Sunday 12 May 2013


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
g/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 

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