Wind & Evaporation

Weather plays a large part in the life cycle of the pond, not only the species which may be present but also other factors which contribute to the physical changes which occur within the water column. We have mentioned some effects of wind, and temperature in other sections. But now we shall look at the overall environmental impact of these, the benefits and the loses they have on the pond and its physical structure.

Water Temperature

There are some things that need to be understood about the behaviour of water as its temperature drops and from this we can form an overview of what is happening below the surface.

Water is a poor conductor of heat and for this reason it takes longer to warm and cool than the air above it. This creates a relatively stable habitat as changes are not sudden as in the atmosphere. Slow changes are an advantage in a climate in which sudden cold spells or hot periods occur. But if the weather remains constantly at high temperature then it can create problems we will discuss later under evaporation, or the reverse if constanly frozen.

As the water temperature drops, a thin layer of ice will be formed across the surface, in some locations it can progress to totally freeze to the full depth of the pond, but conditions need to be very severe to achieve this. The reason for this is the way that freshwater behaves as it cools, as water gets colder it contracts and becopmes denser. This continues until it reaches a temperature of about 39.2º F (4º C). At this point if further cooled it starts to expand and get lighter floating to the surface. As can be invisaged the water column during this time is mixing, as the waters as they cool sink pushing the warmer water to the surface. This will continue until the whole water column reaches the temperature of 39.2º F (4º C). At this point the water if further cooled is unable to sink and  starts to form an ice sheet, whilst the lower waters temperature remains constant at the above temperature. As the ice develops it acts rather like a blanket slowing even further the cooling effect, and so even in the most cold winters some clear waters will remain for the ponds inhabitants to survive.