Citation: Sen,H.S. & Ghorai Dipankar (2017). Coastal ecosystem: risk factors for development and threats due to climate change. In "Soil Salinity Management in Agriculture: Technological Advances and Applications", S.K.Gupta & Megh R. Goyal (eds). Apple Academic Press, USA, pp. 63-95.
Coastal Ecosystem: Risk Factors for Development and
Threats due to Climate Change
H.S. Sen and
Dipankar Ghorai
H.S. Sen, Ph D, Former
Director, ICAR-Central Research Institute for Jute & Allied Fibres,
Barrackpore -700 120, West Bengal, India, Present address: 2/74 Naktala,
Kolkata 700 047, West Bengal, India, Phone; +91987418962, Email:hssen.india@gmail.com
Dipankar
Ghorai, Ph D, Subject Matter Specialist
(I/C), Krishi Vigyan Kendra, ICAR-Central Research Institute of Jute &
Allied Fibres (ICAR), Burdwan -713403,
West Bengal, India, Phone, +919433122515,
1.
INTRODUCTION
In one of its report IFPRI [16] has projected that globally about 1
billion people are ‘absolutely’ or ‘ultra’ poor living on less than US $ 1 a
day and about 800 million people are hungry. Although, this level of poverty
has decreased marginally overall from 28.6% of the population in 1990 to 18.0%
in 2004, large changes in regional disparities in poverty level have been
observed during the period, 1990 to 2004, from 39% to 47% in South Asia, 38% to
17% in East Asia & Pacific, 19% to 31% in Sub-Saharan Africa, and 4% to 5%
in Latin America and Caribbean. Various risk factors have been identified to affect
poverty in different time frames, which are socio-technological constraints
including macro-economic imbalances limiting agricultural and related
productivity, rising food prices and resource scarcity, climate change and lack
of environmental sustainability, lack of infrastructure, ethnic and other
social crises, inappropriate mindset for the acceptance of improved
technologies, health related issues, etc.
Of all the major ecosystems which factor in agricultural or food
production, being at the very base of poverty alleviation program, ‘coastal’ is
probably the most important one because of its high potentiality and production
of a large number of value added goods, yet confronted with high risk factors
due to a multiple of issues, which is the theme of discussion in this paper. Current
challenges and management of the coastal ecosystem have been overviewed in Wikipedia [42]. Different countries with coastal boundaries
have varying proportion of the total area exposed to the sea, expressed as
coastline: total area of the country (km km-2), some top-most being [43]:
Tokelau (10,100), Federal States of Micronesia (8,706), Palau (3,316), Northern
Mariana Islands (3,107), Maldives (2,147), Monaco (2,051), Marshall Islands
(2,044), Cocos (Keeling) Islands (1,857), Gibraltar (1,846) Macau (1,464),
Nauru (1,429), Kiribati (1,409), Saint Martin (1,093), Pitcairn Islands
(1,085), Seychelles (1,079), and
Christmas Island (1,030). India, Bangladesh and USA have low coast/ area ratio
of 2, 4 and 2, respectively. However, it is not the coast/ area ratio alone but
also the total coastline, population density and anthropogenic factors,
topography and related soil properties, protection measures undertaken, and
natural disasters caused by the sea and through its interaction with climate
and under-sea tectonic movement of the earth, that factor in not only to
influence the agricultural production but also the nature and extent of
vulnerability of the ecosystem per se
in a country.
2.
NEED FOR A THRUST
Coastal ecosystems have an economic value beyond their aesthetic
benefit supporting human lives and livelihoods. By one estimate [26], the
combined global value of goods and services from coastal ecosystems is about
US$ 12-14 trillion annually--a figure larger than the United States' Gross
Domestic Product worked out in 2004. The
problems of livelihood in these areas are compounded manifolds owing to a
series of technological, administrative and socio-economic constraints. A
holistic look at the interaction matrix of factors, which are interdependent on
each other, impacting on the coastal ecosystem is presented schematically in
Fig. 1. Unfortunately, at the global level, until very recently, not much
serious and concerted attention has been paid for mitigating the problems for
sustainable development in the coastal ecosystem. Attempt for improving on the
agricultural front, which is the focal theme of this paper, though should be at
the central stage from daily livelihood point of view in this ecosystem, is
still in the back seat in majority of the areas. This is possibly because of
the ‘slow-poisoning kind of effect’ of this sector, arising out of poor
agricultural practice and/ or inability for the poor to pay for the commodities
as a result of insufficient food production, that normally goes un-noticed
among the poverty-stricken mass, vis-à-vis catastrophic effects with heavy toll
on lives and properties due to climatic disasters. Exceptions are India,
Bangladesh and possibly a few other countries paying concerted attention on the
coastal ecosystem for improvement in agricultural front in particular.
Figure 1. Interaction
matrix of factors influencing stability and livelihood of the coastal ecosystem
[32]
3.
DEFINITION AND DISTRIBUTION
A coastal
ecosystem includes estuaries and coastal waters and lands located at the lower
end of drainage basins, where stream and river systems meet the sea and are
mixed by tides. The ecosystem includes saline, brackish (mixed saline and
fresh) and fresh waters, as well as coastlines and the adjacent lands. Coastal
wetlands are commonly called as lagoons, salt marshes or tidelands [38] .
According to World Resources Institute [51] coastal areas may be commonly
defined as the interface or transition areas between land and sea, including
large inland lakes. Coastal areas are diverse in function and form, dynamic,
and do not lend themselves well to definition by strict spatial boundaries.
Unlike watersheds, there are no exact natural boundaries that unambiguously
delineate coastal areas at the global scale.
