Aquatic ecosystem is the most diverse ecosystem in the world. The first life originated in the water and first organisms were also aquatic where water was the principal external as well as internal medium for organisms. Thus water is the most vital factor for the existence of all living organisms. Water covers about 71% of the earth of which more than 95% exists in gigantic oceans. A very less amount of water is contained in the rivers (0.00015%) and lakes (0.01%), which comprise the most valuable fresh water resources. Global aquatic ecosystems fall under two broad classes defined by salinity – freshwater ecosystem and the saltwater ecosystem. Freshwater ecosystems are inland waters that have low concentrations of salts (< 500 mg/L). The salt-water ecosystem has high concentration of salt content (averaging about 3.5%).

An aquatic ecosystem (habitats and organisms) includes rivers and streams, ponds and lakes, oceans and bays, and swamps and marshes, and their associated animals. These species have evolved and adapted to watery habitats over millions of years. Aquatic habitats provide the food, water, shelter, and space essential for the survival of aquatic animals and plants. Aquatic biodiversity is the rich and harbors variety of plants and animals--from primary producers algae to tertiary consumers large fishes, intermittently occupied by zooplankton, small fishes, aquatic insects and amphibians. Many of these animals and plants species live in water; some like fish spend all their lives underwater, whereas others, like toads and frogs, may use surface waters only during the breeding season or as juveniles.

The study of freshwater habitats is known as limnology. Freshwater habitats can be further divided into two groups as lentic and lotic ecosystems based on the difference in the water residence time and the flow velocity. The water residence time in a lentic ecosystem on an average is 10 years and that of lotic ecosystem is 2 weeks. In lotic ecosystem, the average flow velocity ranges from 0.1 to 1 m/s whereas lentic ecosystems are characterized by an average flow velocity of 0.001 to 0.01 m/s (Wetzel, 2001; UNEP, 1996). The lentic habitats further differentiate from lotic habitats by having a thermal stratification with is created in a lake due to differences in densities. Water reaches a maximum density at 4 0 C, a warm, lighter water floats on top of the heavier cooler water thus creating thermally stratified zones which corresponds to epilimnion, the warm layer, the hypolimnion, the colder layer separated by a barrier called thermocline. The lotic ecosystem is characterized by stream orders depending on the origin and flow and various types of stream pattern namely Dendritic, Radial, Rectangular, Centripetal, Pinnate, Trellis, Parallel, Distributory and Annular, which determines the flooding and soil erosion hazards of the region. However, the basic unity among these ecosystems is that any alteration in the catchment area of these ecosystems will affect the water quality of both lotic and lentic ecosystem. The catchment area is all land and water area, which contributes runoff to a common point, which may be a lake or a stream. The term catchment is equivalent to drainage basin and watershed (Davie, 2002; Tideman, 2000). Physical, Chemical and biological characteristics of lentic and lotic ecosystems are listed in Table 1.

The term lotic (from lavo, meaning ‘to wash') represents running water, where the entire body of water moves in a definite direction. It includes spring, stream, or river viewed as an ecological unit of the biotic community and the physiochemical environment. Lotic ecosystems are characterized by the interaction between flowing water with a longitudinal gradation in temperature, organic and inorganic materials, energy, and the organisms within a stream corridor. These interactions occur over space and time.

Table 1: Physical, Chemical and Biological Characteristics of Lentic and Lotic Ecosystems
The term lentic (meaning ‘to make calm') is used for still waters of lakes and ponds, which offer environmental conditions, which differ sharply with that of the streams. Light penetrates only to a certain depth depending upon turbidity. Temperature varies seasonally and with depth. Because only a small portion is in direct contact with the atmosphere and because decomposition takes place actively at the bottom, the oxygen content of lentic ecosystem is relatively low when compared to the lotic.
The term lotic (from lavo, meaning ‘to wash') represents running water, where the entire body of water moves in a definite direction. These may comprise brooks, streams, rivers and springs. Brook is a term used for the small body of water while river is a term used for a relatively large natural body of water. The stream is generally designated as smaller than a river but bigger than a brook. Spring is an issue of water from the earth, which takes the form of a stream on the surface (Kalff, 2002; Wetzel, 2001).

