Effects of Toxic Chemicals and Other Pollutants on Aquatic Ecosystems - Freshwater Ecology: Concepts and Environmental Applications - page 273

Bioconcentration and bioaccumulation factors can be difficult to de-
termine for animals and plants in their natural environment. Factors influ-
encing uptake and retention of a contaminant (such as metabolic rate, rate
of assimilation of contaminated food, heterogeneous distribution of the
pollutant, and rate of excretion of the contaminant) can all depend on a
variable environment. However, despite the uncertainties, biomagnification
is a well-documented problem and pollutants can be concentrated many
millions of times, even if the range of concentrations and bioaccumulation
factors is wide (Table 14.1).
BIOASSESSMENT
Aquatic organisms, particularly invertebrates, are very useful in rapidly
assessing the acute and chronic effects of pollutants because diversity and
types of organisms present are related to pollution and environmental ex-
tremes. For instance, data on many stream invertebrate species (Fig. 14.5)
can be used to demonstrate two possible responses to environmental ex-
tremes. This evaluation is called bioassessment . In the case of O 2 and pH,
diversity is maximal at intermediate values (pH about neutral, O 2 about
8 mg liter 1 ). In the case of chloride and turbidity, diversity is highest at
the lowest values. These data suggest that biodiversity can serve as an
index of environmental conditions.
Specific indices based on more refined taxonomic characteristics are
most reliable. Some species or groups are commonly found in eutrophic sit-
uations (e.g., cyanobacteria dominate eutrophic lakes, and Tubifex inhab-
its sewage outfalls) and others are sensitive to specific environmental fac-
tors (e.g., amphibians are susceptible to many types of pollution, and
salmonid fishes are limited by water temperature and O 2 concentrations).
A basic invertebrate community indicator of clean streams is the total
number of taxa in the groups Ephemeroptera, Plecoptera, and Trichoptera
(EPT), with more species commonly found in cleaner waters. The EPT in-
dex has been expanded into a more comprehensive index using 10 criteria
related to the presence of invertebrate species (invertebrate community in-
dex) and a rapid bioassessment protocol involving species composition and
relative representation of functional feeding groups of invertebrates (Karr,
1991). The Index of Biotic Integrity provides a detailed habitat rating us-
ing fish as indicator species. It is a measure of stream quality composed of
12 indicators, including total number of fish species, pollution-tolerant
species, food web structure, and fish condition (Karr, 1991). Such indices
are useful for determining the suitability of habitats for supporting aquatic
life and discerning chronic effects of pollutants.
ACID PRECIPITATION
Contamination by acid precipitation has had enormous environmental
and economic impacts on aquatic systems. Loss of fisheries and concomi-
tant loss of many tourist dollars are common in affected areas. Here, I dis-
cuss sources of acid, distribution of the problem, biological effects, and po-
tential solutions to problems associated with acid precipitation. There are