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Decomposers, Aquatic and Nutrient Cycles Heat First Trophic Level Second Trophic Level Third Trophic Level Fourth Trophic Level Solar energy Producers.

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Presentation on theme: "Decomposers, Aquatic and Nutrient Cycles Heat First Trophic Level Second Trophic Level Third Trophic Level Fourth Trophic Level Solar energy Producers."— Presentation transcript:

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

5 Hydrologic Cycle

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 A C B

9 Solar Energy

10 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 Pool Flux rate

14 Hypothetical Phosphorus Nutrient Cycle PlantsHerbivores Water 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 N 2. 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? Besides making beer, they are responsible for: Nitrogen fixation –conversion of gaseous nitrogen (by Rhizobium, Azotobacter, and cyanobacteria) to ammonia (N 2 + 3H 2  2NH 3 ) which can be used by plants. Nitrification - Two-step process in which ammonia is converted first to NO 2 - (by Nitrosomonas) and then to NO 3 - (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 (N 2 ) and nitrous oxide gas (N 2 O) 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 Gaseous N 2 Nitrogen Fixation Ammonia: NH 3, NH 4 + Food Web 1. Nitrification Nitrite: NO Nitrification Nitrate: NO 3 - Denitrification Nitrogenous Waste Ammonification Ecosystem Nitrogen Cycle Loss by Leaching

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

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 (PO 4 ) –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 Food web Soil River Flow Ocean Water Food web Sediments Guano Mining Phosphorous Cycle Geologic Uplifting

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 (SO 4 ) 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 (H 2 S) 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 (SO 4 2- ) enters from volcanoes. –Particles of sulfate (SO 4 2- ) salts, such as ammonium sulfate, enter as seas spray.

25 Sulfur Cycle Food Web Organic MatterH2SH2S Heterotrophic microorganisms SO 4 Anaerobic Sulfur- reducers Aerobic Sulfide- oxidizers S Excretion Sulfur bacteria FeS +Fe 3 FeS 2 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 Primary Productivity CO 2 C 6 H 12 O 6 Photosynthesis Respiration Solar Energy Heat Energy Biomass (g/m 2 /yr) O2O2 Available to Consumers Chemical Energy (ATP) NPP GPP

29 Atmospheric / Aquatic CO 2 Food Web PhotosynthesisRespiration Combustion of wood / fossil fuels Limestone Rocks Carbon Cycle SedimentationWeathering 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#TreesTotal % Above Ground TreesTotal % Above Ground Boreal coniferous351,000226, ,2504 Boreal deciduous197,000491, ,7806 Temperate coniferous13307,000618, ,3007 Temperate deciduous14152,000389, ,6198 Mediterranean1269,000326, ,02573 Average208,000468, ,8937 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 NKCaMgP Boreal coniferous Boreal deciduous Temperate coniferous Temperate deciduous Mediterranean All Stands 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)* BiomeOrganic matter NitrogenPhosphorousPotassiumCalciumMagnesiumNPP (g C/m 2 /yr) Boreal forest Temperate forest Chaparral Tropical rain forest * 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: SpeciesBarkWoodTwigsLeaves Chestnut Oak 1.25 ± ± ± ± 0.07 Flowering Dogwood 2.36 ± ± ± ± 0.11 Rhododendron 0.30 ± ± ± ± 0.29 Mean calcium concentrations (% dry wt) in three plant species.

43 Normal Nutrient Loss Rain runoff is the major vector of nutrient loss from most ecosystems Precipitation (mg/L)Streamwater (mg/L) Calcium Magnesium Potassium Sodium Aluminum--- a 0.24 Ammonium Sulfate Nitrate Chloride Bicarbonate--- a 1.90 Dissolved silica--- a 4.61 b 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 1)Weathering of rock 2)Deposit of sediments by erosion 3)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 O horizon Leaf litter A horizon Topsoil B horizon Subsoil C horizon Parentmaterial Mature soil Young soil RegolithRegolith BedrockBedrock Immature soil Soil Horizons (Profiles)

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 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.


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