ESS Test Topics 2.3 & 2.4 Flows of energy and matter ★ The fate of solar radiation reaching the Earth ★ Productivity ★ Flows of energy and matter Main concepts: ➔ As Solar radiation enters the atmosphere some energy becomes unavailable for ecosystems as it is absorbed by organic matter or reflected back ➔ The loss of radiation is through reflection and absorption ➔ Pathways of energy: ◆ Light energy to chemical energy ◆ Transfer of chemical energy from one trophic level to another, with different efficiencies ◆ ultraviolet and visible light to heat energy ◆ Reradiation of heat energy to the atmosphere ➔ Conversion of energy into biomass for a period of time = productivity ➔ Gross secondary productivity = total energy / biomass assimilated by consumers. (food eaten - fecal loss) ➔ Net primary productivity = GPP - respiratory losses ➔ Net secondary productivity = GSP - respiratory losses ➔ Maximum sustainable yields = net primary/net secondary productivity of a system ➔ Flows of matter: transfers and transformations ➔ Carbon and nitrogen cycles: illustrate flow of matter using flow diagrams ➔ Storages in the carbon cycle: organisms, forests, atmosphere, soil, fossil fuels and oceans Organic Inorganic ➔ Flows in the carbon cycle: consumption, death and decomposition, photosynthesis, respiration, dissolving and fossilisation. ➔ Storages in the nitrogen cycle: organisms, soil, fossil fuels, atmosphere and water bodies ➔ Flows in the nitrogen cycle: nitrogen fixation, absorption, assimilation, consumption, excretion, death and decomposition, denitrification ➔ Human activities: burning fossil fuels, deforestation, urbanization and agriculture impact energy flows as well as the carbon and nitrogen cycle Key points Almost all energy comes from the sun Solar radiation is made up of visible wavelengths (lights) and those invisible to humans (ultraviolet and infrared) 60% of energy is absorbed by atmospheric gases and dust particles Nearly all ultraviolet light is absorbed by ozone Infrared light (heat) is absorbed by carbon dioxide, clouds and water vapours Ultraviolet and visible light energy (short wave) are converted to heat energy (long wave) The systems depend on the amount of energy that reaches the ground, not the atmosphere. This amount varies according to time, season, clouds, etc Most energy is reflected or absorbed and re radiated as heat 35% of energy is reflected back to space by ice, snow, water and land Some of the energy absorbed heats up the land and seas Only 1-4% of energy is available to plants on the surface Green plants: light energy to chemical energy Chemical energy: one trophic level to another The fate of solar radiation reaching the Earth Energy from sun → photons Energy leaving the sun → 63 million J s-1 m-2 Solar energy reaching the atmosphere → 1400 s-1 m-2 → 1400 watts per second → Earths solar constant 100% entering solar radiation → 69% absorbed → 31%total reflection Photosynthesis → solar energy into food Plants absorption: 40% of energy that hits the leaf → only 9% can de used (red&blue wavelengths) 5% reflected 50% lost 5% passes right through the leaf 9% can only be used → GPP 4.5% used to stay alive 5.5% → NPP All solar radiation → 0.06% captured by plants → GPP Left over of that energy captured → NPP → amount of food available to all animals Efficiency of conversion of energy to food: 2-3% in terrestrial ecosystems 1% aquatic ecosystems Productivity Gross: total amount made of something as a result of an activity Net: amount left after reductions made Primary: plants Secondary: animals Biomass: living mass of an organism / dry mass Productivity: conversion of energy into biomass over a given period of time → rate of growth or biomass increase → m-2 yr-1 Gross productivity: total gain in energy or biomass per unit area per unit time → biomass gained before reductions Net productivity: gain in energy or biomass per unit area per unit time after reductions from respiration Gross primary productivity: total gain in energy or biomass per unit area per unit time in green plants → energy fixed by photosynthesis → light energy into chemical energy (sugars) Can