Chapter 24

Question 1

Scientists monitoring acidified precipitation in the northeastern United States and Eastern
Europe during the 1960s found that the pH of rainwater dropped to as low as __________.
A) 0.0 B) 2.0 C) 4.0 D) 6.0

Answer 1

C) 4.0

Question 2

Which of the following substances is an important precursor of acidified precipitation?
A) lead emitted in automobile exhaust
B) sulfur dioxide created from burning of fossil fuels
C) dust particles carried into the atmosphere from agricultural fields
D) sodium chloride and other salts from oceanic sources
E) chlorofluorocarbons from industrial sources

Answer 2

B) sulfur dioxide created from burning of fossil fuels

Question 3

Acidified precipitation leaches various elements from forest soils. Heavy leaching of two
elements in particular leads to poor growth and even mortality of trees. Which elements are
these?
A) aluminum and boron D) calcium and magnesium
B) zinc and manganese E) iron and silicon
C) chromium and nickel

Answer 3

D) calcium and magnesium

Question 4

Following passage of the Clean Air Act by the United States Congress in 1970, what happened
to emissions of sulfur oxides and particulate matter emitted from factories and power plants?
A) These emissions continued to increase.
B) These emissions began to decline almost immediately.
C) These emissions showed no change whatsoever.

Answer 4

B) These emissions began to decline almost immediately.

Question 5

Following passage of the Clean Air Act by the United States Congress in 1970, researchers
working at the Hubbard Brook Experimental Forest found which of the following responses in
forest growth?
A) Forest growth rebounded quickly to pre‐industrial levels.
B) Forest growth showed no immediate signs of recovery.

Answer 5

B) Forest growth showed no immediate signs of recovery

Question 6

Which of the following elements was monitored to determine the rate of bedrock weathering
in the Hubbard Brook Experimental Forest?
A) calcium B) magnesium C) potassium D) nitrogen E) phosphorus

Answer 6

A) calcium

Question 7

What did researchers estimate to be the rate of bedrock weathering (in terms of bedrock
depth) in the Hubbard Brook Experimental Forest?
A) 1 meter/yr B) 1 centimeter/yr C) 1 millimeter/yr D) 1 micrometer/yr E) zero

Answer 7

C) 1 millimeter/yr

Question 8

Which of the following elements is usually absent from soil parent material?
A) calcium B) magnesium C) potassium D) nitrogen E) phosphorus

Answer 8

D) nitrogen

Question 9

Which of the following contribute to breakdown of litter on the forest floor?
A) leaching of soluble components by water
B) consumption of litter by large detritus‐feeding organisms
C) activity of fungi
D) activity of bacteria
E) all of the above

Answer 9

E) all of the above

Question 10

Leaves of different plant species decompose at different rates, depending largely on which of
the following properties?
A) size of the leaves C) lignin content of the leaves
B) manganese content of the leaves D) moisture content of the leaves

Answer 10

C) lignin content of the leaves

Question 11

You have a choice among leaves of a variety of different tree species to add to your compost
heap. You are interested in rapid decomposition of the leaves because you wish to use the
compost soon as an amendment for your garden. Which of the following kinds of leaves would
you prefer to add to your compost?
A) mulberry B) oak C) beech D) pine

Answer 11

A) mulberry

Question 12

While mycorrhizae assist plants in obtaining nutrients from soils, they may also provide an
additional benefit to plants. What is it?
A) protection from pathogenic organisms
B) production of supplemental sugars
C) creation of a fire‐retardant layer in the soil
D) all of the above

Answer 12

A) protection from pathogenic organisms

Question 13

Under what conditions of available soil phosphorus are mycorrhizae most likely to benefit
plants through uptake of phosphorus?
A) high
B) medium
C) low
D) equally at all levels

Answer 13

C) low

Question 14

Research by Björn Lindahl and colleagues has shown that mycorrhizal fungi tend to be more
active in which portion of the vertical profile of a forest soil?
A) surface
B) deep
C) equally at both levels

Answer 14

B) deep

Question 15

In which of the following ecosystems would you expect to find litter on the forest floor
contributing the largest percentage of total organic biomass?
A) temperate needle‐leaved forest C) tropical rain forest
B) temperate hardwood forest

Answer 15

A) temperate needle‐leaved forest

Question 16

Where in the Neotropics would you expect to find oligotrophic soils?
A) Andes Mountains
B) Central America
C) West Indies
D) Amazon Basin

Answer 16

D) Amazon Basin

Question 17

Traditional slash‐and‐burn agriculture in the humid tropics alternates 2–3 years of crop production with how many years of forest regeneration?
A) 2–3 years B) 5–10 years C) 50–100 years D) 500–1000 years

Answer 17

C) 50–100 years

Question 18

Michael Goulden and colleagues conducted a study of carbon evolution from boreal forest soils.
One of the principal findings of this study was that:
A) soil respiration was sensitive to fertilizer application.
B) soil respiration was sensitive to depth of thawing.
C) soil respiration was sensitive to acidified precipitation.
D) there was no detectable respiration in these soils.

