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The operational definition of Dissolved Organic Carbon (DOC) specifies that it includes any organic carbon that cannot pass through a filter with a pore size of 1 micrometer.
Answer: False
Explanation: The standard operational definition for Dissolved Organic Carbon (DOC) typically involves filtration through membranes with pore sizes between 0.22 and 0.7 micrometers, not 1 micrometer.
Dissolved Organic Matter (DOM) and Dissolved Organic Carbon (DOC) are precisely equivalent measures of organic material present in water.
Answer: False
Explanation: DOM encompasses the total mass of dissolved organic compounds, including elements beyond carbon. DOC specifically refers only to the carbon component within DOM. Typically, DOM mass is approximately twice that of DOC.
Dissolved Organic Carbon (DOC) typically constitutes less than 10% of the total organic carbon found in aquatic systems.
Answer: False
Explanation: Dissolved Organic Carbon (DOC) generally represents approximately 90% of the total organic carbon present in aquatic systems.
What is the operational definition of Dissolved Organic Carbon (DOC) concerning filtration?
Answer: Organic carbon passing through a filter with pore sizes typically between 0.22 and 0.7 micrometers.
Explanation: The standard operational definition for Dissolved Organic Carbon (DOC) involves filtration through membranes with pore sizes typically between 0.22 and 0.7 micrometers.
How does the mass of Dissolved Organic Matter (DOM) typically relate to the mass of Dissolved Organic Carbon (DOC)?
Answer: DOM contains about twice the mass of DOC.
Explanation: DOM encompasses the total mass of dissolved organic compounds, while DOC refers only to the carbon component. Typically, the mass of DOM is approximately twice that of DOC.
What percentage of the total organic carbon in aquatic systems does Dissolved Organic Carbon (DOC) typically constitute?
Answer: Approximately 90%
Explanation: Dissolved Organic Carbon (DOC) generally represents approximately 90% of the total organic carbon present in aquatic systems.
Autochthonous Dissolved Organic Carbon (DOC) originates from sources external to the water body, such as terrestrial soils.
Answer: False
Explanation: Autochthonous DOC originates from within the water body itself (e.g., from aquatic plants or algae). DOC originating from external sources, like terrestrial soils, is termed allochthonous.
The primary sources of oceanic Dissolved Organic Carbon (DOC) are exclusively derived from terrestrial runoff and atmospheric deposition.
Answer: False
Explanation: While terrestrial runoff and atmospheric deposition contribute, primary production by marine plankton and other autochthonous sources are also primary contributors to oceanic DOC.
Dissolved Organic Carbon (DOC) originating from sources external to a water body is referred to as:
Answer: Allochthonous DOC
Explanation: DOC originating from sources external to a water body, such as terrestrial soils, is termed allochthonous.
Which of the following represents a major source of oceanic Dissolved Organic Carbon (DOC)?
Answer: Primary production by phytoplankton and grazing by zooplankton
Explanation: Primary production by phytoplankton and grazing by zooplankton are major sources contributing to oceanic Dissolved Organic Carbon (DOC).
Biodegradable Dissolved Organic Carbon (BDOC) is primarily composed of molecules that are resistant to utilization by heterotrophic bacteria.
Answer: False
Explanation: Biodegradable Dissolved Organic Carbon (BDOC) is defined as the fraction of DOC comprising molecules that heterotrophic bacteria can readily utilize for energy and carbon.
Labile Dissolved Organic Matter (DOM) is characterized by its resistance to decomposition and its capacity to persist in environments for extended periods.
Answer: False
Explanation: Labile DOM is defined by its rapid decomposition through microbial or photochemical processes, contrasting with recalcitrant DOM which persists for extended durations.
What is the primary characteristic of Biodegradable Dissolved Organic Carbon (BDOC)?
Answer: It is composed of molecules that heterotrophic bacteria can utilize for energy and carbon.
Explanation: Biodegradable Dissolved Organic Carbon (BDOC) is defined as the fraction of DOC comprising molecules that heterotrophic bacteria can readily utilize for energy and carbon.
Which classification describes Dissolved Organic Matter (DOM) that decomposes rapidly?
Answer: Labile DOM
Explanation: Labile DOM is defined by its rapid decomposition through microbial or photochemical processes, contrasting with recalcitrant DOM which persists for extended durations.
The degradation rate of Dissolved Organic Carbon (DOC) is solely determined by its intrinsic chemical composition and molecular size.
Answer: False
Explanation: While chemical composition and molecular size are critical, the degradation rate of DOC is also significantly influenced by environmental factors such as microbial diversity, nutrient availability, sunlight exposure, and associations with mineral particles.
