Udaipur Lakes
: Problems and Options for Eco-remediations for
Conservation
Udaipur- the lake city attracts thousands of tourists from India and
abroad. These lakes are indeed perfect water harvesting structures which were
designed and constructed by the ex-rulers of mewar state. Earlier to 1970s
these lakes were catering the need for irrigation waters. However, drinking
water being the first priority, since last over four decades these are used as
a source of raw water for drinking water supplies.
In general, the
Udaipur lake system comprising of lakes Picchola, Swaroop Sagar, rang Sagar,
Khmaharia talab and Dudh talai together with Fatehsagar is an integral part of
Berach river. Therefore, this lake system is ultimately connected to the great ganges river basin
through Banas, Chambal and Yamuna rivers.
Lake environment then and now : Till 1970s
the lake environment was relatively having meagre pollution because of limited
human interferences of various kinds. However, with growing human settlement
along the lake shores especially around Pichhola lake system and subsequent
discharge of domestic sewage effluents into lake has accelerated the process of
nutrient enrichment (Eutrophication) to an alarming level.
The lakes of Udaipur
are known to harbour rich biodiversity which is evident from several research
studies. Six major research projects sponsored by Department of
Environment(Jaipur & N.Delhi),Indian Council of Agricultural Research,
N.Delhi, dept. of science & Technology, Jaipur were conducted on Udaipur
lakes. Besides these, more than 30 M.Sc. and Ph.D. thesis have been submitted
on various lakes of Udaipur. a variety
of flora and fauna as listed below :
Biota
|
Numbers
|
Phyloplankton
|
30
|
Zooplankton
|
108
|
Benthos
|
37
|
Macrophytes (Aquatic weeds)
|
17
|
Fishes
|
39
|
Birds
|
280
|
Besides such a rich biodiversity stated above, Reptiles and Mammals
(Crocodiles,turtles, snakes, otters etc.) were also available abundantly . Occurrence of such top carnivores earlier in
the lake ecosystem is a valid evidence of prestine condition and ecological
health of Udaipur lakes.
With growing human interferences of various kinds the environmental
scenario in Udaipur lakes has changed mainly because of following factors :
• Deforestation in the catchments & subsequent
silting of lakes due to induced soil erosion.
• inflow of nutrients by way of disposal of solid
& liquid (domestic sewage) pollutants.(In 1980 about 40 points were
identified where sewage channels were discharging sewage into pichhola lake
system).
• For checking pollution in lakes an effluent
diversion scheme was implemented in Picchola lake system wherein a drainage
line was installed along the lake periphery. However, it has some technical
problems related to design, establishment and maintenance. This some times
results in leakages and overflow of sewage effluents into lake thus stimulating
excessive weed infestation and algal growths. Under NLCP yet another sewage
scheme has been designed with the prime objective of pollution control in Udaipur lakes.
• Encroachment along shores of lake thus reducing
the water holding capacity of lakes.
• Increased bathing and washing activities and use
of detergents thus adding more amount of phosphorus into lake ecosystem.(Soap
which was used traditionally is relatively more eco-friendly as it easily gets
biodegraded as against detergent which is more injurious to aquatic life ).
• Increased use of fertilizers & pesticides in
agriculture in the catchment of lakes as well as in exposed lake bed during
summer months or years of low rainfall also aggravated the nutrient enrichment.
This also enhances the process of eutrophication especially due to addition of
organic and inorganic fertilizers.
• It is also noticed that many a times lakes are
used as a convenient site for dumping of garbage. This degrade water quality
and fills up the lake basin at exceedingly high speed. Desilting operations in
Udaipur lakes were also made by the citizen groups and under NLCP. Desilting
certainly helps in ecorestoration leading to increased biodiversity, water
holding capacity and improvement in water quality.
• Due to erratic rainfall the lakes are not
receiving surplus water every year from the catchment for overflow. Under such
situation, all the nutrients and pollutants added to lake from outside
sources(Allochthonous) or generated within the lake(Autochthonous) further
aggravates the problem of eutroplication.
• For drinking water supplies water is drawn from
the lakes(20 MLD). This reduces the volume of water mass. Besides this, water
losses also occur due to seepage and
evaporation. Such reductions in lakes may be about 2 meters during one hydrological cycle.
• Due to altered water quality scenario and
degradation in water quality as a result of organic loading, biodiversity of
aquatic flora and fauna has been affected adversely. This causes reduction in
capacity of lake ecosystem to cope up with increased organic pollution. Thus,
notably some species of fishes have declined drastically due to failure of
their breeding in the lake ecosystem. Labeo
gonius, Puntins sarana, Tor Khudree are
examples of such dwindled fishes in Udaipur lakes.
• Lakes maturation process is accelerated : Because of various kinds of human interferences
stated above the process of lake maturation is accelerated. This in general
speeds up the nutrient enrichment in lakes which may reduce the life span of
lakes. Unless suitable remedial measures at required scale are taken, the lakes
of Udaipur are reported to loose their entity as lakes in another 70-90 years
as evident from sediment studies.
