
Fig. 12.8 A simplified diagram of top-down and bottom-up control measures in the foodweb of shallow lakes.
Nutrient reductions in the inflows and major biomanipulation measures are indicated with arrows. Among the
latter, fish-stock manipulation (reduction of planktivore standing stock and restocking with pike or pike and perch)
are the main steps. Refuges for young fish and zooplankton against predation by fish are created by fixing stacks
of willow twigs to the lake bottom. From Gulati and van Donk (2002).
 
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