biogeochemical cycles

Question 1

what is the main source of natural phosphorous?

Answer 1

Sahara
Bodele depression - deposits 50 million tonnes of dust loaded with phosphrous every year

Question 2

how much dust Does the Bodele depression deposit in South America each year?

Answer 2

50 million tonnes

Question 3

what is phosphorus used for in organisms?

Answer 3

DNA,RNA, ATP and cell membranes

Question 4

outline how phosphorous works its way through the trophic levels?

Answer 4

• Herbivores obtain phosphorous by eating plants
• Carnivores get is by consuming herbivores
• When plants and animals die, decomposers (bacteria, fungi) break down organic matter = releases phosphorous back into the soil
• Settles in sediments and can form new phosphate rocks over millions of years

Question 5

humans have ——– the flow of phosphorous

Answer 5

tripled

Question 6

what is the main challenge that phosphorus presents?

Answer 6

once situated in an environment the element has a long residence time = makes removal of excess phosphorous build up a challenging and time-consuming process.

Question 7

why have humans increased phosphorous flow?

Answer 7

-way of increasing agricultural productivity, synthetic fertilisers containing phosphorous are being used in food production leading to the accumulation of excess phosphorous in agricultural soils

Question 8

what are the 3 main impacts of increased phosphorous?

Answer 8

1) Freshwater eutrophication
2) marine dead zones
3) Loss of plant diversity (biotic homogenisation)

Question 9

explain how phosphorus can cause Freshwater eutrophication

Answer 9

Phosphorous acts as a limiting factor for algae growth, elevated levels result in an increase in algal blooms
Algal blooms create anoxic conditions and reduce light reaching organisms underwater.
Inability for vegetation and animals within the water to access key resources (light and oxygen) = disruption to biomass and plant composition
Vegetation growth decrease because slower rates of photosynthesis
Species unable to adapt die off

Question 10

example of an area experiencing freshwater eutrophication as result of increased P

Answer 10

Chaohu Lake, Central China
Estimated that 544.22 tonnes of phosphorus has been discharged into local surface water – 72% is coming from agricultural practices

Question 11

how many tonnes of phosphorus has been discharged into local surface water in Chaohu Lake (china) ?

Answer 11

544 tonnes - 72% from agriculture

Question 12

how does P increase result in Marine Dead Zones?

Answer 12

Increase in phosphorous = enhancement of primary and secondary production

Trophic interactions have been disrupted = effecting animals in the water column, in the sediments and those attached to hard substrates

Zooplankton species have migrated to oxygen rich environments to survive
Whilst jellyfish species have been seen to increase in number, thriving under hypoxic conditions outcompeting fish

Benthic communities such as crustaceans have been placed under food strain as macroinfauna populations have declined
whilst stationary species fall under increasing conditions of stress and mortality

Biodiversity decreases as hypoxic conditions increase towards anoxic levels
frequency of marine dead zones appearing across the world

Question 13

what is the second largest Dead zone in the world?

Answer 13

Northern Gulf of Mexico between outflows of the Mississippi and Atchafalaya Rivers

Question 14

what has increased nitrogen led to?

Answer 14

widespread nitrogen enrichment in the atmosphere and soil

Question 15

where has anthropogenic nitrogen come from?

Answer 15

• Anthropogenic nitrogen mainly coming from fertilisers

Question 16

• Anthropogenic nitrogen has ——– fixation rates

Answer 16

doubled

Question 17

what is the use of nitrogen for plants and animals?

Answer 17

The natural nitrogen cycle is critical for allowing the conversion of atmospheric nitrogen into a form usable by organisms

Bacteria Rhizobium and Azotobacter can fix nitrogen by converting it to ammonia or ammonium.

Nitrifying bacteria Nitrosomonas and Nitrobacter convert ammonia into nitrites and then to nitrates which is the most usable form of nitrogen for plant uptake.

plants use the Nitrites to build proteins and nucleic acids allowing organism growth

Question 18

study showing changes in plant communities as nitrogen increase

Answer 18

Lu et al (2014)
uk study

Question 19

Lu et al (2014) - UK study looking at changes in plant communities as nitrogen increase

Answer 19

-As nitrogen increase PH decrease (more acidic)

-As nitrogen deposition in soils levels have been decreasing the number of species has been increasing

-Ecosystems have been recovering as result of less nitrogen deposition

• as result of less nitrogen deposition ecosystem biodiversity is recovering

Question 20

study on effects of nitrogen increase on species composition

Answer 20

Soons et al (2017) - in oligotrophic systems nitrophilic species outcompete the species adapted to nitrogen deficiency

Question 21

Soons et al (2017) - – in oligotrophic systems nitrophilic species outcompete the species adapted to nitrogen deficiency

Answer 21

-A meta analysis combining the results of 189 field studies measuring nutrient enrichment in terrestrial and wetland ecosystems found that nitrogen deposition has reduced plant species richness by 16%

-The increased homogeneity of species within the terrestrial and wetland ecosystems creates a more vulnerable environment to the spread of disease and environmental disasters (disturbance events)

-Therefore as climate change increased the frequency of extreme weather events and new pathogen emergence = ecological communities exposed to high nitrogen enrichment will be among the first to collapse.

