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Water
temperature
Well the water temperature is obviously one of the most important
weather
factors when you're in the pond so there's a separate wireless
temperature
set up with the sensor in the pond - at a depth of about 15-20cm. |
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On the right:
wireless sensor box poorly disguised as part of a plum tree - the
sensor
cable comes down the right side of the tree between two of the
flagstones
and you can see where it goes down the liner and into the pond. The
aerial
of the transmitter is at the top left of the box.
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The graph on the left
shows the pond water temperature over the previous 24 hours or so. The temperature sensor is fairly accurate but not particularly precise - it only records to the nearest degree Fahrenheit (an obscure unit of temperature used in the USA, where this kit was designed) which it then converts to Celsius. So the temperature seems to stay the same for a long time - then jumps about half a degree. Because of the large thermal capacity and inertia it takes a long time for the pond to cool down or warm up - in a normal day you will find the lowest temperature of the day is often an hour or so after dawn and the warmest temperature is often around dusk. |
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Compare the graph of the outside air temperature over the previous 24
hours - on the left - with the graph above it. The pond
temperature usually changes much less than the air temperature and lags
behind - so on a warm day the hottest part of the day might be around
13:00-14:00 GMT and yet the pond is only just starting to warm up then.
Remarkably the frogs lay their first frogspawn very early in the year often around the start of March. Most of the pond life becomes more active as the temperature of the water rises - the fish spend much of the winter deep n the pond and the newts and frogs overwinter out of the pond. |
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Even
when the pond is completely frozen over, the water below the ice
stays at about 4C (the temperature at which liquid water is most
dense). The pond water at a modest depth stayed at about 4C
throughout the cold spell in late January 2004 - when the photo on the
left was taken - for about 5 days. The main reason to add a hole in the
ice (using a pond heater or warm water please - not a hammer) is to
allow waste gases to escape (and allow a little more oxygen to diffuse
in). |
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| Water
quantity and other pond weather |
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Because the pond has
a number of
oxygenating plants
in it, additional sunlight should not prove a problem in terms of losing oxygen, but of course sunlight does encourage evaporation. The solar
radiation reading on the far left (in Watts per square metre) is a
crude measure of the additional evaporation due to the sun. The air and
water temperatures, the humidity of the air above the pond, the wind
speed above the pond and the barometric pressure will all influence the
rate of evaporation - all of these are measured on this weather
station. Evapotranspiration (ET) is the measure of the quantity of moisture transpiring from the leaves of a crop and evaporating from the ground. It might be thought of as “negative rain.” and this provides a crude measure of how much water is being lost. The graphic in the middle on the right shows the current month's ET Of course the water is replaced by rainfall - so for instance the month's rain shown in the graphic on the near right will indicate how much has been topped up since the start of the current month. |
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