The aquatic environment ought to always be taken as a lawful consumer of water, whose requirements ought to be fulfilled alongside the fundamental human requirements, and at the forefront of any other demand.
In the case of water projects requiring impoundment, this means the maintenance of flow in the reaches of the river downstream of the impounding structure, dam, or diversion. Environmental flows are essential to:
•keep up the riverine ecology
•revitalize the riverine aquifers
•keep up the river channel
Factors Affecting Aquatic Ecosystems
Inconsistency and change are natural processes in aquatic ecosystems, and ecosystem communities and individual organisms have on several occasions adapted to diverse environmental conditions. The factors affecting the aquatic environment can be as a result of natural causes or as a result of human factors.
Human activities that affects the aquatic ecosystem can be due to pollution, changes or alteration to the landscape or hydrological systems, and their overall long lasting larger-scale effects like the global climate change.
The complexity of aquatic ecosystems and the connections within them can make it difficult to predict the effect or what may be the result of such disturbances on them.
These interconnections among them entail that any damage or harm done to a single component of the ecosystem can result to impacts on other components of the ecosystem.
Augmenting or amplifying our understanding of aquatic ecosystems can result to enhanced practices that reduce the effect these would have on aquatic environments.
It can therefore be concluded that influences on the aquatic ecosystem can be as a result of:
•Natural or physical factors
•Human factors and their practices
Example of such factors that affects the aquatic ecosystem is the eutrophication.
Another factor that could affect the aquatic ecosystem significantly and which possess a serious threat to the survival of organim in aquatic environment everywhere in the world is the invasion of species Water Hyacinth (Eichhornia crassipes) and Water Fern (Azolla filiculoides).
These two aquatic plants, native to South America, have invaded varoius sections of the Vaal River and many other rivers of the world. Whereas Water Fern is limited to the upper catchments of the Vaal River, Water Hyacinth is seen in the upper-middle Vaal and extends as far as Douglas Weir.
Biological control agents, which includes the weevil, Stenopelmus rufinasus, has been comparatively useful and successful in the control of the invasion; nevertheless, they go on spreading, with Water Hyacinth currently discovered occasionally in the lower reaches of the main-stem of Orange-Senqu River.
In South Africa for example, a few introduced species include two species of trout (Salmo trutta and Oncorhynchus mykiss).
These species were originally introduced for sport fishing in South Africa but have currently had effects on the populations of local minnow species in Lesotho and South African parts of the Orange-Senqu River basin, and are seen all through the basin, although in smaller numbers, from the Maluti Mountains downstream to the Gariep and Vanderkloof dams.
Other factors that have effects on the aquatic ecosystems are listed in the table below.
Factors affecting aquatic ecosystems
-Foreign species: Opening up foreign species out-compete indigenous species for space, nutrients and sunlight availability.
-Dams, inter-basin transfers, hydro-electrical flow releases, irrigation and mining activities: Customized flow regime or hydrology.
-Pollution from mines and return water flows from irrigation: Reduction in water quality, including nutrient build-up on the surface of the water and salanisation
-Reduced flood management and made to order seasonal flows: Geomorphologic modification of the river channel as a result of lower flows which results in less or no scoured
-Riparian and in-stream vegetation is laid out of action and continues to get worse: Floating aquatic plants rise in number with reduced flow. Alterations to the shape of the wetted perimeter of the river channel, with lower water levels leading to the dryness of river banks, temporary exposure of open to attack banks and water bank collapse Enhanced advantage to pioneer reeds, like the Common Reed (Phragmites australis), under reduced flow, with improved distribution and patch size, and in so doing gathering up sediments, blocking channels and leading to large disturbances when washed out during the time of large floods. These frequently lead to the formation of reed mats that cause blockages downstream and make worse the effect of floods. Loss of local trees and gallery forest in the riparian belt as a result of reduced floods (moisture), reduced seed dispersal, more recurrent or everyday hot fires due to the increase in the reed beds and a reduced amount of cooling effect as the formerly moist riverbanks are now drier Agricultural encroachment into the riparian belt would be greater than before due to less than before flooding activities and waterlogged soils Invasion by foreign vegetation, particularly Mesquite (Prosopis spp.), got worse due to a loss of home-grown vegetation and disturbance for example through fires and agricultural activities Alterations in the compositions of species and abundance as a result of fertilizers and salts draining into the river, for example Common Reed (P.australis) and Wild Tamarisk (Tamarix usneoides) increasing and posing a negative effect on safsaf willow, Kaapse wilger or Cape Willow (Salix mucronata).
The Factors Affecting Terrestrial Ecosystem
It is not uncomplicated to compare terrestrial and aquatic systems due to the fact that there are a very big variety of these environments.
