PCB 2030 Environmental Science
PCB 2030: Environmental Science Chapter 7: Environmental Systems and Ecosystem Ecology Central Case: The Gulf of Mexico’s “Dead Zone” Background on the Dead Zone • The dead zone is a region in the Gulf of Mexico so depleted of oxygen that it cannot support marine organisms, a condition called hypoxia. • The spread of the hypoxic zone threatens the Gulf’s fishing industry, one of the most productive fisheries in the United States. • Environmental advocates and fishermen across the country joined local shrimpers in expressing anxiety about the dead zone. Southern Louisiana Background on the Dead Zone • Scientists studying the dead zone have determined that fertilizer runoff from Midwestern farms is the likely cause. • In 2002, the dead zone grew to its largest size ever—8,500 square miles—the size of the state of New Jersey. • The dead zone forms each April and lasts through the summer, generally reaching a peak in late July. Earth’s Environmental Systems Systems show several defining properties • A system is a network of relationships among a group of parts, elements, or components that interact with and influence one another through the exchange of energy, matter, and/or information. • Systems receive input, process it, and produce output. What are Feeback Loops? • Sometimes a system’s output can serve as input to that same system in a circular process called a feedback loop. – In negative feedback loops, output driving the system in one direction acts as input that moves the system in the other direction. – In positive feedback loops, the output drives the system further toward one extreme or another. Feedback Loops aid in Homeostasis • The inputs and outputs of a complex natural system often occur simultaneously, keeping the system constantly active. • Systems that use negative and positive feedback loops to maintain a balance are said to exhibit Homeostasis. Boundaries of systems are often hard to define • Often, it is difficult to fully understand systems by focusing on their individual components because systems can show emergent properties, characteristics that are not evident in the system’s components. • Systems rarely have well-defined boundaries, so deciding where one system ends and another begins can be difficult. The Mississippi River System • The Mississippi River is an environmental system. • Understanding the hypoxia problem requires considering the river and the gulf together as a system. • The cause of hypoxia in the Gulf of Mexico stems from excess nitrogen from the Mississippi River watershed. • This process of nutrient enrichment is called eutrophication. Nutrients run off the land and drain into the Mississippi River Eutrophication Environmental systems may be perceived in different ways • Earth can be divided into several structural spheres: – The atmosphere is comprised of the air surrounding our planet. – The hydrosphere encompasses all water in surface bodies, underground, and in the atmosphere. – The lithosphere is everything that is solid earth beneath our feet. – The biosphere consists of the sum total of all the planet’s living organisms and the abiotic portions of the environment with which they interact. The Biosphere Biosphere 2 Ecosystems are another level of key environmental systems. • An ecosystem is defined as all interacting organisms and abiotic factors that occur in a particular place at the same time. • Ecosystems differ from communities in that they include abiotic elements and involve the flow of energy and nutrients. Many ecosystems link together to produce the biosphere • Ecosystems are open systems, so they interact with other ecosystems. • Landscape ecology is the study of geographical areas that include multiple ecosystems. • Many animals move between ecosystems; thus they must be studied on the landscape scale. • Ecotones = transitional zones where ecosystems meet • Considering these linkages has proven to be a useful tool in understanding ecology. Energy in ecosystems • Energy for most ecosystems comes from the sun and is converted to biomass by producers through photosynthesis. • Producers convert solar energy into biomass (matter in organisms) • Rapid conversion = high primary productivity (coral reefs) • Rapid plant biomass availability for consumers = high net primary productivity (wetlands, tropical rainforests) Net primary productivity Different ecosystem types show varying net primary productivities. Satellites can help us look at Global Net Primary Productivity Nutrients can be a limiting factor for ecosystem productivity • Nutrients are elements and compounds that organisms consume and require for survival. • Nutrients