Spring 2004

Dr. Largen

Energy Flow and Matter Cycling

Energy flow vs. Matter Cycling

• energy flows through the earth system
• Matter cycles through the earth system

Matter cycles within ecosystems

• Organisms depend on the ability to recycle basic of "nutrients" of life
• nutrients (matter)
• any atom, molecule, or ion an organism needs to live, grow, or reproduce
• some required in fairly large quantities
• C, H, O, N, phosphorus, sulfur, calcium
• some required in small or trace amounts
• sodium, zinc, copper, iodine
• globally, only small portion of these substances is contained within organisms
• most exist in nonliving reservoirs
• atmosphere, water, rocks

• Matter cycles
• continually through both biotic and abiotic components of ecosystems
• called biogeochemical cycles.
• cyclic pathways involving biological, geological and chemical processes
• driven directly or indirectly by incoming solar radiation and gravity
• connect past, present, future forms of life

• cycling of matter through ecosystems
• begins with incorporation of substances into bodies of living organisms from non-living reservoirs
• materials pass from organisms that first acquire them into bodies of organisms that eat eat them
• until they complete the cycle and return to the nonliving world, through decomposition

• there are many biogeochemical cycles
• unified by involvement of four reservoirs of earth system through which matter cycles
• lithosphere (rocks and soils)
• atmosphere
• hydrosphere(oceans, surface waters, groundwater, glaciers)
• biosphere (living organisms)

• matter in these reservoirs have different average times of storage or cycling
• depending on two main determinants
• chemical reactivity of the substance
• whether it has a gaseous phase at some point in cycle

• Generalized average times of storage or cycling based on reservoir
• long
• lithosphere (rocks and soils)
• intermediate
• hydrosphere(oceans, surface waters, groundwaters, glaciers)
• biosphere (living organisms)
• short
• atmosphere

• 3 main categories of biogeochemical cycles
• Hydrologic
• Gaseous
• Sedimentary

• hydrologic
• hydrologic (water) cycle
• Gaseous
• involves exchanges among atmosphere, biosphere, soils and oceans
• include
• carbon Cycle
• oxygen Cycle
• nitrogen Cycle
• Sedimentary
• involves materials that move from land to oceans and back
• include
• phosphorous cycle
• sulfur cycle

• Main biogeochemical cycles
• hydrologic cycle
• hydrologic cycle
• gaseous
• carbon cycle
• nitrogen cycle
• sedimentary
• phosphorous cycle

Biogeochemical cycles: hydrologic

• hydrologic cycle
• most familiar of all biogeochemical cycles
• all life depends on water
• main constituent of bodies of most organisms
• source of H⁺, whose movements help generate ATP
• ~98% of all water on earth is free water
• circulating between atmosphere and oceans
• ~2% of all water on earth is captured in any form
• frozen
• held in soil
• incorporated into bodies of organisms
• function
• collects, purifies, distributes earth’s fixed supply of water
• main processes
• evaporation
• transpiration
• condensation
• precipitation
• infiltration
• percolation
• runoff
• hydrologic cycle - main processes
• evaporation
• conversion of liquid water (from surface waters and soils) to water vapor (in atmosphere)
• source of water vapor in atmosphere
• ~84% - evaporation from oceans
• which cover 3/4th of earth’s surface
• driven by energy from sun
• evapotranspiration
• evaporation from leaves of plants
• of water extracted from the soil by roots and transported throughout the plant
• driven by energy from sun
• condensation
• conversion of water vapor into droplets of liquid water
• necessary in order for precipitation to occur
• changes in temperature
• affect amount of moisture that can be "held" by an air mass
• precipitation
• conversion of water vapor into droplets of liquid water
• can take form of
• rain, sleet, hail, snow
• requires condensation nuclei
• tiny particles on which droplets of water vapor can collect
• sources include
• volcanic ash, soil dust, smoke, sea salts, particulate matter from human activities (factories, vehicles, power plants, etc.)
• fate
• becomes locked in glaciers
• impinges directly on oceans or other surface water bodies
• infiltrates soil or porous rock
• becomes surface runoff
• infiltration
• movement of water into soil and porous rock
• affected by
• substrate type
• vegetation cover
• degree of saturation
• topography
• percolation
• downward flow of water through soil and permeable rock formations
• to groundwater storage areas called aquifers
• to oceans
• dissolves and transports minerals and nutrients
• runoff
• down slope surface movement back to the sea to resume cycle
• replenishes surface waters such as lakes and streams
• causes soil erosion
• movement of soil and weathered rock fragments from one place top another
• human impacts
• have increased over past century via
• withdrawal of large quantities of freshwater from streams, lakes, underground sources
• for
• needs in heavily populated areas
• irrigation
• leads to
• groundwater shortages
• intrusion of ocean salt water into groundwater supplies
• vegetation removal
• for
• agriculture, mining, roads, timber harvesting, building construction
• leads to
• increased runoff
• reduced infiltration that recharges groundwater supplies
• increased risk of flooding
• accelerated soil erosion
• modification of water quality
• by adding
• nutrients (such as phosphates and nitrates in fertilizers
• pollutants
• changing ecological processes that purify water naturally

