Effects of Toxic Chemicals and Other Pollutants on Aquatic Ecosystems - Freshwater Ecology: Concepts and Environmental Applications - page 291

TABLE 14.5 Classification of Suspended Solids and Their Possible Impacts on Freshwater

Systems a

Type of solid Physical and chemical effects Biological effects

Clays, silts, sands Sedimentation , erosion, light Interference with respiration, restriction of

attenuation, habitat alteration habitat, burial, light limitation, stress,

increased scour

Natural fine particulate Sedimentation, BOD A food source, anoxia

organic matter
Sewage fine particulate Sedimentation, BOD, A food source, anoxia, eutrophication,

organic matter nutrient enrichment associated toxins, disease transmission

Toxicants on particles All of the above Toxicity

a Adapted from Wilber (1983).

or the reservoir is shallow. Reservoirs with deep hypolimnia and hypolim-
netic release can yield colder water than would be natural. Hot springs are
discussed later. The data on thermal effects may prove useful when con-
sidering the effects of global warming on aquatic ecosystems.
Increases in temperature cause an increase in growth rate up to a point.
Above some threshold, damage occurs. When thermal pollution is released
into wetlands, trees can be killed. As temperatures increase, green algae and
diatoms are replaced by cyanobacteria. One of the key issues in thermal pol-
lution is the replacement of cold-water fishes with warm-water fishes. Fi-
nally, rapid changes in temperature associated with power plant operations
can kill fish by thermal shock (Ottinger et al., 1990). Mitigating the ther-
mal effects of power plant effluent obviously has a significant financial cost.

SUMMARY

1. All surface waters on Earth are influenced by human activities.
2. Toxicologists are concerned with the acute and chronic effects of
pollutants. Natural variations in uptake, sensitivities, concentration,
additive effects of different pollutants, and effects of other
environmental factors all complicate predictions of how strongly a
particular toxicant will influence a specific organism.
3. Biomagnification of pollutants can cause high concentrations of toxic
compounds in the tissues of organisms at the top of food webs. The
most lipid-soluble compounds usually are magnified to the greatest
degree.
4. Bioassessment protocols can be used to assess the impacts of
pollutants and other habitat alterations on aquatic communities.
Indices for bioassessment are generally constructed using data on the
invertebrates or fish that are present and the state of their habitat.
5. Acid precipitation is mainly caused by humans burning fossil fuels,
leading to increased sulfuric and nitric acid in the atmosphere.
6. Acidification of aquatic ecosystems impacts all aquatic organisms.
Under acidic conditions, microbes degrade complex organic