According to them, the world coastline extends from 350,000-1,000,000 km
in length, depending upon how finely the ‘length’ is resolved. More
comprehensively, the coastal ecosystem has been defined as representing the
transition from terrestrial to marine influences and vice versa by [29
]. It comprises not only shoreline
ecosystems, but also the upland watersheds draining into coastal waters, and
the near shore sub-littoral ecosystems influenced by land-based activities.
Functionally, it is a broad interface between land and sea that is strongly
influenced by both.
Soils in the coastal ecosystem along with their characteristics have
been described comprehensively on a global scale but no attempt has been made
to delineate the zones from inlands based on scientific criteria. Estimates made
world over have generally been arbitrarily done based on length of the
coastline times a fixed distance landward, varying from 50 to 200 km as
followed in different countries, from the shore assuming the zone representing
coastal ecosystem different from that for inland part of the country.
Velayutham et al. [40] for the first
time described soil resources and their potentials for different
Agro-ecological Sub Regions (AESR) in the coastal ecosystems of India showing
total of 10.78 million hectare (M ha) area under this ecosystem (including the
islands). Soil in the coastal ecosystem per
se does not have separate significance as far as its productivity is
concerned unless it is considered in association with other relevant ecological
factors describing the ecosystem owing to the latter’s significant influence on
threatening its very stability—a fact, unlike any other ecosystem. It should
therefore be necessary, in priory, to delineate and characterize the coastal
soils in each country based on sound scientific criteria, and alongside
consider the relevant ecological factors which render the ecosystem concerned
generally fragile in nature due to various risk factors, often complementing
with each other, involved for planning for sustainable development with a
holistic approach (Fig. 1). The topic is discussed in a series of two sections,
the first of which is devoted to the various risk factors including climatic
change threatening the stability, and the second one will discuss various
issues impacting on productivity in agriculture and finally the integrated coastal
area planning towards livelihood security in the ecosystem.
4.
RISK FACTORS
According to an estimate by Dirk et
al. [7], 51% of the world’s coastal
ecosystems appear to be at significant risk of degradation from development
related activities. Europe, with 86% of the coastline at high or medium risk,
and Asia, with 69% in these categories, are the regions most threatened by
degradation. Worldwide, nearly three-fourths of marine protected areas within
100 km of continents or major islands appear to be at risk. These were
preliminary estimates and lack precision as commented upon by WRI [51]. However, the data suggest already an
alarming state towards destabilizing the ecosystem, notwithstanding that the
estimate did not even take into consideration other important factors like
agricultural and allied developments, deforestation, fishing, population
density, and climatic disturbances with significant adverse contribution.
4.1 Different Coastal Ecosystems
The
‘main’ ecosystems of the coastal areas, besides taking into account about
50-100 km area landward to be designated as coastal plain and utilized mostly
by agriculture and allied activities as well as for domicile and a few other
occupational purposes, are reefs, salt marshes and the remaining continental
shelves The global distribution of major classified into components, like
estuaries, macrophyte communities, mangroves, coral 
reefs,
salt marshes and the remaining continental shelves components of the coastal
ecosystems. The global distribution of major components is shown in Fig.
2.
Figure
2. Major wetland areas and world distribution of
mangrove swamps and salt marshes (Source: [10] By
courtesy of Encyclopaedia Britannica, Inc., copyright 1997; used with
permission)
4.2 Salt Marsh
According
to Encyclopedia Britannica [10], salt marsh is an area of low, flat, poorly
drained ground that is subject to daily or occasional flooding by salt water
or brackish water and that is covered with a thick mat of grasses and such
grass like plants as sedges and rushes. Salt marshes are common along low seacoasts,
inside barrier bars
and beaches, in estuaries, and on deltas and are also extensive in deserts and
other arid regions that are subject to occasional overflow by water containing
a high content of salts. Maritime salt marshes often extend many miles inland
and are variably subject to tidal action; inland brackish marshes are found
frequently on mineral substrates of alluvial and lacustrine origin. According to
Gedan et al. [11] salt marshes provide more ecosystem
services to coastal populations than any other environment. Coastal wetlands
all over the world have vanished or are threatened in spite of various
international agreements and national policies. Losses due to human activities
include effects of urbanization, development of tourism resort, industrial
pollution, increase of inflow nutrients from the upstream reclaimed lands,
changes in hydrology, conversion to aquaculture ponds and some drillings for gas
exploitation. In addition, as a transition zone between land and sea, coastal
wetlands are particularly vulnerable to sea-level rise caused by both oceanic
thermal expansion and the melting of Artic and Antarctic glaciers as
consequence of global warming [52]. According to them, the diversity of saltmarsh plant species increases with increasing
latitude. This contrasts with mangrove diversity, which is highest in the lower
latitudes of the tropics. In Australia, when saltmarshes and mangroves coexist,
saltmarshes are typically found at higher elevations where they are inundated
less frequently than mangroves. However, this is not always true in an international
context. When seagrass beds are found adjacent to saltmarshes and mangroves, many
material links and shared plant and animal communities can exist.
OzCoasts [22] reported
characterization of salt marsh sediments generally consisting of poorly sorted
anoxic sandy silts and clays. Carbonate concentrations are generally low, and
concentrations of organic material are generally high. As with salt flats, the
sediments may have salinity levels that are much higher than that of seawater. These
sediments are also usually anoxic and have large accumulations of iron sulphides. Disturbing these acid sulphate soils can cause sulphuric acid to drain into coastal waterways.
Salt marshes are often associated with salt flats or exposed bare areas.
