Environmental Engineering Reference
In-Depth Information
biological activity in the system. Temperature, dissolved oxygen, and pH are among
those parameters most prone to diurnal fluctuations as a result of the combined effects
of solar heating, radiant cooling, photosynthesis, and respiration, although diurnal
variation in parameters such as conductivity and alkalinity have also been observed
(Ryder and Horwitz
1995
; Stratford et al.
2004
; Sisodia and Moundiotiya
2006
;
Tuttle et al.
2008
;Reeder
2011
). Cornell and Klarer (
2008
) report dissolved oxygen
levels in a Lake Erie coastal wetland varied between 20 and 150 % saturation over the
course of the day and comparable dissolved oxygen fluctuations have been observed
in stands of emergent vegetation in restored and natural floodplain wetlands (Boon
2006
;Reeder
2011
). High levels of photosynthetic activity can also lead to significant
increases in pH, although these may be attenuated by other chemical characteristics
of the system. Boon (
2006
) discusses studies of an Australian wetland that exhibited
daily pH changes of up to 2 pH units and observed that this fluctuation could
influence nitrogen dynamics in the system if the pH were to rise above 8 and convert
ammonium to the more volatile ammonia. In contrast, Reeder (
2011
)didnotobserve
a significant influence of primary productivity or respiration on the pH of restored
floodplain wetlands, and attributed these results to buffering by divalent cations in the
sediments and/or reduced effects of microbial respiration due to low levels of
sediment organic matter.
The intensity of diurnal fluctuations in wetland water quality variables may vary
based on habitat type and water source. As compared to open water zones, diurnal
fluctuations in temperature may be dampened near stands of emergent vegetation,
although daily fluctuations in dissolved oxygen and pH may be greater in beds of
both emergent and submergent plants (Rose and Crumpton
1996
; Chimney
et al.
2006
; Reeder
2011
). Diurnal fluctuations in temperature and dissolved oxygen
were reduced during hydrologic pulses in created riparian wetlands (Tuttle
et al.
2008
), while groundwater input in vernal pools has also been found to reduce
daily temperature fluctuations (Korfel et al.
2010
). Daily fluctuations in conductiv-
ity and water color in Great Lakes coastal wetlands was attributed to seiche-induced
inflow of lake water that increased levels of dissolved ions and diluted color
(deCatanzaro and Chow-Fraser
2011
).
In temperate zones, seasonal changes in thermal input can lead to significant
seasonal variation in wetland water temperature, with differences of 30
C or more
between minimum and maximum temperatures not uncommon (Black
1976
;
Boeckman and Bidwell
2007
). These temperature differences drive seasonal
changes in biotic and abiotic processes that influence other water quality
parameters. For example, dissolved oxygen levels are often higher during cooler
months owing to higher gas solubility and lower respiration (Boeckman and
Bidwell
2007
). Diel fluctuations in dissolved oxygen, pH, and alkalinity may be
greater in summer due to increased rates of photosynthesis and respiration and
reduced solubility of oxygen and CO
2
. Levels of nitrate and orthophosphate in
wetland water may be lower in summer due to greater uptake by plants or, in the
case of nitrate, increased rates of denitrification (Mitsch and Reeder
1992
;
deCatanzaro and Chow-Fraser
2011
). However, Eser and Rosen (
1999
) report
seasonal maxima for nitrate and ammonium in late summer which was attributed