Question 22

where is anthropogenic carbon coming from?

Answer 22

fossil fuel combustion

Question 23

when is an ecosystem a carbon sink?

Answer 23

An ecosystem is a sink if the balance between net primary productivity and respiration is negative (take in more than give out

Question 24

how much carbon dioxide emitted by human per year is removed via terrestrial ecosystems?

Answer 24

30%

Question 25

what is carbon dioxide needed for?

Answer 25

photosynthesis component

Question 26

carbon storage capacity is effected by 5 key processes - list them

Answer 26

1) land abandonment 2) Atmospheric co2 has a fertilising effect 3) Warming temperatures increase C storage 4) increased Nitrogen or Phosphorous 5) Old growth forests

Question 27

explain effect of land abandonment on carbon storage capacity

Answer 27

*As forests grow primary productivity exceeds ecosystem respiration *Respiration in fully mature forests may equal primary productivity

Question 28

Sink effect 2: Atmospheric co2 has a fertilising effect: Not as significant as models suggest explain

Answer 28

*Higher concentrations carbon dioxide increases rates of net primary productivity *More co2 more plants grow *Although the response varies in magnitude, most experiments are consistent

Question 29

Sink effect 3: Warming temperatures increase C storage explain

Answer 29

*Warming temps increase photosynthesis and respiration *The net effect is negative – the photosynthesis rates increase more than respiration ones *Longer growing seasons = as these are starting earlier and earlier

Question 30

Sink effect 4: increased Nitrogen or Phosphorous explain

Answer 30

*More N or P favours primary productivity and thus carbon storage

Question 31

Sink effect 5: Old growth forests

Answer 31

* Old growth forests may accumulate carbon for centuries

Question 32

what are the ecological implications of carbon enrichment on forest ecosystem?

Answer 32

- Assumed tat increased co2 abundance increases plant uptake and growth = the fertliser effect = [provides important negative feedback cycle to climate change

Question 33

Author of study of fertiliser effect and carbon enrichment

Answer 33

Jiang et al (2020) - mature forests Australia

Question 34

Jiang et al (2020)

Answer 34

Found that young forests generally indicate a strong fertilisation effect on biomass growth but in mature forests this effect is diminished NSW Australia = experiment in mature temperate eucalyptus forest found that despite co2 enrichment of 38% increasing carbon uptake this did not result in ecosystem sequestration most of excess carbon reemitted in respiration Findings challenge the suggestion that increased co2 will increase net gross primary productive of forests The age of forests complicates the fertiliser effect showing differential impacts on the ability for plant biomass to increase and thus carbon sink abilities

Question 35

what can be concluded from the Jiang et al (2020) study about the fertiliser effect?

Answer 35

-Findings challenge the suggestion that increased co2 will increase net gross primary productivity of forests -The age of forests complicates the fertiliser effect showing differential impacts on the ability for plant biomass to increase and thus carbon sink abilities

Question 36

what are the ecological implications of carbon enrichment on ocean ecosystem?

Answer 36

ocean acidification

Question 37

study on ocean acidification

Answer 37

Doney et al (2016)

Question 38

Doney et al (2016) - effects of increased carbon sequestrations in oceans

Answer 38

- Oceanic uptake accounts for just under a third of anthropogenic carbon released into the atmosphere and results in the lowering of ph -Lowered PH increases ocean acidity which is commonly referred to as the ‘other co2 problem’ -Ocean acidification alters the biogeochemical cycles of many elements and compounds in turn effecting a range of species within marine systems -Commonly a lowered ph also lowers calcium carbonate saturation states resulting in the inability for calcifying species to form shells and skeletons -With the inability to develop shells as protection these species are left more vulnerable to predation.

Question 39

what natural acidic areas foreshadow the effects of ocean acidification: how and what are they?

Answer 39

volcanic vents - have high CO2 and a low PH (high acidity) an absence of corals and reduced populations of sea urchins in places of these species high numbers of non native species and sea grass naturally acidic conditions foreshadow the impacts of ocean acidification causing shifts in community composition at much larger scales