Climate Change and Aquatic Ecosystem | Term Paper | Geography

Here is a term paper on ‘Climate Climate and Aquatic Ecosystem’ for class 9, 10, 11 and 12. Find paragraphs, long and short term papers on ‘Climate Climate and Aquatic Ecosystem’ especially written for school and college students.

Term Paper # 1. Introduction to Climate Change:

Recent changes in global climate are apprehended to cause massive alterations in the environment, unprecedented in the history of human civilization. Millions of people around the globe have already been affected and hundreds of millions more are threatened to be affected in the next few decades due to climate-related impacts.

Productivity of the terrestrial and aquatic ecosystem are threatened to be disturbed seriously, which in turn may jeopardize food security of man in the next century. The extent to which fisheries sector has been affected by such climate changes has not been evaluated thoroughly.

But there is strong evidence that aquatic ecosystem and the fisheries resources are most vulnerable to climate changes. To understand the ability of the aquatic ecosystems to adapt to these changes and predict what might occur in the future careful observations of the present and past conditions of the climate are essential.

Term Paper # 2. Global Climate System and the Changing Scenario:

Rise in temperatures and changes in precipitation are the two most important factors of climate change that affect the biodiversity, distribution of species and productivity of the terrestrial and aquatic ecosystem. Associated with this are rise in sea level and increase in frequency and intensity of extreme events such as storms, droughts and flood. The ability of the terrestrial and aquatic ecosystems to adapt to such climate changes is dependent on the rate and extent of these changes.

Climate is a result of dynamic interrelationship among atmosphere, oceans, the ice cover, living organisms and the geosphere consisting of soil, sediment and rock. Of these five components, the atmosphere plays the most crucial role and any change in atmosphere influences the other components and the climate as a whole. Global temperature is determined by the balance of solar and terrestrial radiation budget of the earth.

The atmosphere, which has a role in maintaining this balance, is practically a mixture of gases and suspended liquid and solid particles. It envelops the earth in four distinct layers: the troposphere, stratosphere, mesosphere and thermosphere. The troposphere and stratosphere play the most important role in controlling the energy budget through thermodynamic process. The troposphere contains more than 75 per cent of the atmospheric gases.

But density of the gases and the suspended particles decrease with the altitude resulting in decrease of temperature from an average of 15°C at the sea level to -56°Cat the end of troposphere (an average decrease of 6.5°C per km height). Temperature begins to increases in the stratosphere from – 56°C to -2°C due to absorption of UV radiation by the ozone layer, the characteristic constituent of stratosphere. The entire atmosphere is otherwise almost transparent to visible spectrum of light (little absorption).

As a result, visible solar radiation enters the earth atmosphere of the troposphere unhindered and heat the surface of the earth. When the earth surface radiates the infrared radiation, a significant part of it is absorbed by water vapour, CO₂, methane and other trace gases. Absorption of terrestrial infrared radiation is important to the energy budget of earth. Some of this is released into space while most is radiated back to earth. The net effect is storage of energy near the surface of earth.

The process is known as greenhouse effect and is an essential phenomenon to maintain optimum temperature and diurnal fluctuation required for the survival of life on earth. The gases which absorb the outgoing infrared radiation are known as the greenhouse gases (GHG), which include the water vapour, CO₂, methane and others. Despite the absorption, there is an atmospheric window through which terrestrial infrared radiation can pass. It is gradually closing as a result of anthropogenic emissions of greenhouse gases (Figure 18.1).

The changing composition of the atmosphere, including its greenhouse gas and aerosol (suspended liquid and solid particles) content is a major internal forcing mechanism of climate change. The anthropogenic factors, like burning of fossil fuels, forest cleaning and other industrial processes have increased the amount of carbon dioxide and other greenhouse gases since the eighteenth century. CO₂ alone has increased from 280 ppm during the pre-industrial age to 379 ppm in2005, while the total GHG emissions have been increased by 70 per cent between 1970 and 2004 (IPCC, 2007).

The developed nations have contributed the major share of the global concentration of GHGs in contrast to meager contribution by India and other developing or underdeveloped nations. Per capita consumption of CO₂ in India is only 1.2 ton as against 20.6 ton in USA, 20 ton in Canada and around 10 ton each in UK, Germany and Japan. The global share of CO₂ emissions by India is only 4.6 per cent as against 20.9 per cent by USA and 17.4 per cent by China.

