Decomposers, Aquatic and Nutrient Cycles

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Decomposers, Aquatic and Nutrient Cycles
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Three Major Types of Nutrient Cycles

• Hydrologic (or water) Cycle water in the form
  of ice, liquid water and water vapor cycles
  through the biosphere.
• Atmospheric Cycle a large portion of a given
  element exists in a gaseous form in the
  atmosphere.
• Sedimentary Cycle An element does not have a
  gaseous phase, or its gaseous compounds do not
  make up a significant portion of its supply.

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Hydrologic Cycle

• Collects, purifies, and distributes the Earths
  fixed supply of water powered by the sun.
• Distribution of Earths Water Supply
• Salt water (oceans) 97.4
• Freshwater 2.6
• 80 in glaciers and ice caps
• 20 in groundwater
• 0.4 in lakes and rivers (0.01 of all water!)
• Anytime of year, the atmosphere holds only
  0.0001 of water on the planet.
• Although large quantities are evaporated and
  precipitated each year
• About 84 of water vapor comes from the ocean

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Main Processes of the Hydrologic Cycle

1. Evaporation conversion of water into water
   vapor
2. Transpiration evaporation from leaves of water
   extracted from soil by roots
3. Condensation conversion of water vapor into
   droplets of liquid water
4. Precipitation rain, sleet, hail, and snow
5. Infiltration movement of water into soil
6. Percolation downward flow of water through soil
   and permeable rock formations to groundwater
   storage areas called aquifers
7. Runoff downslope surface movement back to the
   sea to resume cycle

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Hydrologic Cycle
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Global Air Circulation Regional Climates

• Uneven heating of the Earths Surface
• Air is more heated at the equator and less at the
  poles.

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Global Air Circulation Regional Climates

• Seasonal changes in temperature and precipitation

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Insolation
B
A
C
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Solar Energy
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Rainy Season
Seasonal shift in rainy/dry seasons
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Matter Cycling in Ecosystems

• Nutrient any atom, ion, or molecule an organism
  needs to live, grow, or reproduce
• Some (such as C, O, H, N, P, S, and Ca) are
  needed in fairly large amounts
• Some (such as Na, Zn, Cu, and I) are only needed
  in trace amounts.

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Nutrient Cycles

• Compartment represents a defined space in
  nature
• Pool amount of nutrients in a compartment
• Flux rate the quantity of nutrient passing from
  one pool to another per unit time.

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Major Nutrient Cycle Pathways
Flux rate
Pool
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Hypothetical Phosphorus Nutrient Cycle
81
126
9
1.4
133
7
45
19
100
9.5
Flux rate and pool size together define the
nutrient cycle within any particular ecosystem
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Nitrogen Cycle
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Have You Hugged Your Microbes Today? Besides
making beer, they are responsible for

• Nitrogen fixation conversion of gaseous nitrogen
  (by Rhizobium, Azotobacter, and cyanobacteria) to
  ammonia (N2 3H2 ? 2NH3) which can be used by
  plants.
• Nitrification - Two-step process in which ammonia
  is converted first to NO2- (by Nitrosomonas) and
  then to NO3- (by Nitrobacter).
• Denitrification conversion of nitrate ions (by
  Pseudomonas or other anaerobic bacteria in
  waterlogged soil or in the bottom sediments of a
  water body) into nitrogen gas (N2) and nitrous
  oxide gas (N2O)
• Ammonification the conversion (by decomposer
  heterotrophic bacteria) of nitrogen-rich organic
  compounds, wastes, cast-off particles, and dead
  bodies into available ammonia (which can be used
  by plants).

