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1 Environmental Change and Ecosystem Stability The student expected to describe how environmental change can impact ecosystem stability. Ecosystems contain a community of living organms along with environmental factors like soil, water, light and air. All of the organms and environmental factors in an ecosystem are connected, and every healthy ecosystem maintains a stable balance of organms and resources. Changes in the community of organms or the quality of an ecosystem s environmental factors can have a huge impact on the stability of the ecosystem. Thesee environmental changes can be the result of natural events and processes, but it most often human actions thatt change the environment in ways that destabilizes the ecosystems of the world. Grassland ecosystem Algal Blooms Farmers around the world use fertilizers to increase the production of their plant crops. These fertilizers support plant growth by increasing the amount of nitrogen and phosphorous available to the plants in the soil. Animall feces produced by the animals contained at ranches and meat production plants also contribute large amounts of nitrogen to the environment. Although it may seem like th extra nitrogen would only affect a small area around each farm or ranch, the effectss of th additional nitrogenn can actually be seen in ecosystems hundreds of miles away. Th because when it rains, the additional nitrogenn that has been added to the environmentt dsolved in the rainwater. Th water then flows through thee ecosystem into creeks, ponds, lakes, streams and rivers. Th excess rainwater, called runoff, contains the nitrogen that was originally placed into the soil. Once th freshwater runoff reachess a river, the Surface runoff flowing river can carry th nitrogen all of the way to the ocean. into a storm drain Algal bloom The addition of nutrients like nitrogen to the water called eutrophication, and it drupts the natural balance of resources making it easier forr algae to grow. When algae begin to grow rapidly, it called ann algal bloom. Algal blooms can be very harmful to aquatic lifee because the excessive growth of algae decreases the amount of dsolved oxygen that available in the water. If an algal bloom significantly lowers the amount of dsolved oxygen, fh will begin to die off in large numbers. An area where thee amount of dsolvedd oxygen has been removed from the water called a hypoxic zone. These areas are also called dead zones because aquatic organmss cannot survive without the dsolved oxygen that they need.

2 Biological Magnification Pesticides are commonly used to protect the human food supply from insects and other pests. These pesticides are directly added to the ecosystem as they are sprayed onto crops. Humans also add heavy metals like mercury to the environment by mining for minerals and burning coal at electrical power plants. Heavy metals and other pollutants are also dcarded by humans and added to landfills. Althoughh landfills are designed to contain these harmful substances, it possible for these pollutants to be found throughout the ecosystem. All of thesee substances can have harmful effects on the organms in the surrounding community and drupt the stability of an ecosystem. Heavy metals and many pesticides are particularly harmful because they can build up in the fat tsues of animals. Th causes the concentration of these pollutants to increase in animals that are higher on the foodd chain. These animals tend to be larger with more fat tsue. The process of thesee pollutants being more concentrated as they move up the food chain called biological magnification. Over time, these pollutants can become concentrated enough to cause serious health and reproductive sues. Certain pesticides can affect the structure of bird eggs. In ecosystems where these pesticides are found in high concentrations within the tsues off birds, the eggs of these birds break very easily. Th makes it difficult for these birds to reproducee and can cause large declines in their populations.. Heavy metals like mercury are commonly passedd throughh aquatic food chains, and they can also have adversee effects on the reproductive and neurological health of birds and other animals that eat fh containing high levels of mercury. Humans that have a diet that includes fh have to be careful not to ingest too much mercury since th mercury could build up in their fat tsue and cause serious medical problems. Brown pelican with fh Pesticides, heavy metals and other pollutants can be spread throughout an ecosystem in the same way thatt fertilizers spread. When it rains, these pollutants can be washed away from terrestrial ecosystems by the freshwater runoff. These pollutants can then make their way into the waterwayss that travel throughout various ecosystems. Because these pollutants are often collected in water sources by runoff, they are often observed in the tsues of aquatic organms. Th causes shorebirds and other animals that eat large amounts of fh to be the most deeply affected byy biological magnification.

3 Human Expansion and Construction As the human population continues to grow, humans continue to expand the amount of land that being used for farming and cities. Th expansion usually leads to the destruction and removal forests and other important habitats. Deforestation describes the removal of forests for other uses. The removal of The deforested area of a jungle these forests greatly reduces the amount of biomass and biodiversity found in these environments. Tropical rainforests are the most diverse ecosystems s in the world, but they are being destroyed by humans at an alarming rate. Th deforestation does not just remove trees, but it also causes the declinee of many other species. Th s because the forest provides habitats for these species, and removing these habitats leads to a decline in their populations. Human construction also has a large impact on ecosystemss around the world. Dams are a great example of how humans can build things that significantly change the balance of an ecosystem. These large structures block large rivers and create vast reservoirs of water. These water reservoirs can be used by humans for drinking water and irrigation, and water can be released through the dam as a way of generating hydroelectric power. However, because thesee dams block the natural flow of water down the river, they can have negative effects on the ecosystem. Many types of fh migrate up rivers in order to reproduce. Dams prevent thesee fh from migrating and can significantly reduce the ability of these fh to reproduce. Dams also prevent nutrient-rich sediments from being washed down the river. These sediments would carry vital nutrients to ecosystems down the river, but if these sediments are blocked by the dam, the natural flow of nutrients will be stopped. Th druption in the natural cycle of nutrients can cause massive druptions in many ecosystems. As sediment builds up behind the dam, the water that flows through the dam goes on to collect more sediment as it travels down the riverbed which also to massive amounts of The Hoover Dam erosion along the river past the dam. The construction of highways and other roads that travel through ecosystems can also have a negative impact on the organms that live in these areas. The construction of these roads removes large patches of vegetation and breaks apart ecosystems into smaller sections. It may not seem like it, but these roads can act as barriers to many smaller species that might have previously migrated through these areas. Th can separate these organms from important resources like lakes and ponds.

