AP Environmental Science:: Unit 8 - Aqterr

Point source water pollution and nonpoint source water pollution, two broad categories used to classify water contamination, are distinguished from one another primarily by the fact that a point source:

- **A)** Originates from a single, identifiable, discrete location - such as a factory discharge pipe or a wastewater treatment plant outfall - making it comparatively easier to monitor, regulate, and hold a specific responsible party accountable for, compared to nonpoint source pollution (discussed further below), which instead originates from many diffuse, widely-scattered sources across a broader landscape
- **B)** Originates from many diffuse, widely-scattered sources across a broader landscape, a description that instead corresponds to nonpoint source pollution, not point source pollution specifically
- **C)** Point source pollution has no meaningful, describable relationship to any single, identifiable discharge location of any kind
- **D)** Is, in every documented case, considerably more difficult to monitor, regulate, or attribute to a specific responsible party than nonpoint source pollution, the general opposite of point source pollution's own actual, well-established comparative regulatory advantage over nonpoint source pollution

Nonpoint source water pollution, in contrast to point source pollution discussed above, is generally considered more difficult to regulate primarily because it:

- **A)** Originates from a single, easily-identifiable discharge location, a description that instead corresponds to point source pollution (discussed above), not nonpoint source pollution specifically
- **B)** Nonpoint source pollution having no meaningful, describable relationship to agricultural runoff, urban runoff, or diffuse contamination sources of any kind
- **C)** Originates from many diffuse, widely-scattered sources spread across an entire watershed (the same watershed concept discussed in an earlier unit) - such as fertilizer and pesticide runoff from numerous individual farm fields (per the agricultural runoff discussed in an earlier unit), oil and debris washing off numerous city streets and parking lots, and sediment eroding from many separate construction or logging sites - rather than from any single, easily-identifiable discharge point that a regulator could straightforwardly monitor or hold accountable
- **D)** Nonpoint source pollution being, in every documented case, considerably easier to monitor, regulate, or attribute to a specific responsible party than point source pollution, the general opposite of nonpoint source pollution's own actual, well-established comparative regulatory difficulty relative to point source pollution

Eutrophication, a water pollution process already introduced conceptually in an earlier unit's coverage of agricultural fertilizer runoff, is best defined as:

- **A)** A process in which a body of water's total dissolved oxygen level increases dramatically as a direct result of excess nutrient input, the general opposite of eutrophication's own actual, well-established relationship to dissolved oxygen, discussed further below
- **B)** Eutrophication having no meaningful, describable relationship to nutrient input, algae growth, or dissolved oxygen depletion of any kind
- **C)** A process that occurs, in every documented case, only in a marine/ocean setting, with no meaningful applicability to any freshwater lake or river discussed elsewhere in this unit or curriculum
- **D)** The excessive enrichment of a body of water with nutrients (particularly nitrogen and phosphorus, both discussed in an earlier unit's coverage of biogeochemical cycles and limiting nutrients), typically originating from agricultural fertilizer runoff (a nonpoint source, discussed above) and/or inadequately-treated sewage discharge (a potential point source, discussed further below) - this excess nutrient input can trigger a cascade of water-quality problems, beginning with a rapid overgrowth of algae, discussed in more detail next

The full eutrophication process, once excess nutrients (discussed above) enter a body of water, generally proceeds through which of the following sequence of events?

- **A)** Excess nutrients directly and immediately increase the water's dissolved oxygen level, with no intervening algae bloom or decomposition step of any kind occurring at any point in the process
- **B)** Excess nutrients fuel a rapid overgrowth (bloom) of algae and/or cyanobacteria at the water's surface; this dense algal bloom can block sunlight from reaching submerged aquatic plants below (potentially killing off producers that would otherwise generate oxygen via photosynthesis, per the photosynthesis concept discussed in an earlier unit), and when the excess algae eventually die, decomposer microorganisms (discussed in an earlier unit) breaking down that dead algal biomass consume large quantities of dissolved oxygen from the surrounding water in the process, potentially depleting oxygen levels enough to kill fish and other oxygen-dependent aquatic organisms
- **C)** Excess nutrients have no meaningful, describable relationship to algae growth, sunlight blockage, decomposition, or dissolved oxygen depletion at any point in the full eutrophication process
- **D)** Excess nutrients directly kill fish through acute toxicity alone, with no intervening algae bloom, sunlight blockage, or decomposition-driven oxygen depletion step occurring at any point in the actual eutrophication process