It is possible to be aware of the terrestrial part of the biosphere, a small number of units with characteristic vegetation and climate, each of which is made up of a complex of communities to a large extent. These units are referred to as biomes and six major biomes are by and large recognized, namely the:
1.Tundra,
2.Taiga ( coniferous forests ),
3.Deciduous Forests,
4.Grasslands,
5.Tropical Rain Forests,
6.Deserts.
Similarities between Terrestrial and Aquatic ecosystems
•In both terrestrial and aquatic environments the ecosystems include communities made up of a diversity of species,
•within both terrestrial and aquatic communities there are populations at the different trophic levels of the ecosystem,
•There is a great deal of reciprocal interdependence that exists between species in both the eco systems of the terrestrial and aquatic environments,
•In terrestrial and aquatic ecosystems that are without interruption, equilibrium is attained, i.e. exceptionally few major changes are noticed over a period of time,
•In both aquatic and terrestrial ecosystems stratification also known as vertical zonation takes place.
Differences between Terrestrial and Aquatic systems
•The fact that aquatic ecosystem environments are very rich in nutrients makes it possible for them to support more live than the corresponding terrestrial ecosystems environment.
The minute wandering photosynthetic organisms of the oceans, known collectively as phytoplankton are taken to be the main photosynthesizers, or primary producers, of the earth,
•In aquatic ecosystem environments their tendency to remain stable are much more stable than the corresponding terrestrial environments, due to the fact that it is only affected by smaller fluctuations in temperature and other variables than terrestrial environment,
•aquatic organisms are hardly ever open to the elements of desiccation whereas the terrestrial organisms are over and over again exposed to desiccation and are normally comparatively resistant to drying out,
•oxygen due to their less availability is every now and then a limiting factor an aquatic habitats but this is hardly ever the case in terrestrial habitats,
•light can be a limiting factor in a few aquatic habitats and ecosystems, but in the majority of terrestrial eco system environments, there is hardly ever a limiting factor of light,
•Terrestrial animals are influenced to a greater extent by gravity, whereas in the aquatic ecosystem, the greater influence on their life is made by the availability and quality of water.
The kinds and numbers of species in a typical environment whether it is terrestrial environment or aquatic, environment are typically determined by physical environmental factors. In areas where there are alterations to the physical factors, there will be a transition zone that exit between two communities known as an ecotone.
In an ecotone, plant species from the communities will be discovered and a diversity of wildlife species.
The terrestrial community on an archetypal farm in Tennessee for example includes the cottontail rabbit, hayfields, northern bobwhite quail and grain.
Other species present include the woodlot, which is composed of foxes, trees, deer and songbirds. Other members of the community include the meadow mouse, stream bank willow, dogwood, opossum, skunk and sparrow hawk.
A few more other species are fence-row trees and shrubs, groundhogs, blacksnakes and weasels.
The cottontail rabbit, groundhog and meadow mouse eat from the same clover field and are seen to be present in the same fencerow and end up as food for a fox or hawk.
The skunk looks for refuge in a groundhog burrow, searches fields and pass through lanes to get grubs and mice, and rarely finds and feasts on birds’ eggs. In due course, an owl, nesting in an old dead hurdle in the woodlot, may possibly prey upon the skunk.
A hawk hovers over the hayfield and jumps over for insects as well as mice to feed itself and its young ones
Every plant and animal members of a community live and function in their own place and fill up their niche. This is how complicated a community can be.
The Interrelatedness of Life
Interrelatedness is a main concept in ecology. For instance, a plant may put up with different extremes of temperature based on the amount of moisture on hand. And, the way the environmental factors are interrelated, is also the manner in which biological factors are related.
Man is situated at the top of a lot of food chains, and is dependent on phytoplankton or grasses at the bottom of those chains for his survival.
Apart from the clear food chain relationships, relationships between predator-prey or host-parasite communities is made up of a lot of numerous interrelationships of which we are not fully conscious of. Man is presently starting to be aware of these.
Ecological Succession
Communities do not remain the same but alter over a period of time. This is majorly due to a process known as ecological succession. We see this process all around us as abandoned farmland alters to weed fields, brush land and subsequently to a forest.
One community succeeds another in various stages as conditions change that is favorable to another suite of wildlife species.
The first stage in succession is known as the pioneer stage, which is made up of bare habitat conditions, like an exposed rock. This stage stays until conditions alter to the extent that soil gathers up and plants are capable of thriving there.
These changes go on and on till formation of a climax community, which is in equilibrium with soil and climatic conditions. Species of a climax community do not generate conditions unfavorable to themselves or additionally favorable to other species.
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