Examples of human activities that disrupt the ecosystem are:
1. deforestation
2. uncontrolled fishing
3. pollution in the form of pollution by discharge of (i) untreated sewage (ii) toxic, industrial waste such as mercury.
Deforestation involves the removal of trees in the forest. The soil that is exposed can be eroded and washed into nearby rivers and seas. During a heavy downpour, these rivers and seas would overflow and flood surrounding land. Long periods of dry weather would also cause exposed soil to dry and desertification may occur. Forests are also homes to various animal species and removal of trees may result in these animal species to migrate and some may die leading to a loss of biodiversity.
Uncontrolled fishing such as trawling, cyanide fishing and dredging may allow large quantities of fish and seafood to be harvested. However, unwanted species such as turtles, corals and small fish that have no commercial value are caught too. These fishing practices may lead to a large loss of marine biodiversity.
Discharge of untreated sewage into common waterbodies leads to extensive bacteria growth that causes dissolved oxygen levels in the waters to decline sharply and this will cause the fishes to die. Excessive use of fertilisers on farmlands are washed into common water bodies such as rivers. Fertilisers that contain ammonium compounds and nitrates lead to algal blooms. The phenomenon of algal blooms in rivers and streams is known as eutrophication and serious cases would cause the rivers and streams to turn green. The algae in the river waters blocks the entry of light into the rivers. This causes the aquatic plants in the river bed to be unable to photosynthesise. Aquatic plants die and decompose, removing oxygen supply to the river waters. This will also decrease the numbers of fishes and shrimps in the river.
Non-biodegradable chemicals used in the ecosystem such as discharge of mercury into river waters or use of non-biodegradable pesticides (eg DDT) are bioaccumulated by different trophic levels in the food chains and food webs. These chemicals reach toxic levels at the highest trophic levels and would result in effects such as death at a younger age and infertility. This would then affect its numbers and therefore the balance of the ecosystem.
Conservation involves the protection and preservation of the natural resources. Main approach of conservation is to use resources carefully to manage the rate of resource removal and resource regeneration. Methods of managing tree and fish resources are elaborated in the other pages.
Managing sources of pollution that would in turn affect plant and animal biodiversity is equally important. Approaches would be to apply sufficient amounts of fertilisers and pesticides on farm lands, use of biodegradable chemicals, control the discharge of industrial wastes such as mercury into common waterbodies and treat sewage before discharging into common waterbodies.