Central Case: The Gulf of Mexico s Dead Zone

Transcription

1 Central Case: The Gulf of Mexico s Dead Zone The Gulf of Mexico brings in a billion pounds/year of shrimp, fish, and shellfish Gulf dead zone = a region of water so depleted of oxygen that marine organisms are killed or driven away Hypoxia = low concentrations of dissolved oxygen in water From fertilizer, fossil fuel emissions, runoff, sewage 1

2 Earth s environmental systems Our planet s environment consists of complex networks of interlinked systems Matter and molecules Organisms, populations, interacting species Nonliving entities (rocks, air, water, etc.) A systems approaches assesses questions holistically Helping address complex, multifaceted issues But systems can show behavior that is hard to understand and predict 2

3 Systems show several defining properties System = a network of relationships among parts, elements, or components They interact with and influence one another They exchange energy, matter, or information Systems receive inputs of energy, matter, or information They process these inputs and produce outputs Feedback loop = a circular process in which a system s output serves as input to that same system Negative and positive feedback loops do not mean "bad" and "good" 3

4 Negative feedback loop Negative feedback loop = output from a system moving in one direction acts as input Then moves the system in the other direction Input and output neutralize one another Stabilizes the system Example: predator prey interactions Most systems in nature 4

5 Positive feedback loop Positive feedback loop = instead of stabilizing a system, it drives it further toward one extreme or another Exponential growth in human population, erosion, melting sea ice Rare in nature But is common in natural systems altered by humans 5

6 Systems are active Dynamic equilibrium = system processes move in opposing directions Balancing their effects Homeostasis = a system maintains constant (stable) internal conditions Emergent properties = system characteristics are not evident in the components alone The whole is more than the sum of the parts It is hard to fully understand systems; they connect to other systems and do not have sharp boundaries 6

7 Environmental systems interact Environmental entities: complex, interacting systems For example, river systems consist of hundreds of smaller tributary subsystems Impacted by farms, cities, fields, etc. Solving environmental problems means considering all appropriate components in the system of interest 7

8 Eutrophication: a systems perspective Fertilizer from Midwestern farms adds nutrients to the Mississippi River, which causes Phytoplankton to grow, then Bacteria eat dead phytoplankton and wastes Explosions of bacteria deplete oxygen, causing Fish and other aquatic organisms to suffocate Sources of nitrogen and phosphorus include: Agricultural sources, nitrogen fixing crops Livestock manure, sewage treatment plants, street runoff, industrial and vehicle emissions 8

9 Eutrophication The process of nutrient over enrichment leads to: Blooms of algae Increased production of organic matter Decomposition and hypoxia 9

10 Systems are perceived in various ways Categorizing environmental systems helps make Earth s dazzling complexity comprehensible For example, the Earth consists of structural spheres Lithosphere = rock and sediment Atmosphere = the air surrounding our planet Hydrosphere = liquid, solid or vapor water Biosphere = the planet s living organisms and the abiotic (nonliving) portions of the environment Boundaries overlap, so the systems interact 10

11 Ecosystems Ecosystem = all organisms and nonliving entities that occur and interact in a particular area at the same time It includes abiotic and biotic components Biological entities are tightly intertwined with chemical and physical entities Through interactions and feedback loops Ecosystems receive, process and transform inputs of energy While cycling and recycling matter Outputs produced include heat, water, wastes 11

12 Systems of interacting entities in ecosystems Energy from the sun flows in one direction Arriving as radiation and leaving as heat Matter is recycled within ecosystem Through food web relationships and decomposition 12

13 Energy is converted to biomass Primary production = conversion of solar energy to chemical energy in sugars by autotrophs Gross primary production (GPP) = assimilation of energy by autotrophs Net primary production (NPP) = energy remaining after respiration which is used to generate biomass Available for consumption by heterotrophs Secondary production = biomass generated by heterotrophs from consuming autotrophs Productivity = rate at which ecosystems generate biomass 13

14 Net primary productivity of ecosystems High net primary productivity = ecosystems whose plants rapidly convert solar energy to biomass 14

15 NPP variation causes global geographic patterns NPP increases with temperature and precipitation on land, and with light and nutrients in aquatic ecosystems 15

16 Ecosystems interact spatially Ecosystems vary greatly in size From a puddle of water to a bay, lake or forest The term ecosystem is most often applied to self contained systems of moderate geographic extent Adjacent ecosystems may share components and interact i.e. prairie and forests interact where they converge Ecotones = transitional zones between two ecosystems Elements of each ecosystem mix 16

17 Landscape ecology Landscape ecology = studies how landscape structure affects the abundance, distribution, and interaction of organisms Helpful for sustainable regional development Patches = form the landscape Are spread spatially in complex patterns (a mosaic) i.e. forested patches within an agricultural landscape Widely spaced patches endanger organisms 17

18 Ecosystems provide vital services Human society depends on healthy, functioning ecosystems They provide goods and services we need to survive Ecosystem services = provided by the planet s systems Soil formation, water and air purification, pollination Breakdown of some pollutants and waste Quality of life issues (inspiration, spiritual renewal) Nutrient cycling 18

19 Ecosystem goods and services 19

20 Nutrients circulate through ecosystems Matter is continually circulated in ecosystems Nutrient (biogeochemical) cycles = the movement of nutrients through ecosystems Atmosphere, hydrosphere, lithosphere, and biosphere Pools (reservoirs) = where nutrients reside for varying amounts of time (the residence time) Flux = the rate at which materials move between pools Can change over time Is influenced by human activities 20

