- Ponds
- Canals
- Reservoirs
- Ditches
- Dew Ponds
- Moats
As lentic habitats are all land locked they renew their water supplies mainly from rainfall, this can be directly into the water or through draining from the ground; without this the habitat would eventually dry up through evaporation.
Some lentic waters have drains built to draw water from nearby lotic habitats to keep them replenished. The water renewal also plays apart in the level of permanence to the habitat, for example puddles can be classed as lentic habitats but are temporary as they only occur when rain has fallen and evaporate pretty quickly.
Lentic habitats can be classed in three levels of permanence; temporary, semi-permanent and permanent. It all depends on the structure of the habitat and ecological influences such as duration of rainfall and climate.
Areas such as lakes and big ponds will be permanent fixtures in places that have plenty of rainfall and cool temperatures, where as in hot dry climates they would probably be a semi permanent body of water because of the lack of rain and increased levels of evaporation at certain times of year. The depth of the habitat also will affect its level of permanence: the deeper it is the more water it can afford to lose and still be a quality habitat. These permanent habitats are home to creatures all year round.
Semi permanent habitats are often seasonal, places such as ditches will come into this category, they fill up over the wetter seasons and spend the rest of the year drier. Semi permanent habitats are not a constant water habitat and during its dry season will be home to non-water dependant animals. The potential habitat is always there but water renewal rate controls the frequency of it being a water habitat.
Temporary habitats are unreliable habitats for creatures dependent on living in water, they can come and go on a day to day basis, the animals that live in these habitats must be highly adapted or be able to migrate when the need arises. Temporary water habitats can appear in any divot or dip in the landscape and are not constrained by defined margins.
Lentic habitats will vary in their nutritional status; this will affect the diversity of species that inhabit the water. The nutritional status is generally put into four groups
Oligotrophic - Areas of water will very few nutrients and offers little in which to sustain life.
Most of what is found here are bacteria; a creature would have to be very
Specialised to survive in this environment.
Mesotrophic - This is used to describe areas of water with beds of submerged vegetation and medium levels of nutrients. Places like this are more suited to assisting
life than oligotrophic waters.
Eutrophic - Relates to areas of water with rich mineral and nutrient properties, habitats
with these levels of nutrients are often covered with excessive amounts of
algae which can be detrimental to other species inhabiting the water.
Dystrophic - The water has a very acid content and poor in other nutrients, this limits the
vegetation and creatures that can survive in these waters. Often very ‘boggy’
areas.
Zones
Lentic habitats are divided into three zones, littoral, limnetic and profundal. These zones are the layers that support different organisms; each zone has its own special characteristics that certain species will favor over others.
Littoral zones are closest to the shore, they tend to be shallower and hold a lot of vegetation as light can reach all the way to the floor. This zone tends to be abundant with life due to its food source and plenty of shelter. This is where you will tend to find emerging plants, which will increase the diversity of species living here.
The next zone is the limnetic, this is a layer of open water away from the shore, this is the area where most photosynthesis occurs as thw water gets a lot of light and doesn’t run to deep. Floating micro-organisms and swimming creatures dominate this area.
The profundal zone is the deeper level of a body of water more common in lakes than ponds, as this is a deep area with little light. This zone relies on dead organic matter dropping down from the other zones: which is then recycled into nutrients by bacteria and fungi decomposing it. There is less life down in the profundal zone due to its lack of light and cooler temperatures.
Thermocline formation
A thermocline is a layer within a body of water that acts as a barrier between the higher and lower levels. It is formed when sunlight hits the surface layer of the water (epilimnion) and heats the water. Most of the heat is absorbed in the epilimnion and is circulated to warm the rest of the water, however the lower level of water (hypolimnion) is to deep and dark to get heated by the sun, here the temperature is much lower. The area between these two layers where the temperature begins to change rapidly is known as a thermocline. The hypolimnion continues to drop in temp but at a more gradual rate.
The thermocline then acts as a barrier, preventing the two layers from mixing: this means that we end up with two different habitats within the same are of water. The epilimnion is warm with higher levels of oxygen and the longer the thermocline continues the more stable this layer becomes. However the thermocline prevents nutrients from rising to the surface from DOM, which reduces the resources available to this layer.
The hypolimnion at this time is affected by various factors including lack of light and heat and oxygen: which prevents plants from growing, restricting food for organisms living in this layer. The bacteria in this layer will also consume most of the oxygen creating a difficult environment for non-specialised creatures to live in.
References: www.broadwaters.fsnet.co.uk
http://home.comcast.net
http://en.wikipedia.org
www.answers.com
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