1. Decomposers, Aquatic and Nutrient Cycles
Heat
First Trophic
Level
Second Trophic
Third Trophic
Fourth Trophic
Solar
energy
Producers
(plants)
Primary
consumers
(herbivores)
Tertiary
(top carnivores)
Secondary
(carnivores)
Detritvores
(decomposers and detritus feeders)

2. 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.

3. 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 % of water on the planet.
Although large quantities are evaporated and precipitated each year
About 84% of water vapor comes from the ocean

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

5. Hydrologic Cycle 1 2 4 3 5 6 7

6. Global Air Circulation & Regional Climates
Uneven heating of the Earth’s Surface
Air is more heated at the equator and less at the poles.

7. Global Air Circulation & Regional Climates
Seasonal changes in temperature and precipitation

8. Insolation B A C

9. Solar Energy

10. Seasonal shift in rainy/dry seasons
Rainy Season
Seasonal shift in rainy/dry seasons

11. 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.

12. 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.

13. Major Nutrient Cycle Pathways
Flux rate
Pool

14. Hypothetical Phosphorus Nutrient Cycle
Plants
Herbivores
Water
126 81
1.4 9
133 7 45 19
100
9.5
Flux rate and pool size together define the nutrient cycle within any particular ecosystem

15. 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

16. Have You Hugged Your Microbes Today
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).

17. Ecosystem Nitrogen Cycle
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

18. Energy and the Nitrogen Cycle
Provides Energy
Nitrate
Proteins
Requires Energy

19. Nitrogen Cycle

20. 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

21. Phosphorous Cycle Guano Food web River Flow Soil Ocean Water
Geologic Uplifting
Food web
Mining
Sediments

22. 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.

23. Phosphorous Cycle

24. 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.

25. Sulfur Cycle Food Web Organic Matter H2S SO4 S FeS FeS2
Heterotrophic microorganisms
SO4
Anaerobic Sulfur-reducers
Aerobic Sulfide-oxidizers S
Excretion
Sulfur bacteria
FeS
+Fe3
FeS2
OH SH
Soluble Phosphorous
Black Anaerobic Mud
Very Slow Flux Rate
Rapid Cycling
Volcanoes, Sea spray

26. Sulfur Cycle

27. 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

28. Available to Consumers
Primary Productivity
CO2
C6H12O6
Photosynthesis
Respiration
Solar Energy
Heat Energy
Biomass (g/m2/yr) O2
Available to Consumers
Chemical Energy (ATP)
GPP
NPP

29. Atmospheric / Aquatic CO2 Combustion of wood / fossil fuels
Food Web
Photosynthesis
Respiration
Combustion of wood / fossil fuels
Limestone Rocks
Carbon Cycle
Sedimentation
Weathering
Volcanic Action

30. 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

31. Detritus Feeders and Decomposers
Without detritus feeders and decomposers, the lack of nutrients would quickly stop primary production!

32. 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)

33. Nutrient Cycles in Forests
Inputs – outputs = storage
Nutrients accumulate in the leaves and wood over time

34. Nutrient Storage in Trees is Temperature and Vegetation Type Related
Organic matter (kg/ha)
Nitrogen (kg/ha)
Forest Region #
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
269,000
326,000 83
745
1,025 73
Average
208,000
468,000 45
429
5,893
In cold climates nutrients are tied up in the soil.

35. 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
3.6
0.2
3.8
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

36. 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.

37. 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

38. 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

39. 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?

40. 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

41. 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.

42. 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

43. 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
4.61b
a Not determined, but very low; b Watershed 4 only

44. 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%

45. 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.

46. Three Zone Riparian Buffer

47. Other Methods to Control Erosion
Silt Fence / hay bales
Allows water to pool so that sediment is dropped.

48. 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

49. 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.

50. Soil Horizons (Profiles)
O horizon
Leaf litter
A horizon
Topsoil
B horizon
Subsoil
C horizon
Parent
material
Mature soil
Young soil
Regolith
Bedrock
Immature soil

51. 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.

52. 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

53. Soil Texture

54. Topsoil – Renewable Resource?
Is regenerated by renewable resources, but it takes ,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

55. 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).

56. 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.

57. Harmful Effects of Soil Erosion
Loss of soil fertility and its ability to hold water
Runoff of sediment that pollutes water, kills fish and shellfish, and clogs irrigation ditches, boat channels, reservoirs, and lakes.