Fertiliser is often added to ponds to increase fish yields by
increasing the availability of food organisms for fish. However,
fertilisation programs are usually ineffective in ponds with acidic
waters and sediments
3
. This reduced response is caused by two
factors. The first is a deficiency of carbon in the alkalinity
system, which cannot support high rates of photosynthesis by
phytoplankton and plants
8
. The second is the increased
adsorption of dissolved inorganic phosphorus by sediments
9
.
Phosphorus is a key nutrient for phytoplankton growth and its
availability limits phytoplankton production
8,10
. Liming
materials may be used to support fertilisation programs or to
improve productivity in acidic waters by addressing both of these
factors. Lime is generally recommended as a treatment for ponds
when total alkalinity and total hardness are below 20 mg/litre
11
.
Heavy phytoplankton growth can deplete free CO
2
which is
required by phytoplankton and aquatic plants for
photosynthesis
4,5
. Bicarbonate ions provide an alternative carbon
source for photosynthesis in the absence of free CO
2
1
. The
increase in total alkalinity resulting from properly applied liming
materials is primarily by bicarbonate ions
3
. Liming can therefore
favour greater rates of photosynthesis at times when the
availability of free CO
2
is limited, leading to substantially higher
phytoplankton densities
4,5
.
Phosphorus added to ponds rapidly disappears from solution.
Some of this dissipation is due to adsorption by phytoplankton,
but most phosphorus is removed through reaction with the
sediment to form iron and aluminium phosphate compounds.
This process is pH dependent
9
. Applying lime to neutralise the