Effects of Algal Blooms on Water Quality
197
PERIDINIUM BLOOMS IN LAKE KINNERET
Blooms of Peridinium have been recorded since the lake has been systematically
investigated e.g. in the last 25 years (Kimor and Pollingher, 1965). But fishermen recall
discolored water in certain seasons of the year as early as they can remember.
The bloom starts usualty in January, reaches its peak in March to May and terminates
in June. The above table summarizes data on the occurrence of blooms in the lake during
the years 1965 - 1970.
During the bloom there is no uniform distribution of the algal mass in the lake. The
algae tend to concentrate in patches of few hundred meters in diameter. Here one can
find concentrations of Peridinium an order of magnitude higher than the average. These
patches are not defined in shape and size as there is permanent migration of the algal
population. Berman and Rodhe (1970) who studied this migration, distinguish between
active vertical movement affected probably by light cycle, and horizontal migration,
which is more difficult to explain, but is affected by water currents, wind and is mostly
passive.
The above mentioned investigators estimated the total biomass of Peridinium in the
lake during the peak of the bloom up to 20,000 metric tons.
The causes of the bloom are not yet established. However there are indications that
the prevailing form of available nitrogen together with hydrometeorological conditions
determine which organism dominates during the spring period in the lake. (Serruya and
Pollingher, (1970).
PERIDINIUM IN NORTHERN RESERVOIRS
The INWS pumps annually from Lake Kinneret some 350 million cubic meters of
water. From the previously mentioned figure of the biomass ofPeridinium'm the lake and
from algal concentrations in the pumped water we estimate that 500 — 1,000 metric tons
of Peridinium cells enter the INWS during one year. From this total algal mass some 100
- 200 tons settle in each of the three northern reservoirs of the system: Tsalmon
reservoir, settling basin and Eshkol reservoir.
At the bottom of the reservoirs the algal cells are decomposed. First the inner parts of
the cell are degraded and empty thecas of alga remain in the mud. These shells built from
polysaccharides are more persistent, but in a few weeks they are also broken down by
microorganisms. We isolated two species of Myxobacteria and one Nocardia which were
able to decompose Peridinium thecae.
Decomposition of Peridinium and other organic material by microorganisms at the
bottom of the reservoirs causes oxygen depletion in the sediment and a gradient in
dissolved oxygen in the mud-water interface (Leventer & Eren, 1970). Under these
conditions a blue-green alga Oscillatoria chalybea developed on the bottom. This alga
synthesises odorous metabolites which gave the water an unpleasant musty and earthy
taste and odor. The outbreak of taste and odor was especially conspicuous in the
summers of 1966 and 1967 when many consumers complained about the quality of
water. Each summer the reservoirs were drained to stop the taste and odor. In addition to
loss of water due to drainage, it required extra costs in man-power and equipment. Since
1968 the intensity of the nuisance has decreased, but also in the following summers there
were some complaints about malodorous water. There is evidence that this improvement
was due to development of a fish population and especially of the bottom feeding fish
Tilapia aurea.
197
PERIDINIUM BLOOMS IN LAKE KINNERET
Blooms of Peridinium have been recorded since the lake has been systematically
investigated e.g. in the last 25 years (Kimor and Pollingher, 1965). But fishermen recall
discolored water in certain seasons of the year as early as they can remember.
The bloom starts usualty in January, reaches its peak in March to May and terminates
in June. The above table summarizes data on the occurrence of blooms in the lake during
the years 1965 - 1970.
During the bloom there is no uniform distribution of the algal mass in the lake. The
algae tend to concentrate in patches of few hundred meters in diameter. Here one can
find concentrations of Peridinium an order of magnitude higher than the average. These
patches are not defined in shape and size as there is permanent migration of the algal
population. Berman and Rodhe (1970) who studied this migration, distinguish between
active vertical movement affected probably by light cycle, and horizontal migration,
which is more difficult to explain, but is affected by water currents, wind and is mostly
passive.
The above mentioned investigators estimated the total biomass of Peridinium in the
lake during the peak of the bloom up to 20,000 metric tons.
The causes of the bloom are not yet established. However there are indications that
the prevailing form of available nitrogen together with hydrometeorological conditions
determine which organism dominates during the spring period in the lake. (Serruya and
Pollingher, (1970).
PERIDINIUM IN NORTHERN RESERVOIRS
The INWS pumps annually from Lake Kinneret some 350 million cubic meters of
water. From the previously mentioned figure of the biomass ofPeridinium'm the lake and
from algal concentrations in the pumped water we estimate that 500 — 1,000 metric tons
of Peridinium cells enter the INWS during one year. From this total algal mass some 100
- 200 tons settle in each of the three northern reservoirs of the system: Tsalmon
reservoir, settling basin and Eshkol reservoir.
At the bottom of the reservoirs the algal cells are decomposed. First the inner parts of
the cell are degraded and empty thecas of alga remain in the mud. These shells built from
polysaccharides are more persistent, but in a few weeks they are also broken down by
microorganisms. We isolated two species of Myxobacteria and one Nocardia which were
able to decompose Peridinium thecae.
Decomposition of Peridinium and other organic material by microorganisms at the
bottom of the reservoirs causes oxygen depletion in the sediment and a gradient in
dissolved oxygen in the mud-water interface (Leventer & Eren, 1970). Under these
conditions a blue-green alga Oscillatoria chalybea developed on the bottom. This alga
synthesises odorous metabolites which gave the water an unpleasant musty and earthy
taste and odor. The outbreak of taste and odor was especially conspicuous in the
summers of 1966 and 1967 when many consumers complained about the quality of
water. Each summer the reservoirs were drained to stop the taste and odor. In addition to
loss of water due to drainage, it required extra costs in man-power and equipment. Since
1968 the intensity of the nuisance has decreased, but also in the following summers there
were some complaints about malodorous water. There is evidence that this improvement
was due to development of a fish population and especially of the bottom feeding fish
Tilapia aurea.