• During
lake maturation process lake passes through various stages of trophy(Nutrient
levels). Thus, the life span of any lake is grossly influenced by natural as
well as anthropogenic factors. Obviously, anthropogenic factors play a
significant role in lake maturation process. Fortunately, there are several
ecoremedial measures available for slowing, halting or even reversing the
eutrophication in lakes for achieving desired trophic state.
• Lake maturation process
Oligotrophy Mesotrophy Eutrophy Dystrophy Bog lake
|
The Characterstic
features of the main trophic stages are given below :
Table : Trophic state index (TSI) as
per cartson(1997) :
Trophic state
|
TSI
|
Secchi disc
(m)
|
Total Phosphorus
(µg/l)
|
Chlorophyll
(µg/l)
|
Oligotrophic
|
0
10
30
|
64
32
08
|
0.75
1.50
06
|
0.04
0.12
0.94
|
Mesotrophic
|
40
50
|
04
02
|
12
24
|
2.6
6.4
|
Eutrophic
|
60
80
100
|
1
0.25
0.062
|
48
219.0
768
|
20
154
1183
|
Considering the TSI
proposed by Carlson(1997) the lakes of Udaipur fall under eutrophic category
whereas it is desirable to maintain these lakes as mesotrophic lakes. This
would mean that the present nutrient level especially phosphorus has to be
monitored(02-04µg/l) and managed effectively so that algal biomass(phytoplankton) is
reduced to make the water more transparent(water clarity of 2-4 meters). This
obviates the need for eutrophication reversal by appropriate means. There are
several examples where the process of eutrophication has been not only halted
but even reversed. The recommended processes of eutrophication reversal are
following :
• Dilution : by augmenting inflow of pollution free water
the accumulated nutrients, obnoxious
gases can be flushed out. This helps in depollution as well as for restoring
the biodiversity. This also helps in improving sanitary condition of bottom
sediment and overlying water mass.
• Diversion
of effluents : By and large,
nitrogen and phosphorus govern the process of biological production in lakes.
Thus, if the supply of these nutrients is checked in lakes, this helps in
controlling eutrophication. By this way excessive growth of algae and aquatic
weeds can be checked.
• Desilting : In
eutropic lakes, the basin is filled with silt and associated nutrients and
pathogens. Thus, by removing superficial stratum of silt not only the water
holding capacity of lake can be increased but this will also improve the
sanitary condition of lake ecosystem. However, it would be appropriate that
large scale desilting (wet or dry type)
should be carefully planned on the basis of sediment core studies.
• Aeration : This is effective method for algal control and
oxygen enrichment. As the surface aerators (Fountains) stimulate water loss by
evaporation, it is appropriate to use bottom aerators. Aeration also helps in
biodegradation of accumulated organic matter. In well oxygenated water release
of phosphorus from the sediment is also limited which helps in efficient
nutrient management in the lakes.
• Withdrawal
of hypolimnetic water : As most nutrients remain accumulated in the
bottom sediment and associated water(Hypolimnetic), it is better to discharge
surplus water from bottom instead of surface. This helps in reducing nutrient
levels in lake.
• Periodical
weed harvesting : Weeds
efficiently absob nutrients from water. Thus, periodical weed removal can be an effective tool for harvesting excess
nutrients from the lake. In many lakes it is regularly practised. However,
floating type of weeds such as water hyacinth, Pistia, Alligator weed,
Nymphoides, Ipomea, Typha etc. should be removed on priority and used as suitable
resource especially to replace pulp of
trees. Submerged aquatic plants such as Hydrilla, Vallisneria, Najas, Potamogeron,
Ceratophyllum etc. commonly found in Udaipur lakes may be maintained in
justifiable manner in the littoral zone of lakes as these plants not only
absorb nutrients & obnoxious gases from water but provide dissolved oxygen
as a product of photosynthesis. Thus, in marginal littoral zone submerged
aquatic plants can be regularly cut and harvested by human power or machines.
Total removal of submerged aquatic plants from lake by uprooting these may lead
to production of intense algal blooms
especially the blue-greens which may degrade the water quality and adveresely
affect its potability. Certain herbicides and chemicals can also kill the weeds
but these are ueseful only for small fishery waters and as such not recommended for large lakes and
drinking water resources.
• Biological
control & fisheries management : These are eco friendly methods for controlling algae or aquatic
weeds. For bio-control of phytoplankton(algae) a Chinese fish Hypophthalmichtyes molitrix has been found very effective. Similarly,
for the control of higher aquatic submerged plants grass carp(Ctenopharyngodon idella) is useful as it
can consume certain submerged weeds and duck weeds double to its own weight
each day. Insect wevils namely Neochaetina
bruchi and N.eichhornie have been also reported to control water hyacinth
as biocontrol measure but indicated limited success in Udaipur lakes. Moreover,
these wevils gradually kills the plant which needs to be removed from the lake
before it starts decomposing in the lake.
Quality fish seed of desirable species in
adequate number should be introduced and harvested in the lakes regularly for
effective nutrient management and ecological balance.
Scientific fisheries activities and technique of
biomanipulation are considered recent
and popular methods for effective nutrient management in lakes. Adoption of
such methods in Udaipur lakes may help to convert pollutants into highly priced
fish protein and yet improving water quality in lake ecosystem.
-Photographs and Article by Dr. L. L. Sharma