A dead zone, an area of a body of water with dissolved oxygen levels too low to support most fish and other aquatic animal life, is generally caused by:

- **A)** Severe hypoxia (very low dissolved oxygen) resulting from the full eutrophication process discussed above - some of the largest documented dead zones occur where a major river (carrying accumulated agricultural fertilizer runoff from a very large watershed, per the watershed concept discussed in an earlier unit) discharges into a coastal ocean area, seasonally triggering a large-scale algal bloom and subsequent oxygen depletion over a substantial area of coastal water
- **B)** A dead zone having no meaningful, describable relationship to dissolved oxygen levels, eutrophication, or fish/aquatic animal survival of any kind
- **C)** Unusually high, rather than unusually low, dissolved oxygen levels, the general opposite of the severe hypoxia that actually characterizes and defines a dead zone
- **D)** A phenomenon that occurs, in every documented case, only in a fully enclosed freshwater lake, with no meaningful applicability to any coastal ocean area located at a major river's outflow

Biochemical oxygen demand (BOD), a water-quality metric measuring the amount of dissolved oxygen consumed by microorganisms as they decompose organic matter present in a water sample, is generally used by water-quality monitors as:

- **A)** A direct, one-to-one measure of a body of water's total nitrogen or phosphorus nutrient concentration, rather than accurately describing what biochemical oxygen demand itself actually measures
- **B)** A measure that has no meaningful, describable relationship to organic matter decomposition, dissolved oxygen consumption, or water pollution assessment of any kind
- **C)** A measure that applies only to marine/ocean water samples, with no meaningful applicability to any freshwater lake or river sample discussed elsewhere in this unit
- **D)** A useful indicator of a body of water's organic pollution level - a water sample with a high BOD contains a large quantity of decomposable organic matter (potentially from sources such as sewage discharge or agricultural runoff, both discussed elsewhere in this unit), and decomposing that organic matter will consume a correspondingly large quantity of dissolved oxygen, directly connecting to the same oxygen-depletion mechanism already discussed above in this unit's coverage of eutrophication and dead zones

Wastewater treatment plants generally process incoming sewage through a sequence of treatment stages, commonly categorized as primary, secondary, and (where required) tertiary treatment. Primary treatment specifically involves:

- **A)** Physically screening out large debris and allowing heavier solid particles to settle out of the wastewater via simple gravity sedimentation - primary treatment addresses only the most easily-removed physical/solid contaminants, and generally still leaves a considerable quantity of dissolved and finer organic pollutants (contributing to the biochemical oxygen demand concept discussed above) in the wastewater, requiring the further secondary treatment stage discussed next before that water can be safely discharged
- **B)** Using microorganisms to biologically break down dissolved and finer organic pollutants remaining in the wastewater, a description that instead corresponds to secondary treatment (discussed next), not primary treatment specifically
- **C)** Primary treatment having no meaningful, describable relationship to physical screening, sedimentation, or wastewater solid-particle removal of any kind
- **D)** Removing specific dissolved nutrients such as nitrogen and phosphorus (both discussed elsewhere in this unit's coverage of eutrophication) from wastewater, a description that instead corresponds to a more advanced tertiary treatment stage, not primary treatment specifically

Secondary wastewater treatment, the stage following primary treatment (discussed above), generally involves:

- **A)** Physically screening out large debris and allowing heavier solid particles to settle out via simple gravity sedimentation, a description that instead corresponds to primary treatment (discussed above), not secondary treatment specifically
- **B)** Using microorganisms (typically in an aerated tank that supplies the oxygen those microorganisms need) to biologically decompose much of the remaining dissolved and finer organic pollutants left over after primary treatment - this biological decomposition process reduces the wastewater's biochemical oxygen demand (discussed above) considerably further than primary treatment alone could achieve, though secondary treatment generally still does not remove all dissolved nutrients (such as nitrogen and phosphorus) from the treated wastewater, which may require an additional tertiary treatment stage if further nutrient removal is specifically required
- **C)** Secondary treatment having no meaningful, describable relationship to microbial decomposition, biochemical oxygen demand reduction, or wastewater organic pollutant removal of any kind
- **D)** Removing specific dissolved nutrients such as nitrogen and phosphorus from wastewater, a description that instead corresponds to a more advanced tertiary treatment stage, not secondary treatment specifically