Field Observation
The effects of flood on ecosystems with special reference to
August 2018 floods in Kerala: A report based on field observation
T. Cherian
Former Faculty Member, UAE University and Kuwait University, Kuwait
Corresponding Author: T. Cherian, E-mail: tcvazhuvelil@gmail.com
Received: 10/05/2024; Revised: 16/07/2024; Accepted: 03/08/2024; Published: 29/01/2025
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Abstract
Floods are unpredictable natural disasters and there is no way to prevent them. However, in some cases,
anthropogenic factors can contribute to or accelerate these events. In Kerala, seasonal flooding has become a
common occurrence in recent years, particularly during the heavy monsoons as in 2018 and 2019. Flooding
causes widespread damage, including soil degradation, loss of biodiversity, extensive agricultural destruction,
the spread of invasive plant and animal species, and increased sedimentation and nutrient loading. It is hoped
that the restoration of degraded ecosystems may be possible through projects under the "Rebuild Kerala
Development Programme" of the Government.
Keywords: Floods, invasive species, biodiversity, nutrient loading, flood mitigation.
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Seasonal floods play an important role in maintaining natural ecosystem functions and may have some
beneficial effects. The rivers, lakes, ponds, wetlands, paddy fields, marshy places and other extended water
canals in an ecosystem are closely linked with the land surrounding it. Floods refill wetlands and thereby
facilitate ground water recharging, increase the connectivity between aquatic habitats, and move both sediments
and nutrients around the landscape. Many of our coastal resources, including fish and other marine organisms,
are dependent on the nutrients supplied from the mainland during floods. Several species take advantage of
floods for breeding, migration and dispersal. The natural systems are resilient to the effects of usual floods; but
not to the unusual heavy floods.
Kerala has been witnessing heavy rains and floods during monsoon, consecutively for the last two years. The
floods of August 2018 have wreaked havoc in almost the entire state of Kerala, being the worst one after the
great flood in 1924, popularly known as the 99-flood. Over 483 people died, 14 were missing and a million
people were evacuated during the floods. 14 districts were affected and put on red alert and the satellite pictures
show barely any land mass in this area during this time. The government had declared it a Level 3 Calamity.
Due to heavy rains, the water levels in most dams reached almost close to the FRL (Full Reservoir Level) and
this forced the KSEB who managed these dams to open shutters. Landslides that accompanied heavy rains
further increased the severity of the disaster.
Cycling of sediments and nutrients is essential to a healthy ecosystem but too many sediments and nutrients
entering a waterway may produce negative impacts on downstream water quality. Other negative effects include
loss of habitat, dispersal of weed species (in Kerala 360 wild weeds were identified so far), the release and
redistribution of pollutants, lower fish production and loss of biodiversity and disruption of the normal
functioning of ecosystems. Modifications of both dry and wetlands by human activity have a detrimental effect
on various ecosystems. During the last few decades there have been widespread constructions particularly on
riversides.
These constructions block the natural flood water corridors and ultimately exert too much pressure on the
available passages for flood water. The clogging of water channels due to deposition of solid waste, bottle necks
created because of constructions and encroachments etc., have compounded this problem. Floods tend to further
degrade the already degraded ecosystems. Destruction of natural barriers on the riversides which are the natural
regulators of water flow have intensified the gravity of floods in neighboring areas. The negative effects of
floodwaters on coastal marine environments are mainly due to the introduction of excess sediments, pollutants
such as pesticides, detergents, a wide variety of harmful chemicals, heavy metals and plastics including micro
plastics and debris. [1] These can degrade aquatic habitats, lower water quality, reduce coastal production and
contaminate food resources.
The rivers have become the dumping zones for all types of solid, chemical and organic wastes. During the last
two decades this problem has increased tremendously due to the widespread use of plastic bags. Flood water
collects plastics, organic wastes and other pollutants together with eroded soil and ultimately dumps everything
collected on its course to the lakes and the sea. Water pollution is a major problem affecting the fauna and flora
in freshwater bodies. The opening of sewerage systems into rivers and canals in many parts of Kerala has badly
affected the quality of water. The Pampa Irrigation Canal network connecting the Pampa and its tributaries now
appears dry and has become a dumping zone for waste as reported from many areas. The canal sides have an
abundance of wild weeds and are not cleaned for years. The rainwater collected in this area is contaminated and
forms the breeding zones for mosquitoes and other pests (Figure1). The rainwater from these canals opens into
the riverbeds, wetlands and marshy places contributing to the severity of water and soil pollution. The diverse
fish fauna including Aplocheilus (Manathukanni), Macropodus, once abundant in almost all freshwater bodies
including the drains, are no longer visible. Most of these feed on mosquito larvae and have been acting as
natural biological control agents against mosquitoes. The composition of aquatic flora and associated plants has
considerably changed due to pollution, paving the way for harmful algal blooms, bacterial and fungal biofilms,
which poses health hazards to the local population.
