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Lecture 7

Environmental Science 1021F/G Lecture Notes - Lecture 7: Thermal Pollution, Environmental Toxicology, Ecotoxicology

Environmental Science
Course Code
Christie Stewart

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Environmental Issues EnviroSci1021G Lecture 7, March 1, 2012
PART ONE: Pollution and Disturbance as Environmental Stressors
Freedman Chapter 15
The nature and causes of environmental stress
How ecosystems respond to stressors
Contamination and pollution
Naturally occurring vs anthropogenic stressors
Toxicology and ecotoxicology
Voluntary & involuntary risks; risk assessment
The nature and causes of environmental stress and how ecosystems respond to
changes in their intensity
Environmental stress refers to factors that constrain productivity, reproductive
success, and ecological development
To some degree, stressors affect all organisms, populations, communities, and
Stressors can increase or decrease in intensity
They can be natural or anthropogenic
They can be episodic or chronic
Exposure to a stressor elicits a biological or ecological response
Environmental stressors
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Environmental Issues ES1021F Lecture 10, November 16, 2011
Physical stress involves intense exposure to kinetic energy – e.g., a
hurricane or tornado, seismic sea wave, an explosion, trampling
Wildfire involves combustion of ecosystem biomass – occurs as an event
(or disturbance)
Chemical pollution is caused by intense exposure to one or more
substances – e.g., toxic gases, pesticides, excessive nutrients …
Thermal pollution involves exposure to a high intensity of heat – e.g., hot
water effluent from industries using water as coolant in manufacturing process
Environmental stress
Radiation stress is excessive ionizing energy, such as ultraviolet or gamma
Climatic stress is associated with excessive or insufficient regimes of
climate-related factors – temperature, wind, moisture, insolation
Biological stressors involve interactions among species – through
competition, herbivory, predation, parasitism, or disease
Biological pollution is caused by invasive alien species, including introduced
How ecosystems respond to changes in the intensity of stressors
Biological and ecological responses to changes in stressor intensity are
complex, depending on:
Intensity and duration of the stressor
Susceptibility of species and communities
Mitigating circumstances, including other stressors
Resistance (tolerance) is the ability to tolerate increasing stressor intensity
without responding
Eventually, resistance can be overcome
Resilience is the ability to recover after stressor intensity is relaxed
How ecosystems respond to changes in stressors
Patterns of response to increasing stress are:
Rates of disease and mortality increase
Species richness and diversity decrease
Community-level stocks of nutrients and biomass are depleted
Community respiration exceeds production (net production is less
than zero)
Sensitive species are replaced by tolerant ones
Top predators and large-bodied species are lost
Anthropogenic management is needed to conserve ecological values
– the system is no longer self-maintaining
Contamination and pollution
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Environmental Issues EnviroSci1021G Lecture 7, March 1, 2012
Contamination : the presence of a stressor at an intensity that exceeds the
normal, background value, but where no biological or ecological response has
been detected
e.g. All metals are present in all parts of the environment and in all
organisms; thresholds of resistance (tolerance) must be exceeded before a
response is detected
Pollution : the presence of a stressor where the intensity exceeds the
tolerance, and so damage is caused
Naturally occurring stressors and anthropogenic stressors
Natural stressors occur without any apparent influence of humans
Anthropogenic stressors are associated with people or their economic
Either may cause biological and ecological responses, including those
considered to be damage
Natural & anthropogenic stressors
Examples of natural environmental stressors:
Wildfire ignited by lightning
Metal-rich deposits occurring at the ground surface
Extreme weather events, or severe climate
Natural biological interactions – herbivory, predation, parasitism,
disease …
Examples of anthropogenic stressors:
Wildfire ignited by people
Pollutants emitted by industry or vehicles
Activities in forestry, agriculture, fishing, or hunting
Introduced invasive species and pathogens
Knowledge of natural stressors helps us understand anthropogenic ones
Natural stressors may be similar in some respects to anthropogenic ones
Understanding their biological and ecological effects provides insight
into similar human stressors
Similarities may include potential long-term effects, e.g. of recent
human stressors on evolutionary responses
Examples of such similarities:
Wildfire and clear-cutting (in fire-adapted forest)
Smoking Hills and large smelters
Toxicology and ecotoxicology
Toxicology is the science of the study of poisons
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