V - Nutrient Cycling & Soils Flashcards
Nutrient cycles
natural processes that involve the flow of nutrients from the nonliving
environment (air, water, soil, rock) to living organisms (biota)
& back again.
three major types
Hydrologic
Atmospheric
Sedimentary
Hydrologic
involving flows through the hydrosphere,
in the form of liquid water, compounds dissolved in
water, & sediments carried by water
Atmospheric
involving flows through the
atmosphere, as gases or airborne particles
(particulates)
Sedimentary
involving flows through the lithosphere
(Earth’s crust = soil & rock), as solid minerals
Nutrient cycles involve
one–way flow of high– quality energy from the sun through the environment & recycling of crucial elements.
Carbon main nonliving storehouse
Atmospheric carbon dioxide
Carbon main forms in living organisms
Carbohydrates and all other organic molecules
Carbon other nonliving storehouse
Hydrologic dissolved carbonate/ bicarbonate
Nitrogen main nonliving storehouse
Atmospheric: nitrogen gas
Nitrogen main forms in living organisms
Proteins & other nitrogen-containing organic molecules
Nitrogen other nonliving storehouse
Hydrologic : dissolved ammonium, nitrate, nitrite in water & soils
Phosphorus main nonliving storehouse
Sedimentary phosphate containing minerals in rocks
Phosphorus main forms in living organisms
DNA, other nucleic acids- ATP -& phospholipids
Phosphorus other nonliving storehouse
Hydrologic dissolved phosphate
Sulfur main nonliving storehouse
Sedimentary rocks -iron disulfide & pyrite - and mineral - sulfate
Sulfur main forms in living organisms
Sulfur-containing amino acids in most proteins, some vitamins
Sulfur other nonliving storehouse
Atmospheric hydrogen sulfide, sulfur dioxide, sulfur trioxide, sulfuric acid
Hydrologic sulfate & sulfuric acid
Role of water
• terrestrial ecosystems – major factor determining
distribution of organisms;
• aquatic ecosystems – literally matrix that surrounds &
serves as environment of aquatic organisms;
• flows of water are major means of material & energy
transport;
• water is critical for human activities – agriculture,
industry, & municipal use
Main processes in water cycle?
Evaporation Transpiration Movement in atmosphere Condensation Precipitation Infiltration Percolation Flow in aquifers Runoff
Evaporation
conversion from liquid to vapor form (surface
to atmosphere)
Transpiration
evaporation from leaves of water extracted
from soil by roots & transported through the plant (surface to
atmosphere)
Movement in atmosphere
transport as vapor
Condensation
conversion of vapor to liquid droplets
Precipitation
movement as rain, sleet, hail, & snow
atmosphere to surface
Infiltration
movement into soil
Percolation
downward flow through soil to aquifers
Flow in aquifers
belowground flow of water.
Runoff
surface flow downslope to ocean.
Human Influences on water cycles?
• withdraw large quantities of fresh water – water
diversion, groundwater depletion, wetland drainage
• clear vegetation – increase runoff, decrease infiltration
& groundwater recharge, increase flooding & soil
erosion;
• modify water quality – add nutrients (P, N…) & pollutants
Role of carbon
• building block of organic molecules (carbohydrates,
fats, proteins, & nucleic acid) – essential to life;
• currency of energy exchange – chemical energy for
life stored as bonds in organic compounds;
• carbon dioxide (CO
2) greenhouse gas – traps heat
near Earth’s surface & plays a key role as “nature’s
thermostat”.
How is Carbon Cycled?
Carbon cycling between the atmosphere & terrestrial ecosystems.