However, the most dangerous are the chloroflurocarbons (CFCs), which are entirely anthropogenically produced. CFCs were absent in the atmosphere before 1930s, but their concentrations have steadily increased over the last few decades. They not only possess longer life time in atmosphere, but also are thousands of time stronger than CO₂ as greenhouse gas. Since CFCs enter into stratosphere and destroy ozone layer, these are more dangerous and being phased out as part of Montreal protocol and replaced by hydroflurocarbons (HCFCs).

The neat effect of increase in GHGs and CFCs is the rise of global mean temperature, which has been recorded as 0.75 °C during 1906 to 2005. However, model based projections made in the Fourth Assessment Report of the International Panel on Climate Change (IPCC) predict a rise of average global temperature between 1.1 and 6.4°C by the year 2100.

Warming in the mid troposphere and cooling in the much of the stratosphere are useful detection fingerprint of greenhouse warming. The cooler stratospheric temperature would be an expected consequence of the increased trapping of terrestrial radiation in the troposphere. However, stratospheric cooling may not solely be attributed to greenhouse forcing and may also result from ozone depletion.

Term Paper # 3. Impact of Climate Change on Aquatic Resources:

i. Melting of Ice, Sea Level Rise and Oceanic Circulation:

The changing scenario of climate has the potential to influence the marine and freshwater fisheries indirectly through alterations in the aquatic ecosystem and directly through influencing the physiology of the fish and other aquatic resources. The principal effects of global warming on the marine ecosystem are increase in sea level, changes in oceanic circulation, increase in salinity and acidification.

Increased global temperature is likely to increase global mean sea level partly due to thermal expansion of sea and partly due to melting of land based ice masks. There is strong evidence of melting of ice core that has survived warming for long period. These include breakdown of Larsen ice shelf on the Antarctic continent, disintegration of sea ice blocking the Gustav channel between the Antarctic Peninsula and James Ross Island and substantial recession of mountain glaciers since the later half of the nineteenth century.

Global sea level rise has been recorded at 1.8 mm/year during 1961-2003. The average rise during the recent past (1993 to 2003) was even faster (at the rate of 3.1 mm/year). The current global climate mean projects a 4 cm rise of sea level per decade. If it is reasonable, it may cause serious threats to the low lying islands and coastal zones increasing the risk of coastal flooding, damage of fisheries and salination of fresh ground water supplies. India having a long coast line of about 8000 plus km is most vulnerable to such rise in sea level.

One meter rise in sea level can put as many as 7.1 million people, including all coastal fishing communities whose livelihood is directly linked to the ocean, of the country at risk of displacement. Current records indicate an average of 1.30 mm sea level rise per year along the coasts in India (URL-1).

Changes in oceanic circulation, a consequence of changing global climate, influence the marine ecosystem and its fisheries. Increasing frequency of El Nino episode is considered as evidence of such changes. El Nino is defined as sustained sea surface temperature anomalies of magnitude greater than 0.5°C across the central tropical Pacific Ocean.

El Nino’s warm current of nutrient-poor tropical water, heated by its eastward passage in the equatorial current during Christmas, replaces the cold, nutrient-rich surface water of the Humbolt current, also known as the Peru Current, which support great populations of food fish.

In most years the warming lasts only a few weeks or a month, after which the weather patterns return to normal and fishing improves. During this period walker circulation is seen at the surface as easterly trade winds which move water and air warmed by the sun towards the west. This also creates ocean upwelling off the coasts of Peru and Ecuador and brings nutrient rich cold water to the surface, increasing fishing stocks.

However, when El Nino conditions last for many months, more extensive ocean warming occurs and their impacts on local fishing become serious. Some fish population increase while others decrease during El Nino years. The horse mackerel and scallop population increased, while the jack mackerel and anchoveta population decreased during the conspicuous El Nino episodes in 1971, 1982, 1991 and in recent years.