Answer 18

B) soil respiration was sensitive to depth of thawing.

Question 19

The study by Goulden and colleagues (previous question) showed that the boreal forest
ecosystem was not in equilibrium, as evidenced by a small net carbon loss from the system.
A) True
B) False

Answer 19

A) True

Question 20

Regeneration of nutrients from aquatic sediments and from terrestrial soils differs in
fundamental ways. Aquatic sediments are distinctive in that nutrient regeneration typically
occurs:
A) close to plant roots and under aerobic conditions.
B) close to plant roots and under anaerobic conditions.
C) far from plant roots and under aerobic conditions.
D) far from plant roots and under anaerobic conditions.

Answer 20

D) far from plant roots and under anaerobic conditions.

Question 21

Two situations in which high nutrient availability (and thus high productivity) occurs in the
oceans are:
A) shallow seas and coastal areas with upwelling of deeper water.
B) shallow seas and coastal areas without upwelling of deeper water.
C) deep seas and coastal areas with upwelling of deeper water.
D) deep seas and coastal areas without upwelling of deeper water.

Answer 21

A) shallow seas and coastal areas with upwelling of deeper water.

Question 22

In a careful study conducted in “limnocorrals” in the Bay of Quinte, Lake Ontario, researchers
found that uptake of nitrogen from the water column accelerated from early summer (June) to
late summer (September). However, uptake of nitrogen by phytoplankton exceeded losses to
zooplankton grazing and sedimentation in both periods.
A) True
B) False

Answer 22

A) True

Question 23

Vertical mixing in aquatic systems is inhibited when a layer of less dense water lies above a
layer of denser water. This situation can arise when:
A) sunlight heats surface water.
B) fresh water from a river rides over denser saline water in an estuary.
C) glacial ice melts in the ocean.
D) precipitation is particularly high over the ocean.
E) All of the above are correct.

Answer 23

E) All of the above are correct.

Question 24

Thermal stratification of lakes during the summer months is most likely to happen at:
__________.
A) high (polar) latitudes. C) low (tropical) latitudes.
B) intermediate (temperate) latitudes.

Answer 24

B) intermediate (temperate) latitudes

Question 25

In marine systems, peak productivity may occur in:
A) stratified water
B) unstratified water
C) in areas of contact between stratified and unstratified water

Answer 25

C) in areas of contact between stratified and unstratified water

Question 26

During prolonged periods of vertical stratification, the sediments and adjacent bottom waters
in temperate lakes become anaerobic because bacterial respiration depletes all available
oxygen. Once oxygen has been depleted, can bacterial respiration continue?
A) Yes, because bacteria can continue to use sulfate as an electron acceptor.
B) No, because bacterial respiration is dependent on the presence of molecular oxygen.

Answer 26

A) Yes, because bacteria can continue to use sulfate as an electron acceptor

Question 27

Under anaerobic conditions in lake sediments and adjacent bottom waters, which of the
following forms of essential nutrients would you not expect to find?
A) ferrous iron (Fe2+) C) ammonia (NH3)
B) nitrate (NO3
) D) phosphate (PO4
3+)

Answer 27

B) nitrate (NO3

)

Question 28

In thermally stratified temperate lakes, bottom waters become increasingly depleted of oxygen
through the summer months. Anoxia results in increased concentrations of soluble reduced
forms of several important nutrient elements in sediments and bottom waters. Following fall
overturn, oxygen is replenished in deeper waters, resulting in production of oxidized insoluble
forms of these elements. The only element in the list below with a soluble form under such
conditions is __________, which can achieve relatively high concentrations of its oxidized form.
A) phosphorus
B) iron
C) nitrogen

Answer 28

C) nitrogen

Question 29

Productivity in small lakes on the Canadian Shield increased dramatically upon experimental
addition of this element, which has been shown to limit biological activity in many freshwater
ecosystems.
A) nitrogen B) phosphorus C) potassium D) carbon E) silicon

Answer 29

B) phosphorus

Question 30

Salt marshes are considered by ecosystem ecologists to be particularly important habitats
because:
A) they are highly productive.
B) they export substantial portions of their net production to surrounding marine ecosystems.
C) they are important habitats for larval and immature stages of many marine fishes and
invertebrates.
D) All of the above are true.

Answer 30

D) All of the above are true.