Natural & synthetic admission of carbon
Volcanoes & wildfires
Burning of fossil fuels
Role of ocean in carbon cycle
Large amounts of carbon are buried in sediments in the form of calcium carbonate (CaCO3)
Main processes in carbon cycle
Movement in atmosphere Primary production Movement through food web Aerobic respiration Combustion dissolving in oceans Movement to sediments
Movement in atmosphere
atmospheric C as CO2 (0.036%
of troposphere)
Primary production
photosynthesis (= carbon fixation)
moves C from atmosphere to organic molecules in organisms;
Movement through food web
C movement in organic form
from organism to organism;
Aerobic respiration
organic molecules broken down to
release CO2 back to atmosphere;
Combustion
organic molecules broken by burning down to
release CO2 back to atmosphere;
Dissolving in oceans
: C enters as to form carbonate (CO32–)
& bicarbonate (HCO3–);
Movement to sediments
C enters sediments, primarily as calcium carbonate (CaCO3);
Human Influences on Carbon cycle?
• removal of vegetation – decreases primary production
(decreases carbon fixation);
• burning fossil fuels & biomass (wood) – increase
movement of carbon into the atmosphere;
• the resulting increased concentration of
atmospheric CO2 is believed to be sufficient to
modify world climate through global warming
Role of nitrogen
• building block of various essential organic
molecules – especially proteins & nucleic acids;
• limiting nutrient in many ecosystems – typically,
addition of N leads to increased productivity.
How is Nitrogen Cycled?
Atmosphere
Ecosystem
Soil
Main processes in nitrogen cycles
Nitrogen fixation Nitrification uptake Ammonification Denitrification
Nitrogen fixation
conversion of N
2 (nitrogen gas) to NH
4+(ammonium), atmospheric by lightning, biological by
bacteria & blue-green algae (anaerobic), e.g., Rhizobium in
legumes;
Nitrification
conversion of NH
4+ to NO3- (nitrite) to NO3- (nitrate) by microbes
Uptake
by plants, forms proteins and other N containing
organic compounds, enters food chain;
Ammonification
returned to NH
4+ inorganic forms by
saprophytes and decomposers;
Denitrification
conversion of NH
4+ to N2 by combustion or
microbes
Human Influences on nitrogen cycle?
• emit nitric oxide (NO), which leads to acid rain – huge quantities of nitric oxide emitted; contributes to photochemical smog; forms nitrogen dioxide (NO2) in atmosphere, which can react with water to form nitric acid(HNO3) & cause acid deposition (“acid rain”)
• emit nitrous oxide into the atmosphere – nitrous oxide (N2O) is a potent greenhouse gas & also depletes ozone in stratosphere
• mine nitrogen–containing fertilizers, deplete nitrogen
from croplands, & leach nitrate from soil by irrigation
– leads to modification of nitrogen distribution in soils;
• remove N from soil by burning grasslands & cutting
forest – leads to decreased N in soils;
• add excess N to aquatic systems – runoff of nitrates &
other soluble N–containing compounds stimulates algal blooms, depletes oxygen, & decreases biodiversity;
• add excess N to terrestrial systems – atmospheric
deposition increases growth of some species (especially weeds) & can decrease biodiversity
Role of Phosphorus?
- essential nutrient for plants & animals
* limiting nutrient in many ecosystems
Essential nutrient for plants & animals
especially building block for DNA, other nucleic acids
(including ATP; ATP stores chemical energy), various
fats in cell membranes (phospholipids), & hard calcium–
phosphate compounds (in bones, teeth, & shells);
limiting nutrient in many ecosystems
typically,
addition of P leads to increased productivity, especially
for fresh water aquatic systems.
How is Phosphorus Cycled?
Hydrospheric
Ecosystem
Main processes in phosphorus cycle?
Weathering Uptake Movement through food web Breakdown of organic forms Leaching Burial in ocean sediments
Weathering
P slowly released from rock or soil minerals
as phosphate (P04
3-), which dissolves in H20 & is readily
leached;
Uptake
by plants to form organic phosphates;
Movement through food web
nucleic acids (including
DNA & ATP), certain fats in cell membranes (phospholipids),
bones/teeth/shells (calcium–phosphate);
Breakdown of organic forms
to phosphate (P043-) by decomposers
Leaching
P043- from soil
Burial in ocean sediments
not cycled in short time scale, only over geologic time
Human Influences on phosphorus cycles?
