1.2 Study Design
17
TABLE 1.7 GENERAL GUIDANCE REGARDING WATER QUALITY STUDY
DESIGN
If What You Want to Know Is
You Should Consider the Following
Kind(s) of Study Design
Number of lakes, length of streams, or
percentage of the regional population
of lakes or stream length that is
above or below a particular criteria
value (i.e., ANC ≤ 50 μeq/L)
Some form of stratified random sampling,
which will allow extrapolation of results
from individual sites to the larger area
Status of the acid-base chemistry of
the most (or some of the most)
sensitive lakes or streams in an area
Nonstatistical survey of selected lakes or
streams in portions of the study area and
landscape positions expected to contain
the most sensitive aquatic resources.
General assessment of lake or stream
chemistry in an area, with
identification of some of the more
sensitive water bodies in the area
Statistical or nonstatistical screening of a
relatively large number of water bodies
across the expected gradient of
sensitivity, measuring specific
conductance or pH in the field for
making a rough assessment of condition,
and collecting samples for full laboratory
analyses for a subset of those samples.
Estimate of seasonal or episodic
variability in the chemistry of an
acid-sensitive lake or stream
Frequent interval sampling during the
period of interest (typically snowmelt or
during rainstorms). Sampling can range
from hourly to monthly during the season
or period of interest and can include
multiple years to capture the range of
variation.
Analysis of changes in water chemistry
over time
Periodic sampling (usually monthly to
annual) over a period of usually at least 8
years, focused on an index period or
standardized by hydroperiod. More
robust studies (with greater statistical
power to detect trends) will entail more
frequent sampling (weekly to seasonal) or
will extend for longer periods of time.
Assessment of temporal variability in
water chemistry of a particular lake
or stream
Frequent interval (hourly to seasonal)
sampling that captures major changes in
hydrology during the season(s) of
interest. Should include multiple years.
Continued
17
TABLE 1.7 GENERAL GUIDANCE REGARDING WATER QUALITY STUDY
DESIGN
If What You Want to Know Is
You Should Consider the Following
Kind(s) of Study Design
Number of lakes, length of streams, or
percentage of the regional population
of lakes or stream length that is
above or below a particular criteria
value (i.e., ANC ≤ 50 μeq/L)
Some form of stratified random sampling,
which will allow extrapolation of results
from individual sites to the larger area
Status of the acid-base chemistry of
the most (or some of the most)
sensitive lakes or streams in an area
Nonstatistical survey of selected lakes or
streams in portions of the study area and
landscape positions expected to contain
the most sensitive aquatic resources.
General assessment of lake or stream
chemistry in an area, with
identification of some of the more
sensitive water bodies in the area
Statistical or nonstatistical screening of a
relatively large number of water bodies
across the expected gradient of
sensitivity, measuring specific
conductance or pH in the field for
making a rough assessment of condition,
and collecting samples for full laboratory
analyses for a subset of those samples.
Estimate of seasonal or episodic
variability in the chemistry of an
acid-sensitive lake or stream
Frequent interval sampling during the
period of interest (typically snowmelt or
during rainstorms). Sampling can range
from hourly to monthly during the season
or period of interest and can include
multiple years to capture the range of
variation.
Analysis of changes in water chemistry
over time
Periodic sampling (usually monthly to
annual) over a period of usually at least 8
years, focused on an index period or
standardized by hydroperiod. More
robust studies (with greater statistical
power to detect trends) will entail more
frequent sampling (weekly to seasonal) or
will extend for longer periods of time.
Assessment of temporal variability in
water chemistry of a particular lake
or stream
Frequent interval (hourly to seasonal)
sampling that captures major changes in
hydrology during the season(s) of
interest. Should include multiple years.
Continued