Dissolved Organic Matter in Natural Waters - Photobiogeochemistry of Organic Matter - page 9

low (3 years) in temperate forest soils (central Massachusetts, USA), and high-
est (16 years) in boreal forest soils (Manitoba, Canada) (Trumbore 2000 ).
Experimental studies using δ 13 C or 14 C to track sources and turnover of DOC
indicate that DOM, which is transported over decimetres or metres down into sub-
soil, mainly represents highly altered residues of organic matter processing (Schiff
et al. 1997 ; Flessa et al. 2000 ; Hagedorn et al. 2004 ; Fröberg et al. 2007 ). Note
that allochthonous DOM is mostly derived, in zero to a few decimeter depth from
the decomposition of plant material by microbial processes in soils and shallow
groundwater (Uchida et al. 1998 , 2000 ; Fröberg et al. 2007 ; IPCC 1996 ; Buckau et
al. 2000 ).
DOC leached from soil is partly retained in the vadose zone before reach-
ing aquifers (Siemens and Kaupenjohann 2003 ; Mikutta et al. 2007 ; Kalbitz
and Kaiser 2008 ; Scheel et al. 2008 ). For the range of groundwater recharge of
95-652 mm yr − 1 , it is shown that a constant flux of DOC from soil into surface
waters often takes place (Kindler et al. 2011 ). Therefore, allochthonous DOM is
partly discharged through hydrological processes directly into streams or riverbeds
or surrounding water bodies, which ultimately flux to lake or oceanic environ-
ments as final water reservoir.
3.2 Origin of Autochthonous DOM in Natural Waters
Production of autochthonous DOM is generally observed at the epilimnion (upper
water layers) compared to the hypolimnion (deeper layers) during the sum-
mer stratification period, particularly in lakes and oceans. A rough estimation by
comparing the upper with the deeper layers demonstrates that the contribution of
autochthonous DOM is largely varied in lakes and oceans: it reaches 0-55 % in
Lake Hongfeng (181-250 μ M C at 0-6 m and 161-223 μ M C at 22-25 m depth,
respectively, during March-September), 3-47 % in Lake Baihua (183-264 μ M C
at 0-3 m and 157-206 μ M C at 14-15 m during March-September), 6-35 % in
Lake Baikal (93-142 μ M C at 0-100 m and 88-105 μ M C at 600-720 m during
August-September in 1995, 1998, 1999), 3-82 % in Lake Biwa (93-183 μ M C
at 2.5-10 m and 78-101 μ M C at 70 m during May-September in 1999-2002),
21-49 % in Lake Ashino in Japan (99-111 μ M C at 0-10 m and 74-84 μ M C at
30-38 m in September 1997), 81-102 % in Lake Ikeda in Japan (101-112 μ M C
at 0-10 m and 55-56 μ M C at 200-233 m for site I1; at 41 m for site I2 in
October 1997), 52 % in Lake Suwa in Japan (216 μ M C at 0 m in September and
142 μ M C at 0 m in December 1997), 61-81 % in Lake Inawashiro in Japan (42-
47 μ M C at 0-10 m and 26 μ M C at 70 m), 13-29 % in Lake Fuxian (123-135
μ M C at 0-10 m and 95-105 μ M C at 50-140 m in June 2001), 19 % in Lake
Hovsgol (95 μ M C at 0 m and 80 μ M C at 50-200 m in July 1999), 0-88 % in
Lake Kinneret (270-485 μ M C at 0-10 m and 258-368 μ M C at 38 m during the
summer period in 2004), 17-41 % in Lake Peter (data not shown), 11-29 % (bio-
logical production) in Lake Bret, 0-104 % in Middle Atlantic Bight (82-98 μ M C