EcosystemsEcosystems

Structural & Functional aspectsStructural & Functional aspects

• Atom Atom • C, N, P – chief constituents of building blocks of life C, N, P – chief constituents of building blocks of life

MoleculeMolecule• A molecule of DNAA molecule of DNA

OrganelleOrganelle• Mitochondria Mitochondria

Cell Cell • Nerve cellNerve cell

Tissue Tissue • Nervous tissueNervous tissue

Organ System Organ System • Nervous systemNervous system

Organism Organism • Fish Fish

Population Population • Group of same type of Fish say Salmon FishGroup of same type of Fish say Salmon Fish

Community Community • Complete under water sea lifeComplete under water sea life

Ecosystem Ecosystem • Complete ocean including living and non-living Complete ocean including living and non-living

mattermatter

Levels of organization Levels of organization

Ecosystem • A community of organisms and it’s corresponding abiotic

environment through which matter cycles and energy flows Types

• Natural / wild • Managed / artificial

Common features• Energy flow • Nutrient cycling

Biosphere• The sum total of all the ecosystems on the planet

Biome• Areas of predominant flaura & fauna

Ecotone• Areas of transition

Basics Basics

Basics Basics Food chainFood chain

• Path of energy exchange Path of energy exchange through..through..

Food websFood webs• Interconnected feeding Interconnected feeding

relationships in an relationships in an ecosystemecosystem

Trophic levelTrophic level• Feeding relationshipsFeeding relationships• Individuals positionIndividuals position

Ecological pyramidEcological pyramid Recyclers of biosphereRecyclers of biosphere

Energy flow in an ecosystem

Primary ProductivityPrimary Productivity Secondary productivitySecondary productivity

GPP (Gross Primary GPP (Gross Primary Productivity)Productivity)

NPP (Net Primary NPP (Net Primary Productivity)Productivity)

Rs (Respiration)Rs (Respiration)

NPP = GPP – RsNPP = GPP – Rs Biomass: Reflection of

primary productivity

What is A Niche?What is A Niche?Set of conditionsSet of conditions within which an organismwithin which an organism can maintain a viablecan maintain a viable populationpopulation

Multi-dimensionalMulti-dimensional with as manywith as many dimensions as theredimensions as there are limiting conditionsare limiting conditions temperature

light intensity

okay

salinity

ecologicalniche

The NicheThe Niche

Ecological niche:Ecological niche:• The sum total of an The sum total of an

organisms use of biotic organisms use of biotic & abiotic resources in & abiotic resources in its environment with its environment with unique ecological roleunique ecological role

Fundamental NicheFundamental Niche Realized NicheRealized Niche Co-existance vs Co-existance vs

Identical niches Identical niches

Nutrients…what are they? The basic chemical building blocks of all life Recycled in a living system. Key nutrients - 95% of all living matter.

Factors effecting Nutrient cycling Factors effecting Nutrient cycling &/or availability &/or availability

Transformation / cycling – oxidation or reduction reactions

Metabolism related Mineralization Immobilization Rates of decomposition Presence of nitrogen fixers Microbial activity Fire Precipitation patterns Soil drainage Soil temperature, moisture

Residence Time• Length of time taken for a nutrient to be completely

decomposed or recycled from the forest floor Nutrient Use Efficiency (NUE)

• Selective advantages in low nutrient conditionsNUE = A / L

A – the nutrient productivity (dry matter production per unit nutrient in the plant)

L – nutrient requirements per unit of plant biomassTypes of relationships

based on Nutrient limitations

• A - Production - independent of resource availability

• B - Production - a linear function of resource availability

• C - At some point, another resource becomes limiting

Nutrient Pools and Nutrient FluxNutrient Pools and Nutrient Flux

Nutrient pool – a specific Nutrient pool – a specific component or compartment where component or compartment where a nutrient residesa nutrient resides• Can be a single organism, a population, Can be a single organism, a population,

a community, a trophic level, and an a community, a trophic level, and an abiotic feature (e.g., lake, soil, abiotic feature (e.g., lake, soil, atmosphere, etc.)atmosphere, etc.)

