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commonly occurring substance, far higher
than any metals for example.
This high specific heat capacity of water is
vital in biology; it means that water can buffer
changes in air temperature. As such, on the
hottest day ever recorded in the UK (when
the mercury soared to 38.5˚C in Faversham
in Kent) the temperature of lakes, ponds and
rivers would not have risen equally high.
Data on the average temperatures in these
freshwater environments across the country
would be rather meaningless as they are all
so variable, however data from the Met Office
for UK sea-surface temperatures reveals a rise
of about 0.7˚C over the past three decades,
and we can infer average freshwater
temperatures are rising slightly too.
HOT SUMMER WEATHER:
WHAT CHALLENGES DO
PONDKEEPERS FACE?
It is the extremes of weather than can be a
problem for pondkeepers. In the intense heat
of a hot, dry summer, the main challenge for
outdoor fish is meeting their oxygen demands.
Warmer water can hold less oxygen, yet at
higher temperatures the fish require more
oxygen because their metabolic rate depends
on the water temperature.
As a result, in the summer months
pondkeepers must ensure they are aerating
their ponds as much as possible, via
fountains, waterfalls or with an air pump. Look
out for signs of oxygen distress in your fish,
such as gasping at the surface or hanging
around filter outlets or waterfalls where the
dissolved oxygen is marginally higher. With
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the help of Tetra’s Test O2 kits, pondkeepers
can test oxygen levels in their pond easily and
precisely, allowing them to react before it gets
too serious.
It’s also worth mentioning that shallow
ponds are much more susceptible to an
increase in temperature in hot weather, with
a subsequent drop in dissolved oxygen. A
pond for goldfish should be at least three ft
deep in places, for Koi carp, a five ft. depth is
a minimum. What’s more, do not rely on so-
called ‘oxygenating weeds’, as these will add
precious oxygen during the daylight hours, but
this will cease at night.
It is not only the pond fish that are
susceptible to deoxygenation, the precious
bacteria that colonise the biofilter, breaking
down toxic waste ammonia into nitrate are
also utterly dependent on dissolved oxygen.
With this in mind, the vigilant pond keeper
should be testing ammonia and nitrate
levels in the pond water frequently. The
concentration of both should be zero, as any
rise above this could be a symptom of these
bacteria struggling due to a lack of oxygen.
Tetra’s Pond FilterStart Bacteria can help ponds
recovering from an oxygen shortage, as it
combines two types of natural, highly active
bacteria to promote optimal pond care. The
solution is able to boost effective biological
filtration and eliminate ammonia and nitrate,
helping to replenish lost bacteria to restore
biological balance in your garden pond.
COMBATTING COLDER
WEATHER
When considering climate change in the UK,
we tend to focus on hot weather, but in fact the
Met Office predicts that over the year, and on
average, we will see more extreme weather
events. Hot summers may be a more common
feature, but there may also be extremes of
precipitation or sudden extremes of cold
weather in the winter months.
For the pond keeper in winter this presents
some very unique challenges. Oxygenation is
rarely a problem for ponds in cold weather. In
winter, the water is around 4˚C, and will hold
much more dissolved oxygen than it could
in the summer, yet the metabolic rate of fish
has decreased so they require less oxygen.
Any aerating devices still running are likely to
cool the water too much for the fish, as they
circulate the pond water in contact with the
icy cold air. In winter, the pond water can be
circulated near the surface, only minimising
the contact between water and air. Fish must
still be monitored for signs of oxygen distress,
but this is unlikely in winter, compared to high
summer.
In summary, the changing UK climate
poses huge challenges for pondkeepers. The
unique properties of water mean that rapid
profound changes in water temperature
will not arise, however, sustained
seasonal weather extremes should be on
pondkeepers’ radar. Looking out for signs of
water deoxygenation in long bouts of dry,
warm weather, as well as monitoring your
pond’s aerating features during the colder
months is advised, to ensure the water quality
of your garden pond is not compromised,
providing an optimum environment for your
fish through the seasons.
June 2019