Air is the most important natural resource that should be taken care of at all cost. The effects of pollution to the air cause a lot of imbalance in the ecosystem making the living organism to be affected adversely. According to this document, lichen is covered in relation to the effect it has in the air pollution. It also covers the ability of lichen to be used as air pollution indicator. It discusses various objectives that can increase the use of the lichen in the regulation of the pollution and in air management.Air resource managementFor each federal government there are provisions provided in different acts to protect and preserve the environment. Such important composition of the environment is air. In United State, each organization is given the mandate under Clean Air Act to protect the quality of air and its related values. Other than air conservation, water quality, soil and vegetation among others are stipulated in the act also. Therefore, vascular plants and lichen have been in study to help in assessing the effects of air pollution. This help the people concerned to evaluate whether such plants should be grown in the environment. Therefore, in united state, the Clean Air Act Amendment of 1977 came up with a provision bill called Prevention of Significant Deterioration (PSD) (Garty, 2000). This provision mandated the federal manager to come up with recommendation on the effects of pollution if the pollution source were built with level of emission stipulated in the provision.This necessitated the use of such plants as lichen to pred9ct the outcome. This was brought about by lack of proper quantitative method to help determine the effects.Thus, due to the diverse importance of lichen there was need to ensure that the plant is protected under the law. Therefore, the Clean Air Act and National Park Service Organic Act in US provided for this. The reason as to why they are protected is that the environmental diversity should be protected for future generation. In addition, the effect of poor air management that leads to it pollution, has adverse effect in the sensitive organisms that maintain the ecosystem stable. Such organisms like lichen, bryophytes play a great role in the biodiversity and help to integrate nutrients in the soil. They also help in provision of shelter to animals' and they are main source of forage. If such organisms are lost from the ecosystem, it causes imbalances and leads to decline in the productivity.
Good ecosystem provides many services to the environment. Such services are provision of clean oxygen, clean water supply, and beautification of the environment, animal shelters and productive land among others. Lichen has shown to be adversely affected by air pollution. Therefore, well-organized studies can help the people involved to come with a solution whether the pollution of air is in any way linked with the lichen habitant and its viability.According to Herzig, R. (1990), lichen is used as indicators for environmental health. The study shows that dormant lichen should be used as passive monitor of air pollution. Then use of lichen does not give direct information on how approve government regulators. This is because equipments that are more precise should be used to determine the exact amount of the concentration of air pollution. If the concentration of the pollution is the one desired the lichen cannot be used. However, the lichen can used to show us the presence of air pollutants and the amount in relative to different areas. Thus, it can be helpful in identification of the hot spot for later examination of the concentration. They are very important to set screening mechanism for areas that requires subsequent intervention.Despite of lichen being very useful in the study of causes of air pollution, it also give the concerned personnel great problem. They make them not certain in predicting the because of the air pollution and ways to be prevent the cause. Thus, there is no effective method stipulated by the study that can be effective by use of the lichen. Thus, more research is required to improvise this.Lichen as air pollutant indicatorLichens are organisms that are formed by fungus and they are composite in nature. It is used as air pollution monitor because low concentration of the organic compounds pollutants affects it. Such compound as sulfur, nitrogen and fluorine affects lichens growth, its reproduction and morphology greatly. They are also very useful because they are capable of concentrating the pollutants in their tissues. This help the researchers able to leant the pollution type and the difference of the air pollution around the area in relative to others to help in taking appropriate action (Kauppi, 1983).There several methods that can be used to monitor air pollution using lichen. These are called biomonitoring method s that include, lichen tissue analysis, transplant studies and community analysis. The lichen community analysis can be used to check the quality of air in a place with more trees and its change in the environment. Lichen tissue analysis can be use in the study of the air quality improvement by studying its composition. This help in showing air oxidation level by the air pollutants such as sulfur dioxide.The benefit of lichen is that it lives for a long time thus ensuring that studies can be done in any time of the year. They also can grow in wide range of geographical area. This allows studies to be conducted in a wide pollution gradient. Such properties are very helpful during temporary studies of air pollution. The best lichen that is use in the study of effects of the air pollution is the one that grow on the trees called epiphytic lichen. It does not have roots and it is well exposed to the environment as it hangs over the tree. This expose it well to the pollutants of air and their effects are not tempered with by soil minerals, as they are not in contact at any one time. This lichen depends on atmospheric gas, water seeping and deposition for their food. Therefore, these lichens tissues reflect the type of the air pollutants. Lichens that grow on the soil absorbs nutrient from the ground thus making their concentration to be tempered. Therefore, they are not good for pollution study.
