Water Chemistry Field Sampling
44
the environment. Mercury present in fossil fuels is released to the atmosphere
during combustion and is subsequently available for long-range atmospheric
transport and deposition to Earth’s surface. Coal combustion in power plants
is a major source of atmospheric Hg. It enters lakes and rivers from atmospheric deposition of the Hg emitted by air pollution sources and from nonpoint sources via erosion and runoff.
Mercury is known to bioaccumulate in aquatic organisms, reaching potentially high concentrations in larger, piscivorous fish and the species that consume them. Such Hg bioaccumulation is an important human health concern,
especially among subpopulations of people who consume large quantities of
fish, children, and women of childbearing age. Mercury is a toxin that can
damage the human brain and nervous system. Human exposure to Hg mostly
occurs via consumption of fish and other seafood that has accumulated high
concentrations of Hg. Fish consumption advisories for various lakes and rivers have been issued in most states throughout the United States. Mercury can
also accumulate in fish-eating wildlife such as loons, river otters, bald eagles,
and other piscivores.
Monitoring studies to evaluate the extent to which atmospheric deposition of Hg affects aquatic ecosystems could focus on the concentrations of
total or MeHg in water, invertebrates, fish, or piscivorous birds and mammals.
Alternatively, methylation rates or bioaccumulation within different environmental compartments might be quantified.
We do not recommend widespread efforts to measure or monitor Hg concentrations in surface waters as part of routine water quality evaluation.
Rather, focused studies are recommended in areas where atmospheric deposition of Hg is known or suspected to be high. Such focused studies might begin
by investigating Hg concentrations in muscle tissue of a fish biomonitor such
as yellow perch (Perca flavescens) or large piscivorous fish such as bass. Such
data might be more useful than measurement of Hg concentrations in water
to make preliminary judgments regarding Hg cycling and toxicity issues.
Furthermore, measurement of ambient Hg concentrations in water is technically difficult and requires advanced training of field crews.
2.2.3 When to Sample
There is no one answer to the question of when to collect samples of surface
water for evaluating potential impacts of atmospheric deposition. The answer
depends on the type of study and its specific objectives. A general breakdown
of sample timing is given in Table 2.4. It is fairly standard procedure to target
sampling to a particular season under base flow conditions. Lakes are often
sampled during summer or fall base flow. Streams are often sampled during
spring base flow for acidic deposition research and summer for nutrient work.
44
the environment. Mercury present in fossil fuels is released to the atmosphere
during combustion and is subsequently available for long-range atmospheric
transport and deposition to Earth’s surface. Coal combustion in power plants
is a major source of atmospheric Hg. It enters lakes and rivers from atmospheric deposition of the Hg emitted by air pollution sources and from nonpoint sources via erosion and runoff.
Mercury is known to bioaccumulate in aquatic organisms, reaching potentially high concentrations in larger, piscivorous fish and the species that consume them. Such Hg bioaccumulation is an important human health concern,
especially among subpopulations of people who consume large quantities of
fish, children, and women of childbearing age. Mercury is a toxin that can
damage the human brain and nervous system. Human exposure to Hg mostly
occurs via consumption of fish and other seafood that has accumulated high
concentrations of Hg. Fish consumption advisories for various lakes and rivers have been issued in most states throughout the United States. Mercury can
also accumulate in fish-eating wildlife such as loons, river otters, bald eagles,
and other piscivores.
Monitoring studies to evaluate the extent to which atmospheric deposition of Hg affects aquatic ecosystems could focus on the concentrations of
total or MeHg in water, invertebrates, fish, or piscivorous birds and mammals.
Alternatively, methylation rates or bioaccumulation within different environmental compartments might be quantified.
We do not recommend widespread efforts to measure or monitor Hg concentrations in surface waters as part of routine water quality evaluation.
Rather, focused studies are recommended in areas where atmospheric deposition of Hg is known or suspected to be high. Such focused studies might begin
by investigating Hg concentrations in muscle tissue of a fish biomonitor such
as yellow perch (Perca flavescens) or large piscivorous fish such as bass. Such
data might be more useful than measurement of Hg concentrations in water
to make preliminary judgments regarding Hg cycling and toxicity issues.
Furthermore, measurement of ambient Hg concentrations in water is technically difficult and requires advanced training of field crews.
2.2.3 When to Sample
There is no one answer to the question of when to collect samples of surface
water for evaluating potential impacts of atmospheric deposition. The answer
depends on the type of study and its specific objectives. A general breakdown
of sample timing is given in Table 2.4. It is fairly standard procedure to target
sampling to a particular season under base flow conditions. Lakes are often
sampled during summer or fall base flow. Streams are often sampled during
spring base flow for acidic deposition research and summer for nutrient work.