Compounds typically considered recalcitrant, such as petroleum, are incapable of degradation under any environmental conditions.
Answer: False
Explanation: Even compounds generally classified as recalcitrant, like petroleum, can undergo degradation if they are present in an environmental setting conducive to their breakdown.
Particulate Organic Carbon (POC) can be transformed into Dissolved Organic Carbon (DOC) through degradation processes.
Answer: True
Explanation: Degradation of Particulate Organic Carbon (POC) is a known pathway through which Dissolved Organic Carbon (DOC) is formed in aquatic environments.
The primary processes responsible for removing Dissolved Organic Carbon (DOC) from the ocean water column include thermal degradation, abiotic reactions, and biotic degradation.
Answer: True
Explanation: Key processes that remove DOC from the ocean water column are thermal degradation, photochemical reactions (abiotic), and microbial utilization (biotic degradation).
Photodegradation of Colored Dissolved Organic Matter (CDOM) typically results in the formation of larger, more complex organic molecules.
Answer: False
Explanation: Photodegradation of CDOM generally leads to the formation of smaller, less complex molecules, or conversion into inorganic carbon, often increasing the lability of the remaining organic matter.
The 'dilution hypothesis' posits that Dissolved Organic Carbon (DOC) recalcitrance is primarily attributable to the intrinsic chemical stability of the molecules.
Answer: False
Explanation: The dilution hypothesis suggests that DOC recalcitrance arises not from intrinsic molecular stability, but from the low individual concentrations of labile compounds, which are insufficient to support microbial populations.
The 'microbial carbon pump' describes the process whereby microbes convert recalcitrant Dissolved Organic Carbon (DOC) into more labile forms.
Answer: False
Explanation: The 'microbial carbon pump' refers to the process where microbes transform labile DOC into more recalcitrant forms, thereby contributing to long-term carbon sequestration in the ocean.
'Sloppy feeding' by zooplankton is characterized by efficient consumption that minimizes the release of Dissolved Organic Carbon (DOC).
Answer: False
Explanation: 'Sloppy feeding' by zooplankton refers to inefficient consumption of food particles, which leads to the release of Dissolved Organic Carbon (DOC) into the water column.
The mixing of river water and seawater generally does not alter the state of Dissolved Organic Carbon (DOC) in the water.
Answer: False
Explanation: The mixing of river water and seawater, particularly due to changes in salinity, can induce abiotic flocculation of certain DOC components, leading to their removal from the dissolved phase.
Which of the following is NOT identified as a factor influencing the degradation rate of Dissolved Organic Carbon (DOC)?
Answer: Atmospheric pressure
Explanation: While microbial diversity, nutrient availability, and sunlight exposure are recognized factors influencing DOC degradation, atmospheric pressure is not typically cited as a primary determinant.
Which process is considered a major sink for Dissolved Organic Carbon (DOC) in the ocean water column?
Answer: Photochemical and microbial degradation
Explanation: Photochemical and microbial degradation are considered the major sinks responsible for removing Dissolved Organic Carbon (DOC) from the ocean water column.
The 'dilution hypothesis' proposes that Dissolved Organic Carbon (DOC) recalcitrance is primarily due to:
Answer: The extremely low concentration of labile compounds, insufficient to support microbial populations.
Explanation: The dilution hypothesis suggests that DOC recalcitrance arises not from intrinsic molecular stability, but from the low individual concentrations of labile compounds, which are insufficient to support microbial populations.
What role does Dissolved Organic Carbon (DOC) play in the marine 'microbial loop'?
Answer: It serves as a primary food source for heterotrophic bacteria.
Explanation: DOC is a vital component of the microbial loop in marine ecosystems, serving as a primary food source for heterotrophic bacteria.
The 'microbial carbon pump' is significant primarily because it:
Answer: Transforms labile DOC into more recalcitrant forms for long-term storage.
Explanation: The 'microbial carbon pump' refers to the process where microbes transform labile DOC into more recalcitrant forms, contributing to long-term carbon sequestration in the ocean.
What is described as 'sloppy feeding' by zooplankton?
Answer: The process of releasing DOC due to inefficient consumption of food.
Explanation: 'Sloppy feeding' by zooplankton refers to inefficient consumption of food particles, which leads to the release of Dissolved Organic Carbon (DOC) into the water column.
How do viruses contribute to the Dissolved Organic Carbon (DOC) pool in the ocean?
Answer: By causing lysis of cells, releasing their contents, including DOC.
Explanation: Viruses contribute to the DOC pool by causing lysis of marine organisms, including bacteria and phytoplankton, which releases their cellular contents, including DOC.
What occurs during the abiotic flocculation of Dissolved Organic Carbon (DOC) when river water mixes with seawater?
