Environmental Engineering Reference
In-Depth Information
plantations through rainfall or water overflow (Mostofa et al.
2005a
,
2007a
).
Rapid photo- and microbial respiration or assimilation of soil OM might be
responsible for high releases of DOC into water during agricultural activities.
(ii) DOC concentrations are increased with afforestation in catchments (Ciglasch
et al.
2004
; Neal et al.
1998
,
2004
). In addition, deforestation can reduce
evaporation and increase surface temperature. Changes in land-surface cover
can enhance the degradation of soil DOM and OM by both photoinduced
and microbial processes (Brandt et al.
2009
; Rutledge et al.
2010
; Raich and
Schlesinger
1992
; Borges et al.
2008
). Therefore, either afforestation or defor-
estation in soil environments can contribute to the rapid washout of allochtho-
nous DOM and OM to water catchments by precipitation or runoff.
(iii) Controlled heather burning as a management tool for red grouse (Lagopus
lagopus) husbandry in peat surface is often (but not always) identified as a
highly significant driver of spatial variance in DOC concentration in drain-
age water (Yallop and Clutterbuck
2009
; Yallop et al.
2006
,
2008
; Ward et al.
2007
; Worrall et al.
2007
).
(iv) Increased precipitation and runoff can lead to higher DOC export from the
catchment into natural surface waters (Pace and Cole
2002
; Zhang et al.
2010
;
Monteith et al.
2007
; Hongve et al.
2004
; Sobek et al.
2007
; Ciglasch et al.
2004
; Gielen et al.
2011
; Anderson et al.
1997
; Evans et al.
1999
). Total solar
radiation and precipitation can account for 49-84 % of the variation in the
long-term DOC patterns in various catchments (Zhang et al.
2010
). The DOC
concentrations in Swedish lakes and streams have substantially increased dur-
ing the 1970-1980s, mostly due to higher precipitation (Tranvik and Jasson
2002
). DOC concentrations vary from 4
μ
M C to 3675
μ
M C in rainwater,
which may largely affect the natural surface waters (Table
2
) (Likens et al.
1983
; McDowell and Likens
1988
; Guggenberger and Zech
1993
; Chebbi and
Carlier
1996
; Willey et al.
2000
,
2006
; Ciglasch et al.
2004
; Avery et al.
2006
;
Kieber et al.
2006
,
2007
; Miller et al.
2009
; Santos et al.
2009a
,
b
; Southwell
et al.
2010
; Pan et al.
2010
). Factors affecting the variation in DOC concen-
trations are rainwater volume, season (winter, spring or summer), location of
the rain events, wind speed, storm trajectory, and the air mass pathways dur-
ing precipitation. During highly rainy seasons, DOC concentrations are sig-
nificantly increased through flushing of organic-rich waters from upper soil
horizons, agricultural and forest runoff, primary production and subsequent
flooding of the ox-bow or flood-plain lakes, through lake out-flowing into the
nearby catchment waters (Mostofa et al.
2005b
; Ittekkot et al.
1985
; Safiullah
et al.
1987
; Ishikawa et al.
2006
; Newbern et al.
1981
; Richey et al.
1990
;
Depetris and Kempe
1993
; Mulholland
2003
). Leaching and heterotrophic
processing of newly flooded terrestrial vegetation, leaching of organics from
floodplain soil and catchment areas can also affect the DOC concentrations
(Wetzel
1992
; Duff et al.
1999
; Mladenov et al.
2007
; Reche et al.
1999
). The
flow path of water in the catchment after precipitation is an important factor
that can reduce soil erosion (Sobek et al.
2007
), thereby reducing the rapid
washout of allochthonous DOM, POM and nutrients to water catchments.