Biogeochemical cycles: carbon

• carbon cycle
• carbon
• essential to life as we know it
• building block of molecules of life
• based on carbon dioxide (gas)
• constitutes ~0.04% by volume of troposphere
• is key component of "nature’s thermostat"
• if too much CO₂ is removed from atmosphere, it will cool
• if too much CO₂ is added (or remains in) atmosphere, it will warm
• dissolved in ocean
• can trace carbon cycle by considering how carbon enters and leaves each of the four main reservoirs
• lithosphere
• largest reservoir for earth’ carbon
• rocks such as limestone (CaCO₃) deposited as sediment on ocean floor and on continents
• enters
• death, burial, compaction over geologic time
• becoming sediment, marine sediments, sedimentary rock, fossil fuels
• leaves
• very slowly
• weathering, uplifting over geologic time, volcanic activity
• exception: combustion of fossil fuels
• biosphere
• enters
• photosynthesis, consumption
• leaves
• cellular respiration, death
• hydrosphere
• oceans
• are second largest reservoir of earth’s carbon
• play role in regulating amount of CO₂ in atmosphere
• CO₂ is readily soluble in water
• fate
• some stays dissolved in sea water
• some is removed by marine photosynthesizing producers
• some reacts with sea water to form carbonate ions (CO₃^2-) and bicarbonate ions (HCO₃^-)
• enters
• weathering, leaching, runoff, diffusion, cellular respiration
• leaves
• photosynthesis, diffusion, incorporation into sediments
• atmosphere
• enters
• cellular respiration, combustion of wood, combustion of fossil fuels, volcanic action, diffusion from ocean
• leaves
• photosynthesis
• diffusion from the ocean
• flow of carbon in form of carbon dioxide from atmosphere to biosphere (photosynthesis) and back to atmosphere (respiration)
• is approximately in balance
• human impacts
• since industrial revolution and especially since mid-1950s, humans activities have been adding CO₂ to atmosphere in two ways
• clearing trees and plants that remove CO₂ via photosynthesis
• burning fossil fuels and wood
• fossil fuels
• over millions of years, buried deposits of dead organic matter become compressed between layers of sediment where they form carbon-containing fossil fuels such as coal and oil
• carbon in fossil fuels is not released into atmosphere for recycling until
• long-term geologic processes expose deposits to chemical and mechanical processes that can liberate carbon
• fossil fuels are extracted and burned
• in past few hundred years, humans have extracted and burned fossil fuels that took millions of years to form
• thus, removing carbon from its major reservoir far faster than it can be added to that reservoir
• causing disruption in carbon cycle
• in past few hundred years, humans have extracted and burned fossil fuels that took millions of years to form, resulting in
• removal of carbon from its major reservoir far faster than it can be added to that reservoir
• addition of carbon to atmosphere far faster than it can be removed
• human impacts
• consequence of increased atmospheric concentration of CO₂
• enhances planet’s natural greenhouse effect
• producing "global warming"
• consequences "global warming"
• will be discussed in detail later in course
• include
• disruption of global food production
• increase average sea level