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Energy and the Nitrogen Cycle
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Nitrogen Cycle
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Phosphorous Cycle

• The phopsphorous cycle is slow, and on a human
  time scale most phosphorous flows from the land
  to the sea.
• Circulates through the earths crust, water, and
  living organisms as phosphate (PO4)
• Bacteria are less important here than in the
  nitrogen cycle
• Guano (bird poop), mined sediments, and uphill
  movement of wastewater are the main ways
  phosphorous is cycled in our lifetime
• Geologic process (mountain formations / uplifting
  of ocean sediments) cycle phosphorus in geologic
  time

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Phosphorous Cycle
Guano
Food web
River Flow
Soil
Ocean Water
Geologic Uplifting
Food web
Sediments
Mining
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Phosphorous is Important

• Most soils contain very little phosphorous
  therefore, it is often the limiting factor for
  plant growth on land unless added as fertilizer.
• Phosphorous also limits primary producer growth
  in freshwater aquatic ecosystems.

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Phosphorous Cycle
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Sulfur Cycle

• The sulfur cycle is a gaseous cycle.
• Sulfate (SO4) is the principal biological form
• Essential for some amino acids
• Usually not limiting, but the formation of iron
  sulfides converts the insoluble form of
  phosphorous to a soluble form
• Sulfur enters the atmosphere from several natural
  sources.
• Hydrogen sulfide (H2S) is released by volcanic
  activity and by the breakdown of organic matter
  in swamps, bogs, and tidal flats (you can smell
  this at low tide in the salt marsh).
• Sulfur dioxide (SO42-) enters from volcanoes.
• Particles of sulfate (SO42-) salts, such as
  ammonium sulfate, enter as seas spray.

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Sulfur Cycle
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Sulfur Cycle
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Carbon Cycle

• Carbon is the basic building block of organic
  compounds necessary for life.
• The carbon cycle is a global gaseous cycle
• Carbon dioxide makes up 0.036 of the troposphere
  and is also dissolved in water
• Key component of natures thermostat
• Too much taken out of the atmosphere, temps
  decrease
• Too much added to atmosphere, temps increase

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GPP
NPP
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The Recyclers

• Detritus parts of dead organisms and cast-off
  fragments and wastes of living organisms
• Detritivores organisms that feed on detritus
  (detritus feeders and decomposers).
• Detritus feeders extract nutrients from
  partially decomposed organic matter in leaf
  litter, plant detritus, and animal dung (crabs,
  carpenter ants, termites, earthworms).
• Decomposers (certain types of bacteria and fungi)
  are very important in recycling nutrients in an
  ecosystem

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Detritus Feeders and Decomposers
Without detritus feeders and decomposers, the
lack of nutrients would quickly stop primary
production!
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Turnover and Residence Times

• Turnover rate the fraction of the total amount
  of a nutrient in a compartment that is released
  (or that enters) in a given period
• Turnover time the time needed to replace a
  quantity of a substance equal to its amount in
  the compartment
• Residence time the time a nutrient stays in a
  compartment (similar to turnover time)

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Nutrient Cycles in Forests

• Inputs outputs ?storage
• Nutrients accumulate in the leaves and wood over
  time

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Nutrient Storage in Trees is Temperature and
Vegetation Type Related
Organic matter (kg/ha) Organic matter (kg/ha) Organic matter (kg/ha) Nitrogen (kg/ha) Nitrogen (kg/ha) Nitrogen (kg/ha)
Forest Region Trees Total Above Ground Trees Total Above Ground
Boreal coniferous 3 51,000 226,000 19 116 3,250 4
Boreal deciduous 1 97,000 491,000 20 331 3,780 6
Temperate coniferous 13 307,000 618,000 54 479 7,300 7
Temperate deciduous 14 152,000 389,000 40 442 5,619 8
Mediterranean 1 269,000 326,000 83 745 1,025 73
Average 208,000 468,000 45 429 5,893 7
In cold climates nutrients are tied up in the
soil.
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Nutrient Turnover Time is Temperature Related
Mean turnover time (yr) Mean turnover time (yr) Mean turnover time (yr) Mean turnover time (yr) Mean turnover time (yr) Mean turnover time (yr)
Forest Region Organic matter N K Ca Mg P
Boreal coniferous 3 353 230.0 94.0 149.0 455.0 324.0
Boreal deciduous 1 26 27.1 10.0 13.8 14.2 15.2
Temperate coniferous 13 17 17.9 2.2 5.9 12.9 15.3
Temperate deciduous 14 4 5.5 1.3 3.0 3.4 5.8
Mediterranean 1 3 3.6 0.2 3.8 2.2 0.9
All Stands 32 12 34.1 13.0 21.8 61.4 46.0
Turnover time the time an average atom will
remain in the soil before it is recycled into the
trees or shrubs
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Net Primary Production and Nutrient Cycling