Physical characteristics

Stratification and Water movement: The presence of stratification is created by the difference in density resulting from differential heating of lake waters. In the presence of strong winds, the lake water is well mixed if the temperature is uniform at more than 4 0 C. If the temperature is not uniform, due to density difference, the lake is stratified into epilimnion, hypolimnion and thermocline. According to the circulation patterns, lakes are thus classified into amictic, meromictic, holomictic, oligomictic, monomictic, dimictic and polymictic lakes. Thus the water movement is strongly influenced by wind pattern and temperature. Often, the movement of water in lake is multidirectional.
Currents and stream pattern: The velocity of current in running waters depends on the nature of their gradient and substrates. In contrast to lentic waters, wind has little influence on currents in running waters. The continual downstream movement of water, dissolved substances and suspended particles is depended primarily on the drainage basin characteristics. There are many stream patterns according to this gradient and they include dendritic, rectangular, radial, trellised, parallel, annular, deranged and pinnate. The stream pattern determines the soil erosion hazards.
Suspended solids: Materials in suspension can be divided into two types depending on origin. Autochthonous matter, which is generated from lake itself, and allochthonous matter originating from outside the lake and brought into it. The autochthonous matter is mainly derived from growth of algae and macrophytes. The allochthonous organic matter is derived from peat, fallen leaves and other decaying types of vegetation.
Suspended solids: The erosion, transportation and deposition of solid materials within a running water is closely linked to current velocity. The organic matter in suspended form is mainly from litter that is brought into the river. The other suspended matter includes inorganic matter such as silt, detritus and materials removed from the sediments, which cause turbidity to the water.
Light: The depth to which rooted macrophytes and attached algae can grow on suitable substrates is largely controlled by the spectral composition and intensity of light there. According to penetration of light, a lake can be divided into tropogenic zone and tropolytic zone. Light determines the primary productivity of lake and phytoplankton inturn determine the depth of light penetration.
Light, temperature and runoff: The penetration of light in running waters is strongly influenced by the turbidity. In addition to scattering by particles, there is also a loss due to absorption by water. If water is clear or hollow adequate light can reach the substrate and photosynthesis can take place. The stratification due to temperature is absent and due to more contact with air, the temperature of a stream follows that of air temperature. The temperature of lotic water is influenced by many factors and they include: Origin, depth, substrate, tributaries, exposure and time of the day. The contribution of surface and ground waters to the flow of stream varies according to a number of factors especially local geology and climate. Running water fed mainly by surface runoff have variable flow and may spate with each heavy rainfall and those fed largely by ground water are usually regular in flow.

Chemical characteristics:

Dissolved gases:

The quantities of oxygen in a lake depend on the extent of contact between water and air, on the circulation of water and on the amounts produced and consumed within each lake. The thermal stratification produces a marked difference in oxygen levels. The oxygen in the hypolimnion is always low and the surface layer has adequate oxygen. The lake productivity also plays an important role and the balance between primary production and respiration influences the oxygen level. In the bottom sediments it may be completely anoxic and gases such H 2 S and CH 4 are produced. The free carbondioxide plays an important role in the regulation of pH. In well-mixed waters, the pH and CO 2 concentrations are uniform from surface to bottom. In stratified lakes, the algae and macrophytes reduce the amount of CO 2 , thus increasing the pH, whereas in deeper water, there is a tendency for increase in the carbondioxide and calcium carbonate and reduction in pH.

Dissolved gases:

Of the dissolved gases present in running waters, oxygen is the most abundant and important. The concentration of oxygen is high due to turbulence and mixing. Low concentration usually indicates organic pollution. However, there is a difference in the oxygen concentration in diurinal basis. The amount of oxygen present is related to current, the water temperature and the presence of respiring plants and animals. The carbondioxide content of the running waters tend to be scarce due to constant turbulence of water and its frequent contact with air.

Dissolved solids:

The quantity of dissolved solids is dependant on the stratification of the lake. It is also dependant on the water inlet that comes to the lake. Thus the dissolved solids content of standing water is dependant on the catchment area. The dissolved solids are also fixed by phytoplankton. Major nutrients like nitrogen, phosphorus, iron, silicon and others may be depleted and so limit production or alter the composition of algal community.

Dissolved solids:

The dissolved solids present in a river may vary greatly from source to mouth, usually increasing in downstream direction. The effect of rainfall also plays an important role. The quality and quantity of solids dissolved from the ground depend on the character of soil and rocks in the substratum (Maitland, 1990).

Biological characteristics:

The biological characteristics of still water bodies may be broadly classified into – pelagic and benthic systems. Benthic system is subdivided into littoral and profundal types. The species composition of communities of all those types is greatly influenced by the nutrient status of the water concerned. The pelagic habitat is that of the open water away from the influence of shore or bottom substrate, while benthic habitat is associated with the substrate of the lake. The littoral habitat is extending from the shoreline out to the deeper water. The plankton community, phytoplankton and zooplankton, occupy the regions of high light intensities namely on the surface layer of pelagic zone and the littoral zone. Some of the zooplankton members also inhabit the benthic zone feeding on detritus and sinking phytoplankton. Fishes occupy the littoral, pelagic and occasionally profundal zones, when the dissolved oxygen content in the lake is high. Macroinvertebrates are confined to the benthic zone.
In the lotic habitats, the water moves continually in one direction. The current is more pronounced at the surface than in the bottom substrate. Hence, the bottom substrate conditions are similar to lentic habitats. Often the plankton community is at the mercy of currents. In riffles and pools, the plankton exhibit the characteristics similar to lentic ecosystem. The fishes are highly adopted to resist water currents. Since the dissolved oxygen levels are high throughout the water column due to water turbulence, the fishes are distributed from surface to bottom substrate and often among the rocks (Moss, 1998).

