RESEARCH TOPICS IN BIOLOGY FOR UNDERGRADUATES ON EFFECT OF BIOCHAR ON AUTOTROPHIC NITRIFIERS IN CRUDE OIL-CONTAMINATED SOIL https://emrislot.com/product/research-topics-in-biology-for-undergraduates/
INTRODUCTION AND LITERATURE REVIEW
The Niger Delta area is the hub of crude oil production and processing activities in Nigeria. It is also known to have one of the largest wet lands, encompassing over 20,000 km2 in Southern Nigeria (Obire and Anyanwu, 2008). The region is also regarded as one of the richest part of Nigeria in terms of natural resources, which include large oil and gas deposits, as well as vast forests, suitable agricultural land and abundant fish resources. Despite the tremendous natural and human resources base, a report from the World Bank showed that the region’s potential for sustainable development remains unfulfilled and its future is being threatened by diverse environmental problems of which oil pollution is most paramount (Obire and Anyanwu, 2008). RESEARCH TOPICS IN BIOLOGY FOR UNDERGRADUATES
The Niger Delta ecosystem is subject to man-induced changes and seriously threatened by increasing environmental deterioration. The aquatic and terrestrial ecosystems of the region face increasing ecological and toxicological problems from the release of petroleum pollutants (John et al., 2012).
Crude oil is a naturally occurring, flammable and viscous liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth’s surface (Guerriero et al., 2011). It is recovered mostly through oil drilling. It is refined and separated, most easily by boiling point, into a large number of consumer products, from gasoline and kerosene to asphalt and chemical reagents used to make plastics and pharmaceuticals (Adel, 2012). Crude oil is often attributed as the “Mother of all Commodities” because of its importance in the manufacture of a wide variety of materials (Adel, 2012). The economy of Nigeria is largely dependent on crude oil tapped from the Niger Delta region through the operations of the petroleum industry which is involved in the global processes of exploration, extraction, refining, transporting (often with oil tankers and pipelines), and marketing petroleum products (Alinnor et al., 2014; Onwurah et al., 2007).RESEARCH TOPICS IN BIOLOGY FOR UNDERGRADUATES
Because crude oil is a naturally occurring substance, its presence in the environment need not be the result of human causes such as accidents and routine activities (seismic exploration, drilling, extraction, refining and combustion). Regardless of source, crude oil’s effects when released into the environment are similar. This is because some components of crude oil are carcinogenic and cultivated plants in the soil will absorb it and this is transferred to man through the food chain (Alinnor et al., 2014).
Crude oil and refined fuel spills from tanker and ship accidents have damaged natural ecosystems in Nigeria, the majority of such cases are found in the Niger Delta of Southern Nigeria and many other places (John and Okpokwasili, 2012).
Hydrocarbon degradation by microbial population in natural environment is influenced by physical, chemical and biological factors that contribute to the degradation of petroleum and individual hydrocarbons. Rate of biodegradation depends greatly on the composition, state, and concentration of the oil or hydrocarbons in the environment. Dispersion and emulsification of crude oil enhance the rates of biodegradation in aquatic systems and absorption by soil particulates being the key feature of terrestrial ecosystems (John and Okpokwasili, 2012).RESEARCH TOPICS IN BIOLOGY FOR UNDERGRADUATES
Sensitivity of soil microflora to petroleum hydrocarbons is a factor of the quantity and quality of oil spilled and previous exposure of autochthonous soil microbiota to crude oil (Mishra et al., 2001).
Petroleum hydrocarbon utilizing bacteria such as Pseudomonas putida, Pseudomonas aeruginosa, Bacillus subtilis, Alcaligenes eutrophus, Micrococcus luteus, Acinetobacter lwoffi, Proteus sp., Azotobacter, Beijerinckia, and Klebsiella species can tolerate oil contaminated environments because they possess the ability to utilize oil as energy sources (Kucharski and Jastrzębska, 2005; Okerentugba and Ezeronye, 2003). Other species may not be able to tolerate oil contamination and would be gradually eliminated. Those that cannot tolerate oil contamination but are relevant for maintenance of soil fertility status, include nitrogen fixing, nitrifying and heterotrophic bacteria such as Derxia gumosa, Mycobacterium, Nitrosomonas and Nitrobacter species (Amadi et al., 1996; Van Hamme et al., 2003).