be measured by calculating the amount of sugars plants produce → difficult → easier to look at the NPP Net primary productivity: rate at which plants accumulate dry mass → g m-2 Glucose produced by plants used for: Growth, maintenance and reproduction → energy is lost as heat Depositions: stored dry mass and then potential food source for consumers NPP = rate at which plants photosynthesize (GPP) - rate which they respire Accumulation of dry mass → biomass Total amount of plant material → amount of energy that is available to all the animals. Either: Lost from food chains → dies and decays Eaten by herbivores Amount of biomass: spatially : some biomes have higher NPP rates (tropical forest vs tundra) Temporally: seasonal patterns of productivity change according to basic resource availability (light, water, warmth) Net Secondary Productivity Only food that crosses the wall of the alimentary canal is absorbed and used to power life processes (assimilated food energy) Some is used in cellular respiration Some is removed as nitrogenous waste (urine) Stored in dry mass of new body tissue Some plant material is released as feces (egestion) → not absorbed → no energy NSP herbivores = energy from food ingested - energy lost in egestion - energy used respiration Gross secondary productivity Total energy / biomass assimilated by consumers GSP = food eaten - fecal loss Plants → autotrophs Animals → heterotrophs NSP (net secondary productivity) Total gain in energy / biomass per unit area per unit of time by consumers after losses of respiration NSP = GSP - respiratory losses Carnivores Assimilate 80% of energy from their diets Egest less than 20% Chase moving animals → higher energy intake → increased respiration Biomass locked up in the prey foods → skeletal parts are non-digestible (bones, horns, antlers) → assimilate maximum of energy from digestible food Herbivores Assimilate 40% of energy from diet Egest 60% Feed on static plants Flows of energy and matter Flow Energy flows through systems Matter flows through ecosystems (nutrients, oxygen, carbon dioxide, water) How much? Infinite (sun always shining) finite when? once Cycles and recycles repeatedly outputs All organisms → gove out energy → all the time All organisms → release → nutrients, carbon dioxide, water quality Higher to lower → light to heat → +entropy May change form but does not degrade storages Temporarily as chemical energy Long and short term in chemical forms Transfers and transformations Both matter and energy move and flow through ecosystems Both types of flow → use energy Transfer + simple - energy → transformations Cycles and flows Energy → flows in one direction Solar radiation --------> released as heat through decomposers’ respiration Biogeochemical cycles: Cycle of chemical nutrients Nutrients absorbed by organisms → circulate through trophic levels → released via the detritus food chain Nutrient cycles Biogeochemical cycle: Organic phase (element is in a living organism) → determines how much is available to Liv. org. Inorganic phase (element is outside living organisms) → major reservoir → rocks and soils → slower flow Examples: water, carbon, nitrogen, sulphur and phosphorus Similar characteristics Movement of matter Energy travels from the sun Nutrients and matter are finite and recycled and reused (decomposer food chain) Organisms die and are decomposed and nutrients are released Carbon cycle Where is it stored? Carbon or carbon dioxide sinks: ● Organic (w/ carbon dioxide molecules): ○ Organisms - living plants and animals ○ Fossilized life forms - fossil fuels ● Inorganic (simple carbon molecules): ○ Locked up in sedimentary rocks and fossil fuels - most is stored here ○ The oceans - carbon is dissolved / locked up as carbonates in shells ○ Soil ○ Atmosphere Carbon flows Occurs in the ecosphere Four main storages: - Soil - Living things - Oceans - Atmosphere Carbon not in the atmosphere → stored in carbon dioxide sinks → complex organic molecules Carbon between living and non-living chemical cycles → fixed by photosynthesis and released through respiration Also released through combustion of fossil fuels