The sample should be a good subset of the population of interest, unbiased by
edge-effects or anomalies. Monitoring station selection is problem-specific, but
some general station attributes for each type of water resource are suggested
below.
Stream Monitoring
Locating a stream monitoring station may be difficult since several factors
influence placement.Theeffect oftributary pollutant loading, dilution effects, and
Locations
lateral gradients should be considered. Point source pollutant influences can also
impede NPS monitoring activities. Monitoring a stream reach (length of stream)
with several stations may be necessary. However, a reach may be monitored by
a single station if variability for the constituent of concern is low. Problem
documentation monitoring during high and low flows at several locations will
provide information on site variability and can serve as the basis to select stream
monitoring stations.
Wetland Monitoring
Wetland functions are highly interrelated and can be quite complex. Hydrology
and hydraulic loading rates of pollutants are very important for evaluating wetland
Locations
functions and response to management. Fixed stations are needed to evaluate
changes in hydrology, pollutant concentrations, and biological variables (Ham-
mer 1992).
Monitoring at the inlet and outlet are important if a pollutant budget or information
on loading and wetland treatment efficiency are needed. Monitor pollutants at
selected wetland stream channel stations and one or more nonchannel stations to
characterize water quality gradients and patchiness within the wetland.
Water levels should also be determined for each water quality sample. The area1
extent of the permanent pool is an important measurement for wetland function
and this usually varies with season and other factors.
Vegetation monitoring is important for assessing overall health and may be
accomplished with an analysis of area1 photographs. Vegetation sampling in-
cludes monitoring along quadrants, transects, or bisecting the wetland at random
locations.
Reservoir Monitoring
A horizontal gradient of pollutants with high concentration near tributary
waters decreasing to the outflow is common for reservoirs and their tributary arms.
Stations
If it clearly reflects the condition of the designated use, a single station over the
greatest depth may be the preferred sampling point. Additional stations may be
located in the mainstem, down gradient of a major tributary, or over the deepest
water in a tributary arm, depending upon designated use, additional management
objectives, and knowledge of the pollutant budget. The depth of the sample is also
a concern for managing depth of withdrawal from the reservoir to control tailwater
quality.
Lake Monitoring Stations
For pelagic and profundal water column monitoring in a lake with low shoreline
development (i.e., regular-shaped lakes, not reservoirs), a single station at the
deepest part of the lake may be sufficient for assessing whole lake conditions.
Generally few stations are needed for lakes that mix continuously and do not
stratify. For a lake with more complex morphometry, lake mixing and circulation
3.8
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