Ecosystems and processes Flashcards
(20 cards)
What is an ecosystem?
A community of organisms and the physical environment they inhabit
Includes energy transfer within different trophic levels and nutrient cycling
Net primary productivity (NPP)
The total fixation of energy by photosynthesis per unit area
By autotrophs or primary producers like plants and algae
Measured as energy or carbon fixed per unit area time
A proportion of this E is respired by autotrophs
Energy captured by primary producers flows to heterotrophs - losses to respiration
Net primary productivity (NPP) calculation
GPP - R
The actual rate of production of new organism mass (biomass)
Or E available for consumption by heterotrophs (animals, bacteria, fungi)
Secondary productivity
The rate of production of energy or biomass or carbon by heterotrophs per unit area per unit time
Net ecosystem production
NEP = NPP - R (total)
Where R is the respiration of all organisms in the ecosystem
OR NEP = NPP - R(het) where R is the respiration of heterotrophs
Environmental problems
Food security
Biofuels
Climate crisis
Habitat degradation
Human appropriation of NPP diverts energy to a single species which is the root of major global energy problems and crisis
Factors limiting primary productivity - terrestrial
Temperature - small effect on photosynthesis, effect on respiration in auto and heterotrophs
Soil age - N limitation in young soils, typically at high altitudes as there’s little nitrogen-fixing bacteria
P is heavily available in rocks
P limitation in old and heavily weathered soils, typically in tropical rainforests
Water supply - reduced soil water, closure of stomata, reduced uptake of carbon dioxide
Factors limiting primary productivity - aquatic
Light and nutrients
In the summer the surface water is warm and light which sustains photosynthesis and the production of organic N and P
Redfield ratio N:P
15:1
Hypothesised that N is increased by N-fixing cyanobacteria when N is scarce in relation to P
N is reduced by denitrification when N is in excess relative to P
Trophic levels
Primary producers (autotrophs)
Primary consumers (herbivores)
Primary carnivores
Secondary carnivores
Detritovores
Fate of ingested energy
E ingested - E defaecated / E ingested x100
E in growth / E assimilated = Net growth efficiency
Carbon cycle
Predominantly gaseous
Weathering of C-rich limestones and chalk
Biotic potential to regulate environmental conditions
Nitrogen cycle
Atmosphere is an important source of N
Nitrogen fixation by bacteria in root nodules of legumes and alders
Anthropogenic perturbations from N fertilisers and fossil fuel combustion
Phosphorus cycle
Principal stocks in rocks, water and sediments
A sedimentary cycle from land to ocean
In water via ocean currents
Sulphate cycle
Release of S to atmosphere
Sea spray aerosols
Anaerobic respiration by sulphate-inducing bacteria especially hydrogen sulfide from wetlands and tidal mudflats
Eutrophication
Warming increases community respiration, also increases photosynthesis to a lower degree
Algae uses up oxygen and blocks sunlight
Aquatic plants begin to die and provide food for microbes
Increased competition for oxygen
Oxygen supply is reduced especially in bio-mass rich systems
Implicated in fish death
Acid rain
Soils or water that can exchange cations for H+ have a strong buffering capacity
Cations are positively charged
Cation exchange or buffering capacity from organic matter and clay minerals
Acid rain changes the nutrient balance is soil
What do we get from biodiversity?
Diverse food products
Timber and fuel
Textiles
Fresh water
Medicinal products
Benefits obtained from regulation of ecosystem processes
Regulation of climate
Control of floods
Purify water
Absorbs carbon dioxide gas
Stops erosion
Pollinates crops
Occurance of greenhouse gases
Methane - natural occurrence includes termites, wetlands, ocean and fresh water and methane hydrate
Anthropogenic influences include rice paddies, biomass burning, landfills, coal mining and gas production
