Environmental Engineering Reference
In-Depth Information
than those fed by precipitation and run-off (Korfel et al.
2010
). The influence of
local geology on groundwater and associated wetland water quality is nicely
illustrated by the pH and nutrient content of fen wetlands which vary from quite
alkaline (pH 8.4) and nutrient rich (rich or minerotrophic fens) to acidic (pH 3.5)
and nutrient poor (acidic or poor fens) depending on the nature of the glacial
deposits the source water comes in contact with (Bedford and Godwin
2003
;
Kolka and Thompson
2006
; Nelson et al.
2011
). Similarly, wetlands that receive
significant input from overland flow often have water quality characteristics that
reflect the soil properties of their catchments. This can be observed on a seasonal
basis in some coastal wetlands of Lake Huron (Laurentian Great Lakes) that have
coloured, acidic water with low conductivity and elevated phosphorous in spring
due to input from upland watersheds (deCatanzaro and Chow-Fraser
2011
).
In many cases, the chemical profile and associated variability in wetland water
is driven by multiple water sources and/or by seasonal changes in water source.
In the Lake Huron coastal wetlands mentioned above, upland inflow decreases in
summer while input from seiche-derived lake water increases. This leads to increased
alkalinity, higher conductivity, and reduced phosphorous levels as compared to
springtime when inflow from upland catchments dominates (deCatanzaro and
Chow-Fraser
2011
). Euliss et al. (
2004
) state that while precipitation is generally the
most significant water source for prairie potholewetlands, input fromgroundwater can
increase the concentrations of solutes and other dissolved materials. The relative
solute concentration in these wetlands ultimately represents the combined effects of
groundwater and precipitation. The scenario is further complicated by the length of
groundwater flow paths between wetlands that may be influenced by precipitation
patterns (Euliss et al.
2004
). A comparable interplay between groundwater and surface
water sources has been observed in some Australian wetlands (Boon
2006
;Jolly
et al.
2008
). In some cases, groundwater input to depressional wetlands may also
serve to buffer increases in dissolved solutes caused by evaporative water loss (Rains
et al.
2006
; Korfel et al.
2010
). Variation in water source and connectivity through
groundwater can have important implications for jurisdictional regulation of
depressional wetlands that are considered isolated because they lack a clear connec-
tion to surface water (see Whigham and Jordan (
2003
) for further discussion).
Riparian wetlands that are subject to pulse flooding by rivers can have very distinct
water quality profiles between the times they are flooded by the river and when they
are isolated from it (Gell et al.
2002
; Weilhoefer et al.
2008
). Flood water can dilute
levels of dissolved constituents in floodplain wetland water as observed byWeilhoefer
et al. (
2008
) who report lower levels of conductivity, total phosphorous, and total
nitrogen during and just after a flood event. They also concluded that the magnitude
and duration of the flood was an important determinant of how much the wetland
water quality changed and that flooding could increase nutrient levels in a wetland
depending on the nutrient status of the river. Cabezas et al. (
2009
)alsostudiedthe
water quality of floodplain wetlands and found that the seasonal chemical profiles of
the systems were largely influenced by the relative inputs of river and groundwater.
Wetlands receiving major input from the river during flooding had lower conductivity
but higher turbidity and nitrate levels, while those receiving mostly groundwater had
higher conductivity and lower turbidity.
