Temperature

 

Temperature 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 have on the pond and its physical structure.

Cold

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.

Because of waters high specific heat it takes a longer time to warm up than does air, and is slower in cooling, so the fluctuations in temperature are neither so violent in water as in air 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. If the weather remains constantly at high temperature then it can create effects we will discuss later under heat, but first the effects of cold.

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 becomes 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 envisaged 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 as so 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.

This gradual change in water temperature is of great benifit to the creatures that live in the pond, as the majority are cold blooded it allows them to gradually adapt to the changeing environment. the only effects being a reduction in activity possibly requireing a change of habitat such as moving to deeper levels or into sediment deposits to overcome the colder water and in preparation for over wintering. Some animals are quite capable of surviving being totally frozen in ice during these colder months.

Heat

The effects of heat are somewhat different from those of cold, water becomes less viscous as it is warmed and its ability to absord oxygen is reduced. This impacts the inhabitants by increaseing there activity,causeing increased populations and greater biological activity.