INTRODUCTION:

A lake is a large body of water surrounded by land, inhabited by various aquatic life forms. Lakes are also subjected to various natural processes taking place in the environment like the hydrologic cycle. With unprecedented developmental activities, human beings are responsible for choking several lakes to death. Storm water runoff and discharge of sewage into the lakes are few of the common causes where various nutrients enter the aquatic ecosystems resulting in their death.

Of all the water quality issues facing lakes everywhere, eutrophication is of great concern. Eutrophication is a term used to describe the aging of a lake, resulting due to the accumulation of nutrients, sediments, silt, and organic matter in the lake from the surrounding watershed. It describes the biological reaction of aquatic systems to nutrient enrichment, the eventual consequence of which is the development of primary production to nuisance proportions (Marsden, 1989). The main cause is excessive loading of phosphorus and nitrogen resulting in high algal biomass, dominance by cyanobacteria and loss of macrophytes (Jana and Das, 1995). It is beyond the scope of any monitoring program to sample for every condition in a lake. Therefore, an initial task is required to decide where to focus the sampling efforts.

Eutrophication is accelerated as a result of human activity in the watershed and if proper controls are not in place, pollutants from agricultural, urban, and residential developments can easily be carried into lakes and their tributaries. Symptoms of human-induced eutrophication (cultural) are:

Generally there are two phases in eutrophic water, a macrophyte dominated stage and a phytoplankton dominated stage. Each stage is presumed to be stable within a range of nutrient concentrations and a reduction in nutrient concentration alone is often insufficient to switch from phytoplankton to macrophytes.

According to Sincero and Sincero (1999), eutrophication is the result of a very slow process of natural sedimentation of microscopic organisms, which takes geologic time to complete. The completion of the process results in the extinction of the water body. The concept of nutrient loading as a factor controlling lake productivity or trophic status has been one of the most successful theories in limnology and has stimulated much discussion and research. According to Vollenweider (1976), this concept has a great impact on all subsequent eutrophication research and lake management. There is several other lake conditions that could be a potential focus for a monitoring program. Four notable factors are:

Each of these conditions has the potential to severely affect the water quality and recreational use of a lake. The following sections provide a background on each of the lake conditions that could be considered for a monitoring program.

ALGAE

Algae are photosynthetic plants that contain chlorophyll and have a simple reproductive structure but do not have tissues that differentiate into true roots, stems, or leaves. They do, however, grow in many forms. Some species are microscopic single cells; others grow as mass aggregates of cells (colonies) or in strands (filaments). Some of them even resemble plants growing in the lake bottom. The algae are an important living component of lakes as they:

AQUATIC PLANTS

Aquatic plants have true roots, stems, and leaves. They too are a vital part of the biological community of a lake. Unfortunately, like algae, they can overpopulate and interfere with lake use. They can be grouped into the following four categories:

Through photosynthesis, aquatic plants convert inorganic material to organic matter and oxygenate the water. They provide food and cover for aquatic insects, crustaceans, snails, and fish. Aquatic plants are also a food source for many animals. In addition, waterfowl, muskrats, and other species use aquatic plants for homes and nests. Aquatic plants are effective in breaking the force of waves and thus reduce shoreline erosion. Emergent plants trap sediments, silt, and organic matter flowing off the watershed. Nutrients are also captured and utilized by aquatic plants, preventing them from reaching algae in the open portion of a lake.

DISSOLVED OXYGEN

The amount of oxygen in the water is an important indicator of overall lake health. In fact, much information can be gathered about a lake by examining just this parameter. Oxygen plays a crucial role in determining the type of organisms that live in a lake. Some species, such as trout, need consistently high oxygen concentrations to survive. Other aquatic species are more tolerant of low or fluctuating concentrations of oxygen.

Oxygen is supplied naturally to a lake by:

Oxygen is easily dissolved in water. In fact, it is so soluble that water can contain a greater percentage of oxygen than the atmosphere. Because of this phenomenon, oxygen naturally moves (diffuses) from the air into the water. Aeration of the water surface by winds and waves enhances this diffusion process. Vertical mixing of the water, aided by winds, distributes the oxygen within the lake. In this manner, it becomes available to the lake's community of oxygen-breathing organisms. Water temperature affects the capacity of water to retain dissolved oxygen. Cold water can hold more oxygen than warm water. Therefore, a lake will typically have a higher concentration of dissolved oxygen during winter than summer.

SEDIMENT DEPOSITION

The gradual filling-in of a lake is a natural consequence of eutrophication. Streams, storm water runoff, and other forms of moving water carry sand, silt, clay, organic matter, and other chemicals into the lake from the surrounding watershed. These materials settle out once they reach quieter waters. The rate of settling is dependent on the size of the particles, water velocity, density, and temperature.

