202
Discussion
Reply
The data of Berman indicate that at certain periods of the year phosphorus may be the limiting
factor in the lake. Also our work with unialgal culture of Peridinium shows that availability of
phosphorus affects growth of the alga in lake Kinneret water.
S.U. Hussainy, Australia
Almost all the eutrophic lakes are influenced either culturally or by the salts brought in from the
drainage system. Phosphorus and nitrogen in these lakes are usually present in excess of the normal
requirement of the phytoplankton. According to Sawyer (1960) 10 mg/m
3 of phosphorus is the
critical level for the occurrence of algal blooms. Reference should be made here to the extraordinary
discovery by Rigler (1964a) that the turnover time of ionic phosphorus in the epilimnion of a lake in
summer can be of the order of one minute. In addition to the release of phosphorus from the
sediments during summer stagnation, Zooplankton and phytoplankton contribute phosphates to the
surrounding medium.
Zooplankton influence the phosphorus cycle in a number of ways. They concentrate P
3 2 (Coffin
et al 1949, Rigler 1961) probably by feeding on phytoplankton. However, the assimilation is not
complete (Marshall and Orr 1955) and 10 - 50% of ingested phosphorus is returned in faecal pellets.
This may be returned to solution or lost as pellets and sink from the epilimnion. Phosphorus from the
living or dead Zooplankton is finally returned to solution as inorganic phosphates (Gardiner 1937,
Margelef 1951). Zooplankton take up and release inorganic phosphorus (Rigler 1961) and phosphorus
regeneration in the epilimnion appears to supply the normal requirements of phytoplankton. Rigler
(1964b) calculated that phytoplankton return about 400 times more phosphorus than Zooplankton.
Hargrave and Geen (1968) observed that Zooplankton released twice the daily requirement of
phytoplankton.
All the four forms of nitrogen namely, ammoniacal, organic nitrite and nitrate occur in storm
water, are several agents operating in the lakes themselves and other factors contribute nitrogen.
Nitrogen is also released from sediments, and the biota in the lake assist in recycling this element.
Mackenthun (1962) and Leentveer (1967) discussed the influence of guanotrophy on the
eutrophication of receiving waters. The studies of Ketchum (1961) and Harris (1959) revealed that a
substantial amount of nutrients are excreted directly by Zooplankton. The regeneration of inorganic
nitrogen compound by Zooplankton excreted was computed to be 77% of the average daily
requirement of phytoplankton. Harris and Riley (1956) estimated the ratio in phytoplankton to be
15.7:1. Thus the phytoplankton maintain a higher ratio of N:P in their protoplasm, than in the water.
The Zooplankton N:P ratio is higher than in their food. They must therefore have a lower ratio of N:P
in their excreta (Ketchum 1961). It is likely that the inorganic elements excreted by the Zooplankton
in the euphotic zone are used immediately by the phytoplankton thus eliminating the long delay
which would be required for the slower decomposition of dissolved organic matter. Blue - Green algae
while actively fixing nitrogen excrete combined nitrogen into water, thus producing nitrogen
compounds available to other organisms.
Nitrogen fixation presents a new source of nitrogen which is available to phytoplankton. The decay
of nitrogenous compounds, including nitrogen fixing organisms releases combined nitrogen for use by
other organisms.
Serruya and PoUingher (1971) in attempting to forecast Peridinium blooms in Lake Kinneret infer
that Peridinium is able to develop on the "autochtonous nutrient input" where as Microcystis depends
more on the nutrients brought in through the incoming water.
Microcystis and Peridinium seem to compete for nitrogen. If there is a constant supply of nitrates
Microcystis develop in bloom concentrations. As discussed earlier, the turnover time for
phosphorus is so small, and that the quantity of phosphorus excreted is so much in excess of the
normal requirement of phytoplankton, that the algae probably compete for nitrogen and other micronutrients. Several species recorded in eutrophic lakes in Victoria, Australia - Melosira granulate a
winter species in Lake Kinneret (Serruya and PoUingher 1971) appeared in early winter in Lake
Purrumbete and reached bloom concentrations in late winter (Hussainy 1969), Anabaena also reached
bloom concentrations in winter. Ceratium hirudinella was also recorded in Purrumbete, although it
was present all through the year, it appeared in bloom during late spring and early summer.
Every algal bloom has a feature of its own, but a common feature of dense blooms seems to be a
tendency towards heterogeneous distribution. The heterogeneous distribution of Peridinium in Lake
Kinneret may be due to wind-induced water movements reinforced by the activity of the mobile cells.
Similar blooms of Ceratium hirudinella were recorded during summer in Lake Gorewada, one of the
sources for water supply for the city of Nagpur, India. (Hussainy & Abdul Appa 1970). The problem
created by the bloom Lake Gorewada was overcome by filtering the water through sand-bed filters.