4.3 Salt Flats
Salt flats, or saline supratidal mudflat facies, occur in
dry evaporative environments (often in the tropics) that undergo infrequent
tidal inundation. Sediments comprise poorly-sorted sandy silts and clays,
including mineral deposits, such as gypsum and halite which form crusts. Salt flats tend to be low gradient,
and mostly featureless, with a varying degree of algal colonisation, and often
with vertically accreting algal mats. They generally occur above mean high
water spring, and experience infrequent inundation by king tides. The high salinity levels (surface and ground water) in these environments
often preclude the growth of higher vegetation and biota (some infauna and
epifauna may occur at lower elevations). Saltflats are habitats for birds, particularly during the wet season [22].
4.4 Coral Reefs
Figure 3. World distribution of coral reef (Source: [44])
Coral reefs are either restricted or absent from the west
coast of the Americas, as well as the west coast of Africa.
This is due primarily to upwelling and strong cold coastal currents that reduce water
temperatures in these areas. Corals are also restricted from off the coastline
of South Asia from Pakistan to Bangladesh. They are also restricted along the coast around
north-eastern South America and Bangladesh due to the release of vast quantities of freshwater from
the Amazon and the Ganges Rivers, respectively. Although corals are found in
temperate and tropical waters, shallow water reefs are formed only in a zone
extending at most from 30°N to 30°S of the equator.
Coral reefs cover < 0.5% of the ocean floor and 90% of the marine
species are directly or indirectly dependent on them [26]. About 20% of coral
reefs have been destroyed in the last few decades and an additional 20% or more
are severely degraded, particularly in the Caribbean Sea and parts of Southeast
Asia. Coral bleaching, which results from rising ocean temperatures caused by
climate change is also increasing and further threatens this valuable resource.
A lagoon
on the other hand is a body of comparatively shallow salt or brackish water separated from the deeper sea by a shallow or exposed sandbank, coral reef, or similar feature. Thus, the enclosed body of water
behind a barrier
reef or barrier islands or enclosed by an atoll (an island of coral that encircles a lagoon partially or completely) reef is called a lagoon [45] .
4.5 Mangroves
Swamps
A mangrove is a plant and mangal is a plant community and habitat where mangroves thrive.
They are found in tropical and sub-tropical tidal areas worldwide, like Africa, Americas (including
Caribbeans), South America, Asia, Australasia, and Pacific Islands. The 15
countries having significant areas under mangrove swamp are given in Fig 4. The
areas are typically characterized by high degree of salinity and water logging
due to tidal inundation. Areas where mangals
occur include estuaries and marine shorelines. Plants develop physiological
adaptations to overcome the problems of anoxia, high salinity and frequent tidal inundation. About 110 species have been identified as belonging to
the mangal. Each species has its own
capabilities and solutions to these problems. Small environmental variations
within a mangal may lead to greatly
differing methods of coping with the environment. Therefore, the mix of species
at any location within the intertidal zone is partly determined by the
tolerances of individual species to physical conditions, like tidal inundation
and salinity, but may also be influenced by other factors such as predation of
plant seedlings by crabs. Mangroves protect the coast from erosion, surge
storms (especially during hurricanes), and tsunamis. Their massive root system is efficient
at dissipating wave energy. Likewise, they slow down tidal water enough that
its sediment is deposited as the tide comes in and is not re-suspended when the
tide leaves,
Figure 4. The 15 most
mangrove-rich countries and their global share (data source: [14]; with
permission to use data)
except for fine particles. As a result, mangroves build
their own environment. Because of the uniqueness of the mangrove ecosystems and
their protection against erosion, they are often the object of conservation
programmes including national Biodiversity
Action Plans [46].
Mangroves support unique ecosystems, especially on their
intricate root systems (Fig. 5). The mesh of mangrove roots produces a quiet marine region for many young organisms.
In areas where roots are permanently submerged, they may host a wide variety of
organisms, including algae, barnacles, oysters, sponges, and bryozoans, which all require a hard substratum for anchoring while
they filter feed. Shrimps and mud lobsters use the muddy bottom as their home. Mangrove crabs improve the nutritional quality of the mangal muds for other bottom feeders by
mulching the mangrove leaves. In at least some cases, export of carbon fixed in
mangroves is important in coastal food webs. The habitats also host several
commercially important species of fish and crustaceans. In Vietnam, Thailand, the Philippines, and India, mangrove plantations are grown in coastal regions for the benefits they
provide to coastal fisheries and other uses [46].
Figure 5. Above and below water view at the edge of the mangal (Source: [46])
In the last 50 years, as much as 85% of the mangroves have been lost
in Thailand, the Philippines, Pakistan, Panama and Mexico, globally the value
being about 50%. An estimated 35% of mangroves have been removed due to shrimp
and fish aquaculture, deforestation, and freshwater diversion. In Indonesia
alone over 10,000 square kilometers of mangrove forests have been converted
into brackish water ponds (called tambaks)
for the cultivation of prawns and fish. Valuation of intact tropical mangroves
estimated at US$ 1000 per ha drops to US$ 200 per ha due to clearance by shrimp
farming [26]. Although some successful restoration efforts have taken place,
these are not keeping pace with mangrove destruction.
4.6 Estuaries
Estuaries are partially enclosed bodies of
water along coastlines where fresh water and salt water meet and mix. Most
scientists accept the definition given by D.W. Pritchard in 1967 as: "An
estuary is a semi-enclosed coastal body of water which has a free connection
with the open sea and within which seawater is measurably diluted with fresh
water derived from land drainage" [20]. Estuaries act as a transition zone
between oceans and continents. Fresh water input from land sources (usually
rivers) dilutes the estuary's salt content. An estuary is typically the tidal mouth of a river and is made up of brackish water. Freshwater from the river is prevented
from flowing directly into the open sea by one or more land formations, such as
peninsulas and barrier islands. Estuaries are often characterized by sedimentation or
silt carried in from terrestrial runoff and, frequently, from offshore [21]. The pH, salinity, and water levels of estuaries vary; depending
on the river that feeds the estuary and the ocean from which it derives its
salinity. An estuary retains many nutrients derived from both land and sea, and
it protects water quality. It thus forms an ecosystem that is filled with a rich variety of living organisms.