According to Chukwuma et al., (2012), the predominant factors influencing microbial community composition after crude oil contamination include;
(i) contaminant mixture type
(ii) soil type (i.e., physical, chemical, and biological characteristics of soils), and
Complex petroleum hydrocarbon mixtures, including crude oil and diesel fuel consist of various concentrations of n– and branched alkanes, cycloalkanes, phenolics, aromatics, and polycyclic aromatic hydrocarbons. Although these mixtures contain similar constituents, the relative abundance of mixture components and toxic compounds (e.g., heterocyclics, chlorophenols) vary considerably, and these variations are potentially important in determining which microbial populations are involved in biodegradation and the species that are inhibited (Natsuko et al., 2006).
The effect of oil spillage on soil reduces the oxygen concentration of the soil since crude oil is said to decrease soil porosity. This also may lead to a depression of microbial density and activities since oxygen plays a key role in the physiology of nitrifying bacteria (John et al., 2012). Crude oil, which is known to contain toxins and reduce microbial diversity, has been hypothesized to reduce gross metabolic activity of mixed microbial populations in wetland soils (Chukwuma et al., 2012; Bushaf et al., 2011).RESEARCH TOPICS IN BIOLOGY FOR UNDERGRADUATES
Several methods have been introduced to increase the rate of biodegradation of petroleum products in the soil and they include oxygenation by excavation of the soil, nutrient supplementation and microbial seeding (Ekpo and Udofia, 2008). The reduced ability of nitrifying bacteria to participate in remediation of oil-contaminated soil and sediment shows the toxicity effect of petroleum products on the nitrifying organisms (John et al., 2011; John and Okpokwasili, 2012).
These nitrifying bacteria are responsible for the conversion of ammonium to nitrate through a process called nitrification. Because the conversion process is driven by microorganisms, understanding the environmental conditions that accelerate or delay this formation of nitrate is critical (Castaldi et al., 2009). This is important not only for what can be available to a crop, but also for what can be lost. The nitrification process plays a key role in the nitrogen cycle, and nitrifying bacteria are particularly sensitive to environmental conditions. Soil quality can be evaluated in view of the counts of nitrifying bacteria and the intensity of the nitrification process (Castaldi et al., 2009).
Soil type also affects the process of nitrification as soils with a high sorptive capacity can inhibit the toxic effect of polluting substances, thus enhancing the intensity of nitrification (Kucharski and Jastrzębska, 2005).
Nitrification is the rate limiting transformation that affects the form of nitrogen available to plants (Robertson and Groffman, 2015). This biochemical process was discovered by the Russian microbiologist, Sergei Winogradsky in the year 1890 (Jean-Claude et al., 2011).
The form of nitrogen available to plant roots has important consequence on nitrogen uptake and use. Plants can absorb nitrogen as organic molecules such as urea, or as ammonium and nitrate ions. Although nitrate is being taken up in larger quantities than other forms and produce more desirable plant growth than other forms. The term ‘nitrification’ refers to the biological oxidation of ammonium to nitrite and subsequently to nitrate (Jeanette and Shark, 2011). RESEARCH TOPICS IN BIOLOGY FOR UNDERGRADUATES
In soil, the process is mainly accomplished by two groups of chemoautotrophic bacteria of the Nitrobacteraceae family: ammonium oxidizers and nitrite oxidizers. These organisms must oxidize nitrogen to obtain energy for growth and maintenance. By using CO2 as the sole carbon source and ammonium or nitrite as energy sources, the two groups of nitrifiers have conquered a niche in the natural environments from which they can successfully compete with other organisms (Jeanette and Shark, 2011). The price they must pay is their slow growth compared with heterotrophic organisms.
Heterotrophic nitrification is assumed to be insignificant in agricultural soils (Islam et al., 2007) and will therefore not be dealt with in this research work. Conversion of ammonia to nitrite is usually the rate limiting step of nitrification. Nitrification is an important step in the nitrogen cycle in soil.
