Deck 22: Nutrient Supply and Cycling

Question 1

Which statement about the soils on the Colorado Plateau is false?

A) They are exposed to high levels of erosive forces.
B) They are exposed to great climatic variation.
C) The crusty nature of the soil is largely the work of filamentous cyanobacteria.
D) Humans have had little impact on the soil conditions.

Answer 1

D

Question 2

How do plants and animals differ in how they take in nutrients?

A) Plants take in simple chemicals, which they synthesize into larger molecules; animals take up larger, more complex molecules.
B) Plants need to take in nitrogen-containing molecules, but animals do not.
C) Plants take in complex molecules; animals take up relatively simple chemicals and synthesize larger molecules.
D) Plants must absorb all 20 amino acids, whereas animals are able to synthesize all amino acids.

Answer 2

A

Question 3

All other things being equal, herbivores generally must consume _______ food than carnivores in order to meet their nutritional needs. The reason is that plant material, per gram of carbon, contains _______ nitrogen than animal material does.

A) more; more
B) more; less
C) less; more
D) less; less

Answer 3

B

Question 4

Which element is required by all (or almost all) animals but required by only C₄ and CAM plants?

A) Selenium
B) Sodium
C) Nitrogen
D) Cobalt

Question 5

Refer to the table.
According the table, which of the following statements about the elemental composition of organisms is true?

A) Bacteria have an equal amount of carbon and nitrogen.
B) Plants contain more phosphorus than bacteria or animals.
C) Animals, plants, and bacteria all contain iron.
D) Animals contain less calcium than plants.

Question 6

Which statement best describes the relationship between mechanical and chemical weathering?

A) Chemical weathering promotes mechanical weathering.
B) Chemical weathering impedes mechanical weathering.
C) Mechanical weathering promotes chemical weathering.
D) Mechanical weathering impedes chemical weathering.

Question 7

Chemical weathering of minerals in rocks is an important source of nutrients because it

A) releases soluble forms of nutrients.
B) converts inorganic molecules to organic molecules.
C) changes the size and surface area of rocks through freezing and thawing.
D) recycles nutrients into the atmosphere.

Question 8

The availability of nutrient cations such as Ca²⁺, K⁺, and Mg²⁺ to plants may be insufficient in some soils that have low amounts of _______ particles. These particles have _______ that allow them to hold onto cations and exchange them with the soil solution.

A) sand; strong positive charges
B) clay; weak negative charges
C) sand; semicrystalline structures
D) clay; irregular structures

Question 9

Silt is soil that

A) has particles larger than clay.
B) is very moist.
C) has been leached.
D) is derived from granite.

Question 10

Why is there likely to be a higher diversity of plant species in soil derived from limestone than in soil derived from granite?

A) The higher acidity of soil derived from granite lowers the availability of nitrogen and phosphorus to plants.
B) Limestone attracts more bacteria and fungi, thereby increasing the nutrients in the soil.
C) The higher acidity of soil derived from limestone increases the availability of nitrogen and phosphorus to plants.
D) The lower acidity of soil derived from granite lowers the availability of nitrogen and phosphorus to plants.

Question 11

Refer to the figures.
Based on Gough's study and others, which figure shows the most likely relationship between plant species richness and soil acidity?

A) Figure A
B) Figure B
C) Figure C
D) Figure A in wet climates; Figure B in dry climates

Question 12

Refer to the figure.
The figure shows the relationship between temperature and precipitation in different climate regimes (points A‒D). In which climate regime would you expect rates of weathering and leaching to be the highest?

A) Regime A
B) Regime B
C) Regime C
D) Regime D

Question 13

Refer to the figure.
The figure shows the relationship between temperature and precipitation in different climate regimes (points A‒D). Suppose that the climates in the graph have been maintained for a long period of time. With everything else being equal, in which climate regime would you expect soil quality in terms of mineral-derived nutrients to be the lowest?

A) Regime A
B) Regime B
C) Regime C
D) Regime D

Question 14

Which sequence best describes the order of soil horizons in well-developed soil from top to bottom?

A) Organic matter, mineral nutrients, clay, bedrock
B) Organic matter, clay, mineral nutrients, detritus
C) Mineral nutrients, organic matter, bedrock, clay
D) Mineral nutrients, organic matter, clay, bedrock

Question 15

Refer to the figure.
Soil with a pH of 5 would be hypothesized to have _______ plant species.

