1. Eutrophication1.1 Introduction Eutrophication occurs when an aquaticecosystem becomes enriched with nutrients, causing an increased growth ofphotosynthetic bacteria and the development of dense mats of floating plantssuch as Nile cabbage and water hyacinths in lakes and lower reaches of rivers. Waters with low salt concentrations are calledoligotrophic and the salts are the limiting factor for plant growth. On theother hand, waters with high concentrations of salt are called eutrophic andthere is much limitation on growth.
Eutrophication can occur naturally as thelakes grow old and filled with sediments. However, human activities can speedup the rate of eutrophication through the discharge of chemical nutrients(phosphates and nitrates) into the water systems. This will bring large impactsto the environment and living organisms. Leaching of nutrients from the soil into thewaterways causes populations of algae and photosynthetic bacteria to grow veryrapidly. Algal blooms occur where the water becomes densely populated withspecies of blue-green bacteria. The density of these blooms increases to apoint where light is unable to penetrate into the water.
The algae deep in thethe lake are therefore unable to photosynthesise, and die. 1.2 Processof Eutrophication (Refer Appendix 1.1) The increased nutrients promote rapid growthof algae when they are deposited in rivers and lakes.
This explosive growth ofalgae is called an algal bloom. Some algae produce toxins that are harmful tohigher forms of life. This can cause problems along the food chain and affect otheranimals that feed on them. The densely populated algae cover the watersurface and block sunlight from penetrating into the water.
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Photosyntheticmarine plants under the water surface are unable to carry out photosynthesis.Thus, the marine plants die and the aquatic animals lose their food sources andhabitats. The food chains and ecosystem change. The death of algae and other photosyntheticorganisms encourages the growth of decomposing organisms especially saprophyticbacteria or detritus. Decomposition process may use up large quantity of oxygento decompose the dead organisms. This reduces the oxygen content in the waterand the biochemical oxygen demand (BOD) of the water is increased.
The higherthe BOD value, the more polluted the water as the dissolved oxygen leveldecreases, leaving none for aquatic organisms. As a consequence, all aerobiclife which requires oxygen in the water to live dies. Their bodies add to theorganic material available for the decomposers and so the situation worsens.
1.3 Causes of EutrophicationEutrophication may happen quite naturally.However, sources of human pollution have made eutrophication increasinglycommon, and are leading to the death of many rivers and ponds. The saltsnecessary for eutrophication are largely nitrates and phosphates which areneeded for photosynthesis. They come from different sources:a. Leaching from the surrounding land – This slownatural process involves the removal of salts caused by floods and the flow ofwater from lakes or rivers. Drainage of water can wash excess nutrients off theland into the water systems.
In addition, lakes naturally accumulate sediments andminerals as they grow old, which contribute to the explosive growth of phytoplanktonand cyanobacterial, thus causing dense growth of algal blooms.b. Fertilizers from agricultural fields – Inorganicfertilizer is applied to farmland to replace the nutrients in the soil and toincrease the crop yield.
Fertilizers contain nitrates and phosphates which arehighly soluble and they are readily leached into the soil. These nutrients arequickly run off into lakes and rivers if the soil canno longer assimilate the high concentration of nutrients, causing anincrease in nutrient levels in the water. Photosynthesis of aquatic plant lifeis increased, causing algal blooms.c. Direct sewage discharge and industrialwaste – In some developing nations, sewage water is directly discharged intowater bodies such as rivers, lakes and oceans.
As a result, it introduces largeamount of chemical nutrients which stimulates the dense growth of algal bloomsand other aquatic plants that can threaten the survival of aquatic life. Even ifit is discharged into the water after treatment, it can still cause theaccumulation of excess nutrients, ultimately bringing about eutrophication. d. Run-off of animal waste – Animal wastesthat are pumped into the river or lake form a massive food supply fordecomposing organisms. These decomposers use up much of the oxygen to decomposethe sewage and this results in death of the waterway.e.
Aquiculture – Aquiculture is a techniqueof growing shellfish, fish and aquatic plants (without soil) in watercontaining dissolved nutrients. If aquiculture is not properly managed, theunconsumed food particles together with the fish excretion can significantlyincrease the levels of nitrogen and phosphorous in the water, thus results in excessivegrowth of microscopic floating plants. 1.