The sediment input to a lake can be greatly accelerated by human development in the watershed. In general, the amount of material deposited in the lake is directly related to the use of watershed land. Activities that clear the land and expose soil to winds and rain (e.g., agriculture, logging, and site development) greatly increase the potential for erosion. These activities can significantly contribute to the sediment pollution of a lake unless erosion and runoff is carefully managed. Sediment material from the watershed tends to fertilize aquatic plants and algae because phosphorus, nitrogen, and other essential nutrients are attached to incoming particles. If a large portion of the material is organic, dissolved oxygen can decrease as a result of respiration of decomposers breaking down the organic matter.

Sedimentation also can ruin the lake bottom for aquatic insects, crustaceans, mussels, and other bottom-dwelling creatures. Most important, fish spawning beds are almost always negatively affected. The input of sediments to a lake makes the basin shallower, with a corresponding loss of water volume. Thus, sedimentation affects navigation and recreational use and also creates more fertile growing space for plants because of increased nutrients and exposure to sunlight.

SEDIMENT TURBIDITY

Not all sediment particles quickly settle to the lake bottom. The lighter, siltier particles often stay suspended in the water column or settle so lightly in the bottom that they can be easily stirred up and resuspended with a slight water motion. This causes the water to be turbid and brownish in appearance. Sediment blocks light from penetrating into the water column. It also interferes with the gills of fish and the breathing mechanism of other creatures.

LAKE ACIDIFICATION

Acidity is a measure of the concentration of hydrogen ions on a pH scale of 0 to 14. The lower the pH the higher is the concentration of hydrogen ions. Substances with a pH of 7 are neutral. A reading less than 7 signifies acidity. If the pH is greater than 7, it is basic (alkaline). Because the pH scale is logarithmic, each whole number increase or decrease in the 0 to 14 scale represents a 10-fold change in acidity or alkalinity. Acidity may also occur in lakes due to drainage that passes through naturally acidic organic soils. These soils may become more acidic through land use practices such as logging and mining.

BACTERIOLOGICAL CONDITIONS AT BEACHES

The sanitary quality of bathing sites is a special concern to swimmers. There are a wide variety of disease-causing bacteria, viruses, parasites, and other microorganisms that can enter the water and be transmitted to humans. Some are indigenous to natural waters. Others are carried from wastewater sources including septic systems and runoff from animal and wildfowl areas. Infected swimmers themselves are also a source of pathogens.

The ideal way to determine potential health hazards at natural bathing sites is to test directly for disease-causing organisms. Unfortunately, the detection of these organisms requires very complex procedures and equipment. In addition, there are hundreds of different kinds of pathogens; to test for each one would be impractical. Most public health officials, therefore, simply test for the presence of an indicator organism. The relative abundance of the indicator organism in a sample can serve as a warning of the likely presence of other, more dangerous pathogens in the water. The indicator organisms most often chosen for monitoring are fecal coliform bacteria or enterococci bacteria. The latter group of bacteria is more disease-specific and may be most appropriate for routine sample analysis.

CASE STUDY ON UPTAKE OF HEAVY METALS IN WATER HYACINTH INTRODUCTION:

The concept that water hyacinth (Eichornia crassipes) can be used as a natural aquatic treatment system in the uptake of heavy metals is explored. Water hyacinth, most of the time is considered to be a weed that is responsible for choking lakes to death. It is an aquatic plant that grows on the surface of the water body, with the shoot system above the water level and the roots developing in the water. The shoot system covers the surface of the water body to capture sunlight thereby obstructing the entry of the sunlight into the water, which is required by the algae and other organisms in the water. This leads to a reduction in the growth of algal population. The roots affect the free movement of the aquatic fauna in the water. However, the water hyacinth captures all the excess nutrients present in the water body and prevents it from reaching the algae. It also over-populates in a very short duration. Water hyacinth grows profusely in presence of nutrients that are mainly responsible for its growth.

OBJECTIVE:

The presence of heavy metals in the aquatic systems is increasing at an alarming rate due to the increased human activities. The World Health Organisation (WHO) has set standards for the maximum permissible limits for few of the heavy metals in both aquatic life and drinking water (Table 1).

TABLE 1: MAXIMUM PERMISSIBLE LIMIT FOR SOME HEAVY METALS (WHO STANDARDS)

The major objective of the study was to evaluate the uptake rate of different heavy metals by water hyacinth under varied environmental conditions. This included the concentration and contact time of the heavy metal uptake, characterization of wastewater and heavy metal uptake by various parts of the plant. It also evaluated the influence of water hyacinth on the removal of other wastewater quality parameters.

