Decomposers, Aquatic and Nutrient Cycles
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Transcript of Decomposers, Aquatic and Nutrient Cycles
Decomposers, Aquatic and Nutrient Cycles
Heat Heat Heat Heat
Heat
Heat
Heat
First TrophicLevel
Second TrophicLevel
Third TrophicLevel
Fourth TrophicLevel
Solarenergy
Producers(plants)
Primaryconsumers(herbivores)
Tertiaryconsumers
(top carnivores)
Secondaryconsumers(carnivores)
Detritvores(decomposers and detritus feeders)
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.
Hydrologic Cycle• Collects, purifies, and distributes the
Earth’s fixed supply of water – powered by the sun.
• Distribution of Earth’s 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
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
Main Processes of the Hydrologic Cycle
Global Air Circulation & Regional Climates• Uneven heating of the Earth’s Surface– Air is more heated at the equator and less at
the poles.
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.
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.
Hypothetical Phosphorus Nutrient Cycle
Plants Herbivores
Water100
81126
91.4
7
133
9.519
45
Flux rate and pool size together define the nutrient cycle within any particular ecosystem
Nitrogen Cycle
• Nitrogen is used to make essential organic compounds such as proteins (amino acids), DNA, and RNA.
• Nitrogen is the atmosphere’s most abundant element (global gaseous cycle).• 78% of the volume is chemically un-reactive
nitrogen gas N2.
• Takes a lot of energy to break the triple covalent bonds holding N N
• Microbes mostly responsible for N cycle
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).
Gaseous N2
Nitrogen Fixation
Ammonia: NH3, NH4+
Food Web
1. Nitrification
Nitrite: NO2-
2. Nitrification
Nitrate: NO3-
Denitrification
Nitrogenous Waste
Ammonification
Ecosystem Nitrogen Cycle
Loss by Leaching
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 earth’s 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
Food web
Soil
River Flow
Ocean Water
Food web
Sediments
Guano
Mining
Phosphorous Cycle
Geologic Uplifting
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.
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.
Sulfur Cycle
Food Web
Organic Matter H2SHeterotrophic
microorganisms
SO4
Anaerobic Sulfur-reducers
Aerobic Sulfide-oxidizers
S
ExcretionSulfur bacteria
Sulfur bacteria
FeS
+Fe3
FeS2
OH SH
Soluble Phosphorous
Black Anaerobic Mud
Very Slow Flux Rate
Rap
id C
ycli
ng
Volcanoes, Sea spray
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 nature’s thermostat– Too much taken out of the atmosphere, temp’s
decrease– Too much added to atmosphere, temp’s increase
Primary Productivity
CO2
C6H12O6
Photosynthesis Respiration
Solar Energy
Heat Energy
Biomass (g/m2/yr)
O2
Available to Consumers
Chemical Energy (ATP)
NP
P
GP
P
Atmospheric / Aquatic CO2
Food Web
Photosynthesis RespirationCombustion of wood / fossil
fuels
Limestone Rocks
Carbon Cycle
SedimentationWeathering
Volcanic Action
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
Detritus Feeders and Decomposers
Without detritus feeders and decomposers, the lack of nutrients would quickly stop primary production!
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)
Nutrient Cycles in Forests
• Inputs – outputs = storage• Nutrients accumulate in the leaves and
wood over time
Nutrient Storage in Trees is Temperature and Vegetation Type Related
Organic matter (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.
Nutrient Turnover Time is Temperature Related
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
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)*
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.
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
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
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?
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
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.
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:
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
Mean calcium concentrations (% dry wt) in three plant species.
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
Deforestation Can Increase Loss of Nutrients From Areas Due to Runoff
Note Scale Change
Stream Nitrite Concentration
Other stream nutrient increase two years after the deforestation:
Calcium 417%, Magnesium 408%, Potassium 1,558%, Sodium 177%
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.
Other Methods to Control Erosion
• Silt Fence / hay bales– Allows water to pool so that sediment is
dropped.
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 by1) Weathering of rock2) Deposit of sediments by erosion3) Decomposition of organic matter in dead
animals
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 soil’s inorganic matter. Mostly broken-down rock consisting of varying mixtures of sand, silt, clay, and gravel.
O horizonO horizonLeaf litterLeaf litter
A horizonA horizonTopsoilTopsoil
B horizonB horizonSubsoilSubsoil
C horizonC horizonParentParent
materialmaterial
Mature soilMature soil
Young soilYoung soil
RegolithRegolithRegolithRegolith
BedrockBedrockBedrockBedrock
Immature soilImmature soil
Soil Horizons (Profiles)
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.
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
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
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).
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.