1.1 Background
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degradation from atmospheric deposition of S, N, or toxic materials; and (3) the
extent to which sensitive aquatic natural resources have been harmed in the past
or might be expected to be harmed in the future under assumed scenarios of future
air pollution and atmospheric deposition. Site-specific studies can be further
customized to fit particular regional or local ecosystem conditions and stressors.
Atmospheric deposition can contribute to toxicity responses in several
ways. Water acidification entails several chemical changes. These include
reduced pH (increased hydrogen ion [H + ] activity), decreased ANC, increased
inorganic monomeric aluminum (Al i ) concentration, and changed (increased
or decreased, depending on the extent of acidification) concentrations of calcium (Ca 2+ ) and other base cations (BCs). Hydrogen ion and Al i can be toxic to
many aquatic species at sufficiently high concentrations. Other atmospheric
pollutants of concern with respect to toxicity include Hg and various pesticides. Atmospheric deposition is an important component of Hg cycling and
biogeochemistry. Mercury in its methylated form (MeHg) is known to bioaccumulate in aquatic organisms, reaching potentially high concentrations in
larger, piscivorous fish and species that consume them.
A limited list of key variables does not exist with which to measure ecosystem condition, or ecosystem response to stressors, such as those associated with
atmospheric deposition (i.e., acidification, eutrophication, toxicity). Ecosystems
are highly complex and simply cannot be represented by a handful of variables. Nevertheless, there are variables that have been shown to be, or that are
expected to be (based on existing research), reflective of the general level of ecosystem harm that might be associated with atmospheric deposition (Table 1.1;
Sullivan and Herlihy 2007). The recommended AQRVs and sensitive receptors
summarized here are broadly applicable and reflect a range of aquatic effects of
atmospheric deposition. Identification of these receptors and indicators helps
determine the approaches that will be needed for inventory and monitoring.
Detailed protocols should be an important part of any resource characterization or monitoring program intended to evaluate atmospheric deposition
impacts on AQRVs. Standardized approaches help to ensure that measured differences among locations or changes over time at one location are real (actually
occur in nature) and are not simply a reflection of different methods, sampling
personnel, or timing of sample collection. Protocols are necessary to ensure that
the data collected are appropriate to the questions asked and are of sufficient
quality to allow development of meaningful answers. It must, however, be recognized that there will not be a single appropriate approach in every situation that
will efficiently characterize an important attribute nationwide. Some attributes
and site characteristics are sufficiently variable from region to region so that
supplemental or amended protocols may be justified. Nevertheless, adoption of
standardized procedures for data gathering and analysis and required core data
elements will allow data to be compared across regional boundaries and will
5
degradation from atmospheric deposition of S, N, or toxic materials; and (3) the
extent to which sensitive aquatic natural resources have been harmed in the past
or might be expected to be harmed in the future under assumed scenarios of future
air pollution and atmospheric deposition. Site-specific studies can be further
customized to fit particular regional or local ecosystem conditions and stressors.
Atmospheric deposition can contribute to toxicity responses in several
ways. Water acidification entails several chemical changes. These include
reduced pH (increased hydrogen ion [H + ] activity), decreased ANC, increased
inorganic monomeric aluminum (Al i ) concentration, and changed (increased
or decreased, depending on the extent of acidification) concentrations of calcium (Ca 2+ ) and other base cations (BCs). Hydrogen ion and Al i can be toxic to
many aquatic species at sufficiently high concentrations. Other atmospheric
pollutants of concern with respect to toxicity include Hg and various pesticides. Atmospheric deposition is an important component of Hg cycling and
biogeochemistry. Mercury in its methylated form (MeHg) is known to bioaccumulate in aquatic organisms, reaching potentially high concentrations in
larger, piscivorous fish and species that consume them.
A limited list of key variables does not exist with which to measure ecosystem condition, or ecosystem response to stressors, such as those associated with
atmospheric deposition (i.e., acidification, eutrophication, toxicity). Ecosystems
are highly complex and simply cannot be represented by a handful of variables. Nevertheless, there are variables that have been shown to be, or that are
expected to be (based on existing research), reflective of the general level of ecosystem harm that might be associated with atmospheric deposition (Table 1.1;
Sullivan and Herlihy 2007). The recommended AQRVs and sensitive receptors
summarized here are broadly applicable and reflect a range of aquatic effects of
atmospheric deposition. Identification of these receptors and indicators helps
determine the approaches that will be needed for inventory and monitoring.
Detailed protocols should be an important part of any resource characterization or monitoring program intended to evaluate atmospheric deposition
impacts on AQRVs. Standardized approaches help to ensure that measured differences among locations or changes over time at one location are real (actually
occur in nature) and are not simply a reflection of different methods, sampling
personnel, or timing of sample collection. Protocols are necessary to ensure that
the data collected are appropriate to the questions asked and are of sufficient
quality to allow development of meaningful answers. It must, however, be recognized that there will not be a single appropriate approach in every situation that
will efficiently characterize an important attribute nationwide. Some attributes
and site characteristics are sufficiently variable from region to region so that
supplemental or amended protocols may be justified. Nevertheless, adoption of
standardized procedures for data gathering and analysis and required core data
elements will allow data to be compared across regional boundaries and will