Estuaries
are vital habitats for thousands of marine species, often called the
"nurseries of the sea" because the protected environment and abundant
food provide an ideal location for fish and shellfish to reproduce. Most
commercially important fish species spend some part of their life cycle in
estuaries. Besides fish, many species of birds depend on estuaries for food and
nesting areas. Marine mammals also use estuaries as feeding grounds and
nurseries. All these marine organisms feed in estuaries because a healthy
estuary produces between 4 and 10 times as much organic matter as a cornfield
of the same size. Estuaries provide a wide range of habitats leading to a great
diversity of marine life [20].
According
to USAID [39], complicated interconnections exist between the quality, quantity
and timing of fresh water inflows and the health of estuaries. All of the goods
and services that estuaries provide are threatened when fresh water inflows are
changed. Even a small change in the flow of freshwater may affect the
fundamental functioning of an estuary, which in turn will have ramifications on
the animals and plants, as well as on human populations dependent upon the
estuary. In many cases, upstream alterations to the volume, timing and quality
of fresh water inflows have resulted in catastrophic destruction of downstream
habitats, loss of species and degradation of ecosystems adapted to a certain
range of freshwater inflows.
4.7 Macrophytes
A macrophyte represents a group of aquatic plants that
grow in or near water and is either emergent, submergent, or floating. In lakes
macrophytes provide cover for fish and substrate for aquatic invertebrates, produce oxygen, and act as food for some fish and wildlife.
A decline in a macrophyte population may indicate water
quality problems. Such problems may be the result of excessive turbidity, herbicides, or salinization. Conversely, overly high
nutrient levels may create an overabundance of macrophytes, which may in turn
interfere with lake
processing [47].
4.8 Remaining
Shelf
The Continental
shelf is the extended perimeter of each continent and associated coastal plain, and was part of the
continent during the glacial periods, but is under sea during interglacial periods such as the current
epoch by relatively shallow seas (known as shelf seas) and gulfs.
The continental rise is below the slope, but landward of the abyssal plains (Fig. 6). Its gradient is intermediate between the slope and the
shelf, of the order of 0.13-2.5. Extending as far as 500 km from the slope, it
consists of thick sediments deposited by turbidity currents from the shelf and slope. Sediment cascades down the
slope and accumulates as a pile of sediment at the base of the slope, called
the continental rise [48].
Figure 6. Continental shelf in relation to ocean [48]
An ‘Ice shelf’
is a thick, floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface. Ice shelves are found in Antarctica, Greenland and Canada only. The boundary between the floating ice shelf and the
grounded (resting on bedrock) ice that feeds it is called the grounding line.
When the grounding line retreats inland, water is added to the ocean and sea level rises. In contrast, for Ross Ice Shelf sea ice is formed on water, is much thinner, and forms
throughout the Arctic Ocean. It also is found in the Southern Ocean around the continent of Antarctica [49].
5.
EROSION
AND POLLUTION VIS-À-VIS POPULATION GROWTH
5.1 Population Growth as the Driver
The earth is now home to some 6.5 billion
people and is projected to have 9 billion by 2050. World population is
increasing with time at an accelerated pace and the population will grow even
faster along various coastlines and in already densely populated developing
countries. The number of people living within 100 km of coastlines will
increase by about 35% in 2050 as compared to that in 1995. This type of
migration will expose 2.75 billion people to coastal threats from global warming such as sea level
rise and stronger
hurricanes in addition to other natural disasters like tsunamis [15]. In an
estimate [9], the expected change of the population (or population density) from 2000 to
2025 regionwise shows increase in almost each coastal area. The estimates (population within 100 km of the
coastline) show increase by 25% in Asia (except Middle East), 52% in Middle
East and North Africa, 81% in Sub-Saharan Africa, 20% in North America, 31% in
Central America and Caribbeans, and 32% in each South America and Oceanea,
while there may be decrease by 2.5% in Europe. In India, according to the Department of Ocean Development,
there are 40 heavily populated areas along the Indian coast [8]. Apart
from climate change, which we will discuss hereafter, population growth is
possibly the single most factor impacting on damage to properties in the
coastal ecosystem. Around the world maximum people die of drowning by storm
surge.
5.2 Sedimentation and Erosion
The
dynamics of alluvial landscapes and natural sedimentation patterns that
determine the nutrient and energy flows in coastal areas are increasingly being
modified by human activities, in particular those that affect water flows
(dams, increased water extraction, deviation of rivers) and erosion, especially
due to deforestation. This prevents or slows down vertical accretion, thus
aggravating salt water intrusion and impairing drainage conditions in riverine,
delta or estuarine areas. It reduces or blocks sediment supply to the coast
itself, which may give rise to the retreat of the coastline through wave
erosion. Beach erosion is a growing problem and affects tourism revenue,
especially in island nations. In the Caribbean, as much as 70% of beaches
studied over a ten-year period were eroded. Yet, the long-term success of
tourism in the region is dependent on excellent beaches, a pristine marine
environment, and warm weather.
5.3 Eutrophication, Hypoxia, Dead Zones and Nutrient Cycle
The
urban developments are increasingly expanding to fertile agricultural lands and
leading to pollution of rivers, estuaries and seas by sewage as well as
industrial and agricultural effluents. In turn, this is posing a threat to
coastal ecosystems, their biological diversity, environmental regulatory
functions and role in generating employment and food. Overuse of fertilizer can
result in eutrophication, and in extreme cases, the creation of ‘dead zones’.
