Chapter 5 Topics  Systems concepts  Ecosystems  Matter and energy  Spatial patterns  Services  Biogeochemical cycles  Water  Carbon  Nitrogen  Phosphorus  Human impacts

Why “systems”?  Our planet consists of innumerable parts connected by myriad processes into a vast number of complex networks  Systems approaches allow us to investigate and understand these parts, processes, and networks in both focused and comprehensive ways

Systems fundamentals  System = a network of relationships among parts, elements, or components that interact with and influence one another and exchange energy, matter, or information  When studying systems, scientists identify an arbitrary “boundary” that defines what’s “inside” the system and what’s “outside” the system  Because no system is truly isolated from its surroundings, we must therefore consider “inputs to” and “outputs from” the system being studied

Feedback loops  Feedback loop = a circular process in which a system’s output serves as input to that same system  Depending on the system response, the feedback loop is called either “positive” or “negative”  Positive and negative feedback loops do not mean “good” and “bad”

Positive feedback loop  Positive feedback loop = the system response is amplified (unidirectional), driving the system toward an extreme condition  Rare in nature, but common in systems altered by human actions

Negative feedback loop  Negative feedback loop = the system response is dampened (bidirectional), driving the system toward a more-or-less stable condition  Most systems in nature operate in this way

Other systems concepts  Dynamic equilibrium = system processes move in opposing directions balancing their effects  Homeostasis = systems seek to maintain constant (stable) internal conditions  Emergent properties = system characteristics that are not evident in the components alone

Earth’s systems – a reminder  The framework of Earth’s four systems helps make complexity comprehensible  Lithosphere = rock  Atmosphere = air  Hydrosphere = water  Biosphere = life  The boundaries overlap, so the systems interact

Tools for studying systems - models  A scientific model = a simplified representation of a complex natural process that helps us understand the process and make predictions  Researchers gather data  Form a hypothesis about relationships  The model predict how the system will behave  New data refine and increase the model’s accuracy

Other tools  Remote sensing allows a whole-landscape perspective – especially important for studying climate systems  Geographic information system (GIS) = used to analyze the spatial arrangement of landscape elements

Applying systems concepts  Solving environmental problems requires considering all of the parts and processes in the system of interest  The Gulf of Mexico’s “dead zone”, a region of water so depleted of oxygen (hypoxia) that marine organisms are killed or driven away

Eutrophication – excess nutrients  Nutrients (nitrogen and phosphorous) are added to the Mississippi River from  Fertilizers and manure from Midwestern farms  Sewage treatment plants, run-off, and emissions  Nutrient over-enrichment causes  Phytoplankton to grow rapidly and die, then…  Bacteria eat dead phytoplankton and other wastes  Explosions of bacteria deplete oxygen, causing…  Fish and other aquatic organisms to suffocate

Eutrophication yields hypoxia

Ecosystems  Ecosystem = all organisms and nonliving conditions that exist and interact at a given place and time  Parts and processes…  Living organisms (biotic factors) are tightly intertwined with chemical and physical conditions (abiotic factors)  Through interactions and feedback loops  Inputs and outputs…  Energy flows through ecosystems, arriving as solar radiation and leaving as heat  Matter is recycled within ecosystem, through food-web relationships and decomposition

Energy and matter

Energy becomes biomass  Productivity = rate at which biomass is generated  Primary production = conversion of solar energy to chemical energy in sugars by autotrophs  Gross primary production (GPP) = the total amount of energy assimilated by autotrophs  Net primary production (NPP) = the energy converted by autotrophs into biomass (available for consumption by heterotrophs)  Secondary production = biomass generated by heterotrophs from consuming autotrophs

NPP by ecosystem

Global distribution of NPP

Ecosystems interact spatially  The term “ecosystem” is most often applied to self- contained systems of moderate geographic extent  Adjacent ecosystems, such as prairies and forests, may share components and interact along their boundaries  These transitional zones between ecosystems are called ecotones