As in the terrestrial ecosystem, the main source of energy in aquatic ecosystem is the solar energy. The transfer of solar energy from one community to another takes a specific path. The solar energy is trapped by the phytoplankton, the producers which inturn are consumed by the zooplankton, which are primary consumers and secondary consumers are the macroinvertebrates and planktivorous fish, which are consumed by large fishes. At each step of energy transfer, a proportion of energy is lost as heat. Thus the transfer of food energy from the source (phytoplankton) through a series of organisms that consume and are consumed is called as food chain. Food chains are of two basic types, the grazing food chain, which starts from the phytoplankton to the herbivores and carnivores and the detritus food chain that goes from non-living organic matter into microorganisms and then to detritus feeding organisms and their predators. These food chains are interconnected and often this interlinking pattern is called the food web (Figure 1).

Figure 1: Food web in an aquatic ecosystem


The term “Plankton” refers to those minute aquatic forms which are non motile or insufficiently motile to overcome the transport by currents and living suspended in the open or pelagic water. The planktonic plants are called phytoplankton and planktonic animals are called zooplankton (APHA, 1985). Phytoplankton are the base of aquatic food webs and energy production is linked to phytoplankton primary production. Excessive nutrient and organic inputs from human activities in lakes and their watersheds lead to eutrophication, characterized by increases in phytoplankton biomass, nuisance algal blooms, loss of water clarity from increased primary production and loss of oxygen in bottom waters. The freshwater phytoplankton of the Indian region belongs to the following classes:

•  Cyanophyceae: Cyanophyceae comprises of prokaryotic organisms popularly known as blue-green algae. They are like gram-negative bacteria and due to the nature of the cell wall, cell structure and capacity to fix atmospheric nitrogen these are considered as bacteria and named cyanobacteria. However, they possess the oxygen evolving photosynthetic system, chlorophyll a accessory pigments and thallus organizations resembling other algae. They occur abundantly in freshwater habitats along with other groups of algae. Cyanophyceae members are broadly classified into coccoid and filamentous forms. The coccoid forms range from single individual cell to aggregates of unicells into groups or in regular or irregular colonies and pseudoparenchymatous conditions. The filament forms range from simple uniseriate filaments to heterotrichous filaments, which may be differentiated into heterocysts and akinetes (spores). These are truly cosmopolitan organisms occurring in habitats of extreme conditions of light, pH and nutritional resources. They abound various types of natural and artificial aquatic ecosystems.

•  Chlorophyceae: Chlorophyceae (green algae) constitutes one of the major groups of algae occurring in freshwater habitats. The cells are typically green in colour due to the presence of chlorophyll a and b. The cells contain chloroplast of various shapes, which are dispersed differently in each group of organisms. The chloroplast also contains pyrenoids. In majority of the organisms there is a single nucleus but some genera are multinucleate. Flagellated cells are common either in the vegetative phase or reproductive units. Chlorophyceae is generally divided into several orders based on the diversity of the thallus.

•  Euglenophyceae: The members are single cells, motile found swimming with the help of usually one prominent flagellum and in some cases with two flagella. In the anterior portion a gullet is visible and there are many chloroplasts in the autotrophic forms and the chloroplasts vary in shape. Euglenoid cells are covered by a proteinaceous pellicle and at times help the organisms attain various shapes. These are widely distributed in all types of water bodies specifically in organically rich aquatic ecosystems.

•  Bacillariophyceae: The members belonging to this class are popularly known as diatoms. All are basically unicellular, in some cases become pseudofilamentous or aggregated into colonies. The cell wall of diatoms is impregnated with silica and several diatoms have been well preserved as microfossils. The diatom cell is also called as frustule and the classification of diatoms is based on the pattern of ornamentation on the wall of the frustule. The cells have either bilateral or radial symmetry. The frustules are composed of two halves, epitheca and hypotheca and connecting girdle bands. The valve surfaces have several types of markings. Radial symmetry forms are grouped as Centrales and bilaterally symmetric ones are Pennales.

•  Dinophyceae: The members are unicellular motile cells with two flagella one located in the transversely aligned groove or furrow and other in a longitudinally arranged furrow. One is considered to propel the cell and the other is called the trailing flagellum. The cells while moving forward also get rotated by the flagellar action. The motile cells have a thick pellicle instead of a cell wall, which sometimes becomes very thick, and called theca. Certain genera have thecal plates on their outer covering and called as unarmoured dinoflagellates, while others have horny projections and called armoured dinoflagellates (Anand, 1998).

