Environmental Engineering Reference
In-Depth Information
of the surface of Great Britain, but supply over 70 % of its drinking water (Watts
et al.
2001
). Therefore, all the people uptake a certain amount of DOC everyday from
drinking water. According to the level of DOC in groundwater and considering an
average water intake of 2 liters per day for adults (which can rise to ~5 liters for man-
ual labor at high temperature), on average, every person intakes per day ~50-800
μ
M
C in Asia, ~100-30000
μ
M C in Europe and 20-5000
μ
M C in the U.S.A. The inter-
esting question that arises is that these DOC contents are significant energy sources
for human beings and for the other living organisms. Before addressing this question,
it is important to examine which substances make up DOM in natural waters.
The contribution of humic substances (hydrophobic acids) in groundwater is
very variable in different countries, and is approximately included in the range
of 12-98 % (1-80 % of fulvic acid and 2-97 % of humic acid). The contribu-
tion of hydrophilic fractions is 1-82 % (Buckau et al.
2000
; Bertilsson et al.
1999
;
Peuravuori and Pihlaja
1999
; Leenheer et al.
1974
; Thurman
1985c
; Ford and
Naiman
1989
; Schiff et al.
1990
; Wassenaar et al.
1990
; Malcolm
1991
; Gr
n et al.
1996
; Christensen et al.
1998
; McIntyre et al.
2005
; Mladenov et al.
2008
). Along
with the humic substances, hydrophilic compounds (acidic, basic and neutral) and
carbohydrates (mainly polysaccharides, ~1-10 %) are also present in groundwater
(Thurman
1985a
; Peuravuori and Pihlaja
1999
; Artinger et al.
2000
). The intake
of DOC by every person is approximately 20-30000
μ
M C, or 0.2-360 mg C L
−
1
per day, for the average hydration of a human body in the case of groundwater.
It is generally well-known that carbohydrates can produce energy for all living
organisms. The sources of carbohydrates and humic substances are the same vas-
cular plant material. DOM with its content of organic C and N is a thermodynamic
anomaly that provides a major source of energy to drive aquatic and terrestrial
ecosystems (Tranvik
1992
; Salonen et al.
1992
; Wetzel
1984
,
1992
; Hedges et al.
2000
; Berner
1989
). Energy changes (
±
) such as supply (
+
) or consumption (
−
)
of energy in the aquatic environment generally occur during the photoinduced and
microbial degradation of DOM and organic matter, during the microbial loop and
the photosynthesis (Mostofa et al.
2009a
; Komissarov
1994
,
1995
,
2003
; Miller
and Moran
1997
; Li et al.
2011
; Sherr and Sherr
1989
; Carrick et al.
1991
; Jones
1992
; Tranvik
1992
; Wetzel
1984
,
1992
). In addition, terrestrial DOM represents
a source of allochthonous energy for heterotrophs in receiving lakes, rivers, reser-
voirs, estuaries and coastal oceans (Mostofa et al.
2009a
; Wetzel
1992
; Smith and
Hollibaugh
1993
; Kemp et al.
1997
; Pace et al.
2004
; Aller and Blair
2006
). It has
been shown that DOM makes up 47 % of the energy which enters and 70 % of the
energy which leaves the groundwater ecosystem (Fisher and Likens
1973
). It has
also been shown that undisturbed groundwater basins export only small amounts
of energy (~1 %) from the upland regions, while the ramaining 99 % of forest
production is consumed terrestrially (Fisher and Likens
1972
,
1973
). It is therefore
concluded that the DOM including humic substances can act as energy source and
are vital for all living organisms (Mostofa et al.
2009a
). Note that DOM in drink-
ing water can play a negligible energetic role for humans, due to the uptake of a
substantially lower amount of organic carbon compared to foods (e.g. boiled rice,
vegetables, fish, meat and so on) and beverages (e.g. fruit juices, alcohol, etc.).
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