Purpose and Study Design
10
co-occur with probable geologic sources of Hg or areas that promote Hg
methylation. Regional Hg deposition attributable to long-range atmospheric
transport is also of concern. In general, we do not recommend routine monitoring for Hg concentrations in water. Nevertheless, Hg can pose a health risk
to humans or wildlife (i.e., bald eagle, osprey, loon, and river otter) that consume large quantities of such fish. We recommend that a more effective way to
evaluate Hg contamination issues in surface waters is to analyze, or monitor,
concentrations of Hg in fish rather than in water. Of particular concern are the
larger, older, piscivorous fish, such as bass, pike, and some species of trout.
1.1.1.2 Potential Confounding Factors
In developing and implementing a field-sampling program, it is important to
consider numerous potentially confounding factors. Some of the important
considerations that can complicate aquatic inventory and monitoring assessments include:
• low signal-to-noise ratio, * especially for dilute aquatic ecosystems,
• variation in watershed properties, such as slope, aspect, underlying
bedrock composition, glacial till (if it occurs), depth and composition
of soils, distribution of vegetative cover, role of groundwater, and presence and hydrologic connectedness of wetlands,
• interacting stressors, especially climate, introduced species, and legacy effects of past land use and exposure to pollutants,
• constraints of sampling in designated wilderness areas where land
use rules prohibit access via mechanized equipment and installation
of fixed equipment,
• constraints regarding laboratory analytical holding times,
• national and regional applicability,
• cost and training constraints, and
• quality control issues and the need for peer review.
1.1.2 Study Purpose and Objectives
Prior to selection of study sites and parameters to measure, it is important to
determine the purpose of the sampling program. For example, the main purpose could be to
• evaluate nutrient limitation,
• document temporal variability (i.e., diurnal, episodic, seasonal, annual,
interannual) in water chemistry,
* In other words, natural and sampling variability are high relative to the magnitude of change
that has occurred in response to atmospheric deposition.
10
co-occur with probable geologic sources of Hg or areas that promote Hg
methylation. Regional Hg deposition attributable to long-range atmospheric
transport is also of concern. In general, we do not recommend routine monitoring for Hg concentrations in water. Nevertheless, Hg can pose a health risk
to humans or wildlife (i.e., bald eagle, osprey, loon, and river otter) that consume large quantities of such fish. We recommend that a more effective way to
evaluate Hg contamination issues in surface waters is to analyze, or monitor,
concentrations of Hg in fish rather than in water. Of particular concern are the
larger, older, piscivorous fish, such as bass, pike, and some species of trout.
1.1.1.2 Potential Confounding Factors
In developing and implementing a field-sampling program, it is important to
consider numerous potentially confounding factors. Some of the important
considerations that can complicate aquatic inventory and monitoring assessments include:
• low signal-to-noise ratio, * especially for dilute aquatic ecosystems,
• variation in watershed properties, such as slope, aspect, underlying
bedrock composition, glacial till (if it occurs), depth and composition
of soils, distribution of vegetative cover, role of groundwater, and presence and hydrologic connectedness of wetlands,
• interacting stressors, especially climate, introduced species, and legacy effects of past land use and exposure to pollutants,
• constraints of sampling in designated wilderness areas where land
use rules prohibit access via mechanized equipment and installation
of fixed equipment,
• constraints regarding laboratory analytical holding times,
• national and regional applicability,
• cost and training constraints, and
• quality control issues and the need for peer review.
1.1.2 Study Purpose and Objectives
Prior to selection of study sites and parameters to measure, it is important to
determine the purpose of the sampling program. For example, the main purpose could be to
• evaluate nutrient limitation,
• document temporal variability (i.e., diurnal, episodic, seasonal, annual,
interannual) in water chemistry,
* In other words, natural and sampling variability are high relative to the magnitude of change
that has occurred in response to atmospheric deposition.