Zooplankton are the central trophic link between primary producers and higher trophic levels. The freshwater zooplankton comprise of Protozoa, Rotifers, Cladocerans, Copepods and Ostracods. Most of them depend to a large extent, on various bacterioplankton and phytoplankton for food. Many of the larger forms feed on smaller zooplankton, forming secondary consumers. Some of them are detritivore feeders, browsing and feeding on the substrate attached organic matter, phytoplankton or concentrating on the freely suspended organic matter particles or those lying on the bottom sediment. Many of these organisms are also fish food organisms and are consumed by the other aquatic macrofauna. The freshwater zooplankton is mainly constituted of five groups:

•  Protozoans (first animals): A very diverse group of unicellular organisms are found in this major zooplanktonic community. Most of the protozoans are usually not sampled due to their minute size. Planktonic protozoans are limited to ciliates and flagellates. Among the unicellular protozoa, the heterotrophic nanoflagellates are the major consumers of free-living bacteria and other smaller heterotrophic nanoflagellates. The abundant heterotrophic nanoflagellates (105 to 108 /L in highly eutrophic lentic ecosystems) range in size from about 1.0 to about 20 µm. They include non-pigmented species that structurally have very closely related pigmented species in the phytoplankton. The ciliates are larger in size (8 µm to 300 µm) but are less abundant (102 to 104 /L). While the smallest planktonic ciliates feed on the picoplankton, the larger ciliates feed on the heterotrophic nanoflagellates and small nanophytoplankton. Among the ciliates, those containing captured chloroplasts from the ingested algae or those containing more permanent symbiotic green algae (zoochlorellae) are common. Among the protozoans are two orders of amoebae that are primarily associated with the sediments and littoral aquatic vegetation and large numbers of meroplanktonic species (Edmondson, 1959; Battish, 1992).

•  Rotifers (wheel bearers): Rotifers, typically an order of magnitude less abundant the protozoans, are the most important soft-bodied metazoans (invertebrates) among the plankton. Their name comes from the apparently rotating wheels of cilia, known as corona, used for locomotion and sweeping food particles towards the mouth. The mouth is generally anterior and the digestive tract contains a set of jaws (trophi) to grasp the food particles and crush them. Relatively few (about 100) ubiquitous rotifer species are planktonic and a much larger number (about 300) are sessile and are associated with sediments and the vegetation of the littoral zones. Planktonic rotifers have a very short life cycle under favourable conditions of temperature, food and photoperiod. Since the rotifers have short reproductive stages they increase in abundance rapidly under favourable environmental conditions (Dhanapathi, 2000). The schematic representation of rotifera is given Appendix 1 (figure 15).

•  Crustaceans: This group comprises of members all belonging to the well-known Phylum Arthropoda. This is the largest phylum in terms of number of species and among zooplankton holds the highest position both in terms of systematics and as secondary consumers in the food chain. In healthy habitats wherein external influences of pollution are absent or at least low, members of this group constitute a sizeable population.

•  Cladocerans (Branched horns): Cladocerans are a crucial group among zooplankton and form the most useful and nutritive group of crustaceans for higher members of fishes in the food chain. Cladocerans are normally covered by the chitinous covering termed as the carapace. The two large second antennae are responsible for giving the cladocerans their common name, water fleas and are used for rowing through the water. Cladocerans are filter feeders as they filter the water to trap the organisms in it. Cladocerans are highly sensitive against even low concentrations of pollutants. The food source of this group is smaller zooplankton, bacterioplankton and algae (Murugan, 1998). The schematic representation of cladocera is given Appendix 1 (figure 16).

•  Copepods (Oar foot):

•  The copepods comprise of calanoids, cyclopoids and harpacticoids. The copepods also form important organisms for fish and are influenced by negative environmental factors as caused by excessive human interference in water bodies but to a lesser extent than the cladocerans. Copepods are much more hardier and strongly motile than all other zooplankton with their tougher exoskeleton and longer and stronger appendages. They have long developmental time and a complex life history with early larval stages difficult to distinguish. They are almost wholly carnivorous on the smaller zooplankton for their food needs. Among the three orders of copepods, cyclopoid copepods are generally predatory on (carnivorous) on other zooplankton, and fish larvae. The cyclopoid copepods also feed on algae, bacteria and detritus. The second group of copepods, calanoid copepods change their diet with age, sex, season, and food availability. The calanoid copepods are omnivorous feeding on ciliates, rotifers, algae, bacteria and detritus. The third group harpacticoid copepods are primarily benthic. Copepods, in general can withstand harsher environmental conditions as compared to cladocera (Kalff, 2002). The schematic representation of copepoda is given Appendix 1(figure 17 and 18).

•  Ostracods (Shell like): The Ostracods are bivalved organisms and belong to phylum Arthropoda. They mainly inhabit the lake bottom and among macrophytes and feed on detritus and dead plankton. Ostracods are in turn consumed by fishes and benthic macroinvertebrates (Chakrapani, 1996). The schematic representation of ostracoda is given Appendix 1 (figure 19).

Basic differences among Rotifera, Cladocera, Copepoda and Ostracoda are given in Table 2.1. Protozoa is not included since there is a vast difference between protozoa and other groups. The protozoa are unicellular whereas all the other groups are multicellular. The taxonomic classification of the four groups is given in Appendix 3 (Table 25 and figure 20).


Table 2.1: Basic taxonomic differences among the freshwater Zooplankton community

•  Body divided into head, trunk and abdomen.

•  Locomotion by the means of coronal cilia, which gives them the name wheel bearers.