Landscape ecology  Landscape ecology = studies how landscape structure affects the abundance, distribution, and interaction of organisms  The landscape is divided into patches whose size depends on the relationships being studied  Patches can take on complex patterns, called mosaics, leading to the development of metapopulations, subpopulations in which most members remain within a patch but others move among patches  Widely spaced patches can lead to speciation or endanger an organism’s survival

Ecotones, patches, and mosaics

Ecosystems provide vital services  Humans depend on healthy, functioning ecosystems  They provide goods & services we need to survive  Ecosystem services = economically beneficial services provided by the planet’s natural systems  Soil formation, water and air purification, pollination  Breakdown of some pollutants and waste  Quality of life issues (inspiration, spiritual renewal)  Nutrient cycling

Ecosystem goods and services

Nutrients  Nutrients = elements and compounds required for survival that are consumed by organisms  Macronutrients = required in larger amounts  Micronutrients = nutrients needed in smaller amounts  Nitrogen and phosphorus are the primary nutrients needed for plant and algal growth  Phosphorous in a “limiting nutrient” for freshwater  Nitrogen and iron are the “limiting nutrients” for saltwater

Nutrient cycles  Because of the their importance for plant growth, the cycling of carbon, nitrogen, and phosphorous are of special interest for ecosystems  These are known as biogeochemical cycles and are characterized by their  Pools (reservoirs) where nutrients reside for varying amounts of time (the residence time)  Flux = the rate at which materials move between pools which can change over time

Nutrient sources and sinks  Pools function as sources and sinks for nutrients depending on relative rates of in-flux and out-flux, yielding different residence times

The hydrologic (water) cycle  Process (flux) terms  Evaporation  Condensation  Precipitation  Run-off  Infiltration  Uptake  Transpiration  Extraction  Groundwater terms  Groundwater = water contained in soil/rock  Aquifer = a soil/rock layer that transmits and produces water easily  Water table = the upper surface of groundwater in unconfined aquifers  Discharge = the release of groundwater to surface water bodies

Hydrologic cycle diagram

Human impacts to 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

The carbon cycle  Carbon cycle = describes the route of carbon atoms through the environment  Photosynthesis by plants, algae and cyanobacteria removes carbon dioxide from air and water  Respiration returns carbon to the air and oceans  Sedimentary rocks are the primary long-term sink for carbon  The oceans, atmosphere, plants, and soil are also important pools

Carbon cycle diagram

Human impacts to carbon cycle  Burning fossil fuels moves carbon from geologic pools into the atmosphere  Cutting forests and burning fields moves carbon from vegetation into the atmosphere  Today’s atmospheric carbon dioxide reservoir is the largest in the past 800,000 years  Elevated atmospheric carbon dioxide is the driving force behind climate change  Ocean acidification results when carbon moves from the atmosphere into the ocean

The nitrogen cycle  Nitrogen cycle = describes the routes that nitrogen atoms take through the environment  Nitrogen gas comprises 78% of our atmosphere but cannot be used by organisms  Nitrogen fixation = lightning or nitrogen-fixing bacteria combine (fix) nitrogen with hydrogen to form ammonium (NH 4 + )

Nitrogen cycle processes  Nitrification = bacteria convert ammonium ions first into nitrite and nitrate ions which plants can take up  Animals obtain nitrogen by eating plants (animals)  Decomposers release NH 4 + to nitrifying bacteria  Denitrifying bacteria = convert nitrates in soil or water to gaseous nitrogen releasing it back to the atmosphere

Nitrogen cycle diagram

Human impacts to nitrogen cycle  Haber-Bosch process = production of fertilizers by combining nitrogen and hydrogen to synthesize ammonia  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-N soils  Changes estuaries and coastal ecosystems and fisheries

The phosphorus cycle  Phosphorus cycle = describes the routes that phosphorus atoms take through the environment  Sediments and sedimentary rocks are the primary pool  There is no significant atmospheric component  With naturally low environmental concentrations phosphorus is a limiting factor for plant growth

The phosphorus cycle

Humans impacts to phosphorus cycle  Mining rocks for fertilizer moves phosphorus from the soil to water systems  Wastewater discharges also release phosphorus  Runoff containing phosphorus causes eutrophication of aquatic systems