Environmental Engineering Reference
In-Depth Information
are much richer in DOC than those from hardwood stands or grass lands (Rae
et al.
2001
; Cronan and Aiken
1985
). Lakes with catchments containing 55-65 %
natural grassland and <30 % forest have low DOC concentration (<83
μ
M C),
whilst lakes in moderately forested (50-60 %) catchments have DOC concentra-
tions of 83-208
μ
M C, and those in densely forested (>70 %) catchments have
DOC concentrations of 667
μ
M C (Cronan and Aiken
1985
). Forested wetlands,
particularly those with coniferous trees, are positively related to lake DOC, open-
water wetlands including lakes are inversely related to DOC, and scrub-shrub and
emergent wetlands are not related to DOC (Xenopoulos et al.
2003
). Upstream
rivers covered by coniferous, deciduous or moxed-type forests have generally low
(~<200
μ
M C) DOC concentrations (Table
2
) (Mostofa et al.
2005a
,
b
; Sugiyama
et al.
2005
). A model analysis has shown that the terrestrial land cover such as
conifer boreal forest and barren tundra strongly affects DOC in lakes (Sobek et al.
2007
). The land cover type “conifer boreal forest” is positively related with lake
DOC, while “cool conifer forest” is negatively related to DOC. However, cool
conifer forest is confined to high altitude areas such as the Rocky Mountains and
the Alps, which may explain the relatively low DOC concentrations found in these
lakes (Sobek et al.
2007
).
In polar desert lakes, DOM is generated autochthonously by microbial pro-
cesses in water, since there is no catchment vegetation (Rae et al.
2001
). This
DOM thus differs from that of temperate latitudes by having a reduced ratio of
aromatic to aliphatic residues (McKnight et al.
1994
). It has also been shown that
DOC from predominantly grassland catchments is qualitatively different in terms
of its UVR attenuation properties than DOC from a mainly forested catchment
(Rae et al.
2001
). Therefore, the type and amount of terrestrial vegetation sur-
rounding a catchment plays a significant role in defining the concentration levels
of DOC in the catchment water. It is hypothesized that high ground-water DOC
concentrations are directly related to high DOC concentrations in surface waters
(Mladenov et al.
2007
).
6.2 Land Management and Natural Effects (Precipitation,
Flood and Drought)
Land management and natural effects (precipitation, flood and drought) are
important factors for controlling DOM release from soil environments to natural
water catchments (Mostofa et al.
2005b
,
2007a
; Watts et al.
2001
; Ittekkot et al.
1985
; Safiullah et al.
1987
; Newbern et al.
1981
; Richey et al.
1990
; Depetris and
Kempe
1993
; Shaw
1979
; Worrall et al.
2003
; Worrall and Burt
2004
; Yallop and
Clutterbuck
2009
; Clutterbuck and Yallop
2010
; Yallop et al.
2010
). These pro-
cesses include several phenomena:
(i) DOC is largely released from soil into water during agricultural activities,
particularly in plantation and growing seasons of rice plants as well as other