REFERENCES
COFFIN, C.C., HAYES, F.R., JODREY, L.H., WITEWAY, S.G. (1949) - The Exchange of Material in
Discussion
Reply
The data of Berman indicate that at certain periods of the year phosphorus may be the limiting
factor in the lake. Also our work with unialgal culture of Peridinium shows that availability of
phosphorus affects growth of the alga in lake Kinneret water.
S.U. Hussainy, Australia
Almost all the eutrophic lakes are influenced either culturally or by the salts brought in from the
drainage system. Phosphorus and nitrogen in these lakes are usually present in excess of the normal
requirement of the phytoplankton. According to Sawyer (1960) 10 mg/m
3 of phosphorus is the
critical level for the occurrence of algal blooms. Reference should be made here to the extraordinary
discovery by Rigler (1964a) that the turnover time of ionic phosphorus in the epilimnion of a lake in
summer can be of the order of one minute. In addition to the release of phosphorus from the
sediments during summer stagnation, Zooplankton and phytoplankton contribute phosphates to the
surrounding medium.
Zooplankton influence the phosphorus cycle in a number of ways. They concentrate P
3 2 (Coffin
et al 1949, Rigler 1961) probably by feeding on phytoplankton. However, the assimilation is not
complete (Marshall and Orr 1955) and 10 - 50% of ingested phosphorus is returned in faecal pellets.
This may be returned to solution or lost as pellets and sink from the epilimnion. Phosphorus from the
living or dead Zooplankton is finally returned to solution as inorganic phosphates (Gardiner 1937,
Margelef 1951). Zooplankton take up and release inorganic phosphorus (Rigler 1961) and phosphorus
regeneration in the epilimnion appears to supply the normal requirements of phytoplankton. Rigler
(1964b) calculated that phytoplankton return about 400 times more phosphorus than Zooplankton.
Hargrave and Geen (1968) observed that Zooplankton released twice the daily requirement of
phytoplankton.
All the four forms of nitrogen namely, ammoniacal, organic nitrite and nitrate occur in storm
water, are several agents operating in the lakes themselves and other factors contribute nitrogen.
Nitrogen is also released from sediments, and the biota in the lake assist in recycling this element.
Mackenthun (1962) and Leentveer (1967) discussed the influence of guanotrophy on the
eutrophication of receiving waters. The studies of Ketchum (1961) and Harris (1959) revealed that a
substantial amount of nutrients are excreted directly by Zooplankton. The regeneration of inorganic
nitrogen compound by Zooplankton excreted was computed to be 77% of the average daily
requirement of phytoplankton. Harris and Riley (1956) estimated the ratio in phytoplankton to be
15.7:1. Thus the phytoplankton maintain a higher ratio of N:P in their protoplasm, than in the water.
The Zooplankton N:P ratio is higher than in their food. They must therefore have a lower ratio of N:P
in their excreta (Ketchum 1961). It is likely that the inorganic elements excreted by the Zooplankton
in the euphotic zone are used immediately by the phytoplankton thus eliminating the long delay
which would be required for the slower decomposition of dissolved organic matter. Blue - Green algae
while actively fixing nitrogen excrete combined nitrogen into water, thus producing nitrogen
compounds available to other organisms.
Nitrogen fixation presents a new source of nitrogen which is available to phytoplankton. The decay
of nitrogenous compounds, including nitrogen fixing organisms releases combined nitrogen for use by
other organisms.
Serruya and PoUingher (1971) in attempting to forecast Peridinium blooms in Lake Kinneret infer
that Peridinium is able to develop on the "autochtonous nutrient input" where as Microcystis depends
more on the nutrients brought in through the incoming water.
Microcystis and Peridinium seem to compete for nitrogen. If there is a constant supply of nitrates
Microcystis develop in bloom concentrations. As discussed earlier, the turnover time for
phosphorus is so small, and that the quantity of phosphorus excreted is so much in excess of the
normal requirement of phytoplankton, that the algae probably compete for nitrogen and other micronutrients. Several species recorded in eutrophic lakes in Victoria, Australia - Melosira granulate a
winter species in Lake Kinneret (Serruya and PoUingher 1971) appeared in early winter in Lake
Purrumbete and reached bloom concentrations in late winter (Hussainy 1969), Anabaena also reached
bloom concentrations in winter. Ceratium hirudinella was also recorded in Purrumbete, although it
was present all through the year, it appeared in bloom during late spring and early summer.
Every algal bloom has a feature of its own, but a common feature of dense blooms seems to be a
tendency towards heterogeneous distribution. The heterogeneous distribution of Peridinium in Lake
Kinneret may be due to wind-induced water movements reinforced by the activity of the mobile cells.
Similar blooms of Ceratium hirudinella were recorded during summer in Lake Gorewada, one of the
sources for water supply for the city of Nagpur, India. (Hussainy & Abdul Appa 1970). The problem
created by the bloom Lake Gorewada was overcome by filtering the water through sand-bed filters.
REFERENCES
COFFIN, C.C., HAYES, F.R., JODREY, L.H., WITEWAY, S.G. (1949) - The Exchange of Material in