The shrimps and sardines have been found to migrate southwards during the episode. Based on paleoclimatic studies (records of major episodes of climate change during the course of earth history) and pattern of circulation change it has been predicted that El Nino episode will possibly increase in their intensity or/and frequency in the coming decades.

ii. Sea Surface Temperature, Salinity and Acidification:

Records of past 25 years indicate that sea surface temperature has positively increased and this has been ascribed to greenhouse warming. Dealing with recent Atlantic hurricane activities, Saunders and Lee (2008) predicted that an increase in 0.5°C sea surface temperature could contribute a more or less 40 per cent increase in hurricane frequency and activity of seas. Several hurricanes of the recent past such as Katrina, Rita, Aila etc. are assumed to be effects of increasing sea surface temperature.

But, based on measured refractive index of sea water it has been revealed that infrared radiation cannot penetrate into sea water and contribute to ocean warming. Therefore, effect of greenhouse warming on increase of sea surface temperature is questionable. However, there is no doubt that oceans are warming and the near surface water in the more evaporative regions is increasing in salinity in almost all ocean basins. But high latitudes are showing decreasing salinity due to greater precipitation, higher run-off, melting ice and advection.

Increasing concentration of CO₂ in the atmosphere has resulted in increasing concentration of carbonic acid, a product of reaction between CO₂ and water, in the water and decrease of pH. About 1/3 of the CO₂ from fossil-fuel burning is absorbed by the world’s oceans. Ocean acidification poses a great threat to marine life and ecosystems, especially organisms that use calcium carbonate to form shells and skeletons, like phytoplankton and corals.

In a more acidic marine environment, the sea urchin’s ability to multiply goes down by 25 per cent, as its sperm swim more slowly and move less effectively in acidic water. An estimated decrease of 0.075 pH has occurred in ocean water during the last 250 years. Atmospheric CO₂ concentrations need to remain at less than 500 ppm for the ocean pH decrease to stay within the 0.2 limit set forth by the US. Environmental Protection Agency. Atmospheric CO₂ levels presently stand at 380 ppm, but are expected to reach 500 ppm by mid-century.

iii. Precipitation:

Precipitation is likely to increase with the increase of global temperature due to greater rates of evaporation of sea surface water. But this is only a prediction at present. Neither there is any reliable estimate of evaporation nor is there adequate instrumental data of precipitation. However, some studies indicated that precipitation tended to increase in the mid-latitudes, decrease in the northern hemisphere sub tropics and increase in general throughout the southern hemisphere.

Term Paper # 4. Impact of Climate Change on Fisheries:

i. Individual and Population Effects:

The fish and invertebrates are cold blooded animals and their body temperature varies with the ambient temperature. Thus any change in habitat temperature will significantly influence metabolism of these animals. The consequence of global warming on individual fish and aquatic invertebrates is exhibited in the alterations of physiological functions such as thermal tolerance, growth, metabolism, food consumption, reproductive success and susceptibility to diseases and toxins.

It influences spatial distribution of fishing and aquaculture activities and their productivity and yields. In general, the cold water tolerant species are more susceptible to warming than their warm water tolerant counterparts.

One classical example of cold water species being victim of warming is the outbreak of disease called “excretory calcinosis” in American lobster (Homaras americanas) inhabiting northern end of the Long Island in USA. This is a gill tissue blood disorder resulting directly from warm temperatures and causing massive catastrophic summer fall mortalities since August 1999. The disease appears to be moving northward.

Another example of climate induced effects on fisheries involves the northward expansion of a disease known as “Dermo” that affects the oyster and is caused by a parasite which kills 50 per cent of the oyster in the Gulf of Mexico. From 1980 to 1990 the disease moved 500 km northward from the south of lower Cheaspeake Bay to the Gulf of Maine. In recent years the Dermo has been recorded very high from Delaware Bay to Cape Cod with no signs of abating.

However, global warming may also prove useful for certain species of fish as well as to some localities. Increase in temperature may cause increase in rate of consumption and growth of certain species up to a certain point. Once the temperature increases past the point where the consumption and growth are maximized, cost of respiration is increased and consumption rate is decreased resulting in rapid decline of growth.

In sockeye salmon (Oncorkynchus nerka) food consumption triples between 2.5 and 17.5°C, but decreases above 17.5°C which is thermal optimum of this species. Similar effects of temperature are found in many species of fish. If the temperature is high enough to cause thermal stress the fish may face problems in osmoregulation, possibly due to increased permeability of gills.

