Flux of energy and matter Flashcards
Flux of energy and matter
All biological entities require matter for their construction and energy for their activities
Fluxes of energy and matter strongly link communities with their abiotic environments
Biological community + abiotic environment = ecosystem
Ecosystems include primary producers, decomposers and detritivores, a pool of dead organic matter, herbivores, carnivores and parasites
Plus the physiochemical environment that provides living conditions and acts as a source and sink for energy and matter
Standing crop of biomass – the bodies of the living organisms within an area
Biomass – mass of organisms per unit area of ground or volume of water, usually expressed in units of
- Energy e.g J^-2
- Dry organic matter e.g t ha^-1
- Carbon e.g g C m^-2
The great bulk of biomass in communities is typically plants or algae
Primary productivity – the rate which biomass is produced by photosynthetic organisms, usually expressed in units of
- Energy e.g J m^-2 day^-1
- Dry organic matter e.g kg ha^-1 year^-1
- Carbon e. C m^-2 year^-1
Gross primary productivity – total energy fixation
Net primary productivity = GPP – autotrophic respiration
Patterns in primary productivity
NPP of the planet = approx. 105 petragrams of C per year (1 Pg = 10^15 g)
Of this, 56.4 y^-1 is produced in terrestrial ecosystems and 48.3 Pg C y^-1 in aquatic ecosystems
Oceans cover 2/3 of the planet’s surface, but account for less that ½ of its production
On land, tropical rainforests and savannas together are responsible for 60% of terrestrial NPP – reflecting the large areas and high productivity of these biomes
Productivity of forests, grasslands and lakes follows a latitudinal trend, increasing from boreal, through temperate to tropical
Patterns not so clear in oceans, where productivity is often limited by a shortage of nutrients
High productivity is observed in marine communities where there are upwellings of nutrient rich waters (even at high latitudes/low temperatures)
Also patterns according to seasons
Limiting factors in terrestrial communities
Sunlight, CO2, water and soil nutrients are the required resources for primary production
Temperature has a strong influence on photosynthetic rates
CO2 is unlikely to be limiting
Quality and quantity of light, availability of water and nutrients and temperature all vary dramatically from place to place
Not all radiation is used efficiently – depends on availability of other resources
Shortage of water is a critical factor
Temperature and precipitation interact; high temperatures associated with high evapotranspiration
Drainage and soil texture can modify water availability
Coarse soils are associated with lower nutrient retention, sandy soils are lower in N
Geological conditions are important – nitrogen and phosphorus are limiting factors
Length of the growing season
Deciduous trees drop their leaves, conifers can photosynthesise all year round, conifers are instead limited by temperature and associated with nutrient poor conditions, tropical evergreen rainforests are the most productive
Limiting factors in aquatic communities
Primary productivity (PP) is most frequently limited by light and nutrient availability – most commonly nitrogen and phosphate, but iron can be limiting in open ocean environments, in small forest streams, light and nutrients interact to determine productivity
Nutrients are the most limiting in lakes
In oceans, locally high levels of PP are associated with high nutrient inputs from estuaries and upwelling
Nutrients flow continuously into coastal shelf regions from estuaries – in the euphotic zone, productivity is high because of high nutrients input and waters are clear, allowing light to penetrate, closer to land water is nutrient rich by highly turbid thus less productive, outer shelf and open ocean have low productivity due to low nutrients
Ocean upwellings are the second source of high nutrient concentrations – occur on continental shelves, where wind is consistently parallel to the coast, water is moved offshore and is replaced with cooler, nutrient rich water originating from the bottom (accumulated through sedimentation), consequently there is a phytoplankton bloom that supports a chain of heterotrophic organisms, upwelling brings cool, nutrient rich waters to the surface, phytoplankton blooms support a chain of heterotrophic organisms, great fisheries of the world are located in these areas of high productivity
Iron is a limiting factor in the marine environment – affects 1/3 of the open ocean, iron is insoluble, ultimately derived from wind-blown particulate matter
Productivity varies with depth as light is attenuated
The fate of energy in ecosystems
Secondary productivity – rate of production of new biomass by heterotrophic organisms
Heterotrophic animals, fungi and bacteria cannot manufacture energy rich compounds from simple molecules, derive matter and energy by consumption
Primary producers (plants and algae) comprise the first trophic level primary consumers the second, carnivores the third
General false positive relationship between primary and secondary productivity
However secondary productivity by herbivores is an order of magnitude lower than the PP it is based on
Energy is lost as it moves up through trophic levels
- Not all plant biomass is consumed alive (much decays and supports decomposers)
- Not all plant mass eaten is assimilated (much passes as faeces and supports decomposers)
- Not all energy is assimilated is converted into biomass (much is lost as heat in respiration)
The flux of matter through ecosystems
Chemical elements and compounds are vital for life processes
Living organisms expend energy to extract chemicals from the environment – these are incorporated/used for a period, then lost again, so the activities of living organisms profoundly influence the flux of chemical matter in the biosphere
The great bulk of living matter in any community is water, the rest is mainly carbon compounds
Energy is accumulated and stored in the form of carbon compounds, energy dissipated when C compounds oxidised to CO2 during metabolism = fluxes of energy and carbon are inextricably linked