4 Effects of Eutrophicationa. Threatens the survival of fish and otheraquatic life forms – The increased nutrients in aquatic ecosystems causes thephytoplankton and other photosynthetic plants to grow explosively, whichresults in algal blooms. The algal blooms limit the amount of dissolved oxygenrequired for respiration by the aquatic plants and animals.
When the dissolvedoxygen reaches hypoxic levels, the animal and plant species under the watersuffocate to death. In extreme cases, the anaerobic conditions encourage thegrowth of bacteria that produces toxins which are deadly to the marine mammalsand birds. Decomposition of dead plant life will use up the dissolved oxygentoo. The growth of phytoplankton also reduces light penetration into the lowerdepths of the water. This can bring about aquatic dead zones, loss of aquaticlife and it also lessens biodiversity.b. Deterioration of water quality and declinein the availability of clean drinking water – Algal blooms produce toxic andonce the water reaches the anaerobic conditions, the growth of more toxicbacterial is promoted.
The impact is extensive deterioration of water qualityand limits the access to safe drinking water. The explosive growth of algalblooms and photosynthetic bacteria in the waters can also block water systems, thuslimiting the availability of piped water. c.
Affects living organisms’ health – Thecyanobacteria, also referred to as dinoflagellates generates red tide, thus releasesvery powerful toxins with high poison levels in the water. It can cause deathin humans and animals even at the least concentration when ingested in drinkingwater. Besides, freshwater algal blooms can threaten livestock health. Thetoxic compounds can make their way up the food chain, contributing to variousnegative health impacts such as cancers.
For instance, the shellfish accumulatethe poison in their muscles and can poisons humans upon consumption. Highnitrogen concentration in drinking water can inhibit blood circulation ininfants, a condition known as blue baby syndrome.d. Endangers fishing – The extensive growthof aquatic plants such as algae, Nile cabbage and water hyacinths makes itdifficult to set the fishing nets in water and the floating plants will alsolimit the mobility of boats and other fishing vessels.
e. Degradation of recreational opportunities- The algal blooms and other floating aquatic plants reduces the transparencyand navigation in the water, which will lessen the recreational valuesespecially for boating and swimming. Nile cabbage, algal blooms, and waterhyacinth can spread over the entire surface of the shores and can even floatinto the land area. 1.
2 Ways to reduce Eutrophicationa. Composting – Composting is a practice ofconverting organic matter such as food residues and decaying vegetation intocompost manure. The nutrients in the compost manure are deficient of the highconcentration of nitrates and phosphates that feed the algae and other microbesin water bodies. Manure decompose slowly so that the nutrients are not readilyleached away. All the essential elements are broken down and synthesized by theplants thereby not creating the cycle of eutrophication. b. Proper treatment and breakdown of sewagebefore it is released into the rivers and lakes – This method can reduce theamount of nutrients being disposed into the water.c.
Reducing pollution – To controleutrophication, industries and municipalities should reduce the pollution ofwater by stop discharging waste into water systems so as to reduce the amountof toxins and nutrients ended up in the waters that feed the algae and othermicroscopic organism.d. Strengthening laws and regulations againstnon-point pollution – According to EPA, non-point pollution presents the mostserious challenge in the management of nutrient entry into water systems.
By controllingnutrient sources and minimizing non-point pollution, the amount of nutrientsentering the aquatic ecosystems is lessened, thereby reduce eutrophication. e. Ultrasonic Irradiation – The use ofultrasonic irradiation is a mechanism which has been exploited as analternative solution to control algal blooms. The process works by causing cavitationwhich produces free radicals that will destroy algae cells. Still, research isstill underway to determine the uniqueness of its use in controlling theeutrophication problem.
f. Install mixing devices in lakes – Mixingof stagnant water, for example by air bubbling, enhance vertical mixing of phytoplankton,which can decrease the formation of surface blooms of buoyant cyanobacteria. Increasingthe water flow through lakes or estuaries also reduces water residence time andinhibits cyanobacteria blooms. 1.3 Examples of Eutrophicationa.
