Biogeochemical cycles Our planet consists of many complex large scale interacting systems System 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 Feedback loops Negative feedback Feedback loop a circular process whereby a system s output serves as input to that same system In a negative feedback loop output acts as input that moves the system in the opposite direction This compensation stabilizes the system Feedback loops Positive feedback In a positive feedback loop output acts as input that moves the system further in the same direction This magnification of effects destabilizes the system Dynamic equilibrium homeostasis Dynamic equilibrium or steady state when processes in a system move in opposite directions at equivalent rates so their effects balance out this can be large forces pulling in opposite directions yielding small to no change Homeostasis tendency of a system to maintain constant or stable internal conditions Earth s climate and an animal s body are examples of homeostatic systems in dynamic equilibrium Dynamic equilibrium Many equilibrium states can exist there is rarely just one Linear versus non linear changes movement from one steady state to another can be gradual or abrupt Earth s climate is an example of a system with many steady states and abrupt changes examples Closed and open systems Closed system isolated and self contained Open system exchanges energy matter and information with other systems The Earth is basically a closed system with respect to mass but open with respect to energy But any system is open if we examine it closely enough or long enough System example the Mississippi River Delta Dead Zone A systems approach allows us to expand or contract our area of interest as problems require Connected systems The farms of Minnesota and the Gulf of Mexico interact Understanding the dead zone requires viewing farms in the Mississippi River drainage and the Gulf of Mexico as a single system This holistic kind of view is necessary for comprehending many environmental issues and processes consider the problems that compartmentalizing the government agencies causes here Eutrophication Key to the dead zone Eutrophication excess nutrient enrichment in water which increases production of organic matter which when decomposed by oxygen using microbes can deplete water of oxygen Increasing nitrogen inputs Amount of nitrogen fertilizer used rose greatly 1950 80 Nitrate concentrations in Midwestern rivers in 1980 98 were much more than in 1905 07 Creation of the hypoxic dead zone Nitrogen input boosts phytoplankton which die and are decomposed by microbes that suck oxygen from water killing fish and shrimp Importance of systems The problem persisted because government agencies that regulated pesticide use did not interact with those that regulated fisheries systems approach is not a hallmark of government The problem continues to persist because of the linkages of systems if farming is regulated excess nutrients still in the soil and river sediments continue to leach out Systems that are hard to pollute are often hard to clean up we will see this in many biogeochemical cycles Earth s structural spheres Lithosphere rock sediment soil below Earth s surface Atmosphere air surrounding the planet Hydrosphere all water salt and fresh liquid ice and vapor Biosphere all the planet s living things and the abiotic parts of the environment with which they interact Biogeochemical cycles 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 Nutrients Macronutrients are elements and compounds required in relatively large amounts and include nitrogen carbon and phosphorous Micronutrients are nutrients needed in small amounts but just as critical for survival Terminology and Concepts All matter cycles it is neither created nor destroyed Biogeochemical cycles the movement or cycling of matter and energy through a system by matter we mean elements carbon nitrogen oxygen or molecules water so the movement of matter for example carbon between these parts of the system is a biogeochemical cycle Terminology and Concepts Reservoir a unique definable collection of a material of interest also called a pool Flux the movement of a material of interest from one reservoir to another Residence time the average amount of time something spends in a reservoir Residence Time Reservoir size flux The importance of residence times Reservoirs with Long residence times are hard to pollute but once polluted hard to clean up Reservoirs with Short residence times are easy to pollute but once polluted easier to clean up maybe Key is that cycles exist so long residence times reservoirs can be connected to those with short residence times Example CO2 and the ocean CO2 is forever more on this later Mississippi River dead zone exaample The carbon cycle The carbon cycle How carbon C moves through our environment Producers pull carbon dioxide CO2 from the air and use it in photosynthesis Consumers eat producers and return CO2 to the air by respiration Decomposition of dead organisms plus pressure underground forms sedimentary rock and fossil fuels This buried carbon is returned to the air when rocks are uplifted and eroded Ocean water also absorbs carbon from multiple sources eventually storing it in sedimentary rock or providing it to aquatic plants Key facts in the carbon cycle How much carbon is where Most carbon is in rocks carbonates and other sediments Most carbon not in rocks is in the ocean There is more carbon in the atmosphere than in living plants About 3 times more carbon in soils than in land plants There is 6 times more carbon in fossil fuels than in the atmosphere There is 8 times more carbon in fossil fuels than in living plants Human impacts on the carbon cycle We have increased CO2 in the atmosphere by burning fossil fuels and deforesting forests Atmospheric CO2 concentrations are the highest they have been in at least 800 000 years probably 30 to 40 million years This is driving global warming and climate change Human impacts on the carbon cycle We have increased CO2 in the atmosphere by burning fossil fuels and deforesting forests Atmospheric CO2 concentrations are the