•  With protonephridia for osmoregulation.

•  Reproduction by parthenogenesis

•  No special organs for circulatory or gas exchange system.

•  A pair of biramous antennae used for swimming gives them the name cladocera.

•  Carapace large bivalved enclosing the trunk but not the head.

•  Eyes sessile, ocellus present.

•  Trunk limbs 4 to 6 pairs.

•  No carapace

•  Antennules uniramous.

•  The body has nine appendages usually.

•  Six pairs of biramous limbs.

•  Presence of caudal rami.

•  Carapace forms a bivalved shell.

•  Antennules uniramous.

•  Not more than five pairs of limbs behind mandible.

•  One to three pairs of limbs before mandibles.


In most aquatic food chains, the community interactions are often controlled by abiotic factors or predation at higher levels of food chain. The control of primary production by abiotic factors such as nutrients is called “bottom-up control”. The control of primary production by the upper levels of food chain is referred to as “top-down control”. The idea that predation at upper levels of food chain can have cascading effect down through the food chain is called the “trophic cascade” (Dodds, 2002). The bottom-up hypothesis requires that the biomass of all trophic levels is positively correlated and depend on fertility (limiting resources) of the habitat. The schematic representation of bottom-up control is given in figure 2.

More available nutrients more algae more zooplankton more planktivorous fish More piscivorous fish.

Figure 2: Bottom up control in the aquatic ecosystem

The top-down hypothesis predicts, however, that the adjacent trophic levels will be negatively correlated. The schematic representation of top-down control is given figure 3.

More piscivorous fish fewer planktivorous fish more zooplankton fewer phytoplankton more available nutrients

Figure 3: Top down control in the aquatic ecosystem

Any disturbance to the water body due to over-exploitation of fish resources or due to various anthropogenic activities leads to deterioration of the water quality and hence will have an impact on the communities in the aquatic ecosystem (Lampert and Sommer, 1997). Bio- monitoring the water bodies at regular intervals does help to understand the implications of water quality on trophic structure and vice versa.


With the advent of industrialization and increasing populations, the range of requirements for water has increased together with greater demands for higher water quality . Industrialization coupled with intensive agriculture in early 1980's to meet the growing demand of ever increasing populations, the range of requirements for water has increased manifolds. In addition to many intentional water uses, there are several human activities, which have indirect and undesirable, if not devastating, effects on the aquatic environment, which include uncontrolled and unplanned land use for urbanization or deforestation, accidental (unauthorized) release of chemical substances, discharge of untreated waste or leaching of noxious liquids form solid waste deposits. Similarly, uncontrolled and excessive use of fertilizers and pesticides for agricultural purposes has long-term effects on the ground and surface water resources.

In order to protect the water resources from continuing deterioration, and to supply higher quality water for human consumption, there is a need to assess the quality of water. The main reason for assessment of quality of aquatic environment has been to verify whether the observed water quality is suitable for intended use. The overall process of evaluation of physical, chemical and biological nature of water in relation to natural quality, human effects and intended uses, particularly the uses which may affect human health and health of the aquatic ecosystem itself is termed as water quality assessment (UNEP, 1996).

Water quality assessment includes the use of monitoring to define the condition of water, to provide the basis of detecting trends and to provide the information enabling the establishment of cause-effect relationship. Thus the water quality assessment program aims,

•  To provide water quality details to decision makers and public on the quality of freshwater relative to human and aquatic ecosystem health and specifically,

•  To define the status of water quality

•  To identify and quantify trends in water quality

•  To define the cause of observed conditions and trends

•  To identify the types of water quality problems that occurs in specific geographic areas.

•  To provide the accumulated information and assessment in a form that resource management and regulatory agencies can use to evaluate alternatives and make necessary decisions.

To begin the monitoring of freshwater resources, there is always a need for preliminary survey. A survey of a water body is done with specific objectives. A finite duration, intensive program to measure and observe the quality of the aquatic environment for a specific purpose is termed as a survey. A physicochemical approach to monitor water pollution gives the causes and levels of pollutants in the water body. Biological approach highlights the impact of pollution on the aquatic biota and on the overall status of the water body. However, a combined approach depicts a comprehensive picture of the water quality and aquatic biota enabling effective interpretation and proper decision-making.

The root of the word monitoring means, “to warn” and one essential purpose of monitoring is to raise a warning flag that the current course of action is not working. The essential purpose of monitoring is to raise a warning flag that the current course of action is not working. Thus, monitoring is defined as the collection and analysis of repeated observations or measurements to evaluate changes in condition and progress toward meeting a specific objective (Elzinga et al ., 2001). Biomonitoring involves the use of biotic components of an ecosystem to assess periodic changes in the environmental quality of the ecosystem. A variety of effects can be produced on aquatic organisms by the presence of harmful substances, the changes in the aquatic environment that result from them, or by the physical alteration of the habitat. Some of the common effects on the aquatic organisms are:

•  Changes in the species composition of the aquatic communities,

•  Changes in the dominant groups of organisms in a habitat,

•  Impoverishment of species,

•  High mortality of sensitive life stages (larvae and eggs),

•  Mortality in the whole population,

•  Changes in the behaviour of the organisms,

•  Changes in the physiological metabolism, and

•  Histological changes and morphological deformities.