In 2007, for instance, more than 2 millionresidents of Wuxi, China could not access piped drinking water for more than aweek due to severe attack by algal blooms on Lake Taihu.b. In 2011, Lake Erie experienced the largestharmful algal bloom in its recorded history, with a peak intensity over threetimes greater than any previously observed bloom. Land use, agriculturalpractices, and meteorological conditions may all have contributed toexacerbating the algal bloom. Weak lake circulation has led to abnormally longresidence times that incubated the bloom. Uncommonly warm and quiescentconditions in late spring and summer after bloom makes the algae to remain nearthe top of the water column and prevented flushing of nutrients from thesystem. (Refer Appendix 1.
2)c. According to the latest HELCOM assessmenton eutrophication, in 2007-2011 almost the entire open Baltic Sea was assessedas being eutrophied and only the open Bothnian Bay was assessed as beingunaffected by eutrophication. Number of phytoplankton increases, especialycyanobacteria because of the increases in nutrient concentrations and due tothe changes in the seasonal availability. Cyanobacteria bloom (Nodulariaspumigena) in the western Baltic.
(Refer Appendix 1.3) 2.Deforestation2.1IntroductionDeforestation is the extensive removal oftrees from large tracts of land for logging, agriculture, development andgrazing operations.
Forests are formed over millions of years. Although theycover only a relatively small percentage of the surface of the Earth, they areimportant in absorbing carbon dioxide from the atmosphere for photosynthesis andin maintaining species diversity because they are the homes of an estimated 50to 90 percent of all land-dwelling species.Long before the advent of highlymechanized logging practices, people were practising shifting cultivation. Theycut and burn trees, then till ashes into the soil.
The nutrient-rich ashes cansustain crops for one to several seasons. Afterward, heavy leaching causes thesoil infertile, thereby abandon the cleared plots. When shifting cultivation ispractised on small, widely scattered plots, a forest ecosystem does notnecessarily suffer extensive damage. But soil fertility declines withincreasing in population size. Then, larger areas are cleared, and plots arecleared again at shorter intervals. At one time, tropical forests cloakedregions that were, collectively, twice the size of Europe. However, as the timegoes by, poverty and greed have driven people to ever-increasing destruction ofthese vital ecosystems.
By 1980, around 44% of all the tropical rainforest hadbeen cleared, and in the 1990s, this destruction is continuing at the rate ofaround 35 acres every minute. If it continues at this rate, in about 90 years’time, there may be no tropical rainforests left. 2.2 Importance of Forestsa. Forests help control soil erosion,flooding, and the accumulation of sediments that can clog rivers, lakes, andreservoirs by intervening in the downstream flow of waterb. Forests function as habitat of variousflora and fauna. – Nearly half of all known species live in forests, including80 percent of biodiversity on land.
That variety is especially rich in tropicalrain forests, from rare parrots to endangered apes, but forests teem with lifearound the planet: Bugs and worms work nutrients into soil, bees and birdsspread pollen and seeds, and keystone species like wolves and big cats keephungry herbivores in check.c. Forests are housing plants which producefood and pharmaceutical products. – Forests provide a wealth of naturalmedicines and increasingly inspire synthetic spin-offs. The asthma drugtheophylline comes from cacao trees, for example, while a compound in easternred cedar needles has been found to fight MRSA, a type of staph infection thatresists many antibiotic drugs.
About 70 percent of all known plants withcancer-fighting properties occur only in rain forests.d. Forests help in regulating world’s climate.- Large forests can influence regional weather patterns and even create theirown microclimates. The Amazon, for example, generates atmospheric conditionsthat not only promote regular rainfall there and in nearby farmland, butpotentially as far away as the Great Plains of North America.e. Forests help in regulating the amount ofcarbon dioxide and oxygen in our atmosphere.
– They do this by taking in carbondioxide and giving out oxygen during photosynthesis. Asingle mature, leafy tree is estimated to produce a day’s supply of oxygen foranywhere from 2 to 10 people. Phytoplankton are more prolific, providing halfof Earth’s oxygen, but forests are still a key source of quality air.f. Forests serve as water catchment areas. – Thewatersheds of forested regions absorb, hold, and then release water gradually. Theirleaves slow down the rate of evaporation and the rate at which water reachesthe soil. Forests catches runoff rather than letting it flow across thesurface, but they can’t absorb all of it.
