Environmental Engineering Reference
In-Depth Information
Wetland hydroperiod (seasonal wetting and drying) has an obvious influence on
the abiotic and biotic features of wetlands (Brooks
2000
; Jackson
2006
) and
differences in water between wetlands at different stages of the hydroperiod
could be a significant source of between-site variability. Oxidative metabolism of
organic matter in the substrate of a dry wetland can result in a pulse of nutrients
to the water column when the wetland refloods (Euliss et al.
2004
), although
Boon (
2006
) states that nutrient release in newly-flooded wetlands may be derived
from other sources as well. Regardless, a succession of chemical reactions occurs
in saturated wetland soils as oxygen becomes depleted and new substrates are
used as electron acceptors by respiring microorganisms (Boon
2006
; Mitsch
and Gosselink
2007
). Concurrent changes in variables such as dissolved oxygen,
pH, dissolved organic carbon, conductivity and water clarity would be expected
to occur in the wetland water column as photosynthetic and respiratory processes
become established and suspended material begins to settle out, although few
studies have evaluated this with sufficient sampling frequency to effectively docu-
ment the changes that do occur.
Most discussion of wetland hydroperiod and water quality focuses on how water
loss influences water quality parameters. Euliss et al. (
2004
) discuss the “drought”
versus “deluge” phases in prairie pothole wetlands in reference to changing solute
concentrations that can influence wetland biota. Similarly, evaporative water loss and
associated concentrating effects were used to explain stable isotope signatures and
increased summertime cation levels in New Zealand peatlands (Chague-Goff
et al.
2010
), seasonal variation in salinity of arid and semi-arid zone wetlands in
Australia (Jolly et al.
2008
), and spatial differences in parameters such as conductivity,
dissolved organic carbon, and levels of specific dissolved ions between different
wetland zones of the Okavango delta (Mackay et al.
2011
). Increases in other water
quality parameters including total nitrogen, total phosphorous, pH, alkalinity, and
hardness have also been associated with evapoconcentration as seasonal wetlands
proceed through the hydroperiod (Gell et al.
2002
; Boeckman and Bidwell
2007
).
Water loss and associated evapoconcentration effects on water quality variables can
also vary considerably between wetlands based on factors such as basin size, localized
landscape position of the wetland, and the presence of plants which can enhance water
loss by evapotranspiration (Euliss et al.
2004
;Jackson
2006
).
Interestingly, increases in the levels of water quality variables due to evapocon-
centration may have only limited influence on biotic communities in inland
wetlands unless these exhibit extremely elevated conditions as has been described
for prairie pothole wetlands and some other systems (Euliss et al.
1999
;
Mendelssohn and Batzer
2006
). Batzer et al. (
2004
) report variation of up to two
orders of magnitude in a suite of water quality parameters they measured in a series
of forested wetland ponds that differed in hydroperiod and landform and found
these factors had a relatively minor influence on macroinvertebrate assemblages.
Babbitt et al. (
2003
) used plant assemblages and site visits to group a series of
forested depressional wetlands according to hydroperiod duration and found per-
manently inundated wetlands were slightly warmer and had slightly higher pH,
higher dissolved oxygen, and lower conductivity than wetlands with the shortest
