The Chesapeake Bay [Figure 7] a is one of the most scenic areas on Earth; it is now in distress and is recognized as a case study of a declining ecosystem. In the s, the Chesapeake Bay was one of the first aquatic ecosystems to have identified dead zones, which continue to kill many fish and bottom-dwelling species such as clams, oysters, and worms. Several species have declined in the Chesapeake Bay because surface water runoff contains excess nutrients from artificial fertilizer use on land.
The source of the fertilizers with high nitrogen and phosphate content is not limited to agricultural practices. There are many nearby urban areas and more than rivers and streams empty into the bay that are carrying fertilizer runoff from lawns and gardens. Thus, the decline of the Chesapeake Bay is a complex issue and requires the cooperation of industry, agriculture, and individual homeowners.
Of particular interest to conservationists is the oyster population [Figure 7] b ; it is estimated that more than , acres of oyster reefs existed in the bay in the s, but that number has now declined to only 36, acres. Oyster harvesting was once a major industry for Chesapeake Bay, but it declined 88 percent between and This decline was caused not only by fertilizer runoff and dead zones, but also because of overharvesting.
Oysters require a certain minimum population density because they must be in close proximity to reproduce. Human activity has altered the oyster population and locations, thus greatly disrupting the ecosystem.
The restoration of the oyster population in the Chesapeake Bay has been ongoing for several years with mixed success. Not only do many people find oysters good to eat, but the oysters also clean up the bay. They are filter feeders, and as they eat, they clean the water around them.
Filter feeders eat by pumping a continuous stream of water over finely divided appendages gills in the case of oysters and capturing prokaryotes, plankton, and fine organic particles in their mucus.
In the s, it was estimated that it took only a few days for the oyster population to filter the entire volume of the bay. Today, with the changed water conditions, it is estimated that the present population would take nearly a year to do the same job. Restoration efforts have been ongoing for several years by non-profit organizations such as the Chesapeake Bay Foundation.
The restoration goal is to find a way to increase population density so the oysters can reproduce more efficiently. Many disease-resistant varieties developed at the Virginia Institute of Marine Science for the College of William and Mary are now available and have been used in the construction of experimental oyster reefs.
Efforts by Virginia and Delaware to clean and restore the bay have been hampered because much of the pollution entering the bay comes from other states, which emphasizes the need for interstate cooperation to gain successful restoration. The new, hearty oyster strains have also spawned a new and economically viable industry—oyster aquaculture—which not only supplies oysters for food and profit, but also has the added benefit of cleaning the bay.
Sulfur is an essential element for the macromolecules of living things. As part of the amino acid cysteine, it is involved in the formation of proteins. As shown in [Figure 8] , sulfur cycles between the oceans, land, and atmosphere. Atmospheric sulfur is found in the form of sulfur dioxide SO 2 , which enters the atmosphere in three ways: first, from the decomposition of organic molecules; second, from volcanic activity and geothermal vents; and, third, from the burning of fossil fuels by humans.
On land, sulfur is deposited in four major ways: precipitation, direct fallout from the atmosphere, rock weathering, and geothermal vents [Figure 9]. Atmospheric sulfur is found in the form of sulfur dioxide SO 2 , and as rain falls through the atmosphere, sulfur is dissolved in the form of weak sulfuric acid H 2 SO 4. Sulfur can also fall directly from the atmosphere in a process called fallout. Also, as sulfur-containing rocks weather, sulfur is released into the soil. These rocks originate from ocean sediments that are moved to land by the geologic uplifting of ocean sediments.
Terrestrial ecosystems can then make use of these soil sulfates SO 4 2- , which enter the food web by being taken up by plant roots. When these plants decompose and die, sulfur is released back into the atmosphere as hydrogen sulfide H 2 S gas. Sulfur enters the ocean in runoff from land, from atmospheric fallout, and from underwater geothermal vents. Some ecosystems rely on chemoautotrophs using sulfur as a biological energy source.
This sulfur then supports marine ecosystems in the form of sulfates. Human activities have played a major role in altering the balance of the global sulfur cycle. The burning of large quantities of fossil fuels, especially from coal, releases larger amounts of hydrogen sulfide gas into the atmosphere.
As rain falls through this gas, it creates the phenomenon known as acid rain, which damages the natural environment by lowering the pH of lakes, thus killing many of the resident plants and animals. Acid rain is corrosive rain caused by rainwater falling to the ground through sulfur dioxide gas, turning it into weak sulfuric acid, which causes damage to aquatic ecosystems. Acid rain also affects the man-made environment through the chemical degradation of buildings.
For example, many marble monuments, such as the Lincoln Memorial in Washington, DC, have suffered significant damage from acid rain over the years. These examples show the wide-ranging effects of human activities on our environment and the challenges that remain for our future. Mineral nutrients are cycled through ecosystems and their environment. Of particular importance are water, carbon, nitrogen, phosphorus, and sulfur.
All of these cycles have major impacts on ecosystem structure and function. As human activities have caused major disturbances to these cycles, their study and modeling is especially important. Ecosystems have been damaged by a variety of human activities that alter the natural biogeochemical cycles due to pollution, oil spills, and events causing global climate change.
The health of the biosphere depends on understanding these cycles and how to protect the environment from irreversible damage. Most of the water on Earth is salt water, which humans cannot drink unless the salt is removed. Some fresh water is locked in glaciers and polar ice caps, or is present in the atmosphere. Skip to content Chapter Ecosystems and the Biosphere.
Learning Objectives By the end of this section, you will be able to: Discuss the biogeochemical cycles of water, carbon, nitrogen, phosphorus, and sulfur Explain how human activities have impacted these cycles and the resulting potential consequences for Earth.
Art Connection Figure 4: Nitrogen enters the living world from the atmosphere through nitrogen-fixing bacteria. This nitrogen and nitrogenous waste from animals is then processed back into gaseous nitrogen by soil bacteria, which also supply terrestrial food webs with the organic nitrogen they need. The majority of the water found on Earth is: ice water vapor fresh water salt water.
Why are drinking water supplies still a major concern for many countries? Footnotes 1 Scott L. Morford, Benjamin Z. Houlton, and Randy A. News, Business Insider, Lifescript, Healthline and many other publications. There are many different types of biogeochemical cycles, but the most common ones include:. Elements in the Biosphere. Role of Water in the Ecosystem. Why Is the Rock Cycle Important? Things That Makes Up an Ecosystem.
Nonliving Things in a Forest Ecosystem. Why Are Ecosystems So Important? Four Components of an Ecosystem. What Are the Functions of Photosynthesis? The Plant Life Cycle for Kids. Levi BEST. Thanks for replay. Shortly a concern team touch you. Oh no!
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