Water that gets past their rootstrickles down into aquifers, replenishing groundwater supplies that areimportant for drinking, sanitation and irrigation around the world.g. Keep us cool.
– By growing a canopy to hogsunlight, trees also create vital oases of shade on the ground. Urban treeshelp buildings stay cool, reducing the need for electric fans or airconditioners, while large forests can tackle daunting tasks like curbing acity’s “heat island” effect or regulating regional temperatures.h.
Keep Earth cool. – Trees absorb CO2 thatfuels global warming. Plants always need some CO2 for photosynthesis, butEarth’s air is now so thick with extra emissions that forests fight globalwarming just by breathing. 2.3 Causes of Deforestationa. Worlddemand for tropical hardwoods as timber, lumber and building materials – Ashuman population increases around the world, more trees are being cut down tofulfil the need of wood supply for construction of buildings.b. Highdemand for paper for newsprint, photocopiers, printers and office consumption -Wood based industries like paper, match-sticks and furniture also need asubstantial amount of wood supply.
c. Increasingdemand for firewood and charcoal as fuels. – Wood can be used as fuel,therefore trees are chopped for supplies. d. Clearingof land for farms, cattle ranches, plantations, cropland, agricultural land andgrazing land.
– Because of overgrowing demand for food products, many trees arecut down to grow crops and for cattle grazing. Increase in global demand forcommodities, such as palm oil and soybeans, makes the industrial-scaleproducers to clear the forests at an alarming speed. Even when efforts are madeto replenish barren plantations, the infertile soil is not able to produce thesame biodiversity it once was. e.
Clearingof land for the construction of new roads and towns – With the expansion of populationsand cities, more land is needed to establish housing and settlements. Therefore,forest land is cleared. Road construction can lead to deforestation byproviding an entryway to previously remote land. 2.4Effects of Deforestationa.
Leads to soil erosion, landslides andflash floods. – Clearing of trees causes the loss of leaves to protect the soilfrom the impact of raindrops and wind. Therefore, the soil is exposed directlyto the force of the rain and wind, and it will rapidly become barren. Deforestationalso causes the loss of tree roots to hold the soil and the stability of thesoil is affected.
When it rains for a long period of time during rainy seasons,the top layer of soil loosens and can be washed away by the rainwater easily,especially on steep slopes. This leads to soil erosion and even landslides. Theeroded soil is carried away by water and may deposited in rivers. Moreover,rainwater will flow quickly into the river during heavy rainfall because thereis no retention of water by plant roots and water catchment areas. Due tosilting in the rivers, the water flow is blocked.
Thus, water flows inland andcauses flash floods in low areas. Flash floods may cause loss of lives andproperties. Soil erosion may lead to depletion of minerals for the land too. Thus,the land cannot be used for cultivation.
b. Loss of biodiversity, – Deforestationleads to the loss of habitats for many species of flora and fauna, and theanimals are forced to move to new locations. Several species are finding ithard to survive or adapt to new habitats. Some of them are even pushed toextinction. It also causes local extinction of species of trees. As a result,it reduces biodiversity and the source of food and valuable medicines forhumans. c.
Climatic changes. – Destruction of forestsincreases the amount of carbon dioxide (a greenhouse gas) in the atmosphere asless photosynthesis takes place, and so leads to global warming or greenhouseeffect, as well as the chances of disastrous changes in climate. This willcontribute to the melting of the polar icecaps and shifting patterns of windand rainfall which have huge impact on agriculture throughout the world. In thelarger picture, deforestation alters rates of evaporation, transpiration,runoff, and regional patterns of rainfall. In the logged-over regions, annualprecipitation declines, and rain swiftly drains away from the exposed,nutrient-poor soil. The regions are now hotter and drier, and soil fertilityand moisture have plummeted. In time, sparse grassland or desertlike conditionsmight prevail instead of the formerly rich, forested biomes.
Tropical forestsabsorb much of the sunlight reaching the equatorial regions of the Earth’ssurface. Deforested land is shinier and it reflects more incoming energy backinto space. Trees release water vapour in the air, which is compromised on withthe lack of trees. Trees also provide the required shade that keeps the soilmoist.
This leads to the imbalance in the atmospheric temperature furthermaking conditions for the ecology difficult.