Biogeochemical cycles: nitrogen

• nitrogen cycle
• nitrogen gas (N₂)
• constitutes ~78% of earth’s atmosphere
• cannot be absorbed or used directly by multicellular organisms
• must be "fixed" or combined with hydrogen or oxygen to provide compounds these organisms can use
• occurs via
• atmospheric electrical discharges in form of lightning
• activities of certain bacteria
• several processes involved
• nitrogen fixation
• converts gaseous nitrogen (N₂) to ammonia (NH₃), a form that can be used by plants
• N₂ + 3H₂ è 2NH₃
• carried out by specialized bacteria
• cyanobacteria in soil and water
• Rhizobium bacteria
• living in small nodules on root systems of variety of plants (including legumes such as soybeans, alfalfa)
• nitrification
• two step process carried out by specialized aerobic bacteria
• most of ammonia (NH₃) in soil is converted to nitrite ions (NO₂^-) which are toxic to plants
• nitrite ions are then converted to nitrate (NO₃^-) which are easily taken up by plants
• assimilation
• plants
• roots absorb inorganic ammonia (NH₃), ammonium ions (NH₄⁺), and nitrate ions (NO₃^-)
• use these ions to make nitrogen-containing organic molecules such as DNA, amino acids, proteins
• animals
• obtain their nitrogen by eating plants or plant-eating animals
• ammonification
• process of converting nitrogen-rich compounds of living organisms and their wastes back into
• simpler nitrogen-containing inorganic compounds such as ammonia (NH₃)
• water-soluble salts containing ammonium ions (NH₄⁺)
• carried out by variety of decomposer bacteria and fungi
• denitrification
• process of converting nitrogen compounds (ammonia, ammonium ions, nitrite ions, nitrate ions) back into nitrogen gas (N₂) which can be returned to atmosphere
• carried out by specialized bacteria
• mostly anaerobic bacteria in water-logged soil, in bottom sediments of lakes, oceans, swamps, bogs
• human impacts
• interventions in nitrogen cycle over past 100 years include
• adding adding nitric oxide to atmosphere
• adding nitrous oxide to atmosphere
• removing nitrogen from topsoil
• adding nitrogen compounds to aquatic ecosystems
• adding adding nitric oxide (NO) to atmosphere when burning fuel
• N₂ + O₂ è 2NO
• nitric oxide (NO) can combine with oxygen to form nitrogen dioxide (NO₂) which in turn can react with water vapor to nitric acid (HNO₃)
• droplets of nitric acid dissolved in rain or snow are components of acid deposition
• adding nitrous oxide (N₂O) atmosphere
• through action of
• anaerobic bacteria on livestock wastes
• commercial inorganic fertilizers applied to soil
• which can reach stratosphere
• enhance natural greenhouse effect
• contribute to ozone depletion
• removing nitrogen from topsoil
• via
• harvest of nitrogen-rich crops
• irrigation of crops (leaching)
• burning or clearing forests or grasslands
• adding nitrogen compounds to aquatic ecosystems
• via
• agricultural runoff
• discharge of municipal sewage
• constitutes excess nutrients that
• stimulate rapid growth of algae and aquatic plants
• can lead to
• depletion of water dissolved oxygen(via action of decomposers)
• disruption of aquatic ecosystems

Biogeochemical cycles: phosphorus

• phosphorous cycle
• phosphorous
• plays a critical role in plant nutrition
• is element most likely to be scarce enough to limit plant growth
• exists in soil only in small amounts
• when it weathers out of soil its transported to rivers and oceans and eventually accumulates in sediment
• is found in atmosphere only as small particles of dust
• at normal temperatures and pressures it is not in gas form
• is only naturally brought back up from sediments by the uplift of lands or by marine animals
• which can be consumed by animals such as seabirds
• which then deposit guano (feces) rich in phosphorous, and can be used as fertilizer
• human impacts
• interventions in nitrogen cycle over past 100 years include
• mining
• large quantities of phosphate rock for use in
• commercial inorganic fertilizers
• detergents
• reducing available phosphate in tropical forests
• by removing trees
• causes phosphorus in soil to be washed away
• human impacts
• adding phosphate to aquatic ecosystems
• via
• runoff from animal wastes from livestock feedlots
• runoff of commercial phosphate fertilizers from cropland
• discharge of municipal sewage