As all of these effects are produced by a change in the quality of aquatic environment, they can be incorporated into biological methods of monitoring and assessment to provide information on a diverse range of water quality issues and problems, such as:

•  The general effects of anthropogenic activities on ecosystems,

•  The presence and effects of common pollution issues (eutrophication, toxic organic chemicals, toxic metals, industrial inputs),

•  Common features of deleterious changes in the aquatic communities,

•  Pollutant transformation in water and in the organisms,

•  Long-term effect of substances in the water bodies (biomagnification and bioaccumulation),

•  Condition resulting from waste disposal and of the character and dispersion of wastewaters,

•  The dispersion of atmospheric pollution (acidification arising from wet and dry deposition of acid-forming compounds),

•  The effects of hydrological control regimes (impoundments),

•  The effectiveness of environmental protection measures, and

•  The toxicity of substances under controlled, defined laboratory conditions, (i.e. acute or chronic toxicity, genotoxicity or mutagenicity.

Biological methods can also be useful for:

•  Providing systematic information on water quality (as indicated by aquatic communities),

•  Managing fishery resources,

•  Defining clean waters by means of biological standards or standardized methods,

•  Providing an earlier warning mechanism,

•  Assessing water quality with respect to ecological, economic and political implications.


Biological monitoring (or bio monitoring) of water and water bodies is based on five main approaches (UNEP, 1996).

i. Ecological methods:

 ii. Physiological and biochemical methods:

 iii. The use of organisms in controlled environments:

iv. Biological accumulation:

 v. Histological and morphological methods:


All environmental components and processes within the hydrological cycle depend on and are regulated by the structural, functional and compositional aspects of biodiversity. Environmental components and processes also respond to and impact on society's decisions and actions. Historically, research has been narrowly focused on separate environmental components within the hydrological cycle rather than the processes and relationships between them. This thrust focuses on understanding these relationship leads to monitoring aquatic ecosystems by ecological methods. The use of ecological methods in biomonitoring of aquatic ecosystem is becoming increasingly important due to the deterioration of water bodies through anthropogenic activities. The quality of water affects the species composition, abundance, productivity and physiological conditions of the aquatic community. The structure and composition of these aquatic communities is an indicator of water quality. Some of the advantages of using ecological methods are as follows:

•  Biological communities reflect overall ecological integrity (i.e., physical, chemical and biological integrity). The monitoring of a single representative community for e.g., Zooplankton, among various communities in aquatic ecosystem gives a fair idea of the status of all the communities because of the interrelationship they share in food webs. Therefore, biomonitoring results in directly assessing the status of the entire water body.

•  Biological communities integrate the effect of different pollutant stressors and thus provide a holistic measure of their impact.

•  Routine monitoring of the biological communities can be relatively inexpensive particularly when compared to the cost of assessing toxic pollutants either chemically or with toxicity studies.

•  Where criteria for specific ambient impact do not exist (e.g., non-point source impacts that degrade habitats), biological communities may be the only practical means of evaluation (Ramachandra, T.V. et al ., 2002).

The ecological methods useful in biomonitoring include the collection, identification and counting of bioindicator organisms, biomass measurements, measurements of metabolic activity rates, and investigation on the bioaccumulation of pollutants. The communities that are useful in biomonitoring are plankton, periphyton, macrophytes, fishes, macroinvertebrates, amphibians, aquatic reptiles, birds and mammals. These organisms reflect a certain range of physical and chemical conditions. Some organisms can survive a wide range of conditions and are tolerant to pollution. Others are very sensitive to changes in conditions and are intolerant to pollution. These organisms are called bioindicators (EPA, 1989).


The first step in a biomonitoring programme is setting one's objectives because the methods of monitoring vary according to the objectives . In order to biomonitor a water body the following steps have to be considered.

•  Selection of a biological community, which gives an immediate and holistic picture of slightest of impacts caused by different pollution stressors.

•  To know about the species and ecology of the biological community selected.

•  To select an appropriate sampling method to represent whole of the population (Sutherland, 1997)


Phytoplankton forms the very basis of aquatic food chain. The water quality especially the nutrients influence its population. Phytoplankton survey thus indicates the trophic status and the presence of organic population in the ecosystem. Nutrients enrichment in water bodies is known as eutrophication, which is a common phenomenon with algal blooms.


