Lecture 9 - Biogeochemical Cycles

manhattan project

US investment to make the first atomic bomb resulting in the development and spread of atomic bombs in many other countries

radioactive tracers

putting in a radioisotope instead of cesium to follow the movement of the element through the ecosystem through predation, photosynthesis, etc

how was radiation effects on organisms and ecosystems studied?

by irradiating a pine oak forest with radioactive cesium and observing what happens

what aspects comprise selected biogeochemical cycles

carbon, nitrogen and phosphorus cycle

nitrogen cycle human intervention

use of nitrogen fertilizer for crops using the Haber Bosch process, combustion of fossil fuels

phosphorus cycle human intervention

mining phosphate rock for fertilizer, fishing, sewage, agricultural runoff and erosion

carbon cycle human intervention

combustion of fossil fuels and land conversion

food and decomposer webs

the fact that large organic molecules are constantly being synthesized, consumed and broken down

how does the cycling of chemical elements work?

they are never created or destroyed because they never disappear but just change in different forms by different oxidation states/moving around

what does the notion that the cycle comprises pools and fluxes?

the pool would be a big collection of something like a swimming pool and the flux would be the movement of an element from one location to another

what elements are most likely to limit plant productivity ?

nitrogen and phosphorus

carbon cycle gaseous phase

CO2

carbon cycle limiting steps

the balance between creation by photosynthesis and respiration/combustion of organic matter

why do humans deforest land?

to aid hunting by opening and maintaining grasslands, providing land for agriculture, and removing agricultural waste which accelerates fluxes

how is carbon that is sequestered in trees released?

by fire

what are the main natural strong fluxes of the carbon cycle?

CO2 dissolution, uptake in photosynthesis, respiration, organic carbon in run off and photosynthesis and organic uptake

what are the main strong human fluxes in the carbon cycle?

land clearance, combustion of fossil fuels and extraction of fossil fuels

how has 1/3 of the forests been lost?

due to the increase in crops and grazing expanding agriculture

what is the main driver of tropical deforestation?

beef for cattle, especially Brazilian beef followed by oilseeds and forestry

logging

the process of cutting, processing and moving trees to a location for transport that causes drying of peats making them easier to burn for combustion

peat

dead plant material in soil

how can we infer that there are more woodland species by tracking pollen?

because in the ancient times there was more pollen so more vegetation

how can we infer that there is more grassland species by tracking pollen?

because there would be less pollen in those areas

clearance phase

if humans were burning lands for clearance we would see more ash and charcoal settling into the bottom of the lake

what is the industrial revolution powered by?

fossil fuel combustion accelerating the movement of CO2 in the atmosphere

what is the nitrogen cycle comprised of?

mostly gaseous compounds that are highly soluble and there are very minimal sedimentary pools

what are the limiting steps of the N cycle?

conversion of inert N2 gas (not usable by plants) into usable nitrate or ammonium

eutrophication

nitrogen and phosphorus run off due to the bloom in algae, respiration of oxygen by them making water deoxygenated

how has human intervention affected reactive N inputs?

they exceed natural production rates because in industrial areas, rainwater is now a dilute fertilizer causing deposition of nitrogen into the atmosphere

how has human intervention in the nitrogen cycle enriched ecosystems?

• fast growing weedy plants are favored

• nitrate buildup in groundwater hazardous in agricultural areas

• eutrophication of coastal waters and anoxia

anoxia

absence in oxygen

lake erie

most shallow great lake most prone to eutrophication

what is the P cycle composed of?

compounds that are minimally soluble, sedimentary pools ending up in ocean sediments

what are the limiting steps of the P cycle?

weathering of rocks in soil and geological uplift

phosphate

why cant we make phosphate fertilizer?

because cycle is sedimentary so we have to mine phosphate rich rock and guano deposits but reserves may have exceeded their life so offshore deposits might be a new target for extraction

why do seabirds nest on islands?

because they lack predators

where are seabird colonies best developed?

where there are big fish populations

where are fish populations best developed?

in places with cold water upwelling

what does upwelling do?

brings phosphorus rich ocean sediments to the surface and into the food chain

how does dry climate effect guano

means it cant e rapidly leached by the rain