Lake Melville

Increase in terrestrial organic carbon ratio in Lake
Melville shows sensitivity to river changes
The balance of terrestrial vs. marine organic carbon
in Lake Melville sediments appears to be sensitive to
changes in the supply of terrestrial materials, as may
be expected from climate change or hydroelectric
development. In the sedimentary record of the last
few decades, we find a significant shift in the δ 13 C
proxy upcore, which suggests an increase in terrestrial
organic carbon inputs (Figure 5.8). In Figure 5.7, cores
that lay to the right of the line reveal an increase in
137
Cs sourced from the terrestrial environment while
cores that fall to the left of the line suggest additional
inputs of 210 Pb ex
from seawater. Possible explanations
include increased river flows, flooding of land, or forest
fires/clear cut logging in the watershed. The shift is
particularly pronounced in central Lake Melville, where
it appears that marine organic carbon was once equally
or more important than terrestrial organic carbon
but now terrestrial organic carbon is the dominant
source. With shifts in the balance of terrestrial vs.
marine organic carbon, there would likely be shifts in
the intensity of metabolism in the system (reflecting
terrestrial organic carbon being less metabolizable),
and in food web structure (favouring microbial systems,
for example). Findings suggest that central Lake
Melville is sensitive and responsive to changes in rivers
and/or their watersheds, despite being quite removed
from the actual river mouths.
Figure 5.6. (a) Organic
carbon (%), and (b) δ 13 C org
(‰) in surface sediment
across Hamilton Inlet.
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