• In general, NPP is closely related to the speed
  of nutrient cycling.
• Tracking the decay of a leaf and the cycling rate
  of nutrients provides an indicator of biome
  productivity.

Mean Residence Time (In Years) Mean Residence Time (In Years) Mean Residence Time (In Years) Mean Residence Time (In Years) Mean Residence Time (In Years) Mean Residence Time (In Years)
Biome Organic matter Nitrogen Phosphorous Potassium Calcium Magnesium NPP (g C/m2/yr)
Boreal forest 353 230 324 94 149 455 360
Temperate forest 4 5.5 5.8 1.3 3.0 3.4 540
Chaparral 3.8 4.2 3.6 1.4 5.0 2.8 270
Tropical rain forest 0.4 2.0 1.6 0.7 1.5 1.1 900
Mean residence time is the time for one cycle
of decomposition.
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Rapid Cycling in the Tropics

• Reasons for rapid cycling in the tropics
• Warm climate
• No winter to retard decomposition
• An army of decomposers
• Abundant mycorrhizal fungi on shallow roots
• Fungi that grow symbiotically with plant roots
• Facilitate water and nutrient uptake

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The Tropics A Closed System

• The speed of nutrient cycling in the humid
  tropics promotes high productivity, even when
  soils are poor in nutrients.
• Nutrients are cycled so quickly there is little
  opportunity for them to leak from the system
• Waters in local streams and rivers can have as
  few nutrients as rain water
• Because there is virtually no loss of nutrients,
  many tropical forests have virtually closed
  nutrient cycles.
• The opposite would be an open system, in which
  nutrients are washed out rapidly

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Tropical Rain Forest Paradox

• Most tropical rain forests are poor in nutrients
  especially oxisol.
• When the forests are cleared for farmland, the
  land can only support three or four harvests.
• Well, how can they support the amount of primary
  production we find in a tropical rain forest?

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Standing Biomass

• Standing Biomass - all the plant matter in a
  given area.
• Nutrients are either found in the soil or in the
  standing biomass.
• In a temperate forest system, recycling is slow.
• Consequently, at any given time, a large
  proportion of nutrients are in the soil.
• So when the land is cleared, it is fertile and
  can support many years of agriculture

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Tropical Soils

• In the humid tropics, as little as 10 of the
  total nutrients are in an oxisol (soil) at any
  given time.
• Hence, when the logging trucks take the trees,
  they are carrying the majority of the nutrients!
• An increase in soil acidity often follows timber
  removal to the point that available phosphorous
  is transformed to an insoluble form.

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Watershed Biogeochemistry

• Watershed catchment or drainage basin of a
  river
• Streams and rivers are main conduits of nutrient
  loss
• Vegetation type can influence nutrient loss

Mean calcium concentrations ( dry wt) in three
plant species.
Species Bark Wood Twigs Leaves
Chestnut Oak 1.25 0.17 0.09 0.01 0.68 0.06 0.58 0.07
Flowering Dogwood 2.36 0.26 0.11 0.01 0.80 0.06 1.85 0.11
Rhododendron 0.30 0.10 0.07 0.31 0.99 0.24 1.20 0.29
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Normal Nutrient Loss