Nutrient flux – the rate of exchange Nutrient flux – the rate of exchange (e.g., unit of material per unit time) (e.g., unit of material per unit time) of nutrients between poolsof nutrients between pools

Biogeochemical CyclingBiogeochemical Cycling

Vernadsky 1934Vernadsky 1934• The cycling of nutrients through ecosystems via

food chains and food webs, including the exchange of nutrients between the biosphere and the hydrosphere, atmosphere and geosphere (e.g., soils and sediments)

Biotic / Organic phaseBiotic / Organic phase Abiotic phaseAbiotic phase ReservoirReservoir Major categories

• slowest-changing pool(=reservoir): Sedimentary phaseSedimentary phase Atmospheric phaseAtmospheric phase

FeaturesFeatures• Biological & Chemical processesBiological & Chemical processes• Nutrient transformation by Oxidation, Reduction Nutrient transformation by Oxidation, Reduction

reactionsreactions• LinkedLinked• Metabolism related transformationsMetabolism related transformations• Global impactGlobal impact

Water cycleWater cycle

Hydrologic cycle• Medium for introducing

nutrients• Means of thermal regulation• Means of removal/transport-

local ecosystems Route of water escape

• Evapotranspiration Average rainfall-81.1cm Land precipitation>evaporation

(84% vs.77%) Rapid cycling

• Surface runoff Erosion, weathering

• Ground water Catchment area, Springs, Aquifer

Carbon cycle Relative percentage in atmosphere – 0.03

Route of escape into atmosphere• Photosynthesis /

respiration• Fermentation• Methane

Aquatic form• Carbonic acid,

Bicarbonate, Carbonate

P: photosynthesis, PR: plant respiration, SR: soil respiration, SF: Soil P: photosynthesis, PR: plant respiration, SR: soil respiration, SF: Soil formation, FFF: fossil fuel formation, FFB: fossil fuel burning, formation, FFF: fossil fuel formation, FFB: fossil fuel burning, DEF: deforestation, W:weathering, V: Volcanic eruption, E: DEF: deforestation, W:weathering, V: Volcanic eruption, E: evaporation, D: dissolution evaporation, D: dissolution

Carbon cycleCarbon cycle

Nitrogen cycleNitrogen cycle Key stepsKey steps

• Nitrogen fixationNitrogen fixation• NitrificationNitrification• DenitrificationDenitrification• MineralizationMineralization

Nitrogen FixationNitrogen Fixation Biological or chemical process where gaseous nitrogen Biological or chemical process where gaseous nitrogen

is converted into solid forms of nitrogen. is converted into solid forms of nitrogen. Biological fixation Biological fixation

N N 22 + 8e + 8e -- + 8H + 8H ++ + ATP -----> 2NH + ATP -----> 2NH 33 + H + H 22 + ADP + Pi + ADP + Pi• OrganismsOrganisms

Free livingFree living SymbiontsSymbionts

• Enzymes for nitrogen fixation require anoxic conditionsEnzymes for nitrogen fixation require anoxic conditions Chemical fixationChemical fixation

N N 22 + H + H 22 2 NH 2 NH 33 Physical process Physical process in Naturein Nature

NITRIFICATIONNITRIFICATION The biochemical oxidation of ammonium to nitrite and The biochemical oxidation of ammonium to nitrite and

nitrite to nitrate. nitrite to nitrate. Microbes Microbes

• ChemoautotrophsChemoautotrophs• Aerobes Aerobes • Nitrifiers: Nitrifiers: NitrosomonasNitrosomonas and and NitrobacterNitrobacter

ReactionsReactions• Nitrification I:Nitrification I:

NHNH44 + 1 ½ O + 1 ½ O22 NO NO22- - + H+ H22O + O + Energy

• Nitrification II: Nitrification II:

NO 2 - + ½ O NO 2 - + ½ O 22 NO NO33-- + + Energy

RequirementsRequirements• OxicOxic• N abundancyN abundancy

DENITRIFICATIONDENITRIFICATION

Denitrification Denitrification • Reduction of nitrate (NO3-) to nitrogen Reduction of nitrate (NO3-) to nitrogen

gas or to organic nitrogen compounds. gas or to organic nitrogen compounds. Two types Two types

• Dissimilative Dissimilative Returns nitrogen atoms to the atmosphere Returns nitrogen atoms to the atmosphere

by reducing nitrate to nitrogen gas. by reducing nitrate to nitrogen gas.