Answer: Certain DOC components are removed by transforming into particles.
Explanation: When river water mixes with seawater, changes in salinity can induce abiotic flocculation of certain DOC components, causing them to transform into particles that can be removed from the dissolved phase.
The 'intrinsic stability hypothesis' for Dissolved Organic Carbon (DOC) recalcitrance suggests that the resistance to degradation is due to:
Answer: Inherent chemical properties within the DOC molecules themselves.
Explanation: The intrinsic stability hypothesis posits that the recalcitrant fraction of DOC is resistant to microbial decomposition due to inherent chemical properties within the molecules themselves.
What is the relationship between the lifetime of refractory Dissolved Organic Carbon (DOC) and the Global Overturning Circulation (GOC)?
Answer: A slowing of GOC could potentially lead to an increase in refractory DOC reservoir size.
Explanation: The lifetime of refractory DOC molecules in the ocean is regulated by the rate of global overturning circulation (GOC). A slowing of GOC could potentially lead to an increase in the reservoir size of refractory DOC.
Dissolved Organic Carbon (DOC) constitutes a minor fraction of the total organic carbon cycled globally, containing substantially less carbon than marine biomass.
Answer: False
Explanation: DOC represents a significant portion of the globally cycled organic carbon, comparable in quantity to the atmospheric carbon pool and exceeding the carbon stored in marine biomass.
Inland aquatic systems are considered minor carbon sinks when compared to terrestrial forests.
Answer: False
Explanation: Inland aquatic systems are significant contributors to global carbon sequestration, acting as substantial carbon sinks, second only to terrestrial forests in many regions.
The oceanic Dissolved Organic Carbon (DOC) pool is significantly smaller than the quantity of carbon stored within marine biomass.
Answer: False
Explanation: The oceanic DOC pool is substantially larger than the carbon stored in marine biomass, holding an amount comparable to the Earth's atmosphere.
Dissolved Organic Carbon (DOC) is primarily produced in the deep ocean layers via the dissolution of sinking particles.
Answer: False
Explanation: DOC is predominantly produced in the near-surface ocean layers through processes like primary production by phytoplankton and grazing by zooplankton, rather than in deep ocean layers.
Marine macrophytes, such as macroalgae, release a negligible amount of their Gross Primary Production (GPP) as Dissolved Organic Carbon (DOC).
Answer: False
Explanation: Marine macrophytes, including macroalgae, release substantial amounts of DOC, with estimates suggesting they can release between 1% and 39% of their GPP as DOC.
The estimated global river input of Dissolved Organic Carbon (DOC) to the oceans is approximately 250 Tg C yr^-1.
Answer: True
Explanation: Global estimates indicate that rivers transport approximately 250 Tg C yr^-1 of Dissolved Organic Carbon (DOC) into the world's oceans.
Marine sediments contain lower concentrations of Dissolved Organic Carbon (DOC) relative to the overlying water column.
Answer: False
Explanation: Marine sediments typically exhibit higher concentrations of DOC, often an order of magnitude greater than the overlying water column, driving diffusive fluxes.
The accumulated Dissolved Organic Carbon (DOC) found in the deep ocean exhibits very young radiocarbon ages, typically less than 100 years.
Answer: False
Explanation: Due to its recalcitrance, accumulated DOC in the deep ocean has old radiocarbon ages, ranging from 3,000 to 6,000 years, indicating long residence times.
Phytoplankton typically release less than 1% of their Gross Primary Production (GPP) as extracellular Dissolved Organic Carbon (DOC).
Answer: False
Explanation: Phytoplankton commonly release between 5% and 30% of their Gross Primary Production (GPP) as extracellular DOC.
Which statement best characterizes the significance of Dissolved Organic Carbon (DOC) in global carbon cycling?
Answer: DOC represents a large cycled reservoir comparable to the atmosphere and fuels marine food webs.
Explanation: DOC is a significant component of the global carbon cycle, representing a large cycled reservoir comparable to the atmosphere and serving as a primary fuel source for marine food webs.
Inland aquatic systems are significant in the global carbon cycle primarily because they:
Answer: Receive DOC from terrestrial ecosystems and transport it, bury it, or emit it as CO2.
Explanation: Inland aquatic systems play a crucial role by receiving DOC from terrestrial ecosystems, subsequently transporting, burying, or emitting it as CO2, thus acting as significant carbon sinks.
How does the oceanic Dissolved Organic Carbon (DOC) pool compare in size to the atmospheric carbon pool?
Answer: The oceanic DOC pool contains a similar amount of carbon as the Earth's atmosphere.