and biomass Photosynthesis → recaptures carbon → carbon fixation Carbon releasement: plant harvest for food - wood for firewood - fossil fuels - cut down trees This changes the balance of the carbon cycle Human activity disrupted the balance of the global carbon cycle → increased combustion - land use changes deforestation The carbon budget Carbon sinks and flows → gigatonnes of carbon (GtC) → 1 billion tones Humans and the carbon cycle Annual current global emissions → fossil fuels → 5.5 GtC + 1.6 GtC deforestation = 7.1 GtC ● 20% burning natural gas ● 40% bruning coal ● 40% burning oil 2.4-3.2 GtC → atmosphere 2.4 GtC → oceans 0.5 GtC → Forests 1.8 GtC unaccounted for Amount of carbon in other reservoirs: Atmosphere → 750 GtC Standing biomass → 650 GtC Soils → 1,500 GtC Oceans → 1720 GtC Nitrogen cycle storages/sinks: ● Organisms ● Soil ● Fossil fuels ● Atmosphere ● Water Flows: ● ● ● ● ● ● Nitrogen fixation Nitrification Denitrification Feeding ○ Absorption ○ Assimilation ○ Consumption Excretion Death & decomposition Three basic stages: nitrogen fixation, nitrification and denitrification Nitrogen fixation: Atmospheric nitrogen is made available to plants through fixation Gaseous nitrogen ----> ammonium ions happens by: ➔ Bacteria in the soil ➔ Bacteria in root nodules of leguminous plants ➔ Cyanobacteria in soil or water ➔ Lightning: causes the oxidation of nitrogen gas ➔ Haber process: nitrogen-fixing process used to make fertilizers Nitrification: Conversion of ammonium ions to nitrites Nitrites to nitrates Denitrification: Denitrifying bacteria reverse the nitrification process Located in waterlogged and anaerobic conditions Ammonium - nitrites - nitrates → nitrogen gas Decomposition also provides nitrogen for plants + Nitrogen than other processes Animals: insects, worms, fungi, bacteria Breakdown protein → ammonium ions - nitrite ions - nitrate ions Assimilation: Take up nitrogen → assimilate / build complex molecules Protein synthesis → inorganic nitrogen compounds → complex amino acids → proteins Humans and the nitrogen cycle Removal of humans and plants → remove nitrogen from cycle Add nitrogen → fertilizers Energy flow diagrams Show energy entering and leaving a trophic level Assimilation and productivity efficiencies Efficiency of assimilation = Gp * 100 / food eaten Efficiency of biomass productivity = NP * 100 / GP Trophic efficiency Efficiency from one trophic level to another → 10% → general May be 5% to 20% → depends on energy lost through heat and respiration Trophic inefficiencies: Not everything is eaten Digestion is inefficient Heat is lost Some energy is assimilated in other processes → eg: reproduction Energy budgets Quantity of energy entering, staying within and leaving the animal/population Human activities and ecosystems Process, effect or activity derived from humans → anthropogenic Energy subsidy: additional energy that we have to put into the system above which comes from the suns’ energy Some systems → due to energy subsidies → higher NPP Advantage: feed more people → food production + efficient → energy has to come from somewhere Maximum sustainable yield: Largest crop or catch that can be taken from the stock of a species without depleting the stock → NP of a system Energy: yield ratio Energy in and energy out in the form of food Agriculture + sophisticated → ratio goes down Example: 1:30 → 30 units of food for each unit of input energy as work Energy input can be increased → but has to keep flowing through the ecosystems Biomes, zonation and succession ★ Biomes ★ Succession and zonation ★ K- and r-strategists’ reproductive strategies Main concepts ★ Biomes: collections of ecosystems sharing similar climatic conditions ○ Can be grouped in five major classes: aquatic, forest, grassland, desert and tundra ★ Main factors governing the distribution of biomes: insolation, precipitation, temperature ★ Tricellular model of atmospheric circulation explains the distribution of precipitation and temperature, which influences the structure & productivity of terrestrial biomes ★ Climate change is altering the distribution of biomes = biome shifts ★ Zonation: changes in community along an environmental gradient due to factors such as changes in altitude, latitude, tidal level or distance from shore ★ Succession: process of change over time in an ecosystem involving pioneer/intermediate/complex climax communities ○ Changes in patterns of: energy flow/gross&net prod/diversity/mineral cycling ★ Greater habitat diversity → greater species → greater diversity ★ R and K strategist species: have reproductive strategies that are better adapted to pioneer and climax communities ★ Early stage of succession → GP low → initial conditions ○ Energy lost through respiration→ low ○ Np is high → system is growing ★ Later stage of succession → GP high → increased consumer community ○ Balanced by respiration → NP almost 0 ★ Variety of nutrients and energy → stability of complex ecosystems ★ No climax community → set of alternative stable states ○ Depend on climatic factors, properties of local soil, etc ★ Human activity can divert succession → modifying the ecosystem → fire, agriculture, grazing pressure, deforestation, etc. ★ Ecosystem’s capacity to survive →> relies on → resilience and diversity Biomes How many biomes are there? Biome: collections of ecosystems sharing similar climatic conditions Biosphere: part of Earth inhabited by organisms (upper part of the atmosphere; deepest part of ocean) Aquatic: Freshwater (swamp forests, lakes and onds, stream, rivers) Marine (rocky shore, mud flats, coral reef, deep ocean) Deserts: hot & cold Forests: tropical, temperate, boreal Grassland: tropical, savanna, temperate Tundra: arctic & alpine Each have their own limiting factors, productivity and biodiversity. Insolation, precipitation and temperature affect the distribution of biomes Why biomes are where they are Biomes affected by: Climate (temperature and precipitation) Terrain (slope, aspect, altitude) Temperature → hotter near equator / colder near poles Latitude: distance from north/south from the equator Altitude: height above sea level Increase latitude/altitude → colder Ocean currents and winds: They distributor surplus heat energy → from the equator towards the poles Air moving horizontally = wind Winds cause ocean currents → water responsible for transferring heat Water changes from states → gives out/takes in heat = latent heat Solid → liquid → gas takes in Gas → liquid → solid gives out This change distributes heat around the earth Earth is tilted 23.5 degrees on its axis Insolation + precipitation + temperature → most important abiotic factors influencing biomes +temperature +evaporation → important the relationship between precipitation and evaporation P / E ratio: precipitation to evaporation ratio Example: Tundra P/E ratio = 75/50 → 1.25 → greater than 1 Rains a lot → little evaporation Loss of minerals when washed away Desert P/E ratio = 5/50 → 0.1 → less than 1 Lots of evaporation Leaves salts behind → increased soil salinity P/E ratio = 1 → P & E are about the same → soil is rich and fertile Different biomes have different productivity: May be to limiting factors Low raw material availability Low energy source availability Solar radiation + heat limited in poles Water limited in desert Productivity is greater in low latitudes → nearer the equator Near equator: Temperatures are high Sunlight input is high Precipitation is high Towards the poles: Temperatures decline Sunlight availability declines Rate of photosynthesis is lower → GPP and NPP are lower Arctic & antarctica: Low temperatures Frozen grounds Long periods in winter Low precipitation All this reduces rate of photosynthesis → lower productivity Desert and semi arid areas: Absence of moisture → lower productivity Climate change and biome shift Increase in global temperature → biomes are moving Climate changes: ➢ Temperature increase of 1.5 to 4.5°c by 2100 ➢ Greater warming in higher latitudes ➢ +warming in winter than summer ➢ Dryer areas; wetter areas ➢ Stronger storms Changes are happening fast → organisms change slowly → adapt fast by moving to other areas Moves: ➢ Poles where its cooler ➢ Higher to mountains → +altitude +cold ➢ Towards equator → wetter Examples of biome