4 Fossil Fuels and Greenhouse Gasess Humans use the chemical energy in fossil fuels like coal, natural gas and oil to generate electricity, drive automobiles and provide heat for cooking. Fossil fuels are organic compounds that were formed deep within the earth over millions of years. The heat and pressure of the earth converted the tsues of ancient organms into the energy-rich compounds used today. The energy in fossil fuels released when they are burned. Burning organic compounds like fossil fuels produces carbon dioxide and other greenhouse gases. Coal a fossil fuel To understand greenhouse gases, it helps to understand what an actual greenhouse does. A greenhouse a building that has walls and ceilings made of a transparent insulator like glass. Solar energy can easily travel through the walls of the greenhouse wheree it transformed into heat andd trapped inside the building. Th significantly increases the temperaturee of the air inside the greenhouse. Carbon dioxide a greenhouse gas because it causes the atmosphere to behave like a giant greenhouse. Solar energy passes through the atmosphere where it trapped by carbon dioxide and the other greenhouse gases. Th creates a greenhouse effect that leads to higher temperatur res, and it believed to be one of the primary contributors to global warming. Scientts are concerned that global warming could cause the polar ice caps to melt. Adding too much cold water to the oceans could drupt global ocean currents. Th could potentially lead to very extreme weather and change climates around the Greenhouse gases trap heat in the atmosphere world. Burning fossil fuels also releases compounds containing sulfur and nitrogen into the air. When these compounds mix with water vapor, they react to create acid rain. Acid rain can drupt ecosystems by lowering the ph of the ecosystem s soil and water. Plants and aquatic life can die if the soil and water in an ecosystem become too acidic. Acid rain can also lead to the chemical erosion of stone structures. Reducing Biodiversity The activities of humans can have extremely harmful effects on the community of organms that live within an ecosystem. All of the speciess in an ecosystem are connected throughh a complex food web, and reducing the population of even a single species can drupt the balance of the entire ecosystem. The consequences of reducing an ecosystem s biodiversity are often difficult to predict, and once the damage has been done it sometimess impossible to return the ecosystem back to its original state.

5 One of the main ways that humans reduce the populations of other organms throughh the destruction of their habitats. When humans destroy the area that inhabited by a species, the population of that species will decline. Habitat loss often the result of deforestation and human expansion, and the removal of habitats around the world has led to the extinction of many species. A species becomes extinct when all of the members of its populationn have died. When th happens, the species lost forever. Some species are very close to becoming extinct, and these species are classified as endangered species. Many countries have laws that attempt to protect thesee species from extinction. Humans also contribute to the reduction of other species through overhunting. Th practice removes large amounts of animals from nature so that the animals can be sold for a profit. Many of thesee animals are hunted for their fur, horns or tusks. As a result of overhunting, many of thesee animals are now considered endangered species. It usually illegal to hunt these endangered species, but becausee there so much money to be made off of them they are still killed in large numbers. The illegal hunting of a species called poaching. The black rhinoceros an endangered species that illegally hunted forr its horns, and poachers threaten to drive th animal to the point of extinction. A black rhinoceros Tanzania In Thailand, a great reduction in the population of elephants and native bears has had a negative effect on the Miliusa beech trees found in Thailand s forest. Th becausee these animals dperse the seeds of Miliusa beech trees after eating the fruit that comes from these trees. Since overhunting has greatly reduced the elephant and bear populations, the seeds of these trees are not being dpersedd in the same way. As a result of overhunting, the number of these trees being found in the forests of Thailand quickly declining. A similar problem facing the aquatic ecosystems of the world overfhing. If too many fh are removed from an ecosystem, the population of fh can decline rapidly. Th can harm other populations of aquatic life that use the fh as a food source, and it can also lead to environmental problems like algal blooms. Overfhing can lead to algal blooms if the species of fh that removed a consumer of algae. Without these fh consuming the algae, the algae population can rapidly increase causing an algal bloom. Algall blooms can reduce the amount of dsolved oxygen available in the water which can negatively impact every speciess in the ecosystem. The overfhing of apex predators like sharks can also drupt entire ecosystems. Sharks are predators that help to control the populations of other organms like rays. When sharks are removed, the population of rays in an ecosystem can increase beyond normal levels 400 tons of mackerel being which can have negative consequences on other fhed in Peru populations.