FreshWater Communities: Running Water Ecosystem

Running water freshwater communities are also known as lotic communities. Lotic communities are formed by water being introduced to the freshwater body from a variety of sources, such as;

Rainfall – A percentage of water in the running water community will be present as a result of rainfall directly entering it.

Surface Water – Deriving from previous rainfall, water will flow and eventually join the running water community.

Underground Water – Water absorbed into the soil, which can also resurface and enter the surface water body.

Water Table – Deep underground, there is a reservoir of water, known as the ‘water table’, which can also provide water for the running water community.

There are also many other, less significant ways through which water can enter the stream; for example, due to human interference such as an outlet pipe, or water transpired by plants in the nearby area.

The accumulation of this water from the areas mentioned above also introduces essential minerals and nutrients that are ideal for plant growth, the primary producers of a community.

With that in hand, alongside an abundance of water, pioneers can occupy the running water environment.

Affecting Factors

One of the main differences between lotic and a lentic community is the fact that the water is moving at a particular velocity in lotic communities.

This can have great bearing on what organisms occupy the ecosystem and what particular ecological niche they can exist in.

Running water can bring many factors into play affecting the lives of the organisms in this particular environment. Such factors may include the following;

Movement of minerals and stones caused by the velocity and volume of the water, thereby constantly changing the stream characteristics. The faster and higher volume of water present will result in a direct increase in amount and size of particles shifted downstream.

Standing waves are used by salmon at the bottom of waterfalls to spurn them upstream. At the same time, they cause small air pockets caused by oxygen replacing the splashing water, which results in a small micro-habitat becoming available suited to particular organisms

Erosion is caused by the running water breaking down the river bank and beds, causing the geography of the river to change over a long period of time.

This means that hydroseres previously occupying the river bank may find themselves distanced from the running water for example, and over time this would mean the overall ecosystem characteristics would change.

Such factors play a vital role in determining the overall chemical, physical and biological face of the running water ecosystem.

We shall now look at these physical and chemical differences that make up a running water ecosystem which will inevitable affect the biological make-up of the freshwater ecosystem.

Running Water Freshwater Communities

This section continues from the previous one introducing lotic (running water) communities. The following are some of the physical and chemical factors that provide the framework of a running water community in which organisms in their favoured ecological niches occupy.

Temperature – The difference between running water and still water temperature is that running water communities’ temperature varies more rapidly but over a smaller range.

In Summer, water from the source of the river is usually colder than the water found at the delta because it has not been exposed to the warm air heated by the sun. The reverse occurs in Winter where water is warmer until exposed to the colder air.

Light – On the whole, less light penetrates a running water body due to ripples in the water, debris blocking out sunlight to lower layers as well as overhanging shrubs that perhaps are taking advantage of a tributary water source.

These are all examples of how the intensity of light reaching the lotic community can be affected, and in turn, directly affects the rate of photosynthesis done by plants in the community.

Chemical Composition – Many factors can alter the chemical composition of the freshwater environment, including precipitation, the percolation of water via vegetation and sea spray to name a few.

All in all, various elements and compounds are required by organisms in their daily activities and fluctuations or even an absence of such elements and compounds results in a direct effect on the lives of such organisms.

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Organic Matter – Organic matter (previously external to the running water environment) can also play a part in altering the ecosystem. This mostly occurs due to overhanging vegetation, although organic matter can be drawn into the ecosystem by the various sources mentioned above.

Such factors all play a part in the lives of animals and plants occupying the lotic environment

Lotic Communities and Algae

Generally the diversity of plant species in a lotic community is small compared to that of a still water (lentic) community, although small parts of the lotic community host similar conditions to that of a lentic community.

Most plants have gone through evolutionary adaptations to cope with the force and different conditions that running water brings. Such adaptations have allowed a number of species to successfully take advantage of the lotic community as their ecological niche.

As these conditions are harsher for a typical species of plant, more notably larger plants, smaller species have found the conditions of the lotic community more favourable. This is due to the fact that they are more flexible in regards to the physical conditions of the water.

Algae can grow in all sorts of different places and surfaces, and therefore are a successful constituent of the running water ecosystem. Most of these algae have developed evolutionary adaptations over time that prevents the water current sweeping them away.

There are many species of algae, all of which are capable of growing and reproducing at a quick rate.

This consequence results in competition for niches in the freshwater environment, and in light of this, colonies of algae can heavily occupy one area at one moment in time and weeks later they can be succeeded by other species which can succeed in more favourably conditions.

Algae are also the primary producers of this community, since they harness new energy into the ecosystem from the sun which provides the primary consumers with a valuable food source. Algae communities are always found in the lotic community, and are variable on a short-term basis.

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