ELEMENTAL CONCENTRATIONS
A significant variation of organic carbon flux in terms of BOD
was observed with space and time in Varthur lake and is ~
14.8 kg/ m2
year, which is comparable to eutrophic lakes [32-35]. The variation in TOC can be due to differences in
particulate grains; a constraint of C uptake and breakdown due
to N limitation or could be due to early stage diagenetic
alteration. Limited OM degradation in the anoxic sediments
was reported earlier [36-39].
The atomic C/N ratio in Varthur sediments near the inlet
regions (Z1) was recorded to be 23–33. The macrophyte
derived material as the primary source of sediment OM near
the south shoreline has C: N of 23.11 compared to slightly
higher value of 33 in the middle and the north side. There was
higher accumulation of C near the north side of the lake due
higher terrestrial anthropogenic impact. These results are
comparable to C/N ratios about 20 attributing to input of
vascular plants, and lower C/N ratios [5–8] to algal-derived
OM [3, 39].
The N values were consistently very low below 5% of the dry
wt., which shows an N deficient system. It indicates that either
the N is already leached into the system, or N forms are
rapidly up-taken by the microbes. The volatilization and
denitrification could be significant processes responsible for
the lower sediment N values. The Organic N in the sediments
can however be transformed to various inorganic forms as
nitrites, ammonia, nitrous oxide or molecular nitrogen. The
presence of inorganic N in sediments can alter C/N ratios and
thereby confound the interpretation of OM sources [40]. This
confirms that the OM source in Lake Varthur sediments is
essentially autochthonous macrophyte#derived near the outlets
and terrestrial N near the inlet zones. However the middle part
OM in phycogenic in origin. Moreover, the C/N ratios indicate
that run-off waters from the catchment can increase the
terrestrial OM component, as the lake is surrounded by
agricultural and horticultural lands nearly 67%.
