Conversely, the lower pH in the hypolimnion
(Table 1) can be attributed to decomposition of organic matter that releases C[O.sub.2] and, ultimately, acidifies the water (Horne & Goldman 1994; Cooke et al.
Hypolimnetic water can be withdrawn, exposed to pure oxygen under high pressure and then delivered back to the hypolimnion
. Another method involves introducing pure oxygen into the hypolimnion
through the use of a diffuser to form a rising unconfined oxygen bubble plume.
A weak decrease followed in the hypolimnion
between 7.8 and 8.2 m.
The average for 15-20 m sufficiently characterizes the state of the hypolimnion
. Values of pH for the lower layer were not used, as the variations observed were small.
Bacterioplankton samples were obtained from integrated water samples (from the surface and hypolimnion
), preserved in 2% formaldehyde (final concentration), and stored in the dark at 4[degrees]C.
Differences in temperature between the epilimnion and hypolimnion
were most pronounced in lakes Garais and Geranimova in July, being 18.9 [degrees]C and 21.2 [degrees]C at the surface and 4.8 [degrees]C and 5.7 [degrees]C at the bottom, respectively.
The reservoir is highly productive (eutrophic) with summer stratification occurring, creating anoxic conditions in the hypolimnion
until fall turnover.
of the lake was the site of intermittent mixing episodes indirectly related to external forcing (winds and inflow/outflow flux) by the oscillatory phenomena of the water.
Increases in the severity and extent of hypoxia could result in altered biogeochemical processes in the hypolimnion
and in the epibenthos.
[DELTA]T <1.3[degrees]C), low water transparency (<100 cm), anoxic conditions (DO <1 mg/L) in the hypolimnion
from June to September, and high concentration of orthophosphates.
suggests that temporary or permanent anoxia has developed in the hypolimnion
of the lake, which effectively minimizes bioturbation and is a prerequisite for the preservation of features of seasonal sedimentation.