10. Humans are part of nature and like every other species on earth we depend on the healthy ecosystems for our well being and survival. Nature provides us clean water, food, air, plants and recreational retreats. An intact ecosystems help regulate our weather and climate. However, due to economical and technological progress, man’s activities have created an adverse impact on the fragile ecosystem.

Deforestation has led to the losses of biodiversity. In fact forests are highly responsible in keeping and sustaining global ecosystems. The emissions of carbon dioxide have a great potential effect on global climate through an enhancement of Earth's greenhouse effect. In some cases, indigenous cultures living in the original forest may be displaced by the destruction of their habitat. It is also the home of more than half of all creatures and organisms in this planet. From food to life-saving medicines, forests give mankind a variety of gifts that contribute much to our quality of life. Deforestation is equated to the destruction and extinction of many plant and animal species.


http://www.ces.purdue.edu/vanderburgh/horticulture/weird/deforestation.jpg

Overfishing is catching too much fish for the system to support leads to an overall degradation to the system. Overfishing upsets the ecological balance of the oceans.
For example, when sharks are overfished for their fins, it leads to a depletion of the important grazers of plant life. This is because there are fewer sharks to feed on carnivorous fish such as grouper—causing an increase in their numbers and their ability to prey on parrot fishes. The removal of the plant-eating parrot fishes has been partly responsible for the shift of Caribbean reefs from coral to algae dominated.
Every sea creature exists in the food chain as predator, prey, and/or scavenger. Species like tuna and swordfish are top predators. When their numbers are unnaturally depleted, other species replace them, but biodiversity - the number of different species in an ecosystem - is adversely affected. Loss of biodiversity reduces the ocean's ability to produce seafood, resist diseases, filter out pollutants, and rebound from stresses.


http://assets.panda.org/img/overfish_img1_col2b_75579.jpg

Eutrophication is a process where lakes, rivers or slow-moving streams receive excessive nutrients that come from agricultural field fertilizers, erosion soil and sewage treatment plant discharges. The nutrients stimulate excessive algae and nuisance plants weeds growth. Algal blooms limit the sunlight available to bottom-dwelling organisms and cause wide swings in the amount of dissolved oxygen in the water. Dissolved oxygen greatly increases during the day, but is greatly reduced after dark by the respiring algae and by microorganisms that feed on the increasing mass of dead algae. Fish and other marine animals suffocate and especially immobile bottom dwellers die off.


http://www.rmbel.info/Reports/Static/Eutrophication.aspx


Biomagnification is the sequence of processes in an ecosystem by which higher concentrations of a particular chemical, such as the pesticide DDT, are reached in organisms higher up the food chain, generally through a series of prey-predator relationships.
For example, the grass in a field is sprayed with Dichlorodiphenyltrichloroethane (DDT) with each contaminated 1ppm (part per million) of the chemical. An insect eats many such blades of grass and the chemical accumulates in their bodily tissues, leading to a concentration of 10 ppm. A frog eats many such insects, leading to a concentration of 100 ppm. A fish eats many such frogs, leading to a concentration of 1000ppm. A human eats many such fish and the concentration increases further.
This implies that species higher up the food chain, such as humans, are at greater risk from the effects of biomagnification or food pollution. The levels of such toxins are higher in meat than in fruits, grains and vegetables.





http://dopamine.chem.umn.edu/chempedia/index.php/Pesticides