NONO33-- NO NO22

-- NO NO N N22O O N N 22 Facultative anaerobes: Pseudomonas,

Bacillus, and Micrococcus spp. Oxygen for respirationOxygen for respiration

• Assimilative. Assimilative. Conversion of nitrate to ammonium ionConversion of nitrate to ammonium ion

MINERALIZATION / AMMONIFICATION

Organic nitrogen from decaying plant and animal residues (proteins, nucleic acids, amino sugars, urea) is converted to ammonia (NH3) and ammonium (NH4

+) In Dry soils

• Proteins Amino acids NH3 NH3 Moist soils

• Proteins Amino acids NH3 NH3+H2O NH4+OH- NH4

+ + OH-

Microbes: Bacillus, Clostridium, Streptomyces

Nitrogen fixing bacteria & enzymes they produce

Nitrifying bacteria

Nitrate reductase (Fe, Mo)

Nitrite reductase (Fe)

Nitrogenase(Fe, Mo or V)

Denitrifying bacteria

N2 NH4+

NO3-NO2

-

Nitrogen

All the major N assimilation enzymes require Fe.

R-NH2

Ammonium assimilation

Ammonification

Assimilatory NO3

- reduction

Dissimilatory NO3- reduction

Nit

rite

oxi

dati

on

Nit

rite

Am

mon

ific

atio

n

Ammonium oxidation

NH4+ NO2

-

NO3-NO2

-

NO

N2O

ANAEROBIC PROCESSES

AEROBIC PROCESSES

Den

itri

fica

tion

N2 Nitrogen fixation

Amino groups in cell protein

Sulfur cycleSulfur cycle Sulfur in soil

• 90% - Organic 50% as C-O-S linkages (sulfate esters) 20% as S-amino acids 20% other compounds

In living tissue • S-containing amino acids and sulfate esters

Phosphorous Phosphorous cyclecycle

Changes in the amounts of tracer phosphorous being exchanged within an aquatic food web

The Potassium CycleThe Potassium CycleAnimal

manuresand biosolids

Mineralfertilizers

Crop harvest

Runoff anderosion

Leaching

Soil solution potassium (K+)

Plant residues

Plantuptake

Mineralpotassium

Fixedpotassium

Exchangeable potassium

Input to soilComponent Loss from soil

Bioaccumulation & BiomagnificationBioaccumulation & Biomagnification

Bioaccumulation:• Increase in concentration

of a pollutant from the environment to the first organism in a food chain

Biomagnification:• Increase in concentration

of a pollutant from one link in a food chain to another

DDT has a half-life of 15 years This means, if you use 100 kg

of DDT today (consider this the zero time), it will break down in such a manner that after 100 years from now, there will still be over a pound of DDT in the environment.  If it does bioaccumulate and biomagnify, much of the DDT will be in the bodies of organisms

DDT has brought in the "age of resistance" - a high price to pay to have no mosquitoes.

Year Amount Remaining

0 100 kg

15 50 kg

30 25 kg

45 12.5 kg

60 6.25 kg

75 3.13 kg

90 1.56 kg

105 0.78 kg

120 0.39 kg

Gaia HypothesisGaia Hypothesis

James Lovelock, Lynn Margulis - 1970 Our planet functions as a single organism that

maintains conditions necessary for its survival. A complex entity involving the Earth's biosphere,

atmosphere, oceans, and soil; the totality constituting a feedback or cybernetic system which seeks an optimal physical and chemical environment for life on this planet.

Life, regulates or maintains the climate and the atmospheric composition at an optimum for itself.

Gaia, therefore, can be viewed as a study of the physiology of the Earth, where the oceans and rivers are the Earth's blood, the atmosphere is the Earth's lungs, the land is the Earth's bones, and the living organisms are the Earth's senses.

Ecosystem services - UNEPEcosystem services - UNEPThe UNEP programme focuses on ecosystem services comprising:Regulating services: climate, water, natural hazard and disease regulation, water purification and waste treatment, which are often strongly affected by the overuse of provisioning services;Provisioning services: freshwater, energy (especially the emerging issues around biofuel production) and capture fisheries;Cultural services: Recreation and ecotourism service;Supporting services: nutrient cycling and primary production which underlie the delivery of all the other services but are not directly accessible to people.

Ecosystem servicesEcosystem services

For detailed information on biogechemical cycles For detailed information on biogechemical cycles and information related to the slides in this lecture, and information related to the slides in this lecture, refer to:refer to:

Chapter 4 “Ecology” from the text book Chapter 4 “Ecology” from the text book “Environmental Studies” by Benny Joseph“Environmental Studies” by Benny Joseph

Unit 3 “Ecosystems” from the text book Unit 3 “Ecosystems” from the text book “Environmental Studies” by Erach Bharucha“Environmental Studies” by Erach Bharucha