The nitrifying autotrophs are typically obligate in their dependence upon inorganic materials for energy, not only is organic carbon not utilizable as sole source of carbon for growth, but no energy is obtained from the oxidation of any other inorganic substrates other than those containing nitrogen (Veuger et al., 2013). De-nitrification proceeds only at conditions of lilmited oxygen supply. However, oxygen is necessary for nitrite and nitrate formation and any substance that has the potential of depriving the nitrifiers access to optimum oxygen for growth will inhibit their growth and create a gap in the nitrogen cycle (Veuger et al., 2013).RESEARCH TOPICS IN BIOLOGY FOR UNDERGRADUATES
Oxygen affects nitrification rates through its roles as a substrate for the ammonia monooxygenase enzyme and as the terminal electron acceptor from cytochrome c oxidases (Arp et al., 2002). Oxygen availability is controlled by the interaction of oxygen consumption and diffusion from the surface through the air-filled pores. Sufficient oxygen diffuses into most soils that are at field capacity or drier to maintain nitrification, although microsites lacking oxygen may frequently occur inside soil aggregates (Usirri and Rattan, 2013).
In soils that remain wetter than field capacity for several days or whose pores have been blocked by crude oil molecules, nitrification rates generally decline. The observed decline in net nitrification rates may be due to either a decline in actual nitrification or an increase in denitrification (both of which should occur at lower oxygen concentrations). Low oxygen availability may repress nitrite oxidizer activity before ammonia oxidation and result in the accumulation of nitrite (Usirri and Rattan, 2013; Jeanette and Shark, 2011 ).
Both ammonia and nitrite oxidation are generally considered to be optimal at neutral to slightly alkaline soil pH values. For pure cultures of ammonia oxidizing bacteria, specific growth rates and activity are significantly reduced outside a relatively narrow pH range around the optimum for the organism. Thus, the presence of any substance in the soil that will have a significant change in soil pH will affect the growth and proliferation of the nitrifiers which will have a direct impact on the nitrification process (Jeanette and Shark, 2011).
Biochar incorporation into soil is expected to enhance overall sorption capacity of soils towards anthropogenic organic contaminants (e.g. aliphatic hydrocarbons, polycyclic aromatic hydrocarbons – PAHs, pesticides and herbicides), in a mechanistically different (and stronger) way than amorphous organic matter. This quality may greatly mitigate toxicity and transport of common pollutants in soils through reducing their bioavailability (Verheijen et al., 2009).
Biochar is defined as a carbon-rich product produced by pyrolysis of organic material such as wood or manure with a limited supply of oxygen (Lehmann and Joseph, 2009). Biochar can also be described as: “charcoal (biomass that has been pyrolysed in a low or zero oxygen environment) for which, owing to its inherent properties, scientific consensus exists that application to soil at a specific site is expected to sustainably sequester carbon and concurrently improve soil functions (under current and future management), while avoiding short- and long-term detrimental effects to the wider environment as well as human and animal health” (Verheijen et al., 2009).
Biochar is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. The addition of biochar to soil have the potential to alter soil microbial populations (Bushnaf et al., 2011). The broad array of beneficial properties associated with biochar additions to soil may function alone or in combination in order to influence nutrient transformations.
Ecosystem-wide effects of biochar range from improving water-holding capacity and porosity, enhancing cation-exchange capacity (in combination with organic material), increasing levels of beneficial bacteria, providing a refuge from predation for mycorrhizal fungi, and enhancing beneficial soil-fauna such as earthworm populations (Gundale and DeLuka, 2006; Van Zwieten et al., 2007). In combinations, this array of physical and biological effects has the potential to reduce soil denitrification, and to improve the activity of beneficial microbes. Much of the critical chemistry in soils takes place on the extensive charged nano-porous surfaces in contact with water (Blackwell et al., 2007).
The liming effect of biochar on acidic soils had been confirmed by Yuan and Xu (2011a). This is because the alkaline substances in biochar are more easily released into the soil compared with its feed stock when biochar samples are incubated with the soil (Yuan et al., 2011b). When biochar with higher pH value was applied to the soil, the amended soil generally became less acidic (Yuan et al., 2011c). Biochar has also been found to sorb a variety of heavy metals, including lead (Pb), arsenic (As) and cadmium (Cd) (Cao et al., 2009).