The transparency of water is usually measured
with a white metal disc lowered horizontally into the water on a line. The depth at
which the disc becomes invisible is marked in metres. There are, of course, special
instruments for measuring transparency also. In Baikal, a disc with a 30 cm diameter
is visible up to a depth of 40 metres in the best conditions for observations, that is,
in spring after the lake is freed from ice. Such a high degree of transparency is
usually typical of mountain lakes, situated amongst rocks with small quantities of
easily dissolved substances.
The high degree of transparency of Baikal's waters is due to a
number of factors. The fact that the lake's shores are made up mainly of rock; that
there are few shallow areas along the shores with the result that there is little
stirring up of floor silts; also that, under the influence of complex biochemical
processes including the activity of Baikal organisms, suspended organic matter in part
decays and in part is transported to considerable depths to be deposited in sediment;
diatomic algae assimilate silicon from non organic mineral suspensions drawing it
into floor sediments. Baikal acts like a kind of treatment plant, turning out clear,
pure water.
Over the summer period the transparency of Baikal changes depending on the
quantity of sediment brought to the lake by rivers and the growth of plankton.
Transparency is low at the mouths of rivers and near them. The highest degree of
transparency can be observed in late autumn and early spring.
In its transparency Baikal takes the lead over the Caspian Sea (25 metres), and
lakes Sevan (Armenia) and Issyk-Kul (20 metres). In this respect it competes with
various seas, taking second place only to the extremely transparent Sargasso Sea
(66 metres).
Variations in the transparency of Baikal's water with depth has been studied in
the southern part by the hydrologists M.E.Li, G.G.Neuimin and I.P.Sherstyankin,
using a marine impulse photometer. Transparency at depth depends on the vertical
distribution of temperature and chemical components. Three layers of water have
been defined according to their degree of translucency: surface, deep water and
bottom.
The surface layer goes down to a depth of 250 - 300 metres (where the water temperature
changes abruptly).
In the deep water layer the transparency increases dramatically. This is where
the clearest waters are. The lower boundary of the deep water zone goes down to
300 - 400 metres above the lake floor.
In the bottom layer transparency varies: in some cases it decreases, in others it
remains the same, and in still others it even increases. So it is possible to find very
transparent water even at the bottom of Baikal. In general, the transparency here
depends on the presence or absence of floor currents.
The transparency of Baikal's waters varies at its different shores. The transparency
changes abruptly at a depth of 200 - 250 metres (the
isoclines are closely spaced). The high frequency of the isoclines begins closer to the
surface at the steep western shores and gradually drops towards the eastern shore.
A similar distribution of transparency can be explained by the undercurrent of
transparent deep waters along the western shores of the lake.
Baikal's fishermen differentiate the lake's waters according to their
transparency and colour very well. They catch omul, Baikal's commercial fish, not
only along the shores and at the surface, but also in the open sea at great depths by
letting down special deep water nets to 400 metres. The transparency and colour of
the water are important signs for fishermen. They call deep transparent waters
"golomyanniye" "deep, open waters" and differentiate them from coastal "grey"
and "white" waters. In the XVII century Russians brought the word "golomen" to
Baikal from Northern Rus. Here it has the meaning - fathomless places at Baikal.
This is how the most transparent waters, as representative of great depth, came to
be known as "golomyanny". It is from this that Baikal's most exotic fish received
its name, the endemic, deep water, golomyanka. |
Transparency