A) 10
B) 25
C) 30
D) 42

Question 16

The atmosphere is composed of _______% nitrogen in the form of _______.

A) 21; N₂
B) 21; NH₄⁺
C) 78; N₂
D) 78; NH₄⁺

Question 17

Which statement correctly describes the role of nitrogen fixation in the nutrient cycle?

A) N₂ is taken in by green plants and transformed into nitrogen-rich protein.
B) N₂ is inhaled by herbivores and transformed into ammonia, which can be dissolved in their blood.
C) NH₄⁺ is converted by certain bacteria into complex proteins that can then be ingested by animals.
D) N₂ is taken up by certain bacteria that can change it into chemically available forms usable by plants.

Question 18

Which statement about nitrogen fixation is false?

A) It is energetically expensive.
B) It is more common in late succession than in early succession.
C) It often results in trade-offs in growth and/or reproduction.
D) Legumes are examples of plants that use nitrogen-fixing bacteria.

Question 19

Earthworms contribute to decomposition by

A) breaking down matter into inorganic nutrients through mineralization.
B) breaking up litter into smaller particles, thereby increasing the surface area and allowing for more efficient chemical breakdown.
C) decreasing the amount of oxygen in the soil, thereby increasing mineralization.
D) releasing enzymes that convert inorganic molecules into organic macromolecules.

Question 20

Which intervention would most likely lead to an increase in detritivore activity in warm, moist soils?

A) Decreasing the temperature
B) Filtering oxygen into the soil
C) Filtering carbon dioxide into the soil
D) Adding more water to the soil

Question 21

Refer to the figure.


-Which statement best explains the downward trend that follows the peak of each curve?

A) Low soil moisture limits the activity of decomposers.
B) Soils with over one half of the water content indicated have concentrations of oxygen that are too low for optimal rates of decomposition.
C) Soils with extremely high water content are unable to sustain decomposition activity.
D) Soils with over one half the water content indicated increases the metabolic rate of decomposers.

Question 22

Refer to the figure.


- Which statement is supported by the figure?

A) Decomposers at higher temperatures need less moisture to reach peak levels of activity than decomposers at lower temperatures do.
B) Soils with low water content limit rates of decomposition at all temperatures.
C) High soil moisture decreases microbial activity only at a temperature of 30°C.
D) Microbes in soils at 15°C require less soil moisture to reach their peak rate of decomposition than microbes in soils do at 30°C.

Question 23

Decomposition of organic matter with a C:N ratio _______ than 25:1 (the optimal ratio for microbial growth) would result in a net release of nutrients into the soil. The reason is that microbial growth in this situation would be more limited by the _______ supply than by the _______ supply.

A) less; energy; nitrogen
B) less; nitrogen; carbon dioxide
C) less; nitrogen; energy
D) greater; energy; nitrogen

Question 24

Some slow-growing trees have leaves that are high in lignin. The most likely advantage of lignin to such trees is that lignin

A) has a low C:N ratio, and thus it enriches the soil in its immediate vicinity.
B) kills certain microorganisms that are needed for plants with high growth rates, protecting the trees from competitive exclusion.
C) has high concentrations of phosphorus, which is necessary for slow-growing trees.
D) slows the rate of decomposition, thereby lowering the fertility of the soil and allowing the trees to outcompete plants with high growth rates.

Question 25

Nitrification by certain chemoautotrophic bacteria occurs in _______ conditions; this process, therefore, occurs primarily in _______ environments.

A) anoxic; high altitude
B) anoxic; aquatic
C) aerobic; aquatic
D) aerobic; terrestrial

Question 26

Suppose two agents are introduced into soil: one that results in an increase in nitrification and another that results in an equal addition of denitrification. Compared to the soil before, the combination of equal amounts of nitrification and denitrification in the soil would result in a net increase in

A) ammonium.
B) nitrate.
C) nitrous oxide.
D) dinitrogen gas.

Question 27

By a process known as _______, certain chemoautotrophic bacteria transform ammonia and ammonium into _______, which tends to be more available to plants than other forms of nitrogen.

A) nitrogen fixation; nitrate
B) nitrification; nitrate
C) nitrogen fixation; N₂
D) denitrification; N₂

Question 28

According to measurements taken in the 1990s, the levels of inorganic nitrogen in Arctic ecosystems were substantially lower than the amount of nitrogen actually taken up by plants. Which of the following is a possible explanation for this pattern?