The fish populations may have to achieve new equilibrium dictated largely by the energy costs of coping with a new thermal environment. Achievement of new equilibrium depends on ecological status of the fish (whether stenothermal or eurythermal), the magnitude and rate of thermal change of the ecosystem and opportunities to migrate.

ii. Impact on Marine Fisheries:

Shifting in locality has been detected as a tendency in many species in recent years. As a result many areas are being benefited with catch of fisheries that were not present in the area earlier. But this is at the cost of some other areas from where the fish population is shifting.

During the last 40 years, many familiar species have been shifting to the north where ocean waters are cooler, or staying in the same general area, but moving into deeper waters than where they traditionally have been found. It is apprehended that by 2050 large number of marine fish will migrate from tropical seas to cooler waters specifically the Arctic and Southern oceans.

Investigations by Central Marine Fisheries Research Institute on Indian marine fisheries resources indicate that climate changes have altered the production and distribution of some commercially important pelagic fishes from Indian waters. Historically, the distribution of sardines and mackerels were restricted to the Malabar upwelling system along the southwest coast of India. However, a clear cut distribution shifts in these two species have been observed since 1989.

Oil sardine (Sardinella longiceps) has emerged as a major species along southeast coast of India, while mackerel (Rastrelliger kanagurta) fishery has emerged along the northwest coast. Like many other tropical pelagic fishes, the Indian mackerel and the Indian oil sardine have shown population crashes and sudden recoveries and very strong inverse relationship. Shifts in the vertical distribution of the Indian mackerel have also been observed.

This pelagic species is now caught by bottom trawlers. Demersal species such as threadfin bream (Nemipterus japonicus) appear to shift the month of peak spawning toward colder months off Chennai. Shifts in the relative abundance of finfish bear signature of ocean warming. Some species are able to adjust to the immediate challenge of rise in temperature for a shorter or longer duration.

But the species which are not able to adjust the climatic changes or has hurdles in migration may face severe consequences in the coming decades. The cods are fast disappearing from New England. The effect of ocean warming on spatial distribution of Bombay duck, whose northward distribution is blocked by the terrestrial land, is not known. The oceanic tunas are strongly influenced by thermocline. Effects of ocean warming on their distribution are also not clearly known.

iii. Impact on Inland Fisheries:

Concrete evidence of global warming on inland fisheries is lacking. But many lakes across the globe are showing tendency of warming since last fifty years. African lakes are of great concern, because average temperature of this continent is higher than the global average. A minute increase in average temperature of this continent may result in drying of many lakes. However, warm water fishes are rather tolerant to warming in contrast to the cold water counterparts.

Most of the cold water fishes are stenothermal and are most sensitive to even minute fluctuations in temperature. The trout and salmon thrive in streams with temperatures ranging between 10-18°C. In many areas, these species are already living at the upper end of their thermal range, meaning even modest warming could render streams uninhabitable to them.

In India, the snow trouts (Schizothorax sp.), loaches (Nemacheilus sp., Botia sp. etc.), lesser barils (Barilius sp.), mahaseers (Tor sp.) and the exotic trouts (Salmo sp.), which are distributed in the rivers and lakes of the Himalayas, are vulnerable to even minute warming of the environment.

The wetlands and shallow rivers are also susceptible to changes in temperature and precipitation and water levels may drop to the point of completely drying out in dry summers. Recent surveys on two floodplain lakes of Ichamati river basin of West Bengal in India have indicated an alarming trend in decline of depth of the lakes. Similar decreases in depths have been recorded in many other Indian floodplain lakes.

But in most cases the reasons behind such decrease have been ascribed mainly to eutrophication, macrophyte infestation and discharge of organic debris from human settlements. Impact of climate change on these water bodies has hardly been evaluated. However, it has been established that climate change produces most pronounced effect on wetlands through alterations in hydrological regimes.

Increased temperature may lead to stronger, earlier and longer stratification of lakes and reservoirs and with limited or seasonal turnover, greater de-oxygenation (i.e. hypoxia) of the bottom layer, which in turn may influence the community structure of the floodplain lakes.

Therefore, it is very important to maintain hydrology, reduce pollution, control exotic vegetation and protect wetland biological diversity and integrity to maintain and improve the resiliency of wetland ecosystems so that they continue to provide important services under changed climatic conditions.