Environmental Engineering Reference
In-Depth Information
targeted/tiered sampling, and before-after, control-impact (BACI), with the choice of
approach dependant on the project objectives (USEPA
2002a
). The number of
replicate measurements or samples to be taken for analyses of specific wetland
water quality parameters is also an important consideration, although often appears
to be arbitrarily determined in monitoring studies. An excellent discussion of
approaches to determine effective sample number based on study design is available
in USEPA (
2002b
).
6.6.2 Wetland Classification
Wetland classification is aimed at controlling some of the natural variability in the
monitoring data derived from wetlands by grouping them according to common
physical or biological characteristics such as hydrology, hydrogeomorphology,
and/or vegetative assemblages (e.g., Cowardin et al.
1979
; Brinson
1993
; Reinelt
et al.
2001
; Jackson
2006
). Water quality has also been used to group wetlands or
modify classification systems (e.g. Cowardin et al.
1979
; Warner and Rubec
1997
).
Brinson (
1988
) provides a conceptual discussion of how landscape position and
associated flow characteristics, both of which are attributes used for geomorpho-
logical classification of wetlands, would influence elemental cycles and wetland
water quality.
Studies that have specifically evaluated the extent to which classification helps
control variability in water quality parameters among wetlands are limited, although
those that are available indicate that broad scale classification may not be particularly
effective in this regard. For example, Trebitz et al. (
2007
) and Morrice et al. (
2008
)
found that grouping Great Lakes coastal wetlands according to relatively coarse
hydromorphic types or biogeographic region did not enhance their ability to relate
wetland water quality to land use and Trebitz et al. (
2007
) concluded that finer
hydrologic classification would have been desirable in their study. Similarly, Azzolina
et al. (
2007
) were unable to detect significant differences in surface water quality
between wetlands grouped according to a modification of Brinson's hydrogeomorphic
(HGM) classification (specifically, the LLWW approach as described by Tiner (
2003
)
and Tiner and Stewart (
2004
)). Euliss et al. (
2004
) state that while regional landscape
position often explains many of the chemical and biological properties of wetlands,
finer-spatial scale and temporal influences are also significant determinants of wetland
water quality. This is clearly supported by studies that have demonstrated how
localized landscape factors and basin characteristics can influence water quality in
individual wetlands (e.g., Skelly and Freidenburg
2000
; Batzer et al.
2000
;Hossack
and Corn
2008
). The development of regional wetland subclasses as described in
the HGM approach (Brinson
1993
) or even finer-scale modifiers of wetland classes
may therefore be necessary to effectively reduce natural variation in water quality
among wetlands.
