Environmental Engineering Reference
In-Depth Information
compounds more slowly, cyanobacteria and diatoms are selected
against, filamentous green algae are selected for, invertebrates that use
calcium carbonate become rare, aluminum has a greater impact on
fish gills, and reproduction of many animals is impacted negatively.
7. Metals can have a broad array of negative impacts on aquatic
ecosystems. Mining wastes often cause contamination, but runoff
from industrial applications and naturally occurring sources can
cause problems as well.
8. More than 10,000 organic compounds are discharged by humans
into aquatic habitats, including pesticides, oil, and materials in urban
runoff. Only a few percent of these compounds have been tested for
toxicity. In some cases, microbes can break down these compounds
(bioremediation) given enough time.
9. Suspended solids can cause harm to aquatic organisms. Generally,
interferences with photosynthesis from increased light attenuation
and with respiration by clogging flow of water are the main negative
impacts. In streams, fine solids fill up and destroy gravel and cobble
habitats, can increase scour associated with high flow, and reduce
movement of water into subsurface habitats.
10. Thermal pollution can cause shifts in community structure. This may
allow for establishment of exotic species and local extinction of
native species.
QUESTIONS FOR THOUGHT
1. Why is biomagnification worst with lipid-soluble compounds that are
resistant to abiotic and biotic deactivation?
2. Are there any habitats on Earth that have not been influenced by
human activities?
3. What political conditions have led to a world in which toxicants are
released routinely into the aquatic environment before even cursory
testing of their effects on organisms, including humans, has been
conducted?
4. Why can controls on emissions of greenhouse gasses ultimately
decrease acid precipitation?
5. Why can acid precipitation lead to lower iron availability and greater
phosphorus in some lakes and wetlands with anoxic sediments?
6. Why is bioremediation of metal contamination more difficult than
that of contamination by organic compounds?
7. Why are microbes able to more rapidly evolve ways to inactivate
toxicants than fish?
8. Under what conditions may suspended solids have positive influences
on aquatic ecosystems?
9. Should aquatic scientists assume a role of advocacy with regard to
issues of aquatic pollution, or should their role be primarily to
provide data for informed decisions to be made by managers and
policymakers?
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