Dead zones occur when excess nutrients—usually nitrogen and phosphorus—from
agriculture or the burning of fossil fuels seep into the water system and
fertilize blooms of algae along the coast. As the microscopic plants die and
sink to the ocean floor, they feed on bacteria, which consume dissolved oxygen
from surrounding waters. This limits oxygen availability for bottom-dwelling organisms
and the fish that eat them. In dead zones, huge growths of algae reduce oxygen
in the water to levels so low that nothing can live. There are now more than
400 known dead zones in coastal waters worldwide, compared to 305 in the 1990s,
according to a study undertaken by the Virginia Institute of Marine Science.
Those numbers were up from 162 in the 1980s, 87 in the 1970s, and 49 in the
1960s. In the 1910s, four only dead zones had been identified [19].
The
occurrence of hypoxia in shallow coastal and estuarine areas has been
increasing worldwide, most likely accelerated by anthropogenic activities.
Hypoxia in the Northern Gulf of Mexico, commonly named the 'Gulf Dead Zone',
has doubled in size since researchers first mapped it in 1985, leading to very
large depletions of marine life in the affected regions [25]. He studied
changes in microbial communities as a result of oxygen depletion, the potential
contribution of increasing hypoxia to marine production and emission of N2O
and CH4, and the effect of hypoxic development on methyl mercury
formation in bottom sediments at the Gulf of Mexico's Texas-Louisiana Shelf
during the summer months.
The
World Resources Institute reported that driven by a massive increase in the use
of fertilizer, the burning of fossil fuels, and a surge in land clearing and
deforestation, the amount of nitrogen available for uptake at any given time
has more than doubled since the 1940s. In other words, human activities now
contribute more to the global supply of fixed nitrogen each year than natural
processes do, with human-generated nitrogen totaling about 210 million metric
tons per year, while natural processes contribute about 140 million metric tons (Table 1).
Table
1. Global sources of Biologically Available (Fixed) Nitrogen (Source: [51])
Anthropogenic sources
|
Annual release of fixed nitrogen
(teragram)
|
Fertilizer
|
80
|
Legumes
and other plants
|
40
|
Fossil
fuels
|
20
|
Biomass
burning
|
40
|
Wetland
draining
|
10
|
Land
clearing
|
20
|
Total from human sources
|
210
|
Total
from natural sources, viz. Soil bacteria, algae, lightning, etc.
|
140
|
This
influx of extra nitrogen has caused serious distortions of the natural nutrient
cycle, especially where intensive agriculture and high fossil fuel use
coincide. In some parts of northern Europe, for example, forests are receiving
10 times the natural levels of nitrogen from airborne deposition, while coastal
rivers in the Northeastern United States and Northern Europe are receiving as
much as 20 times the natural amount from both agricultural and airborne
sources. Recently, a new class
of chemical substances with toxic and persistent properties was detected in the
environment - the polyfluorinated compounds (PFCs). At the Institute for
Coastal Research, scientific studies were performed on the PFC-contamination of
coastal waters, marine mammals and the atmosphere with emphasis on the
mechanisms of global transport and distribution of PFCs [5].
6.
CLIMATE
CHANGE
6.1 The
Generic Issue
‘Climate change’ is called for any long-term significant change in
the expected patterns of average weather of a specific region over an
appropriately significant period of time. A number of factors
have been identified which collectively or individually impact on the build-up
of greenhouse gases (GHGs, like carbon dioxide, methane and nitrous oxide) that
threaten to set the earth inexorably on the path to an unpredictably different
climate. The Intergovernmental Panel on Climate Change [17] says
from observations since 1961
that the ocean has been absorbing more than 80% of the heat added to the
climate system, and that ocean temperatures have increased to depths of at
least 3000 m. It has also been predicted that sea surface temperature would increase
in the range of about 1-3 °C to result in more frequent coral bleaching
events and widespread mortality unless there is thermal adaptation or
acclimatisation by corals. According to them, many
parts of the planet will be warmer, as a result of which droughts, floods and
other forms of extreme weather will become more frequent, threatening food
supplies. Plants and animals which cannot adjust will die out. Sea levels would
rise and will continue to do so, forcing hundreds of thousands of people in
coastal zones to migrate. One of the main GHGs which human
populations are adding to the atmosphere, carbon dioxide (CO2), is
increasing rapidly. Around 1750, i.e. at the start of the Industrial Revolution
in Europe, there were 280 parts per million (ppm) of CO2 in the
atmosphere. Today the overall amount of GHGs has topped 390 ppm CO2e
(parts per million of carbon dioxide equivalent – all GHGs expressed as a
common metric in relation to their warming potential) and the figure is rising
by 1.5–2 ppm annually. Reputable scientists believe the earth’s average
temperature should not rise by more than 2°C over pre-industrial levels. Among
others, the European Union indicated that this is essential to minimize the
risk of what the UN
Framework Convention on Climate Change (UNFCCC) calls as dangerous climate
change and keep the costs of adapting to a warmer world bearable. Scientists
say there is a 50% chance of keeping to 2°C if the total GHG concentration
remains below 450 ppm [37].
6.1 Effects on Sea Level Rise and Inundation of Land
Coastal areas are prone
to threats from natural causes such as tidal surges and sea level rise (Fig. 7).
Each year an estimated 46 million people risk flooding from storm surges.