• Rain runoff is the major vector of nutrient loss
  from most ecosystems

Precipitation (mg/L) Streamwater (mg/L)
Calcium 0.21 1.58
Magnesium 0.06 0.39
Potassium 0.09 0.23
Sodium 0.12 0.92
Aluminum ---a 0.24
Ammonium 0.22 0.05
Sulfate 3.10 6.40
Nitrate 1.31 1.14
Chloride 0.42 0.64
Bicarbonate --- a 1.90
Dissolved silica --- a 4.61b
a Not determined, but very low b Watershed 4 only
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Deforestation Can Increase Loss of Nutrients From
Areas Due to Runoff
Other stream nutrient increase two years after
the deforestation Calcium 417, Magnesium 408,
Potassium 1,558, Sodium 177
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Riparian Buffer Zone

• Areas of trees, shrubs and other vegetation, that
  are adjacent to a body of water, that are managed
  for several purposes
• to maintain the integrity of stream channels and
  shorelines
• to reduce the impact of upland sources of
  pollution by trapping, filtering, and converting
  sediments, nutrients and other chemicals
• to supply food, cover and thermal protection to
  fish and other wildlife.
• The main purpose of a riparian buffer is to help
  control non-point source pollution.

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Three Zone Riparian Buffer
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Other Methods to Control Erosion

• Silt Fence / hay bales
• Allows water to pool so that sediment is dropped.

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What is Soil?

• Complex mixture of eroded rock, mineral
  nutrients, decaying organic matter, water, air,
  and billions of living organisms (mostly
  decomposers)
• Soil is created by
• Weathering of rock
• Deposit of sediments by erosion
• Decomposition of organic matter in dead animals

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Soil Horizons (Profiles)

• O horizon - Consists mostly of freshly fallen and
  partially decomposed leaves, twigs, animal
  wastes, fungi, and other organic materials.
• A horizon - A porous mixture of partially
  decomposed organic matter (humus) and some
  inorganic mineral particles.
• Humus is a sticky, brown residue of partially
  decomposed organic material.
• B Horizon (sub-soil) and C horizon (parent
  material) - Contain most of a soils inorganic
  matter. Mostly broken-down rock consisting of
  varying mixtures of sand, silt, clay, and gravel.

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Soil Horizons (Profiles)
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Life in Soil

• The two top layers of most well-developed soils
  teem with bacteria, fungi, earthworms, and small
  insects that interact in complex food webs and
  nutrient cycles.

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Soil Texture

• Clay very fine particles
• Silt fine particles
• Sand medium-size particles
• Gravel Coarse to very coarse particles

Loam roughly equal mixtures of clay, sand,
silt, and humus
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Soil Texture
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Topsoil Renewable Resource?

• Is regenerated by renewable resources, but it
  takes 200 - 1,000 years to produce about an inch
  of topsoil in tropical and temperate climates
• Rate depends on climate and soil type
• If erosion exceeds regeneration, then the
  resource is not renewable

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Soil erosion movement of soil components,
especially surface litter and top soil, from one
place to another. - Typically caused by flowing
water and wind Any activity that destroys plant
cover makes soil vulnerable to erosion (e.g.,
farming, logging, construction, over-grazing by
livestock, off-road vehicles, and deliberate
burning of vegetation).
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Moving Water Causes Most Soil Erosion

• Sheet Erosion fairly uniform sheets of soils
  are removed as surface water flows over a slope
  or across a field in a wide flow.
• Rill Erosion occurs when surface water forms
  fast-flowing rivulets that cuts small channels
  in the soil.
• Gully Erosion occurs when rivulets of
  fast-flowing water join each other and with each
  succeeding rain cut the channels wider and deeper
  until they become ditches or gullies.

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Harmful Effects of Soil Erosion

1. Loss of soil fertility and its ability to hold
   water
2. Runoff of sediment that pollutes water, kills
   fish and shellfish, and clogs irrigation ditches,
   boat channels, reservoirs, and lakes.