shifting: Sahel region (africa): woodlands → savannas Artic: tundra → shrubland Plants migrate slowly → seeds Animals migrate longer distances → whales, albatrosses Obstacle to migration: mountain ranges, seas, human activities Hotspot: areas predicted to have a high turnover of species due to climate change ❖ Himalayas ❖ Equatorial eastern africa ❖ Mediterranean ❖ Madagascar ❖ North america great plains and lakes Changes → new opportunities for exploitation of resources: ● Dreacease ice → drill oil → arctic ocean ● New trade route → north-west passage (north america and north pole) Biomes Tropical rainforest: ➔ Hot and wet areas & Broadleaved forest ➔ Almost in the equator ➔ High rainfall / temperatures (26 - 28°c) / insolation ➔ Rain washes nutrients ➔ High levels of biodiversity ➔ Large trees, vines, climbers, orchids ➔ Stratification within plants and trees ➔ Many niches available ➔ 40% NPP of terrestrial ecosystems ➔ Fast rate of decomposition, photosynthesis and respiration ➔ ➔ ➔ ➔ Rapid recycling of nutrients 50% of world’s population lives near a tropical forest → too many exploiting Issue: logging, clear-felling, conversion to grazing Examples: Amazon rainforest, borneo rainforest Deserts ➔ Dry areas: hot during the day / cold at night ➔ Classification: tropical / temperate / cold ➔ Cover 20-30% of Eartgs surface → 30° from equator ➔ Limited water → E > P ➔ Low biodiversity ➔ Soil rich in nutrients ➔ Plant drought-resistant → cacti and succulents ➔ Reptiles: snakes, lizards / small mammals: kangaroo rat ➔ NP → secondary and primary → low ➔ Population density low → rich in oil and nutrients ➔ Issues: desertification → area becomes a desrt because of overgrazing/drought ➔ Examples: Atacama desert (chile), Sahara desert (africa) Temperate grasslands ➔ Flat areas dominated by grasses and herbaceous plants➔ 40-60° from equator ➔ P = E or P>E ➔ Temperature range high & low precipitation ➔ Grasses, no trees, and burrowing animals (rabbits), antelopes, wolves, coyotes ➔ Not high NP ➔ Used fro agriculture ➔ Issues: overgrazing ➔ Example: pampas in Argentina Temperate forests ➔ Mild climate, deciduous forests ➔ 40-60° from equator ➔ P>E ➔ Freezing winter - wide range of temperatures -30°c to 30°c ➔ Fewer species than tropical rainforests, woodlands show stratification ➔ Flowering plants, mosses, lichens ➔ Forest floor → thick leaf litter ➔ Rapid recycling of nutrients, som lost through leaching → produces brown soil ➔ Well developed food chains → autotrophs, herbivores, carnivores ➔ Deciduous trees → conifer trees towards pole latitudes / increase altitude / vertical slope ➔ 2nd highest NPP ➔ Issues: most cleared for farming, urban developments ➔ Example: US pacific northwest Arctic tundra ➔ Cold, low precipitation, long&dark winters ➔ 10% of earths surface ➔ Permafrost soil and no trees ➔ High winds ➔ Low temperatures → low rate of photosynthesis, respiration and decomposition ➔ Slow growth and recycling of nutrients ➔ Limited water, temperature, insolation and nutrients ➔ spring&summer: animals active, plants start growing ➔ ➔ ➔ ➔ ➔ ➔ ➔ Low growing plants: grasses, mosses, small shrubs Animals adapted: thick fur, small ears → small mammals and predators (lemmings, voles, fox, owl Low biodiversity, inorganic matter and minerals Very low NP Used for mining and oil Issues: take time to recover from disruption, global warming may make them disappear Examples: siberia, alaska Deep ocean ➔ Ocean and seafloor beyond continental shelves ➔ 65% of earth’s surface ➔ +depth +pressure → temperature variates until -2°c ➔ No light below 1000m ➔ Low nutrients and productivity ◆ 200m: phytoplankton and cyanobacteria main producers → eaten by fish, invertebrates ◆ 200-1000m: +pressure → fish are muscular and strong, large eyes ◆ 1000-4000m: high diversity, dark, fish have bioluminescence ◆ 4000m: huge pressure, cold, dark → shrimps, jellyfish ◆ Bottom surface: debris from shells and bones, volcanic rocks ➔ Rocks rich in manganese and iron ➔ Issues: pollution ➔ Examples: arctic, atlantic, pacific oceans Succession and zonation Succession: process of change over time in an ecosystem involving