It was observed that in some areas, particularly on the slopes, the fertile topsoil was washed away by gushing
waters. A study conducted by the Department of Soil Survey and Soil Conservation in 13 flood affected districts
of the state revealed that floods impacted the soil quality by impairing its physical, chemical and biological
properties. [2] The soil samples showed deficiency of potassium, calcium and magnesium. They had low
carbon content and were acidic. The soil profiles also showed obvious changes characterized by the absence of
certain horizons or by the presence of new ones. Inundation for a longer period may cause depletion of soil
fauna comprising microorganisms, microarthropods like collembola, protura, diplura, pseudoscorpions,
pseudocentipedes, mites, millipedes, and centipedes, nematodes and earth worms which play an important role
in the functioning of the soil ecosystems. The very sustainability of the soil ecosystem will be in peril without
these organisms. It is reported that flooding has caused widespread agricultural loss to farmers. Most of the
crops such as rice, banana, tapioca and vegetables were affected. This is due to the fact that inundation for a
longer period may cause water stress in plants and under extreme conditions they may even perish. In some
instances, plants have shown stunted growth. Those plants that have survived inundation and excessive water
stress are prone to microbial infection, mostly fungal. Sediments deposited by flood water are a source of plant
propagules, in the form of seeds and vegetative fragments. Floods facilitate the dispersal of weeds and fungal
spores. In wetlands wild weeds are a common sight. Some of these weeds are not native and they might have
been brought by the flood waters from the forests or other sources. These wild weeds are growing
uncontrollably affecting the local vegetation and agricultural crops. [3] This is evident from figures 2 and 3 that
show abundantly growing wild weeds like Pandanus fascicularis (kaitha), wild grasses, Sphagneticola trilobata
(a plant with yellow flowers), Acacia varieties, and wild creepers, not seen before, in an abandoned marshy
land, now deposited with silt and sediments after the floods, at Eraviperoor, Pathanamthitta District.
Floods and landslides bring several alien invasive plants to the water bodies, wet and dry lands posing great
threat to biodiversity and the aquatic environment. This could be a reintroduction of the already eradicated wild
species from the area or a new arrival. Such weed plants can disturb the ecological system of the area as they
have competitive adaptive capability by eradicating the other species. Wild plants have the capability to grow
and adapt to extreme environmental conditions using available nutrients and water. Non-native plants are more
likely to become invasive when they possess biological traits that are different from those of native flora, which
works to their competitive advantage. Invasive species transform the soil structure and microenvironment to
their advantage by producing allelochemicals, which, however, cause the destruction of native species and local
biodiversity. Invasive plants have the ability to adapt to environmental stress, a phenomenon referred to as
phenotypic plasticity. They generally possess a wide variety of seed dispersal mechanisms, and their seeds are
more viable. The threat of invasive species should be addressed in the process of post-flood reconstruction in the
State. Elimination of invasive plants is a Herculean task, but their spread can be tackled only with the active
participation of the public. Invasive species are introduced to native eco-systems by 'global transportation', as
ornamental plants or for botanical gardens, either deliberately or inadvertently. They alter the environment they
invade and are difficult and expensive to control once they colonize an area. Usually, the invasion becomes
uncontrollable in agricultural land and negatively impacts native species and ecological balance. Similar is the
situation with exotic fauna. Many exotic fishes that were kept in fish farms; aquaria have escaped to the natural
systems during flooding. One such example is the illegally introduced alligator gar, Atractosteus spatula, a
notorious predator on native fish. Other examples include Piaratcus (reported from Alappuzha), Pangas, Gaint
gourami, Tilapia etc.
Floods like other natural calamities are unpredictable and there is no way of preventing them. However, in some
instances anthropogenic factors may also contribute to or accelerate natural disasters. Quarrying, unscientific
and illegal constructions, large scale conversion of forest land into plantations and for housing and infrastructure
development in ecologically sensitive and vulnerable areas have contributed to the present problem. The recent
floods exposed our vulnerability to calamities of higher magnitude. According to a post flood report prepared by
a team of experts consisting of geologists and soil scientists coordinated by Kerala Forest research Institute
(KFRI) landslides occurred mostly on slopes above 220, most commonly between 220-280. [4] Fragmentation
of forest land disrupting slope continuity is cited as the major causative factor of landslides.
As far as ecological damage is concerned, they are not often visible, and the extent of damage can be evaluated
only by scientific studies. The environmental issues caused by recent floods are multifaceted and hence require
different strategies. The management strategies for rivers, forests, biodiversity, ecosystems, flood mitigation, all
need revamping and must be dealt with an ecological perspective. Restoration of degraded ecosystems, natural
as well as artificial, must be given due importance while implementing projects under the “Rebuild Kerala
Development Programme” of the Government.
Figure 1: The Pampa Irrigation Canal
Figure 2: Growth of wild weeds
Figure 3: Growth of wild weeds
Financial support and sponsorship
Nil
Conflict of interest
There are no conflicts of interest.
References
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