Quick questions on Biophysical interactions sustaining ecosystems: HSC Geography

Convert solar energy (or chemical energy in some deep-sea ecosystems) into biomass through photosynthesis or chemosynthesis. Plants, algae, photosynthetic bacteria.

Obtain energy by eating other organisms.

Break down dead organisms and waste, releasing nutrients back into the ecosystem. Bacteria, fungi, termites, earthworms, dung beetles, crabs (in marine systems).

Temperature, humidity, atmospheric CO2, wind, precipitation, sunlight.

Water availability, water chemistry (pH, salinity, dissolved oxygen, nutrients), water movement (currents, tides).

Soil (texture, pH, organic matter, mineral nutrients), topography (slope, aspect, altitude), substrate (rock type, sediment).

Solar radiation is the primary energy source for nearly all ecosystems. Australian ecosystems receive around 5 kWh/m2/day on average. Total solar input to the Great Barrier Reef is roughly 3 x 10^15 kJ/year.

Atmospheric CO2 is fixed into biomass through photosynthesis. Biomass is consumed by other organisms, or returns to soil as litter, or is burned. Respiration, decomposition, fire, and combustion return CO2 to the atmosphere. Long-term storage occurs in fossil fuels, peat bogs, and ocean sediments.

Atmospheric nitrogen (N2) is unusable by most plants. Nitrogen-fixing bacteria (in legume root nodules and free-living in soils) convert N2 to ammonium. Nitrifying bacteria convert ammonium to nitrate, which plants can absorb. Denitrifying bacteria return nitrogen to the atmosphere.

Unlike nitrogen, phosphorus has no significant atmospheric phase. Plants take phosphorus from soil solution; animals eat plants; decomposition returns phosphorus to soil. Long-term storage in marine sediments. Australian native ecosystems are even more phosphorus-poor than the global average; this is why phosphorus fertiliser killed native banksia in WA.

Covered in the Biophysical Interactions topic, but ecosystems are tied closely to water availability. Evapotranspiration by vegetation is a major component of water return to the atmosphere.

Important for coral reefs (calcium carbonate skeletons), shellfish, and bones. Ocean acidification (lower pH from dissolved CO2) reduces calcium carbonate availability and weakens reef builders.