The environment can be exposed to a measured pollutant that is made to accumulate in the lichen and its floristic effects analyzed. It is used to check the effect of air worth on the environment. The study can be used to show the whether the pollutant causes positive effects to the plants or not. An example of a measured pollutant can be grazing animals. Such can be used to show the amount of the effect they have in air by study of lichen tissue. Lichens show difference in sensitivity towards air pollution. This depends with the form of growth of the lichen. The sensitivity in lichen towards the air pollution increases from lichen that grows adhering to trees (crustose); leafy lichens (foliose) to shrubby lichen (fruticose). This is very important when selecting on the lichen to use in the study. When this lichen is exposed to sulfur dioxide, fluorine gases or nitrogen deposition their biomass decreases.The challenge that has been experienced in comparing the concentration of the pollutants in the air and in the lichen tissues is the period is the age of the lichen and the period taken to monitor the pollution of air. When the time of deposition of the pollutant is required, then it is advisable to use growing species. This will help in checking the annual growth increment and the concentration in each tissue range thus establishing the deposition time. Otherwise, substrates of predetermined age can be used and comparison done from different species. A good example is lichen twigs or use mean lichen tissue concentration from several species for comparison. However, caution should be taken when doing such comparison for there can be minor significance. It is not always size related and may vary with rate of growth. In addition, lichen species also matters a lot. Such factors should be put in consideration. For example, if the concentration of air pollution to be considered is desired of not more than two years, lichen adhering on the wood with less than two buds should be used.Sensitivity of lichens to air pollutantsFrom Kauppi, M. (1983), different species of lichens have different response towards air pollutants. The pattern at which they react to pollutants range from being a little bit resistance to very sensitive. Study shows lichen to be very sensitive towards the effect of sulfur pollutant. At ambient sulfur pollutant concentration, the most sensitive species dies of its effect at an annual range of 0.003- 0.012 parts per million (ppm). While concentration of sulfur pollutant exceeding 0.048 parts per million (ppm) cannot be tolerated by most of the species. Lichens tend to be affected by as low and short-term nitrogen dioxide exposure of 0.03 ppm. Ozone (03) also has adverse effects on lichen especially at concentration range of 0.09-0.12 ppm.Lichen is depleted by sulfur dioxide if combined with hydrogen fluoride. The study of the lichen sensitivity shows Fluorine concentration has physical damage to the lichen tissues. In a concentration of 30-80 ppm, results to its tissue damage.The following is a summary table showing effects of different metallic compound air pollutants and their toxicity in lichenEffects to lichenK+, Ca2+ and Sr2+High affinity for o2Has active siteAg+, Hg+, Cu2+Binds with N- and S- moleculesVery toxic even at low concentrationBorderline metalsZn2+, Ni2+, Cu2+, Pb2+Combines readily with sulfur and nitrogen compoundsSpecific air pollutant affecting lichensSimilarly, a number of studies have shown several effects of pollution effects on lichens. According to Kauppi, 1983 it is evident that considering the whole plant, he found out that lichen depicted some characteristics due to pollution. These characteristics include reduction in size of the thallus as well as fertility, convolution and bleaching, high rate o mortality of highly sensitive plants and animals, restriction of the plant only to be found at the base of vegetation.On the same note, air pollution agents do have microscopic as well as molecular impact to lichens and include decreased number of algal cells, destruction of pigments that help plant to photosynthesis, changed ultra-structural of phallus, hampered rate photosynthesis and respiration. Lastly, according to Gries et al., 1995, changes in parameters of chlorophyll fluorescence can be used to determine pollution. For instance, air pollution by sulphur dioxide (SO2) has been shown to interfere with plants fixing nitrogen, higher rates of electrolyte leakage, lowered rates of photosynthesis and transpiration. All these translate to the algae to bleach hence die.It is evident that some species of lichens that develops resistance mechanisms to thrive despite the presence of pollution. However closer examination shows that they depict both internal as well as external morphology. Efforts in mid 1970s that sought to reduce release of sulphur dioxide saw to it that lichen recolonised those areas that they once occupied.Additionally although not well brought out in the clearest manner is the effect of heavy metal to lichens because there are no specific impacts that they have upon the plant. Lichens over time have developed phenotypic characteristics that have resulted to them being tolerant to effects of heavy metal. Nonetheless, due to varying kind of sensitivity, researchers did establish that heavy metal ions affect lichens in three major ways; (modification, blocking and or displacement) of lichen molecules hence interfering with how the plant function. The notable effects of heavy metal impacts to lichen include interfered cell membrane, reduced rates of photosynthesis as well as respiration, effects on drought resistance, enzymes synthesis, molecules that transfer energy, secondary metabolism to mention but a few.Chemical analysis of lichen to test quality of airAnother mechanism that has been perfected and proved fruitful is using chemical tests of lichens to establish the quality of air within any given surrounding. This has been made possible by the way, lichen tend to exchange material from thallus and their surrounding. The wet and dry cycle that they go through especially when it is wet, they absorb water, nutrients, pollutant as well as other substances through their surface. When situation turns to be dry, the absorbed pollutants collect in organelles and crystallize between lichens cells. In rainy season, nutrients are pollutants are washed away.