Carbon enters the trophic structure of a community when a simple inorganic compound (CO2) is taken up by photosynthesis. If incorporated into plant biomass, it is available for consumption as part of a molecule of sugar, fat, protein or usually cellulose. It follows the same route as energy; consumed, defecated, assimilated and perhaps incorporated into secondary productivity in another trophic compartment. When high energy C molecule is used to provide energy for work, energy is dissipated as heat and C is released into the atmosphere as CO2
Energy cannot be recycled or reused, but matter can
Heat produced is lost to the atmosphere, but CO2 can be recycled in photosynthetic pathways
Carbon (and all other nutrient elements) are available as simple inorganic molecules or ions in the atmosphere or dissolved ions in the soil – each can be incorporated into complex organic carbon compounds in biomass but is released in simple inorganic form after metabolised
Chemical nutrients are continually recycled, when locked into living biomass they are unavailable to other members of the community until the living biomass is consumed or decomposed
Not a closed system - some nutrients are exported from land to sea in run-off, or to the atmosphere
Additional nutrient supplies are received in rain water as dissolved minerals derived from weathered rocks
Pools of chemicals exist in compartments
- Atmosphere - CO2, N2
- Lithosphere – calcium in limestone, potassium in feldspar, magnesium in serpentine
- Hydrosphere – dissolved C, N, P
In all cases elements exist in an organic form
Studies of the fluxes of elements between living and non-living compartments = biogeochemistry
Biogeochemical cycles
Occur at a number of scales – locally to globally
Nutrients are lost and gained by ecosystems
Nutrient budgets = inputs minus outputs
If inputs > outputs then nutrients accumulate in living biomass and dead organic matter (e.g succession)
If outputs > inputs then nutrients are lost from the system (e.g fire, deforestation, acid rain)
Terrestrial nutrient budgets
Inputs = minerals from weathering of rock and soil, atmospheric CO2 and N2, minerals in wetfall (rain and snow) or dryfall (settling of dusts), hydrological (stream flow), human activities (burning fossil fuels, agricultural fertilisers, sewage disposal)
Outputs = atmospheric (CO2 in respiration and forest fires, CH4 from bacterial activity in waterlogged soils of bogs, swamps, wetlands and the guts of grazers), groundwater and streams (most plant nutrients dissolved, particulate matter (dead organic matter, inorganic particles))
Aquatic nutrient budgets
Aquatic systems receiver the bulk of their nutrients from stream inflow
In streams, rivers and lakes with outflow, export in outgoing stream is a major factor
In lakes with little to no outflow, or oceans, nutrient accumulation in sediments is the major export pathway
Streams – inflow and outflow determine nutrient status
Lakes – phytoplankton and zooplankton play key roles
Estuaries – benthic and planktonic organisms important
Continental shelves – influenced by their terrestrial catchment areas and local upwelling
Open oceans – plankton play an important role and follow a seasonal pattern
Global biogeochemical cycles
Nutrients are moved over large distances by atmospheric winds, flowing rivers and ocean currents
No boundaries – ocean cycles
Hydrological cycle
Oceans are the principal source of water; evaporation, winds and precipitation
Temporarily stored in soils, lakes, icefields
Lost as evaporation or transpiration or as liquid flow through stream channels and ground water aquifers, back to the sea
Water flows through plants in the transpiration stream
Phosphorus cycle
Phosphorus derived mainly from weathering of rocks
Ultimately ends up in ocean – a sedimentary cycle
A typical P atom released from rock may cycle in a terrestrial community for years before entering a stream
Swiftly carried to ocean and cycled between surface and deep for millions of years
Biotic uptake and decomposition, ocean mixing then sedimentation, continental uplift and erosion
Affected by human activities; marine fishing transfers P from ocean to land, fertilisers add P to land water run-off and thus oceans.
Eutrophication of lakes and coastal estuaries induces phytoplankton blooms and shifts community composition
Nitrogen cycle
Atmospheric phase is predominant
N2 fixation by microbial organisms (legumes)
Denitrification (NH4 to N2) by microbial organisms
Nitrification (NH4 to NO3-) by microbial organisms
Lightning fixes N2 to nitric acid dissolved in rain water
Nitrates in soils and water
Human activities impact this cycle in diverse ways
Affected by human activities; deforestation and land clearance increase NO3- flux into stream flow. N2 fixation by internal combustion engines, plus NOx in acid rain. Agricultural practices cause eutrophication and alter community assemblages
Sulphur cycle
Atmospheric and lithospheric phases of similar magnitude
Sulphur released into atmosphere by:
o Dimethylsulphide (DMS) from phytoplankton (>90%)
o Anaerobic respiration by sulphate-reducing bacteria
o Volcanic activity
Weathering of rocks drains sulphur off land by stream flow, ferrous sulphide forms in marine sediments
Affected by human activities; SOx from fossil fuel combustion falls as sulphuric acid rain. Causes death of aquatic organisms in lakes and rivers, kills vegetation.
Knock-on effects; sulphate mobilises metal ions (Al3+) affecting plant growth and phosphorous increasing phytoplankton blooms
Carbon cycle
Opposing forces of photosynthesis and respiration
Predominantly gaseous; CO2 the main vehicle of flux between atmosphere, hydrosphere and biota
Historically the lithosphere played a minor role, until humans began releasing dormant carbon reservoirs
Terrestrial plants use atmospheric CO2
Aquatic plants and algae use dissolved carbonates
Inland waters and oceans receive CO2 as bicarbonate from the weathering of limestone and chalk
Respiration by plants, animals and microorganisms releases C locked in photosynthetic products
Atmospheric CO2 concentrations are increasing rapidly as a result of human activity
In 1750 280 ppm, today >412 ppm (Dec 2020
Affected by human activities; combustion of fossil fuels, exploitation of tropical forests, land-use changes (agriculture and urbanisation).
Knock-on effects; global warming, destabilised weather systems, species extinctions and range shifts, ocean acidification.