pioneer/intermediate/climax communities How an ecosystem changes over time ● Dynamic and temporal ● Progressive changes Zonation: change in community along an environmental gradient due to factors such as changes in altitude, latitude, tidal level, distance from shore how an ecosystem is changing along an environmental gradient ● Spatial and static ● Abiotic gradient Zonation Abiotic and biotic factors influence each niche ➢ Temperature: decreases → +latitude / +altitude ➢ Precipitation: +altitude → -precipitation ➢ Solar insolation: +altitude + insolation ➢ Soil type: warmer zones → fertile / +altitude = acidic soil ➢ Interactions between species Human activities alter zonation Succession ➔ Change in species composition over time ➔ Two types: primary and secondary ➔ Early stages: GPP and respiration are low → NPP is high ➔ Later stages: GPP high → respiration increases → NPP approaches zero P:R = 1 ➔ Climax community → reached at the end of succession → species composition stops changing ➔ +complex + stable ecosystem ➔ Interruption of succession: human activities ◆ May recover or not ➔ +diversity + resilient Primary succession ❖ Bare inorganic surface ❖ Colonization by organisms in new land created/uncovered → river deltas, volcanic eruptions Stages: 1. Bare Surface: lifeless abiotic environment available for colonization → nutrient poor, erratic water supply 2. Colonization: first species to colonize pioneers (usually r-selected species) 3. Establishment: species diversity increases; invertebrates visit and live in the soil → increase org. mater. 4. Competition: new species colonize; larger plants enable K-selected specie establish → pioneer r-species cannot compete with k-species 5. Stabilization: late colonizers become established; complex food webs develop 6. Climax community: stable and self-perpetuating; steady state dynamic equilibrium; maximum possible development a community can reach Secondary succession ❖ Established community is suddenly destroyed ❖ Fire, flood, human activity ❖ Soil already developed Changes: ● Size of organisms increases ● Energy flow + complex: simple food chain → complex ● Soil depth, humus, water-holding capacity, mineral content and cycling increase ● Biodiversity increases → climax community is reached ● NPP/GPP rise and then fall ● Productivity : respiration ratio falls Species diversity in successions +species + diversity Increase in species diversity continues until balance is reached Pioneer species are never totally wiped off Disturbance Communities are affected by periods of disturbance Trees die, fires, floods, landslides, earthquakes, hurricanes, etc Arrested and deflected successions Succession may be stopped by an abiotic factor → ‘arrested’ This leads to a sub-climax community → can only continue development if factor is romevoed Affected by natural event or human activity Leads to plagioclimax community → pasture, arable farmland, plantations Human activity stops → development continues Significance of changes during succession Biodiversity increases during succession → +species arrive → then decreases when climax com. Is reached Mineral cycling: slow at early stages → increases during succession K- and r-strategists’ reproductive strategies K- / r-strategists K- / r-selected species k and r determine the shape of the population growth curve K: carrying capacity R: shape of exponential part of the growth curve K- & r-strategists: approach different species take into getting their genes into the next generation to ensure survival of species K-strategists: humans and large mammals ➢ Small numbers of offspring ➢ Energy + time in parental care ➢ Offspring survives ➢ Good competitors ➢ Population size close to carrying capacity ➢ Stable climax ecosystems: k out competes r R.strategists: invertebrates and fish ➢ Lots of energy in production of eggs ➢ No energy used in raising them ➢ Lay eggs and leave ➢ Reproduce quickly ➢ Colonize habitats quickly ➢ Make good use of short-lived resources ➢ Exceed carrying capacity → predominate unstable ecosystems Many species combine both Survivorship curve Shows the fate of a group of individuals of a species