Garty, J. (2000) shows that analysis of chemical composition of dry lichen tissue in urban as well as areas in which industrial activities take place has been established to contain 13% of sulphur. Contrary, the same analysis of lichen in regions deemed 'clean' were found to have sulphur content as low as 0.15%. Thus it is apparent that lichen can be used successfully to indicate how polluted an environment is.Advantages of using lichen as air pollution monitorThe quality of air can be known by checking the presence of metallic substance in air and its concentration in different areas. This help in giving important information that is useful for further action. Lichen grows in wide area and thrives in different environment. Thus this help in taking many samples over a wide range of area in very short time. The data obtained can be used to track air pollution changes in a given geographical area at a given span of time.Lichen air pollution monitoring can be used to back up instruments and any other information regarding air pollution. With sufficient lichen sites, deposition of the metals can be well-estimated providing sufficient data for instrument calibration.The results of the study can be used show the effects of a certain air pollutants to the environment. It also avails data that compares concentration of a certain pollutant in different areas of the world. Such data are very vital incase affirmative actions to be taken.Lichen does not move from one place to another thus the effects studied are of local area. These results show concentration of pollutants at specific area. Thus, helps combating effects in such areas only.In places where power is not available limiting the use of instruments, lichen is very useful. Moreover, the data obtained from lichen monitory shows areas that are more prone to pollution effects for subsequent instrument studies.When the results of the lichen are standardized, they can be used in the laboratory to check the precision of the equipments and their accuracy.Limitations of using lichen as pollution indicatorsAmong the limitation of using lichen as indicator of pollution are that it requires experts in the field of biology to interpret data. In addition, heavy metal do accumulate and stay long in plant thus it is a challenge to establish when the contaminant started accumulating; it is also a challenge to compare lichens from various location due to variability in adaptation. All these being very necessary for helping relevant stakeholders make strategic decisions (Munzia, et al., 2007).Additionally, factoring in variations in habitats and climatic elevation it becomes difficult to pinpoint an environmental factor that have influence on pollution, in areas that receive rainfall more frequently, it is not possible to carry out chemical tissue analysis. Lastly even the data is generated, those in position that opt to take necessary steps lack the knowledge or not familiar with all that surround, it is also difficult to attribute what causes air pollution especially if there are a myriad of factors that interplay to bring about the problem.From the review of the study concerning using lichen as indicator of pollution, it is evident that they are highly sensitive to slight changes in ecological conditions, especially air pollution from sulphur dioxide and nitrous compounds. The greatest challenge facing humanity at present is adverse changes in environmental conditions. This has warranted scientist to go to greater heights in trying to arrest the situation. One is to dig into the whole issue through ecological studies such as using lichens.Chemical analysis of lichen to test quality of air, specific air pollutant effects on lichens and sensitivity of lichens to air pollutants are the three main attributes that have made it possible for humanity to evaluate pollution.However, this mechanism does have advantages and shortcomings or limitations. Among the advantages is that results obtained can be used to show the impact of specific contaminant, it is useful in scenario where electrical instruments cannot work, there is a possibility of accurately calibrating heavy metals among other advantages. on the other hand, the limitation include, it needs biologists to carryout the study, varying ecological as well as climatic condition do pose a challenge especially when trying to compare studies from varied regions, it is also difficult to establish when heavy metal or begun accumulating in lichens. Nonetheless, using lichens as indicators of air pollution is a good initiative that just needs to be improved and it will help us in the problem of climate change and global warming.