21 Main components of a biogeochemical cycle Source = a pool that releases more nutrients than it accepts Sinks = a pool that accepts more nutrients than it releases 21

22 The hydrologic cycle Water is essential for biochemical reactions It is involved in nearly every environmental system Hydrologic cycle = summarizes how liquid, gaseous and solid water flows through the environment Oceans are the main reservoir Evaporation = water moves from aquatic and land systems into the atmosphere Transpiration = release of water vapor by plants Precipitation, runoff, and surface water = water returns to Earth as rain or snow and flows into streams, oceans, etc. 22

23 Groundwater Aquifers = underground reservoirs of sponge like regions of rock and soil that hold Groundwater = water found underground beneath layers of soil Water table = the upper limit of groundwater in an aquifer Water may be ancient (thousands of years old) Groundwater becomes exposed to the air where the water table reaches the surface Exposed water runs off to the ocean or evaporates 23

24 The hydrologic cycle 24

25 Human impacts on the hydrologic cycle Removing forests and vegetation increases runoff and erosion, reduces transpiration and lowers water tables Irrigating agricultural fields depletes rivers, lakes and streams and increases evaporation Damming rivers increases evaporation and infiltration Emitting pollutants changes the nature of precipitation The most threatening impact: overdrawing groundwater for drinking, irrigation, and industrial use Water shortages create worldwide conflicts 25

26 The carbon cycle Carbon is found in carbohydrates, fats, proteins, bones, cartilage and shells Carbon cycle = describes the route of carbon atoms through the environment Photosynthesis by plants, algae and cyanobacteria Removes carbon dioxide from air and water Produces oxygen and carbohydrates Plants are a major reservoir of carbon Respiration returns carbon to the air and oceans Plants, consumers and decomposers 26

27 Sediment storage of carbon Decomposition returns carbon to the sediment The largest reservoir of carbon May be trapped for hundreds of millions of years Aquatic organisms die and settle in the sediment Older layers are buried deeply and undergo high pressure Ultimately, it may be converted into fossil fuels Oceans are the second largest reservoir of carbon 27

28 The carbon cycle 28

29 Humans affect the carbon cycle Burning fossil fuels moves carbon from the ground to the air Cutting forests and burning fields moves carbon from vegetation to the air Today s atmospheric carbon dioxide reservoir is the largest in the past 800,000 years It is the driving force behind climate change The missing carbon sink: 1 2 billion metric tons of carbon are unaccounted for It may be taken up by plants or soils of northern temperate and boreal forests 29

30 The phosphorus cycle Phosphorus (P) is a key component of cell membranes, DNA, RNA, ATP and ADP Phosphorus cycle = describes the routes that phosphorus atoms take through the environment Most phosphorus is within rocks It is released by weathering There is no significant atmospheric component With naturally low environmental concentrations Phosphorus is a limiting factor for plant growth 30

31 The phosphorus cycle 31

32 Humans affect the phosphorus cycle Mining rocks for fertilizer moves phosphorus from the soil to water systems Wastewater discharge also releases phosphorus Runoff containing phosphorus causes eutrophication of aquatic systems Produces murkier waters Alters the structure and function of aquatic systems Do not buy detergents that contain phosphate 32

33 The nitrogen cycle Nitrogen comprises 78% of our atmosphere It is contained in proteins, DNA and RNA Nitrogen cycle = describes the routes that nitrogen atoms take through the environment Nitrogen gas cannot be used by organisms Nitrogen fixation = lightning or nitrogen fixing bacteria combine (fix) nitrogen with hydrogen To form ammonium Which can be used by plants 33

34 Nitrification and denitrification Nitrification = bacteria convert ammonium ions first into nitrite ions then into nitrate ions Plants can take up these ions Animals obtain nitrogen by eating plants or other animals Decomposers get it from dead and decaying plants or other animals Releasing ammonium ions to nitrifying bacteria Denitrifying bacteria = convert nitrates in soil or water to gaseous nitrogen Releasing it back into the atmosphere 34

35 The nitrogen cycle 35

36 N 2 NOx N 2 atmospheric fixation Fixation by bacteria Human fixation Uptake by plants NH 3 (ammonia) NO 2 (nitrite) Decomposition N in organic waste NH 4 (ammonium) Denitrification (bacteria) NO 3 N 2 NH 4 (ammonium) Mineralization NO 3 (nitrate) Nitrification: NH 4 NO 2 NO 3 36

37 Humans affect the nitrogen cycle Haber Bosch process = production of fertilizers by combining nitrogen and hydrogen to synthesize ammonia Humans overcame the limits on crop productivity Fixing atmospheric nitrogen with fertilizers Increases emissions of greenhouse gases and smog Washes calcium and potassium out of soil Acidifies water and soils Moves nitrogen into terrestrial systems and oceans Reduces diversity of plants adapted to low nitrogen soils Changed estuaries and coastal ecosystems and fisheries 37

38 Humans put nitrogen into the environment Fully half of nitrogen entering the environment is of human origin 38

39 Solutions to the dead zone The Harmful Algal Bloom and Hypoxia Research and Control Act (1998) Called for an assessment of hypoxia in the dead zone Solutions outlined included: Reduce nitrogen fertilizer use in Midwestern farms Apply fertilizer at times which minimize runoff Use alternative crops and manage manure better Restore wetlands and create artificial ones Improve sewage treatment technologies Evaluate these approaches 39

40 Decreasing pollution Scientists, farmers and policymakers are encouraged to Decrease fertilizer use While safeguarding agriculture Offering insurance and incentives Using new farming methods Planting cover crops Maintaining wetlands There have been some successes Despite a lack of funding 40