A) Arctic trees are able to perform nitrogen fixation with enzymes in their leaves.
B) Microbes in the Arctic soil transform inorganic nitrogen into organic forms.
C) Arctic sedges can take up organic forms of nitrogen.
D) Arctic shrubs take up 60% of their nitrogen in the form of N₂.

Question 29

Which of the following is one example of the ways in which Arctic plant communities have avoided competition through resource partitioning?

A) All Arctic species are able to use both inorganic and organic nitrogen.
B) Arctic species lack chemicals that inhibit growth of other species.
C) Different Arctic plant species take up nitrogen at different depths of the soil.
D) Different Arctic plant species grow at different rates.

Question 30

Which statement about color change during leaf senescence is false?

A) Chlorophyll is broken down and the plant reabsorbs up to 60‒70% of the nitrogen in the leaves.
B) Chlorophyll is broken down and the plant reabsorbs 5‒10% of the nitrogen in the leaves.
C) Carbohydrates and starches are broken down and moved into stems and roots.
D) Chlorophyll is broken down and the plant reabsorbs up to 40‒50% of the phosphorous in the leaves.

Question 31

Which statement best describes the order of the nitrogen cycle?

A) N₂ is converted to proteins in plants > Proteins are converted to NH₄⁺ through decomposition > NH₄⁺ is converted back to N₂ through nitrogen fixation
B) Plant proteins are converted to N₂ through decomposition > N₂ is converted to NH₄⁺ through nitrogen fixation > NH₄⁺ is converted back to proteins in plants
C) N₂ is converted to amino acids through nitrogen fixation > Amino acids are converted to proteins in plants > Proteins are converted to amino acids through decomposition > Amino acids are converted back to proteins in plants
D) N₂ is converted to NH₄⁺ through nitrogen fixation > NH₄⁺ is converted to proteins in plants > Proteins are converted to NH₄⁺ through decomposition > NH₄⁺ is converted back to N₂ via reverse nitrogen fixation

Question 32

Refer to the table.
In a series of experiments, a researcher repeatedly measures the mean resident time for phosphate to be approximately 6 years. What ecosystem type is the researcher studying?

A) Tropical rainforest
B) Temperate coniferous forest
C) Boreal forest
D) Temperate deciduous forest

Question 33

Suppose that the mean residence time of nitrogen in a section of soil is 3.5 years, and the mean rate of input is 150 kilograms per year. If rates of input and output as well as the total pool size have remained roughly constant, what is the expected size of the total pool of nitrogen in that soil?

A) 150 kg
B) 300 kg
C) 525 kg
D) 1,050 kg

Question 34

What would be the mean residence time of phosphorus in a pond if the total pool is 1,250 grams and the mean rate of input is 2,500 grams? (Assume that rates of input, output, and the total pool size have remained constant.)

A) 6 months
B) 1 year
C) 18 months
D) 2 years

Question 35

Which ecosystems have the slowest turnover rates of elements (the greatest mean residence times)?

A) Boreal forests with large nutrient pools and low rates of litter input
B) Temperate coniferous forests with low levels of nitrates in the soil
C) Tropical forests with small nutrient pools and high rates of litter input
D) Chaparrals with low amounts of moisture in the soil

Question 36

The residence times of nutrients in the soils of boreal forests are influenced the most by the

A) rate of litter input, which is increased by severe weather changes.
B) rate of litter input, which is decreased by increased moisture in the soil.
C) decomposition rates, which are slowed by the low soil temperatures and by secondary compounds.
D) decomposition rates, which are increased by the anoxic soil conditions caused by the low soil temperatures.

Question 37

Refer to the figure.
Which figure best illustrates the relationship between temperature and primary productivity and temperature and rates of decomposition?

A) Figure A
B) Figure B
C) Figure C
D) Figure D

Question 38

When studying terrestrial ecosystems, ecologists commonly focus on an area that is drained by a single stream, which is called a(n)

A) catchment.
B) occlusion.
C) weir.
D) ravine.

Question 39

Of nitrogen and phosphorus, which is the most limiting nutrient to primary production early in primary succession, and why?

A) Phosphorus, because it undergoes occlusion over time
B) Nitrogen, because it undergoes chemical reactions with the phosphorus
C) Nitrogen, because it takes a long time to accumulate in the soil through decomposition
D) Phosphorus, because it is very soluble and is easily leeched from the soil

Question 40

What is the input of calcium into a catchment if the flow of water into the catchment is 150 liters per day and the concentration of calcium is 0.04 mg/liter?