Question 31

Unproductive “dead zones” can be found in the bottom waters of many estuaries and near the
mouths of rivers. The ultimate cause of such zones is:
A) influx of toxic organophosphates and other biocides from terrestrial sources.
B) influx of toxic heavy metals from terrestrial sources.
C) influx of inorganic and organic nutrients from terrestrial sources.
D) All of the above are true.

Answer 31

D) All of the above are true.

Question 32

Primary production in the oceans may be limited by insufficient nitrogen and phosphorus.
However, low oceanic productivity has been documented where both nitrogen and phosphorus
occur in abundance. What other nutrient elements may have been limiting in these cases?
Chapter 24: Nutrient Regeneration in Terrestrial and Aquatic Ecosystems
Page 80
A) aluminum and boron D) calcium and magnesium
B) zinc and manganese E) iron and silicon
C) chromium and nickel

Answer 32

) iron and silicon

Question 33

Areas in the Southern Ocean with relatively high productivity include those:
A) throughout the entire area.
B) downcurrent of Australia, New Zealand, South America, and the Antarctic Peninsula.
C) west of southern South America between 40oS and 50oS latitude.
D) close to the continent of Antarctica.

Answer 33

B) downcurrent of Australia, New Zealand, South America, and the Antarctic Peninsula

Question 34

Although not always achieved, the Redfield ratio of 16:1 N:P characterizes the relative
abundances of these two elements in deep waters of the open ocean. The reason for this
consistent ratio, as proposed by Redfield, is:
A) the relative supply of these two elements in runoff from terrestrial systems.
B) the relative abundance of these elements in superheated waters emanating from deep‐sea
hydrothermal vents.
C) the relative solubilities of these two elements in seawater.
D) the relative requirements for these two elements by phytoplankton.

Answer 34

D) the relative requirements for these two elements by phytoplankton

Question 35

In an enormous experiment conducted in 1993, John H. Martin demonstrated that primary
productivity by phytoplankton in the southern Pacific could be enhanced by addition of iron.
However, increased primary production did not result in enhanced net uptake of CO2 by the
system because:
A) CO2 was not limiting.
B) other elements, such as silicon, were also limiting in this system.
C) the added iron failed to complex with CO2.
D) zooplankton populations also increased, regenerating CO2 through respiration.

Answer 35

D) zooplankton populations also increased, regenerating CO2 through respiration

Question 36

The entire drainage area of a stream or river is called a __________.

Answer 36

watershed

Question 37

The decomposition of bedrock or other soil parent material in a terrestrial ecosystem is called
__________.

Answer 37

weathering

Question 38

When mycorrhizal fungi form sheaths over the surfaces of roots, the resulting structures are
classified as __________.

Answer 38

ectomycorrhizae

Question 39

Mycorrhizae represent a partnership between a plant’s roots and a fungus. Both partners
benefit from the interaction, which is thus classified as a __________.

Answer 39

mutualism

Question 40

The initial step in decomposition of organic detritus, this process breaks down large organic
polymers, such as proteins, into their monomeric subunits.

Answer 40

depolymerization

Question 41

When microorganisms degrade organic compounds into inorganic forms, they may incorporate
these into their own biomass, thus rendering unavailable the nutrients contained therein. This
process is called __________.

Answer 41

immobilization

Question 42

When exposed tropical soils dry out, upward movement of water containing iron and aluminum
oxides leads to formation of a bricklike material called __________.

Answer 42

laterite

Question 43

Not all tropical soils are nutrient‐poor. __________ soils develop in geologically active areas
where natural erosion is high and soils are relatively young.

Answer 43

eutrophic

Question 44

Although not often thought of as an essential nutrient element, __________ is required in large
amounts by diatoms to form their shells.

Answer 44

silicon

Question 45

Organic pollution, or high primary productivity stimulated by inorganic nutrients, creates high demand for __________ in aquatic systems, resulting from the oxidative breakdown of detritus
by microorganisms.

Answer 45

oxygen

Question 46

The portion of the water column where temperature changes most rapidly with depth in a
thermally stratified lake is called the ___________.

Answer 46

thermocline

Question 47

Salt marshes and estuaries tend to __________ a substantial portion of their net production to
adjacent marine ecosystems.

Answer 47

export

Question 48

In the Gulf of Mexico, adjacent to the mouth of the Mississippi River, is a large “dead zone”
characterized by __________ of bottom waters.

Answer 48

hypoxia

Question 49

The Redfield ratio, as applied today, incorporates concentrations of __________, nitrogen, and
phosphorus in deep waters of the open ocean.

Answer 49

carbon

Question 50

Vast areas of the open oceans are nutrient‐deficient and therefore quite unproductive. We
refer to such unproductive areas as ___________.

Answer 50

oligotrophic