stimulate production by plants, and the lack of nutrients can limit production. • Nutrients move through ecosystems in nutrient cycles or biochemical cycles. • All organisms require 24 of the naturally occurring chemical elements to survive Artificial Nutrification Experiment Satellite Image of Algal Bloom off the Mouth of the Mississippi The nitrogen cycle • Nitrogen makes up 78% of the atmosphere and is the sixth most abundant element. • Inert nitrogen gas becomes ―fixed‖ so that plants can use it by: nitrogen fixation or nitrification. • Consumers get the nitrogen they need by consuming plants or other animals. The Nitrogen Cycle • Decomposers get nitrogen via dead and decaying organic matter in the form of nitrates • Nitrates in the soil or water are converted back to nitrogen gas by Denitrifying bacteria. The Nitrogen Cycle has changed dramatically in recent decades • Many human activities, such as burning fossil fuels and using fertilizers, alter the nitrogen cycle. – By fixing nitrogen, we speed up its movement into other areas of the cycle. – Human Activities increase the amounts of nitrogen available to aquatic plants, producing a boom in aquatic plant growth. Phosphorous Cycle • Primary consumers acquire phosphorus from water and plants, and pass it on to secondary and tertiary consumers. • Decomposers return phosphorus to the soil. • Concentrations of available phosphorus in the environment are very low. • Humans influence the phosphorous cycle by releasing sewage and using fertilizers. The phosphorus cycle plays a key role in energy conversion • The element phosphorus is a key component of DNA and RNA. • Organisms also use elemental phosphorus to build ADP and ATP. • Phosphorus is most abundant in rocks, and weathering releases phosphates into water. The carbon cycle moves organic nutrients through the environment. • Through photosynthesis, producers pull carbon dioxide out of the atmosphere to produce oxygen and carbohydrates. • During respiration, consumers and decomposers break down carbohydrates to produce carbon dioxide and water. • Remains of organisms may settle as sediments in water bodies to eventually be converted to fossil fuels. Carbon Cycle • The world’s oceans are the second largest reservoir in the carbon cycle. • The burning of fossil fuels, forests, and fields has altered the relative rates at which parts of the carbon cycle occur. The Hydrosphere The hydrologic cycle influences all other cycles • Water moves into the atmosphere via evaporation and transpiration. • Water returns to the surface as precipitation, most of which flows into water bodies as runoff. • Some precipitation and surface water soaks down through the soil and rock to recharge underground water reservoirs known as aquifers. • Human activity affects the water cycle. The Lithosphere The rock cycle is a slow, but important, environmental system • The Rock Cycle is the process where rocks are formed, reshaped and eventually recycled in the lithosphere. • Three types of rocks are found in the rock cycle: – Igneous – Sedimentary – Metamorphic Igneous Rocks • Rocks that form when magma cools are called igneous rocks. – Intrusive igneous rocks form when magma cools slowly well below Earth’s surface. – Extrusive igneous rocks form when magma is spewed from a volcano and it cools relatively quickly Sedimentary Rock • Sedimentary rock is formed when dissolved minerals seep through sediment layers and crystallize and bind sediment particles together. – Limestone and rock salt are chemical sedimentary rocks. – Sandstone and shale are classic sedimentary rocks. Metamorphic Rock • When great heat or pressure is exerted on rock, it is transformed into metamorphic rock • Limestone becoming marble and shale becoming slate are examples of this metamorphic process. Earth’s Lithosphere has layers • Earth’s lithosphere consists of the – crust – mantle – core Plate tectonics shapes the Earth • The crust is divided into several plates that float on the mantle. As the mantle moves, it drags the plates of crust along. • New crust is formed where two plates are pushed apart. • Old crust is destroyed when one plate slides under another, a process called subduction. • Plates may also collide and cause uplift of the crust. Conclusion • Approaching questions by taking a systems approach is helpful in environmental science. • The case of the Gulf of Mexico’s hypoxic zone provides evidence that systems thinking can lead the way to solutions. • The ecosystems and other environmental systems that we see on Earth today are those that have survived the test of time • Many times we alter natural cycles before we even fully understand them.