A) 0.4 mg
B) 1.2 mg
C) 4 mg
D) 6 mg

Question 41

Soluble phosphorus combines with iron to form a compound that is no longer useable by organisms. This process is an example of

A) chemical weathering.
B) aparite.
C) occlusion.
D) leaching.

Question 42

Refer to the figure.
Based on research by Vitousek and colleagues, an Ohi'a tree that grows about 2.6 mm in diameter a year when fertilized with nitrogen and phosphorous would most likely be living on a Hawaiian island approximately _______ years old.

A) 150
B) 1,500
C) 21,500
D) 2.15 million

Question 43

If the flow of water into a catchment is 800 liters per day and the concentration of phosphorus is 0.02 mg per liter, the daily input of phosphorous into the catchment is

A) 0.4 mg.
B) 4 mg.
C) 16 mg.
D) 64 mg.

Question 44

How does the nutrient cycle of aquatic systems differ from that of terrestrial systems?

A) Inputs of nutrients from outside the ecosystems are more important in aquatic ecosystems.
B) Nitrogen cycles are less important in aquatic ecosystems.
C) Aquatic ecosystems are not dependent on decomposition.
D) Chemical weathering does not contribute to nutrient supply in aquatic ecosystems.

Question 45

Rivers and streams subjected to high amounts of nitrogen pollution export less nitrate than would be expected because moving stream water is affected by the processes of _______ and _______.

A) nitrification; decomposition
B) denitrification; biological uptake
C) mineralization; biological uptake
D) denitrification; decomposition

Question 46

Refer to the figure.
A river with 5,000 kg/km²/yr of nitrogen input from human activities would be expected to export _______ kg/km² of nitrogen per year.

A) 500
B) 800
C) 1,150
D) 1,500

Question 47

In the 1950s, anthropogenic eutrophication of Lake Washington was caused by

A) nitrates from road runoff caused by severe rainstorms.
B) introduced species of fish.
C) high winds that caused increased turnover of benthic layers.
D) phosphates from wastewater.

Question 48

A nutrient-poor lake with low primary productivity is referred to as

A) eutrophic.
B) mesotrophic.
C) oligotrophic.
D) hypotrophic.

Question 49

Which of the following is not a primary source of nitrogen in marine ecosystems?

A) From rivers
B) Atmospheric decomposition
C) Internal cycling through decomposition
D) Leaching

Question 50

Why is upwelling important for the commercial fishery industry?

A) Upwelling brings nutrient-rich waters to nutrient-poor surface waters.
B) Upwelling takes nutrient-rich water from the surface to the bottom of the ocean.
C) Upwelling deposits detritus on surface waters.
D) Upwelling equally distributes anoxic sediment throughout the water column.

Question 51

Refer to the figure.
Figure 1
You are studying a river in its natural state, unaffected by human activities. Your data are graphed in Figure 1. You began collecting data at the source of the river ("0 km" on the figure) and continued to sample the river every 1 km.

-Answer the following questions:
a) At what distance from the source is the river water moving the fastest?
b) At what distance from the source is the river water moving the slowest?
c) At what distance from the source is the river the deepest?
d) At what distance from the source is the river the shallowest?
e) Where is the river most likely flowing over the steepest terrain?
f) Where is the river most likely flowing over the most level terrain?

Question 52

Refer to the figure.
Figure 1
You are studying a river in its natural state, unaffected by human activities. Your data are graphed in Figure 1. You began collecting data at the source of the river ("0 km" on the figure) and continued to sample the river every 1 km.

-Where would you expect to find the greatest mechanical weathering of the rocks? Why? Where would you expect to find the greatest amount of sand on the river bottom? Why?

Question 53

Refer to the figure.
Figure 1
You are studying a river in its natural state, unaffected by human activities. Your data are graphed in Figure 1. You began collecting data at the source of the river ("0 km" on the figure) and continued to sample the river every 1 km.

- Use your knowledge of nutrient cycles to answer the following questions:
a) Why is the nutrient cycle in a lake depicted as a circular cycle, while in a river it is depicted as a spiral?
b) In general, when would you expect the structure of the nutrient cycle of a river to most closely resemble that of a lake? In the case of your data, which location in the river most closely fits the conditions seen in a lake?