Plankton has been used recently as an indicator to observe and understand changes in the ecosystem because it seems to be strongly influenced by climatic features (Beaugrand et al., 2000, Le Fevre-Lehoerff et al., 1995 and Li et al., 2000). The variability observed in the distribution of zooplankton is due to abiotic parameters (e.g. climatic or hydrological parameters: temperature, salinity, stratification, advection), to biotic parameters (e.g. food limitation, predation, competition) or to a combination of both (Beyst et al., 2001, Christou, 1998, Escribano and Hidalgo, 2000 and Roff et al., 1988). Although zooplankton exists under a wide range of environmental conditions, yet many species are limited by temperature, dissolved oxygen, salinity and other physicochemical factors. The use of zooplankton for environmental characterization of lakes is potentially advantageous. Zooplankton species tend to have wide geographic distributions (Carter et al., 1980 and Shurin et al., 2000), so local differences in community occurrence do not generally result from dispersal limitation. Trophic roles (predators, herbivores, omnivores) are well represented in the zooplankton, and individual generation times are short enough that they quickly respond to acute stress but long enough for them to integrate the effects of chronic problems, making them favorable candidates for a community indicator of ecosystem health (Cairns et al., 1993). Finally, zooplankton are relatively easy to identify, so they are particularly useful when community sensitivity can be detected based on zooplankton body sizes or gross taxonomic classifications.

Multi-lake studies have been used to explore variations in the zooplankton community along a number of limnological gradients. For example, zooplankton community size structure has been used as an indicator of lake trophic status (Bays and Crisman, 1983, Beaver and Crisman, 1990, Canfield and Jones, 1996 and Pace, 1986). Studies have compared the abundance and biomass of micro- and macrozooplankton (Bays and Crisman, 1983, Pace, 1986 and Sprules et al., 1988) to algal chlorophylls (Canfield and Jones, 1996), Carlson's Trophic State Index (Bays and Crisman, 1983), and nutrients (Pace, 1986 and Sprules, 1977). Zooplankton indicator species have been used to determine shifts in trophic state (e.g., Fuller et al., 1977 and Sprules, 1977). Several studies have examined differences in rotifer communities in lakes of various trophic states (Beaver and Crisman, 1990, Fuller et al., 1977 and Gannon and Stemberger, 1978). Abundance of selected major zooplankton groups (e.g. Rotifera, Copepoda) has also been used to show changes in trophic state (Gannon and Stemberger, 1978 and Pace, 1986).

Moreover, prey-predator interactions play an important role in determining population densities such as absence or presence of some fish species. Pollution levels can further alter species composition and community structure. Thus the changes in the physicochemical nature of water, interspecific and intraspecific competition, pollution level and presence or absence of planktivorous or piscivorous fish are some of the factors influencing zooplankton species composition and structure in any aquatic ecosystem. Zooplankton as indicators for the assessment of water quality has the following advantages:

•  Zooplankton are sufficiently large in numbers in any aquatic ecosystem to follow the trends in changes of water quality.

•  Samples can be collected easily and processed rapidly.

•  Their reproductive cycle is short enough to enable the study through several generations in a relatively short time.

•  Some of the commonly occurring species like Daphnia, Cyclops, Brachionus and Moina can be easily cultured to ensure constant supply of for experimental purposes.

•  They respond more rapidly to environmental changes than fishes, which have been traditionally used as indicators of water quality.

Zooplankton constitute an important link in food chain as grazers (primary and secondary consumers) and serve as food for fishes directly or indirectly. Therefore any adverse effect to them will be indicated in the wealth of the fish populations. Thus, monitoring them as biological indicators of pollution could act as a forewarning for the fisheries particularly when the pollution affects the food chain (Mahajan, 1981). Thus, the use of zooplankton for ecological biomonitoring of the water bodies helps in the analysis of water quality trends, development of cause-effect relationships between water quality and environmental data and judgement of the adequacy of water quality for various uses.

More often an issue raised by the public, concerning the deteriorating quality of a particular water body, forms the basis for water quality assessment. Thus water quality assessments is done to understand the quality of water, to show the causes of impacts, the level of impact, to verify the suitability for the current use and finally if the interpretation reveals the polluted status, outlining the restoration measures and alternatives for implementation by the decision makers. The decline in water quality and quantity has a great bearing on the social, economic and environmental status of a region. This necessitates restoration of degraded ecosystems as a part of conservation and sustainable management of aquatic ecosystems.

As in the case of productivity, lake size is likely to moderate the potential effects of biotic interactions like predation and competition. This is because lake size is an important determinant of pelagic community structure. For instance, a small pelagic zone cannot sustain populations of obligate plankton-feeding fish. Small lakes are dominated by generalist fish species that feed only facultatively on zooplankton, and only large pelagic zones can sustain one further trophic level (pelagic piscivores). Finally, as stated above, larger lakes will generally provide a larger number of microhabitats than smaller lakes. A summary of factors influence zooplankton population is discussed in Table 2.2.