Coasts in many countries currently face severe problems of sea level rise as a
consequence of climate change, leading to potential impacts on ecosystems and
human coastal infrastructure. The worst scenario projects a
sea level rise of 95 cm by the year 2100, with large local differences
(resulting from tides, wind and atmospheric pressure patterns, changes in ocean
circulation, vertical movements of continents, etc.) in the relative sea level
rises [24]. The impacts on sea level rise are therefore expected to be more
local than global. The relative change of sea and land is the main factor. Many
cities, for instance, even suffer land subsidence as a result of ground water
withdrawal. This may be compounded with sea level rise, especially since rates
of subsidence may exceed the rate of sea level rise between now and 2100. Under the worst scenario, the majority
of the people who would be affected in different countries are China (72
million), Bangladesh (13 million people and loss of 16% of national rice
production), and Egypt (6 million people and 12 to 15% loss of agricultural
land), while between 0.3% (Venezuela) and 100% (Kiribati and the Marshall
Islands) of the population are likely to be affected. In India, potential
impacts on 1 m sea level rise might lead to inundation of 5,763 km2
of land [23]. According to IPCC, regions especially
at risk are low lying areas of North America, Latin America, Africa, populous
coastal cities of Europe, crowded delta regions of Asia, like Ganges-Brahmaputra delta
facing flood risks from both large rivers and
ocean storms, and many small islands, whose very existence is threatened by
rising seas. In North America, current preparedness for rising seas, more
frequent severe weather, and higher storm surges is low.
The Greenland and West Antarctic ice sheets face
substantial melting if the global average temperature rises more than ~2 to
~7°F (1 to 4°C) relative to the period 1990–2000—eventually contributing to an
additional sea level rise of ~13 to ~20 ft (4 to 6 m) or more. This would
result in the inundation of low lying coastal areas, including parts of many
major cities. Even more significant than the direct
loss of land caused by the sea rising are the associated indirect factors,
including erosion patterns and damage to coastal infrastructure, salinization
of wells, sub-optimal functioning of the sewage system of coastal cities (with
resulting health impacts), loss of littoral ecosystems
and loss of biotic resources. In coastal areas, and particularly deltas,
factors such as modified ocean circulation patterns (and their impact on
building and erosion of the
Figure 7. Global average sea level change (Annually
and globally averaged sea level change relative to the average over the period
1986 to 2005; sheds indicate different
data sets used. Source: [17]; used with permission)
coast), climate change in
the catchment basin and change in coastal climate, not to mention changes in
the frequency of extreme events, should be taken into account.
Destruction
of habitats in coastal ecosystem is also caused by natural disasters, such as
cyclones, hurricanes, typhoons, volcanism, earthquakes and tsunamis causing
colossal losses worldwide [50]. The frequency of natural disasters is increasing
with time (Fig. 8), predictably due to climate change, as sea level rise also
follows almost the similar trend (Fig. 7). Trenberth [36] argues that higher
sea surface temperatures in the Atlantic Ocean and increased water vapour in
the lower atmosphere—caused by global warming—are to blame for the past
decade’s intense storms. These factors are causing significant physical damage
to reefs or move large amounts of bottom material, thus altering habitat,
biological diversity, and ecosystem function. There is however no denying of
the fact that human induced activities are to a significant extent responsible
for climate change accelerating the pace of natural disasters with time
resulting in such damages to coastal 
lives
and properties.
Figure 8. Trend of change of cyclonic storms, hurricanes and
typhoons with time in different oceans in the world [13]
6.2
Effect on Agriculture
Climate change directly affects sensitive
sectors like agriculture, forestry and fishery and thereby the livelihoods of
millions of coastal communities [33,35]. Wide
array of impacts due to climate change on factors affecting food production has
been predicted. One could stipulate the
following changes in forcing variables as likely to materialize sometime during
the next century [4].
·
A gradual, continuing
rise in atmospheric CO2 concentration entail in increased
photosynthetic rates and water-use efficiencies of vegetation and crops, hence
increases in organic matter supplies to soils.
·
Minor increases in
evapotranspiration in the tropics to major increases in high latitudes caused
both by temperature increase and by extension of the growing period.
·
Increases in amount and
in variability of rainfall in the tropics; possible decrease in rainfall in a
band in the subtropics poleward of the present deserts; and minor increases in
amount and variability in temperate and cold regions could take place. Peak
rainfall intensities could increase in several regions
·
A gradual sea level rise
could cause deeper and longer inundation in river and estuary basins and on
levee backslopes, and brackish water inundation leading to encroachment of
vegetation that accumulates pyrite in soils near the coast
6.2.1
Low
lying coastal soils
The probable effects on soil characteristics
of a gradual eustatic rise in sea level will vary from place to place depending
on a number of local and external factors, and interactions between them [1].
In principle, a rising sea level would tend to erode and move back existing
coastlines. However, the extent to which this actually happens will depend on
the elevation, the resistance of local coastal materials, the degree to which
they are defended by sediments provided by river flow or longshore drift, the
strength of long shore currents and storm waves, and on human interventions
which might prevent or accelerate erosion.
6.2.2
Sediment
supply and deltaic aggradation
In major deltas, such as those of the
Ganges-Brahmaputra and the major Chinese rivers, sediment supplies delivered to
the estuary will generally be sufficient to offset the effects of a rising sea
level. Such deltaic aggradation could decrease, however, under three
circumstances:
- where human interventions inland,
such as large dams or successful soil conservation programmes, drastically
reduce sediment supply to the delta, e.g. the construction of the Aswan
high dam in 1964 has led to coastal erosion and increased flooding of
lagoon margins in the Nile delta [34];
·
where construction of
embankments within the delta interrupts sediment supply to adjoining back
swamps, exposing them to submergence by a rise in sea level, e.g. embankments
along the lower Mississippi river have cut off sediment supplies to adjoining
wetlands which formerly offset land subsidence occurring due to compaction of
underlying sediments [6]; and
·
·where land subsidence
occurs due to abstraction of water, natural gas or oil, e.g. as is presently
happening in Bangkok and in the northern parts of the Netherlands.