MATERIALS AND METHODS:

The domestic wastewater near the Kukkarahalli lake was used for the study. This was characterized for 19 parameters as shown in Table 2 (APHA, 1995). There were four heavy metals that were chiefly concentrated upon viz., Chromium, Nickel, Lead and Zinc. The experiments were basically conducted in laboratory scale batch experiments. For this purpose plastic bucket of 15-liter capacity was used. The initial concentrations for individual experiments were from 0.1 - 20 mgL-1 and for combined experiments it was from 10 - 60 mgL-1. To study the uptake of heavy metals by various parts of the plant the initial dry weight of the plants were measured accordingly. The batch experiments were done for pure culture in one batch using tap water. In the other batch experiment young (20-25 days old) and mature (40-50 days old) plants were grown using the wastewater in the laboratory scale reactors.

TABLE 2: CHARACTERISTICS OF WASTEWATER BEFORE TREATMENT

STUDY AREA - KUKKARAHALLI LAKE:

Kukkarahalli lake's versatility in nature, strategic position in Mysore city, its enhanced beauty, environmental significance and the controversies surrounding it aroused interest in its status. The lake is located in the Manasagangothri campus in Mysore. The geographical location of the place is 76° 40¢ East longitude and 12° 8¢ North latitude. The 'J' shaped lake spread has a volume of 420,000 cubic meters over 17 hectares, the maximum depth being 5 m. Water is held by a raised east-west bund on one side. The soil in and around ranges between sandy loam to clay loam. This lake is exposed to full sunlight and wind action through out the day.

Domestic wastewater enters from the northern side of the lake. Hence a temporary bund is built over it to avoid the direct flow of the wastewater into the lake. The lake seems to be accumulating nutrients coming through the wastewater, mainly phosphorus and nitrogen, which promote the growth of algae and other aquatic plants. This is accelerating eutrophication and as a result the lake is dying day by day. Apart from this, the lake is gradually losing its storage capacity, mainly on account of siltation, which is accelerated with profuse growth of water hyacinth and other weeds. This has been adversely affecting the fish production, recreational activities and hence the aesthetic value of the lake.

RESULTS AND DISCUSSION:

The wastewater was characterized for all the parameters that were analysed before treatment. The removal of heavy metals in the wastewater was very encouraging. All the four heavy metals were below detection limits, which confirmed the uptake of these heavy metals by water hyacinth. There was also significant removal of bio-chemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), nitrates and phosphates. The removal efficiency of BOD, COD and TSS were respectively 90 %, 70 % and 80 %. The characteristic of the wastewater after treatment is given in Table 3.

TABLE 3: CHARACTERISTICS OF WASTEWATER BEFORE TREATMENT AFTER TREATMENT

It was found that 90 % of the metal was absorbed in the root system and 10 % in the root and shoot system. The influence of initial metal concentration on growth of plants for all metals reached a saturation concentration at 12 mgL-1. Of all the heavy metals nickel was found to be more toxic. The mature plants were highly resistant to higher metal concentrations than young plants. The young plants could not sustain the increased metal concentrations. There was a significant influence on uptake and growth of mature plants at higher metal concentrations. The influence of contact time on the heavy metal uptake was studied for a period of 15 days. There was a rapid uptake in the first five days of contact time. This slowly decreased with time until it reached saturation on the 15th day.

As can be seen from the results, the usage of water hyacinth as a natural aquatic treatment system is very encouraging. But the usage has to be just. In most places water hyacinth is a menace and is responsible for choking lakes. The study recommends a more detailed study for a proper design of a natural aquatic treatment plant using water hyacinth. In the current case, water hyacinth has grown profusely towards the northern side. There have been raised voices for the removal of water hyacinth completely from the water body. This will have an impact on the Purple Moorhens and other waders that wade around these plants in the Kukkarahalli lake. If all the water hyacinth were removed it would cause an increase in the amount of nutrients resulting in algal blooms, which are already affecting the lake.

Hence an efficient monitoring program for the lake water quality is felt necessary. This should chiefly aim at characterising the wastewater entering the lake and suggesting suitable measures of controlling it. The program should be able to suggest the amount of aquatic plants to be removed if found in excess. Further, the restoration of this lake can improve the ground water table and improve the aquatic life in the lake.

ACKNOWLEDGEMENT:

The authors are very grateful for the support and encouragement given by Dr. T.P. Halappa Gowda, Professor and Head and Dr. K.S. Lokesh, Assistant Professor, Department of Environmental Engineering, S. J. College of Engineering, Mysore. The authors also thank all the faculty members, students and staff of the Department of Environmental Engineering, S. J. College of Engineering, Mysore.

REFERENCES:

Address:

1.) Department of Environmental Engineering,
Sri Jayachamarajendra College of Engineering,
Mysore-570 006