Table 2.2: Environmental factors assumed to influence species richness in limnetic zooplankton communities. Effects are given as + (species richness increases more or less monotonically with the factor); u (unimodal response with species richness peaking at intermediate levels of the factor), or – (species richness declines with factor)

Factors Effects Mechanisms
Geography Latitude
Reduced regional species pool, harsher environment Dodson, 1992
Reduced regional species pool, harsher environment Dodson, 1992, Schartau et al., 1997
Habitat Lake area
Number of available niches; probability of immigration Dodson, 1992
Lake depth
Vertical segregation; predation avoidance Dodson, 1992
Littoral development
Indirect effect via macrophyte development; number of available niches Dodson, 1992
More trophic resources with increased productivity Dodson, 1992; Dodson et al., 2000
Biotic interactions Macrophyte stands
Predation avoidance Jeppesen et al., 1997
Fish predation
Reduces dominant competitors via size-selective predation Schartau et al., 1997; Shurin, 2000
Invertebrate predation
Favours large-bodied species which are dominant Competitors Anders Hobaek et al, 2002
Dispersal (Within the region) Number of lakes in proximity
Passive dispersal of propagules; effective within 20 km distance Dodson, 1992;
Distance to nearest lake
No effect? Dodson, 1992
Waterway connections
Influx of live animals and propagules Michels et al., 2001
Waterfowl density
Passive dispersal of propagules Figuerola and Green, 2002


Restoration is the “return of an ecosystem to a close approximation of its condition prior to disturbance” or the reestablishment of predisturbance aquatic functions and related physical, chemical and biological characteristics. It is holistic process not achieved through the isolated manipulation of individual elements. The objective is to emulate a natural, self-regulating system that is integrated ecologically with the landscape that occurs. Often, restoration requires one or more of the following processes: reconstruction of antecedent physical conditions, chemical adjustment of the soil and water; and biological manipulation, including the reintroduction of absent native flora and fauna.

These principles focus on scientific and technical issues, but as in all environmental management activities, the importance of community perspectives and values is to be considered. Coordination with the local people and organizations that may be affected by the project can help built the support needed to get the project moving and ensure long-term protection of the restored area. In addition, partnership with all stakeholders can also add useful resources, ranging from finance and technical expertise to volunteer help with implementation and monitoring (Ramachandra T.V., 2001). Restoration principles are

•  Preserve and protect aquatic resources: Existing, relatively intact ecosystems are the keystone for conserving biodiversity, and provide the biota and other natural materials needed for the recovery of impaired systems.

•  Restore ecological integrity: Ecological integrity refers to the condition of an ecosystem – particularly the structure, composition and natural processes of biotic communities and physical environment.

•  Restore natural structure: Many aquatic resources in need of restoration have problems originated with harmful alteration physical characteristics, which in turn may have led to problems such as habitat degradation and siltation.

•  Restore natural function: Structure and function are closely linked in river, wetlands and other aquatic resources. Reestablishing the appropriate natural structure can bring back beneficial functions.

•  Work within the catchment area: Restoration requires a design based not only on the lake but also on it's catchment area. Activities throughout the catchment area of a lake play have an adverse effect on the water body since the catchment determines the quality and quantity of runoff to the lake.

•  Address on going causes of degradation: Identify the causes of degradation and eliminate or remediate ongoing stresses whenever possible.

•  Develop clear, achievable and measurable goals: Goals direct implementation and provide the standards for measuring success. The chosen goals should be achievable ecologically, given the natural potential of the area, and socio-economically, given the available resources and the extent of community support for the project.

•  Focus on feasibility taking into account scientific, financial, social, and other considerations.

•  Anticipate future changes: As the environment and our communities are both dynamic, many foreseeable ecological and societal changes should be factored into restoration design.

•  Involve the skills and insights of a multi-disciplinary team: Universities, government agencies, and private organizations may be able to provide useful information and expertise to help ensure that restoration projects are based on well-balanced and thorough plans.

•  Design for self-sustainability: Ensure the long-term viability of a restored area by minimizing the need for continuous maintenance of the site. In addition to limiting the need for maintenance, designing for self-sustainability also involves favouring ecological integrity, as an ecosystem in good condition is more likely to have the ability to adapt to changes.

•  Use passive restoration, when appropriate: Simply reducing or eliminating the sources of degradation and allowing recovery time to allow the site to naturally regenerate. Passive restoration relies mainly on natural processes and it is still necessary to analyze the site's recovery needs and determine whether time and natural processes can meet them.

•  Restore native species and avoid non-native species: Many invasive species out compete natives because they are expert colonizers of disturbed areas and lack natural controls. Invasive species cause undesirable structural changes to the ecosystem.

•  Use natural fixes and bioengineering techniques, where possible: Bioengineering is a method of construction combining live plants with dead plants or inorganic materials, to produce, functioning systems to prevent erosion, control sediment and other pollutants, and provide habitat. These techniques would be successful for erosion control and shoreline stabilization, flood mitigation and even water treatment.

•  Monitor and adapt where changes are necessary: Monitoring program is crucial for finding out whether goals are being achieved. If they are not, “mid-course” adjustments in the projects should be undertaken. Post-project monitoring will help determine whether additional actions or adjustments are needed and provide useful information for future restoration efforts. This process of monitoring and adjustment is known as adaptive management. Monitoring plans should be feasible in terms of costs and technology, and should always provide information relevant to meeting the project goals.