2.2 Where, What, and When to Sample
43
geology contains substantial P, this effect can be quantitatively important. It is
therefore helpful to evaluate local geology and human activities throughout the
entire watershed, especially land use actions that contribute substantial erosion to surface waters. Turbidity can sometimes be used (along with an appropriate training set that includes simultaneous measures of TSS and turbidity)
to estimate TSS in stream water. Therefore, it is possible to rely on routine measurement of turbidity and infrequent measurement of TSS (a more expensive
laboratory analysis), along with an empirical relationship between the two in
order to estimate TSS for all sample occasions. Depending on the stream, this
approach can yield relationships that are more or less robust. Secchi depth provides an indication of relative algal density in lake water. It can therefore provide a good index of algal production.
2.2.2.3 Bioaccumulation and Toxicity Studies
Atmospheric deposition can contribute to toxicity of surface water in several
ways. The atmospheric pollutants of greatest concern with respect to toxicity,
in addition to H + and Al i associated with acidification, are primarily pesticides,
mercury (Hg), and other trace metals.
2.2.2.3.1 Pesticides and Other Toxics
Pesticides and other toxics can be air deposited, and some can bioaccumulate
in predator species. The degree of bioaccumulation is generally a function of
the age of the organism and its position in the food web. In general, older individuals at the top of the food web have bioaccumulated more toxic materials
than have younger individuals nearer to the bottom of the food web.
Pesticides applied to agricultural crops can become volatized or suspended
in the atmosphere with dust particles and eventually be transported with prevailing winds to remote areas. For example, organophosphate pesticides have
been detected in precipitation at elevations up to 1920 m in Sequoia National
Park in California (Zabik and Seiber 1993) and measured in plant foliage across
a range of elevations (Aston and Seiber 1997). The effects of atmospheric deposition of pesticides at remote locations are poorly known. However, there is particular concern that fungicide deposition could harm sensitive lichen species
(McCune et al. 2007).
2.2.2.3.2 Mercury
A variety exists of other toxic chemicals that can be atmospherically deposited,
some of which have the potential to bioaccumulate. These include trace metals, polychlorinated biphenyls (PCBs), and some fire-retardant chemicals. The
toxin considered to be of greatest concern is usually Hg.
Atmospheric deposition is an important component of Hg cycling and
biogeochemistry. Mercury is naturally occurring and is found throughout
43
geology contains substantial P, this effect can be quantitatively important. It is
therefore helpful to evaluate local geology and human activities throughout the
entire watershed, especially land use actions that contribute substantial erosion to surface waters. Turbidity can sometimes be used (along with an appropriate training set that includes simultaneous measures of TSS and turbidity)
to estimate TSS in stream water. Therefore, it is possible to rely on routine measurement of turbidity and infrequent measurement of TSS (a more expensive
laboratory analysis), along with an empirical relationship between the two in
order to estimate TSS for all sample occasions. Depending on the stream, this
approach can yield relationships that are more or less robust. Secchi depth provides an indication of relative algal density in lake water. It can therefore provide a good index of algal production.
2.2.2.3 Bioaccumulation and Toxicity Studies
Atmospheric deposition can contribute to toxicity of surface water in several
ways. The atmospheric pollutants of greatest concern with respect to toxicity,
in addition to H + and Al i associated with acidification, are primarily pesticides,
mercury (Hg), and other trace metals.
2.2.2.3.1 Pesticides and Other Toxics
Pesticides and other toxics can be air deposited, and some can bioaccumulate
in predator species. The degree of bioaccumulation is generally a function of
the age of the organism and its position in the food web. In general, older individuals at the top of the food web have bioaccumulated more toxic materials
than have younger individuals nearer to the bottom of the food web.
Pesticides applied to agricultural crops can become volatized or suspended
in the atmosphere with dust particles and eventually be transported with prevailing winds to remote areas. For example, organophosphate pesticides have
been detected in precipitation at elevations up to 1920 m in Sequoia National
Park in California (Zabik and Seiber 1993) and measured in plant foliage across
a range of elevations (Aston and Seiber 1997). The effects of atmospheric deposition of pesticides at remote locations are poorly known. However, there is particular concern that fungicide deposition could harm sensitive lichen species
(McCune et al. 2007).
2.2.2.3.2 Mercury
A variety exists of other toxic chemicals that can be atmospherically deposited,
some of which have the potential to bioaccumulate. These include trace metals, polychlorinated biphenyls (PCBs), and some fire-retardant chemicals. The
toxin considered to be of greatest concern is usually Hg.
Atmospheric deposition is an important component of Hg cycling and
biogeochemistry. Mercury is naturally occurring and is found throughout