Question 54

Refer to the figure.
Figure 1
You are studying a river in its natural state, unaffected by human activities. Your data are graphed in Figure 1. You began collecting data at the source of the river ("0 km" on the figure) and continued to sample the river every 1 km.

-The river you were studying (data in Figure 1) is suddenly diverted at its source and the entire river channel path is changed. The former path of the river is now terrestrial. Based on the data on river flow and water depth collected before the river was diverted (Figure 1), which areas would be most likely to have soils with the highest cation exchange capacity after river diversion, and why? Give your answer as the distance in km from the former source of the river.

Question 55

Refer to the figure.
Figure 1
You are studying a river in its natural state, unaffected by human activities. Your data are graphed in Figure 1. You began collecting data at the source of the river ("0 km" on the figure) and continued to sample the river every 1 km.

-What type of succession would you expect to see in this high cation exchange capacity area, and why? How would the rate of soil formation and succession differ from what you would expect in a terrestrial area disturbed by a lava flow?

Question 56

Refer to the table and the figure.
Table 1
Figure 2
You are studying a river that has been dammed to form a reservoir. You have compiled data collected on this system over time (Table 1 and Figure 2).

-Use your knowledge of nutrient cycles in aquatic systems and the data in Table 1 and Figure 2 to report summary data for this new system.
a) Between which two sample years did dam construction begin? How did you deduce this?
b) Prior to dam construction, what was the natural average flow rate of the river (round to one decimal place)?
c) Prior to dam construction, what was the natural average water depth of the river (round to one decimal place)?
d) By which year had the reservoir likely filled to capacity?

Question 57

Refer to the table and the figure.
Table 1
Figure 2
You are studying a river that has been dammed to form a reservoir. You have compiled data collected on this system over time (Table 1 and Figure 2).

-Use the data in Table 1 and Figure 2 to answer the following questions about the effect damning the river will have on the ecosystem:
a) How would the extent of mixing change when the system changed from a river ecosystem to a reservoir?
b) How would you expect the oxygen levels in the benthic zone of the reservoir to differ from those found at the river bottom when the river was in its natural state? How would you expect decomposition to differ?

Question 58

Refer to the table and the figure.
Table 1
Figure 2
You are studying a river that has been dammed to form a reservoir. You have compiled data collected on this system over time (Table 1 and Figure 2).

-Use the data in Table 1 and Figure 2 to answer the following questions about the effect of changes in water depth on the nutrient status of the reservoir:
a) How did the average water depth change between 1970 and 1985? How can you explain this change in water depth?
b) How do you think this change in water depth affected the nutrient status of the reservoir?

Question 59

Refer to the table and the figure.
Table 1
Figure 2
You are studying a river that has been dammed to form a reservoir. You have compiled data collected on this system over time (Table 1 and Figure 2).

- Use the data in Table 1 and Figure 2 to answer the following questions about the effect of changes in water depth on the nutrient status and water clarity of the reservoir compared to the changes observed in Lake Washington:
a) Compare the changes in the nutrient status of the reservoir to the changes in nutrient status observed in Lake Washington. How are they similar and how do they differ?
b) Based on the changes in water clarity observed in Lake Washington, how would you expect water clarity in the reservoir to change as water depth decreases?

Question 60

Refer to the table and the figure.
Table 1
Figure 2
You are studying a river that has been dammed to form a reservoir. You have compiled data collected on this system over time (Table 1 and Figure 2).

-Suppose you are expanding your research to focus on the entire drainage basin in this area, including the reservoir, the former river channel, and the area where the river flows into the ocean. Answer the following questions:
a) What is the term that best describes the unit of study your work is focused on?
b) What type of ecosystem is likely to occur where the freshwater and marine systems meet?
c) How would you expect dam construction to initially impact the area where fresh water and marine systems meet?
d) Based on the data in Figure 2 from 1990-2010, what could have been done to counteract the effects of the dam on the estuary?

Question 61

Refer to the figure.
Figure 3
Suppose you are now studying soils that vary in the amount of leaching they have undergone. You sample the proportion of nutrients leached from the top soil horizon. Your data are graphed in Figure 3.Answer the following questions:
a) Which study site is likely to have soil with low nutrient levels?
b) Which study site is likely to have soil with high nutrient levels?
c) Which study site likely has the oldest soil? Why? What factors would have to be similar among the sites in order to determine soil age from the data given?