6.2.3 Tidal flooding
In
coastal lowlands which are insufficiently defended by sediment supply or
embankments, tidal flooding by saline water will tend to penetrate further
inland than at present, extending the area of perennially or seasonally saline
soils. Where Rhizophora mangrove or Phragmites vegetation invades
the area, would over several decades lead to the formation of potential acid
sulphate soils. Impedance of drainage from the land by a higher sea level and
by the correspondingly higher levels of adjoining estuarine rivers and their
levees will also extend the area of perennially or seasonally reduced soils and
increase normal inundation depths and durations in river and estuary basins and
on levee back slopes. In sites which become perennially wet, soil organic
matter contents will tend to increase, resulting eventually in peat formation.
On the other hand, where coastal erosion removes an existing barrier of mineral
soils or mangrove forest, higher storm surges associated with a rising sea
level could allow seawater to destroy existing coastal eustatic peat swamps,
which eventually may be replaced by fresh or saltwater lagoons.
6.2.4 Subsidence of land
The
probable response of low lying coastal areas to a rise in sea level can be
estimated on the basis of the geological and historical evidence of changes
that occurred during past periods when sea level was rising eustatically or in
response to tectonic or isostatic movements, e.g. around the Southern North Sea
[18]; in the Nile delta [34]; on the coastal plain of the Guyanas [3] and in
the Musi delta of Sumatera [2]. Contemporary evidence is available in areas
where land levels have subsided as a result of recent abstraction of water,
natural gas or oil from sediments underlying coastal lowlands. Further studies
of such contemporary and palaeo-environments are needed together with location
specific studies in order to better understand the change processes, identify
appropriate responses and assess their technical, ecological and socio-economic
implications [41].
6.2.5 Trend in vegetation growth
Some
major and widespread soil changes expected as a result of any global change are
positive, especially the gradual increases in soil fertility and physical
qualities consequent on increased atmospheric CO2. The increased
productivity and water-use efficiency of crops and vegetation, and the
generally similar or somewhat higher rainfall indicated by several global
circulation models, not fully counteracted by higher evapotranspiration, would
be expected to lead to widespread increases in ground cover, and consequently
better protection against runoff and erosion [4].
6.2.6 Changes in soil properties
According
to Brinkman and Sombroek [4], major but less widespread soil changes, including
greater biological activity and increased extent of periodic reduction in
soils, would be expected where permafrost would disappear. In unprotected low
lying coastal areas, gradual encroachment of Rhizophora mangroves or Phragmites
following more extensive brackish water inundation may give rise to the
formation of potential acid sulphate soil layers after several decades. Deeper
and longer duration flooding of basins and levee back slopes in adjacent river
and estuary plains could lead to more extensive reducing conditions and
increased organic matter contents, and locally to peat formation.
Other
changes due to climate change (temperature and precipitation) are expected to
be relatively well buffered by the mineral composition, the organic matter
content or the structural stability of many soils. However, decreases in cover
by vegetation or annual or perennial crops, caused by any locally major
declines in rainfall not compensated by CO2 effects, could lead to
soil structure degradation and decreased porosity, as well as increased runoff
and erosion on sloping sites and by the concomitant more extensive and rapid
sedimentation. Changes in options available to land users because of climate
change may have similar effects [4].
In
most cases, changes in soils by direct human action, on-site or off-site
(whether intentional or unintended), are far greater than the direct climate
induced effects. Soil management measures designed to optimize the soil's
sustained productive capacity would therefore, be generally adequate to
counteract any degradation of agricultural land by climate change. Soils of these
areas, or other land with a low intensity of management such as semi-natural
forests used for extraction of wood and other products, are less readily
protected against the effects of climate change but such soils too are
threatened less by climate change than by human actions - off-site, such as
pollution by acid deposition, or on-site, such as excessive nutrient extraction
under very low-input agriculture.
To
armor the world's soils against any negative effect of climate change, or
against other extremes in external circumstances, such as nutrient depletion or
excess (pollution), or drought or high intensity rains, the best that land
users could do [4], would be:
·
to manage their soils to
give them maximum physical resilience through a stable, heterogeneous pore
system by maintaining a closed ground cover as much as possible
·
·to use an integrated
plant nutrient management system to balance the input and off take of nutrients
over a cropping cycle or over the years, while maintaining soil nutrient levels
low enough to minimize losses and high enough to buffer occasional high
demands.
6.2.7
Erosion
Coasts are also exposed to increasing risks due to
erosion as a result of climate change and sea level rise [17]. It is an important area
influenced by the climate change with rising temperatures leading to rise in
the sea’s water mass. In India, the mainland consists of 43% sandy beaches, 11%
rocky coast with cliffs, and 46% mud flats and marshy coast [27]. The damages
caused by sea erosion in different coastal states in India alone show a
staggering annual loss of Rs. 3683.87 million (1US$ = Rs. 65). Various
preventive and mitigation measures have been suggested and being adopted are:
· Structural
measures such as construction of sea wall/ revetment, groynes
and off-shore breakwater
§ Non-structural/
soft measures such as artificial nourishment of beaches, vegetation cover and sand
bypassing at tidal inlets
Government
of India provides assistance for protection of vulnerable coastal states from
sea erosion mainly through two schemes, namely (i) Centrally sponsored scheme
for protection of critical stretches (through state sector), and (ii) National
Coastal Protection Project (NCPP) for protection of the maritime states/ UTs
with a view to explore possibilities of funding through external resources or
other domestic resources.
7.