Explanation: The oceanic DOC pool contains a quantity of carbon comparable to that of the Earth's atmosphere.
What is the estimated annual global river input of Dissolved Organic Carbon (DOC) to the oceans?
Answer: Approximately 250 Tg C yr^-1
Explanation: Global estimates indicate that rivers transport approximately 250 Tg C yr^-1 of Dissolved Organic Carbon (DOC) into the world's oceans.
Marine sediments are significant in the Dissolved Organic Carbon (DOC) cycle because they:
Answer: Have high DOC concentrations and act as a significant source via diffusion.
Explanation: Marine sediments typically exhibit high DOC concentrations and act as a significant source of DOC to the overlying water column via diffusion.
How much Dissolved Organic Carbon (DOC) do phytoplankton typically release relative to their Gross Primary Production (GPP)?
Answer: Between 5% and 30%
Explanation: Phytoplankton commonly release between 5% and 30% of their Gross Primary Production (GPP) as extracellular DOC.
In undisturbed watersheds lacking significant wetlands, Dissolved Organic Carbon (DOC) concentrations typically range from 10 to 50 mg/L during baseflow conditions.
Answer: False
Explanation: In undisturbed watersheds without substantial wetland influence, baseflow DOC concentrations generally fall within the range of 1 to 20 mg/L.
In well-drained soils, Dissolved Organic Carbon (DOC) that is leached is completely retained within the soil profile and does not impact groundwater quality.
Answer: False
Explanation: In well-drained soils, leached DOC can reach the water table, potentially contaminating groundwater with organic compounds and affecting its quality.
During transport through the soil column to groundwater, the concentration and composition of Dissolved Organic Carbon (DOC) remain unchanged.
Answer: False
Explanation: As DOC moves through the soil column towards groundwater, its concentration and composition are altered by processes such as sorption, desorption, biodegradation, and biosynthesis.
In the absence of significant wetlands, what is the typical baseflow concentration range for Dissolved Organic Carbon (DOC) in undisturbed watersheds?
Answer: 1 to 20 mg/L
Explanation: In undisturbed watersheds without substantial wetland influence, baseflow DOC concentrations generally fall within the range of 1 to 20 mg/L.
How does Dissolved Organic Carbon (DOC) influence soil processes?
Answer: It affects negative electrical charges, impacts denitrification, and influences nutrient retention.
Explanation: DOC influences soil processes by affecting negative electrical charges, impacting denitrification, participating in acid-base reactions, influencing nutrient retention and translocation, and immobilizing heavy metals.
What can occur to Dissolved Organic Carbon (DOC) leached into well-drained soils?
Answer: It can reach the water table and potentially contaminate groundwater.
Explanation: In well-drained soils, leached DOC can reach the water table, potentially contaminating groundwater with organic compounds and affecting its quality.
Which processes modify Dissolved Organic Carbon (DOC) concentration and composition during transport through the soil column to groundwater?
Answer: Sorption, biodegradation, and biosynthesis
Explanation: As DOC moves through the soil column towards groundwater, its concentration and composition are altered by processes such as sorption, desorption, biodegradation, and biosynthesis.
Colored Dissolved Organic Matter (CDOM) primarily absorbs light within the red and infrared spectrum.
Answer: False
Explanation: CDOM primarily absorbs light in the blue and ultraviolet (UV) portions of the electromagnetic spectrum.
How does Colored Dissolved Organic Matter (CDOM) affect light penetration in aquatic environments?
Answer: It absorbs blue and UV light, reducing light for photosynthesis but potentially protecting from UV radiation.
Explanation: CDOM primarily absorbs light in the blue and ultraviolet (UV) spectrum, which reduces light available for photosynthesis but can offer protection from harmful UV radiation.
What is a primary outcome of the photodegradation of Colored Dissolved Organic Matter (CDOM)?
Answer: Transformation into smaller molecules or inorganic carbon, potentially increasing lability.
Explanation: Photodegradation of CDOM generally leads to the formation of smaller, less complex molecules, or conversion into inorganic carbon, often increasing the lability of the remaining organic matter.
Solid-phase extraction is considered a complex and expensive method for isolating DOM when compared to techniques like ultrafiltration.
Answer: False
Explanation: Solid-phase extraction is often regarded as a cost-effective and straightforward method for isolating DOM, contrasting with the perception of complexity and expense.
Why is a concentration and isolation step often necessary for the analysis of Dissolved Organic Matter (DOM)?
Answer: DOM is present in very low concentrations and samples contain interfering inorganic salts.
Explanation: DOM is found in very low concentrations in natural environments, and samples often contain high levels of inorganic salts that interfere with analytical techniques. Therefore, a concentration and isolation step is crucial before analysis.