Question 62

Which of the following statements about nutrient requirements in organisms is false?

A) Many but not all C₄ and CAM plants require sodium.
B) Differences in nutrient requirements are reflected in the chemical composition of organisms.
C) Animals and microorganisms typically have higher C:N ratios than plants.
D) An organism's mode of energy acquisition affects the amounts and specific nutrients needed.

Question 63

All nutrients are ultimately derived from

A) minerals in rocks and gases in the atmosphere.
B) rivers and streams.
C) microorganisms.
D) detritus.

Question 64

Which of the following does not influence the development and composition of soils?

A) The acidity during development
B) The organisms associated with the parent material
C) The parent material that was constructed through weathering
D) The moisture levels of the parent material

Question 65

In order for most organisms to use the nitrogen in the atmosphere, dinitrogen gas must be

A) taken in by green plants and transformed into nitrogen-rich protein.
B) inhaled by herbivores and transformed into ammonia, which can be dissolved in their blood.
C) taken up by certain bacteria that can change it into ammonium, a form that is available for plants.
D) dissolved in an aqueous solution to form nitrate.

Question 66

_______ is the key process by which nutrients in detritus are made available as soluble organic and inorganic compounds that can be taken up by other organisms.

A) Nitrification
B) Nutrient cycling
C) Occlusion
D) Eutrophication

Question 67

Organic matter with a _______ ratio results in a low net release of nutrients during decomposition. This is because microbial growth is more limited by _______ than it is by _______.

A) low C:N; energy; N supply
B) high C:N; N supply; energy
C) high C:H₂O; water supply; energy
D) low C:H₂O; energy; water supply

Question 68

In the process of nitrification, certain bacteria use inorganic nitrogen released from mineralization as an energy source, influencing the forms of nitrogen available to plants. The chemical transformation that occurs during nitrification is the conversion of _______ into _______.

A) nitrous oxide; atmospheric nitrogen
B) atmospheric nitrogen; ammonia
C) ammonia; nitrate
D) nitrate; ammonia

Question 69

Which statement about nutrient cycling is true?

A) Decomposition is an external input.
B) Denitrification results in the loss of nitrogen due to leaching.
C) Nitrogen fixation makes an external input available for internal cycling.
D) Soluble nitrogen is incorporated into plant tissues.

Question 70

Suppose that the mean residence time of calcium in a section of soil is 6 years and the mean rate of input is 30 kilograms per year. If rates of input and output as well as the total pool size have remained roughly constant, what is the expected size of the total pool of calcium in the soil?

A) 5 kg
B) 30 kg
C) 90 kg
D) 180 kg

Question 71

Which ecosystem has the fastest turnover rates of elements (i.e., lowest mean residence times)?

A) Boreal forest, with large nutrient pools and low rates of litter input
B) Tropical rainforest, with small nutrient pools and high rates of litter input
C) Temperate coniferous forest, with low levels of nitrates in the soil
D) Temperate deciduous forest, with low levels of carbon in the soil

Question 72

During the later stages of succession, the nutrient most limiting to primary production in many terrestrial ecosystems is _______ because it _______.

A) nitrogen; takes a long time to accumulate in the soil
B) phosphorus; undergoes occlusion over time
C) nitrogen; undergoes chemical reactions with phosphorous over time
D) phosphorus; is very soluble and easily leeched from the soil

Question 73

_______ and _______ lower the amount of nitrogen during its transport from terrestrial to marine ecosystems.

A) Nitrification; decomposition
B) Denitrification; decomposition
C) Mineralization; biological uptake
D) Denitrification; biological uptake

Question 74

Lake Condor is at 3,000 meters of elevation. The area around it has a short growing season and the lake is rather deep. Based on this information, we would expect the lake to be

A) eutrophic.
B) mesotrophic.
C) oligotrophic.
D) benthic.

Question 75

In stratified temperate lakes, mixing is most likely to occur in the

A) spring and fall.
B) summer and winter.
C) fall only.
D) winter and spring.

Question 76

Which statement about the nutrient supply in marine ecosystems is false?

A) Because of the lack of oxygen, decomposition does not occur in marine ecosystems.
B) Rates of nitrogen fixation are lower in marine ecosystems than in lakes.
C) Benthic zones contain a mixture of ocean-derived detritus and terrestrial sediments.
D) As freshwater mixes with saltwater, the change in pH and other chemical changes can release phosphorus bound to soil particles.