Purpose and Study Design
20
nutrient deposition effects is the goal, avoiding high-flow conditions can result
in a substantial underestimation of the magnitude of impact. The extent of this
underestimate can be quantified by conducting additional seasonal and episodic sampling for at least a subset of the sampling sites.
1.2.3 Characterization of Stream Chemistry
during Hydrologic Events
Hydrologic events, which are high flows caused by rainstorms or rapid
snowmelt, are episodic and can last from a few hours to a few weeks. Although
these events occur over a relatively small fraction of the year, they often represent the majority of total annual flow (Likens et al. 1977) and constituent
flux. Events can happen throughout the year in most regions of the United
States but are most common during seasons of high precipitation (and during spring snowmelt in regions where snow accumulates) and are generally
least common during summer, when high evapotranspiration reduces soil
moisture.
Stream water chemistry during hydrological events is important to
characterize because high flows often lead to extreme chemical conditions.
Effects on stream biota from episodic variations in stream chemistry can
be as severe or more severe than chronic effects associated with base flow
chemistry. For example, episodic acidification can result in the elimination of an annual age class of fish (McComick and Leino 1999) when the
event is timed with the presence of sensitive life stages. It can also affect
other forms of aquatic life, such as diatom communities, which have been
found to be less diverse in an episodically acidified stream than in a nearby
chronically acidified stream (Passy et al. 2006).
Manual water sampling is generally not effective at characterizing chemical
variability over the course of a hydrologic event because the timing and shape
of the hydrograph is difficult to predict and may occur at inconvenient times
for the sampler. Automated water sampling triggered by changes in water
level (often referred to as stage) provides an effective solution to this problem.
Automatic samplers can collect water at preset time intervals or at intervals
SAMPLING TO SUPPORT MODELING
If modeling is anticipated using the collected data, it is important to
consider which water chemistry variables will be needed to calibrate
the model, for example, application of the Model of Acidification of
Groundwater in Catchments (MAGIC).
20
nutrient deposition effects is the goal, avoiding high-flow conditions can result
in a substantial underestimation of the magnitude of impact. The extent of this
underestimate can be quantified by conducting additional seasonal and episodic sampling for at least a subset of the sampling sites.
1.2.3 Characterization of Stream Chemistry
during Hydrologic Events
Hydrologic events, which are high flows caused by rainstorms or rapid
snowmelt, are episodic and can last from a few hours to a few weeks. Although
these events occur over a relatively small fraction of the year, they often represent the majority of total annual flow (Likens et al. 1977) and constituent
flux. Events can happen throughout the year in most regions of the United
States but are most common during seasons of high precipitation (and during spring snowmelt in regions where snow accumulates) and are generally
least common during summer, when high evapotranspiration reduces soil
moisture.
Stream water chemistry during hydrological events is important to
characterize because high flows often lead to extreme chemical conditions.
Effects on stream biota from episodic variations in stream chemistry can
be as severe or more severe than chronic effects associated with base flow
chemistry. For example, episodic acidification can result in the elimination of an annual age class of fish (McComick and Leino 1999) when the
event is timed with the presence of sensitive life stages. It can also affect
other forms of aquatic life, such as diatom communities, which have been
found to be less diverse in an episodically acidified stream than in a nearby
chronically acidified stream (Passy et al. 2006).
Manual water sampling is generally not effective at characterizing chemical
variability over the course of a hydrologic event because the timing and shape
of the hydrograph is difficult to predict and may occur at inconvenient times
for the sampler. Automated water sampling triggered by changes in water
level (often referred to as stage) provides an effective solution to this problem.
Automatic samplers can collect water at preset time intervals or at intervals
SAMPLING TO SUPPORT MODELING
If modeling is anticipated using the collected data, it is important to
consider which water chemistry variables will be needed to calibrate
the model, for example, application of the Model of Acidification of
Groundwater in Catchments (MAGIC).