Chapter 5

4 Pages
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Department
Environmental Science
Course Code
EESA01H3
Professor
Carl Mitchell

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Description
Chapter 5Earth Systems and Ecosystem Ecology Central Case The Plight Of The St Lawrence Belugas y The cold Labrador current brings an abundant food source of plankton and fish from the Atlantic Ocean into the estuary supporting a small population of beluga whales y Health problems have plagued the St Lawrence belugas for several decades causing their population to decrease to fewer than 700 y The belugas appear to be dying of cancer at the rate of about 14 to 15 per year y Toxicological studies showed that the whales had been exposed to organochloride pollutants notable polycyclic aromatic hydrocarbons or PAHs PAHs come from the burning of fossil fuels and other combustion sources y The concentration of contaminants increases in animals that eat higher up on the good chain through biomagnification PAHs are also lipophilic or fatloving compounds so they combine easily with fats and accumulate over time in the blubber or the belugas through bioaccumulation y The lack of dissolved oxygen reflects a condition known as hypoxia which is not uncommon in estuarine and coastal water around the world It is most likely caused by the increased nutrient availability from fertilizer runoff into the deep water of the estuary where decomposition of the nutrients consumes the available oxygen y Nutrient overenrichment can lead to algal overgrowth called blooms and subsequent ecosystem degradation This process called eutrophication can happen in both freshwater and saltwater systems y Another possible contributor to hypoxia and eutrophication in the Gulf of St Lawrence is an influx of warm oxygendepleted water from the Gulf Stream which displaces the cold oxygenrich water of the Labrador Current Earths Environmental Systems y Earths systems also include cycles that shape the landscape around us and guide the flow of key chemical elements and compounds that support life and regulate climate Systems show several defining properties y A system is a network of relationships among parts elements or components that interact with and influence one another through the exchange of energy matter or information y Systems that receive inputs of both energy and matter and produce outputs of both are called open systems y Systems that receive inputs and produce outputs of energy but not matter are called closed systems y In a closed system matter cycles among the various parts of the system but does not leave or enter the systemy Although it is scientifically more straightforward to deal with closed systems in nature no system is truly perfectly closed
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