Human activities may greatly accelerate the process of eutrophication . Because nutrients are c carried into lakes from farm feedlots and sewage.Even if solid waste are removed, water discharged from sewage treatment plant is often rich in phosphate and nitrate dissolved from waste and determined. Rain water Washes off fertilizer from field where the manure of thousands of cattle is accumulated. The water therefore becomes highly enriched.
The added nutrients support excessive growth of phytoplankton.
Producers like blue_green algae form a scum on the lake surface,depriving the submerged plants of the sunlight, as a result they die. The dead plants bodies are decomposed by bacteria, utilizing the oxygen present in the water, deprived of oxygen, fish,snails and insect larvae die and thier decaying bodies fuel more bacterial growth , further depleting oxygen.
Even without oxygen ,
Certain bacteria that produce foul smelling gases thrive. Although it is full of life and nutrients, polluted lake smells bad. Most of the trophic levels including the fish are eliminated and the bacteria and blue_green algae dominate the community. Another very serious cause of polluted water is the acid produced by burning of fossil fuels, which poses a different threat to fresh_water ecosystem. Few organisms can withstand the low pH of acidified lakes.
In this zone enough light penetrates to support photosynthesis. Here phytoplankton includes cyanobacteria which serve as producers. These are eaten by protozoa and small crustaceans, which in turn are consumed by fishes.
Light, Nutrients And Water:
The ecosystem Present on land or soil is called terrestrial or lithospheric ecosystem. Terrestrial ecosystem receives plenty of light, and the soil provide abundant nutrient. Water ,
however , is limited and very unevenly distributed both in place and in time.
Factors which influence life an hand are given below:
Like water, favourable temperature are very unevenly distributed on land in place and time. On poles, the average temperature is below freezing. In temperature zones, only during certain seasons of the year it is quite . But in tropical zones uniformly , warm, moist climate is present.
In terrestrial ecosystem,air is in constant motion, so its composition is more uniform. The amount of O(2) and CO(2) in air is much constant and most beneficial to terrestrial ecosystem.
Plants and animals shifting from water to land developed various types of adaptation for land habitat E.G
Both plants and animals have evolved supporting tissue like vascular bundles (xylem_phloem) in plants and skeleton in animals to support them on land against the force of gravity.
Plants and animals evolved various method to conserve water in their body e.g homeostasis. The mechanism of temperature regulation was developed by land plants and animals by developing bark and skin respectively.
Division Of Terrestrial Ecosystem
It can be divided into following main types as
1 : Forest Ecosystem.
It is further sub_divided into:
tropical rain forests
temperate deciduous forests
coniferous alpine and boreal Forest
The average rainfall is between 750_1500mm.
Moderate temperature ranges from 4C_30C.
Some dominated plants are taxes . Many herbs and shrubs are with height of 5m. Some grasses, ferns and other herbaceous plants make up field layer. At the bottom or floor level many mosses liverworts and lichens covered with litter layer are present.
Animal life some very common animals are Felix, deer and wolves with various types of microorganisms to convert the litter into organic matter such as bacteria fungi, and earthworms.
The soil of temperature decided forest is brown in colour, very fertile and rich in organic matter with maximum water holding capacity.
Human impacts on temperature deciduous forests largest mammals such as black bear, deer, wolves, bobcats and mountain lions were formerly abundant, but the predators have been largely wiped out by humans. Need of lumber and its use in agricultural has reduced many deciduous forests form the world.
Coniferous Alpine And Boreal Forests
In Pakistan these forests are in upper malam jaba swat valley. In the world, they stretch across Eurasia(Europe+Asia) and North American, Canada just south of the tundra. Northern coniferous forests are also called American. Conditions in taiga are harsher than those in the temperate deciduous forests. The winters weather are too short to allow trees the luxurious growth season is shorter
The few months of warm weather are too short to allow trees the luxurious growth of regrowing.