Environmental Engineering Reference
In-Depth Information
pH is a measure of the hydrogen ion (H + ) concentration of water
with values less than neutral (pH
pH
Hydrology :
7) indicating acidic
conditions and those above 7 indicating alkaline conditions.
¼
Water input from overland flow, precipitation or groundwater can
influence pH- systems with precipitation as the primary water
source often have a pH
The pH of natural waters is significantly influenced by the carbonic
acid equilibrium that develops when carbon dioxide dissolves in
water:
7 because precipitation tends to be
<
slightly acidic
Depending on basin geology and soil type, groundwater input could
be acidic or alkaline, with overland flow similarly influenced
HCO 3 þ
H þ Ð
CO 3 2
2H þ
CO 2 þ
H 2 O
Ð
H 2 CO 3 Ð
þ
Internal and other processes :
Diurnal and spatial variability in pH can result from those same
factors that influence dissolved oxygen
The implications of this are that uptake of CO 2 by
photosynthesizing plants can cause pH to increase while release
of CO 2 due to respiration causes pH to decrease
Seasonal variation is also possible due to temperature effects on
respiration
pH can influence chemical solubility and biogeochemical cycles.
For example, acidic pH can increase the solubility and toxicity
of sediment-bound metals, while increases in pH above 8 can
lead to the loss of ammonia nitrogen (Catallo et al. 1995 ; Boon
2006 )
pH has been used as a water quality modifier in wetland classifica-
tion systems (see Cowardin et al. 1979 ; Wetzel and Likens
2000 )
Alkalinity
Hydrology :
Alkalinity of water is a measure of the capacity of constituent
dissolved chemicals to accept and neutralize protons and is
mostly attributed to the presence of carbonates (HCO 3
and CO 3 2 )
Baseline alkalinity levels in wetlands are influenced by source water
and local geochemistry
Internal and other processes :
Diurnal and seasonal variation in wetland water alkalinity has been
associated with iron and sulphate reduction, denitrification, and
assimilation of ammonium and nitrate (Eser and Rosen 1999 ;
Sisodia and Moundiotiya 2006 )
Alkalinity can indicate the geochemistry of the wetland basin and
catchment since it commonly results from carbon dioxide and
water attacking limestone or dolomite formations
Alkalinity levels in wetlands can influence reactions associated with
nutrient cycling (e.g., oxidation of ammonium (Parkes
et al. 2007 ) and so monitoring this parameter can be important in
assessing treatment wetland efficiency and understanding wet-
land nutrient profiles
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