DETERIORATING
E-FLOWS IN RIVER GANGA: A CASE STUDY
Ghorai and Sen [12], Sen [28], Sen et al. [30] and Sen and Ghorai [31]
raised serious concern over deteriorating water flow in the river Ganga through
a long stretch of run within India owing mainly to unplanned anthropological
factors arising out of scores of hydro-electric and irrigation projects already
commissioned and many others in the pipeline on the river in addition to
adverse climate change impacts, a typical example risking the coastal ecosystem
in the lower delta across India and Bangladesh. The lower Ganga delta of both
India (south of Farakka Barrage) and Bangladesh (south-west) share the same
ecology and face threats due to dwindling water diversion via Farakka Barrage
and deteriorating water quality of the river in the upstream at different
places in India. This being a matter of common concern to both countries there
is need for a holistic and focused attention for which the following suggestions
were made with immediate effect to seek for a lasting solution [31].
·
There appears to be a
need for revisiting the design of the Farakka Barrage, as well as the discharge
and distribution norms of water in the interest of the two countries, keeping
in view the predicted flow of upstream Ganga water in long- term perspectives,
and if necessary, fresh norms to be decided.
·
Predicted flow of water
through Ganga-Brahmaputra river system on account of retreat of glaciers and
other parametric uncertainties due to climate change needs to be refined with
appropriate climate models in deciding the future norms for distribution of
water via Farakka Barrage with higher precision in different time scales.
·
Need for fresh
installation of hydro-electric power and irrigation projects in India must be
given extremely careful consideration with stringent norms for discharge of
river water in the upstream so that ecology of the area is not disturbed.
·
Past hydro-electric power
and irrigation projects in the upstream already
commissioned need to be reviewed in terms of the norms for discharge of
water decided, and if necessary, to be revised, scientifically so that ecology
of the area is not disturbed.
·
Provisions should be
mandatory to make impact analysis of the discharge of water from different
projects, be it hydro-electric power and irrigation projects or any others, on
the ecology of the area for all past and future installations in India.
·
Strict administrative
vigilance to be maintained to stop acts of unscrupulous diversion of water
forthwith by private agencies in India.
·
Location specific
integrated water development and management schemes at strategic points over
the entire flow length in different time scales to be prepared and their
methods of implementation be worked out, with adequate participation and
vigilance from the local inhabitants, to ensure maintaining prescribed water
quality throughout the year in India.
·
In India, in particular,
impacts of the water flow at different strategic points into lower delta in
respect of salinity in soil and water, flow rate, tidal amplitude and
fluctuations, sedimentation/ hydrological parameters, navigation through
rivers, ground water table depths and qualities, all important components of
biodiversity, and any other related parameters should be taken up and monitored
with a holistic plan, over minimum five year phases, through a central task
force comprising of scientists, NGOs, government officials, local inhabitants,
and the same placed in public domain. Similar programmes should be
simultaneously planned and taken up by Bangladesh. A core team consisting of
key members drawn from both countries should interact and monitor the progress
once in each year and suggest for improvement with respect to targets fixed.
Sen and Ghorai [31] have
cautioned that the concerned lower Ganga delta of the two countries is largely
coastal and therefore fragile in nature subject to the increasing vagaries due
to climatic disasters beyond possibly anybody’s control to prevent. Additional
factors originating from the deteriorating E-flows of the Ganga river network
water contribute significantly further to the woes of the inhabitants of the
area. In conclusion, they remarked that there might be no short-cuts to improve
the ecology for sustained livelihood of the inhabitants in this area across the
two countries other than ensuring E-flows via Farakka Barrage, for which
careful considerations must be given to the suggestions made above. It is
fortunate to observe that Government of India has of late taken cognizance of
the fact in the interest of the country to limit future hydro-electric and
irrigation projects in hand although a holistic approach as envisaged is still
warranted in the interest of the entire ecosystem.
8.
SUMMARY
Coastal
areas with high population density along with potentially high aesthetic
benefit supporting human lives and livelihoods, are confronted with high risk
factors on a multiple of issues viz., anthropogenic factors, topography and
related soil properties, protection measures required to be undertaken, and
natural disasters caused by the sea and through its interaction with climate
and under-sea tectonic movement of the earth, among the major ones - influencing
agricultural production and vulnerability of the ecosystem per se in a related country. The resultant effect is that the
livelihood in the ecosystem remains uncertain and the masses remain
poverty-stricken in majority of the countries having reasonably large coastal
boundaries due to the lack of concerted efforts to address the risk factors and
their interactions in a holistic manner. Soil in the coastal ecosystem per se does not have separate
significance as far as its productivity is concerned unless it is considered in
association with other relevant ecological factors describing the ecosystem.
The chapter presents an overview of the distribution of different coastal
components in the world along with analysis of relevant risk factors.
The impact of climate change, being a major risk factor, has been
discussed as a generic phenomenon and with special emphasis on predictability
of sea level rise, oceanic disasters including cyclones, storms, hurricanes,
typhoons and inundation of coastal land in different parts of the world. Its
role on different aspects in agriculture particularly in low lying coastal
lands and on sediment supply and deltaic aggradation, tidal flooding,
subsidence of land, and changes in soil properties is also explained. The
influence of climate change on erosion of soil in the coastal areas has been
discussed along with important structural and non-structural measures
suggested. Finally, a case study on deteriorating water flow in the river Ganga
risking the ecosystem in lower delta across India and Bangladesh has been discussed
and future lines of action suggested.
KEY WORDS
Climate change
Carbon-dioxide
Coastal
ecosystem
Delta
Ecology
Erosion
Inundations
Livelihood
Mangrove ecosystem
Nutrient
imbalance
Natural
disasters
Low lying soils
Risk factors
River Ganga
Sediment supply
Tidal flooding
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