27. Nutrient Cycles II

Question 1

nutrients and organisms

Answer 1

organisms can modify the distribution and cycling of nutrients in ecosystems

Question 2

patterns of nutrient cycling in aquatic ecosystems

Answer 2

greater proportion of autotrophs consumed by herbivores than terrestrial

Question 3

patterns of nutrient cycling in terrestrial ecosystems

Answer 3

greater proportion of autotrophs consumed by detritivores

Question 4

life in aquatic ecosystems

Answer 4

less autotroph biomass = less detritus
more herbivores = less detritus
–> overall quicker cycling of nutrients

Question 5

life in terrestrial ecosystems

Answer 5

more autotroph biomass = more detritus
less herbivores = more detritus
–> overall slower cycling of nutrients

Question 6

nutrient cycling in aquatic ecosystems: streams

Answer 6

water movement –> nutrient cycling doesn’t occur in a single location –> nutrient spiraling

Question 7

spiraling length

Answer 7

the length of the stream required for an atom of a nutrient to complete a cycle from the release into the water-column to re-entry into the benthic environment

Question 8

nutrient retentiveness

Answer 8

the inverse of spiraling length, or the tendency of a stream to retain nutrients
long spiraling length = low nutrient retentiveness
short spiraling length = high nutrient retentiveness

Question 9

spiraling length formula

Answer 9

S = VT
S - spiraling length
V - average velocity at which nutrient atom moves downstream
T - average time for a nutrient atom to complete a cycle

Question 10

short spiraling length

Answer 10

if velocity is low or time to complete cycle is low, spiraling length is short –> a particular nutrient atom may be used many times before it is washed out of a stream system (nutrients stay close to where they started)

Question 11

macroinvertebrates in aquatic nutrient cycling

Answer 11

consume large proportion of available nitrogen –> high abundance of macroinvertebrates = speed up nutrients cycling in streams = greater primary production

Question 12

effect of salmon (vertebrates) on aquatic nutrient cycling

Answer 12

migrate from ocean to freshwater to spawn –> transfer huge amount of nutrients from the ocean to forest ecosystems

Question 13

effect of pocket gopher on terrestrial nutrient cycling (grasslands)

Answer 13

alter nutrient cycling for nitrogen - by burrowing and building mounds, bring high nitrogen soil to the top where there is light and a high amount of primary production can occur (grasses have higher nitrogen content)

Question 14

effect of large grazers (like deer) on terrestrial nutrient cycling

Answer 14

1. may increase primary productivity through increased rates of nutrient cycling
2. heavy grazing shifts composition of plants by eating more palatable species and leaving behind seedlings of less palatable species

Question 15

humans and the nitrogen cycle

Answer 15

we have converted massive amounts of nitrogen from the atmosphere reservoir to terrestrial reservoirs through fertilizer use (haber process)

Question 16

haber process

Answer 16

artificial nitrogen fixation - N gas and H gas combined using metal catalyst under high heat and pressure to form NH3- (discovered in 1910)

Question 17

nitrogen fixation by humans

Answer 17

now exceeds fixation from non-human sources - primary causes are industrial fixation, crop fixation, and fossil fuels - global nitrogen fixation increased exponentially in the 20th century

Question 18

consequences of excess nitrogen

Answer 18

1. acid rain - kills ecosystems by changing pH
2. methemoglobinemia (blue baby syndrome)
3. shift from grasslands to forests

Question 19

acid rain

Answer 19

nitrogen oxides (NOx) produced by internal combustion engines, when combined with water vapour form acid (this is why cars have catalytic converters)

Question 20

methemoglobinemia

Answer 20

nitrates in drinking water (from agricultural runoff) can cause hemoglobin in blood to oxidize, reducing its capacity to carry O2

Question 21

shift from grasslands to forest

Answer 21

increased nitrogen (from combustion engines and agricultural runoff) allow trees to competitively exclude grasses –> expansion of forests into areas historically covered by prairie habitats (ex in Jasper and Elk Island)

Question 22

humans and the carbon cycle

Answer 22

historic atmospheric composition of CO2 can be recreated by studying air bubbles trapped in ice

Question 23

findings from Vostok ice core air bubbles:

Answer 23

• CO2 oscillated between 190-280 ppm over past 160 000 years
• temperature varies directly with changing CO2
• atmospheric CO2 increased substantially since 1800s exceeding all levels in past 160 000 years
• present CO2 levels are strongly influenced by burning of fossil fuels

Question 24

atmospheric CO2 over the past 1000 years

Answer 24

• rapid increase starting in the 1800s (industrial revolution)

Question 25

deforestation and nutrient cycling

Answer 25

clear cut forest = higher nitrates in stream due to soil erosion

Question 26

disturbance and nutrients

Answer 26

young, rapidly growing understory vegetation can act as a nutrient sink after disturbance such as logging or a forest fire

Question 27

phosphorous movement

Answer 27

inputs: geological, meteorological
exports: geological (via the stream)

Question 28

aquatic phosphorous cycling throughout the year

Answer 28

• most inputs during autumn leaf fall

- most losses during storm flows and spring snow melt