1. AQUATIC ECOSYSTEM - INTRODUCTION
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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.
FRESHWATER HABITATS
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LENTIC ECOSYSTEM
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LOTIC ECOSYSTEM
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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. |
Dissolved gases: |
Dissolved gases: |
Dissolved solids: |
Dissolved solids: |
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
PLANKTON IN AQUATIC FOOD CHAIN
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).
ROTIFERA
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CLADOCERA
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COPEPODA
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OSTRACODA
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| • 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. |
TROPHIC INTERACTIONS IN AQUATIC FOOD CHAIN
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.
MONITORING OF WATER BODIES
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.
METHODS IN BIOLOGICAL MONITORING Biological monitoring (or bio monitoring) of water and water bodies is based on five main approaches (UNEP, 1996).
i. Ecological methods:
- Analysis of biological communities of the water body;
- Analysis of biological communities on artificial substrates placed in a water body; and
- Presence or absence of specific species.
ii. Physiological and biochemical methods:
- Oxygen production and consumption, stimulation or inhibition,
- Respiration and growth of organisms suspended in water, and
- Studies of the effects on enzymes.
iii. The use of organisms in controlled environments:
- Assessment of toxic effects of samples on organisms under defined laboratory conditions (toxicity tests or bioassays), and
- Assessing the effects on defined organisms of waters in situ or on site, under controlled situations.
iv. Biological accumulation:
- Studies of the bioaccumulation of substances by organisms living in the environment, and
- Studies of the bioaccumulation of substances by organisms deliberately exposed in the environment.
v. Histological and morphological methods:
- Observation of histological; and morphological changes, and
- Embryological development or early life stage tests.
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).
STEPS IN BIOMONITORING USING ECOLOGICAL METHODS
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 FOR BIOMONITORING OF WATER BODIES
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.
ZOOPLANKTON FOR BIOMONITORING OF WATER BODIES
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
|
Effects
|
Mechanisms
|
References
|
| Geography Latitude |
-
|
Reduced regional species pool, harsher environment | Dodson, 1992 |
| Altitude |
-
|
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 |
| Productivity |
U/+
|
More trophic resources with increased productivity | Dodson, 1992; Dodson et al., 2000 |
| Biotic interactions Macrophyte stands |
+
|
Predation avoidance | Jeppesen et al., 1997 |
| Fish predation |
+/U
|
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 OF AQUATIC ECOSYSTEM
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.
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