• mine large quantities of phosphate rock – used for
organic fertilizers & detergents; can cause local effects from
mining & releases more P into environment;
• sharply decrease P available in tropical forests &
other ecosystems where P is limiting – deforestation
& certain agricultural practices decrease available P;
• add excess P to aquatic ecosystems – leads to
excessive algal growth, depletion of oxygen, & decrease in
biodiversity; such eutrophication (“over nourishment”)
Role of Sulfur?
• component of some proteins & vitamins
– essential for organisms;
• limiting nutrient in some ecosystems
How is sulfur cycled?
Abiotically & Biotically
Main processes in sulfur cycle
Storage in rocks
Atmospheric input from volcanoes, anaerobic decay, & sea spray
Combustion
Movement through food web
storage in rocks
much of Earth’s S is in rock form (e.g.,
iron disulfides or pyrites) or minerals (sulfates);
atmospheric input from volcanoes, anaerobic
decay, & sea spray
S enters atmosphere in form of
hydrogen sulfide (HS) & sulfur dioxide (SO2), & sulfates
(SO42–)
combustion
sulfur compounds released to the
atmosphere by oil refining, burning of fossil fuels, smelting, & various industrial activities
movement through food web
movement through food web & eventual release during decay
Human Influences on sulfur cycles?
contribute about one–third of atmospheric sulfur emissions • burning S–containing oil & coal; • refining petroleum; • smelting; • other industrial processes
soil
complex mixture of inorganic material (clay,
silt, & sand), decaying organic matter, air, water, & living organisms
Characteristics of soil
• rich in biological life, including bacteria, fungi, &
invertebrates;
• complex ecosystem;
• develop & mature slowly –– can take 200 to
1,00 years to develop 2.5 cm (1 inch) or topsoil
(A horizon);
• well developed soils display distinct horizons, or
soil profiles.
Rock cycle
transformations of rock over millions of years. Phosphorus cycle part of rock cycle
Main processes in rock cycle
Weathering Erosion Transportation Deposition Melting Cooling Heat & Pressure
Weathering
g
Erosion
g
Transportation
g
Deposition
g
Melting
g
Cooling
g
Heat & Pressure
g
Soil Profiles
Horizons, or layers, vary in number & composition,
depending upon soil type.
Soils from different biomes display
different profiles.
Soil texture is determined by
the particular mix of
clay, silt, & sand.
Types of soil textures
Clay Sandy clay silty clay Silty clay loam Clay loam Sandy clay loam Loam Silty loam Sandy loam Loamy sand Sand silt
The pH scale is used to measure
acidity & alkalinity of water solutions.
pH is an
important soil property.
Soil Food Webs
Complex
Many different organisms + organic debris
Soil Nutrient Cycling
Nitrogen, phosphorus, and potassium are among the major nutrients
Are ecosystems self–contained?
• immature natural ecosystems tend to have major shifts in
energy flow & nutrient cycling;
• over time ecosystems tend to reach an equilibrium with
respect to energy flow & nutrient cycling, such that these
ecosystems appear self–contained;
• however, there is considerable exchange of water &
nutrients of ecosystems with adjacent ecosystems;
• human disturbance (clear cutting, clearing, etc.) can cause
major loss of nutrients.
How does nutrient cycling relate to ecosystem
sustainability?
• the law of conservation of matter enables us to understand
major nutrient cycles, and observe that given time natural
ecosystems tend to come into a balance wherein nutrients are
recycled with relative efficiency;
• modification of major nutrient cycles may lead to shift in
ecosystems, such that current ecosystems are not sustainable;
• developing a better understanding of energy flow & nutrient
cycling is critical to understanding the depth of environmental
problems.
Organisms found in soil food webs includes
flatworms Rove beetle Ant Centipede Mite Ground beetles Fungi Snail Slug Earthworm Sowbug Adult fly
