Geochemistry of Natural Waters - Term Paper Example

?Geochemistry of Natural Waters Introduction Geochemistry as a science uses the tools and principles of chemistry. By using these principles it tries to best explain the mechanisms behind the major geological systems including those of the earth’s crust and the ocean and this field goes beyond just the earth. It extends to the entire solar system and highly attributing to better understanding of a number of processes such as planets formation and mantle convection. Water is known to be very essential and a basic requirement in the whole geological cycle. Rain water is able to convert the granitic rocks of the continents into sand, clay and other solutes which are better referred to as raw materials that are transported to the ocean. However there a lot of evidence of human influence that either positively or negatively affect the whole cycle. Therefore in studying geochemistry of natural waters we will try to explain how the water cycle, the soil organic matters its importance, the behavior of some soil components and their interactions (Benites, 2005). The geological process involves a series of actions where hot molten material coming to the earth’s surface from the interior forms igneous rocks which are then broken down by weathering to create soil and the sedimentary rocks. The geologic cycle is a collective term used to describe complex interactions between component sub-cycles of the tectonic, hydrologic and biological cycling of elements. These sub-cycles will influence each other and in the end result to natural hazards and other processes which may be important to the environmental geology e. g ground water flow. Soil Chemistry and soil fertility Soil Chemistry Soil being the top layer of the earth’s crust supports the growth of some organic matter and is made up of components such as pH, nutrient level plus the organic content which in the end determines the type of the soil (Regina, 2006). However the factors listed above will either vary depending on the type of crop which grows in that soil type and within a given geographic location. These factors will result to different soil quality types and the soil quality can be best determined by conducting soil test. Soil can be modified to suit other purposes such as farming. This can be done in several ways such as liming. This is the use of lime powder that will be spread on the soil to alter the pH of the soil. This is made possible because of the presence of Calcitic limestone (CaCo3) (Tan, 2011). This is usually a good source of Calcium and neutralizes the soil acidity. For plants survival there are nutrients to facilitate the growth the three most important being Carbon, Hydrogen and Oxygen which can be obtained in large quantities from the atmosphere and water surrounding the plant that is ground water. Therefore the ground water plays a big role in the whole cycle. Soil chemistry began with early observations by experimenters. The first study was by J. Thomas. With time came to prove that, it is indeed true that soils can retain cations in exchange for equal amount of Calcium (Ca2+) ions (Tan, 2011). Soil Fertility With the term soil fertility we refer to that situation where a given type of soil is very rich in nutrients such as potassium nitrogen and phosphorous which are requirements for plant nutrition. With it also would be sufficient minerals and soil organic matter (Cuevas, 1994). The mineral traces are majorly for plant nutrition while the organic matter helps to improve the soil structure and enable the soil retain more moisture. Fertile soils have a good soil structure, facilitating proper drainage. However some soils are known to be wetter and retain more water content than others. Soil formation in itself is a very long process and can take up to 100-10000 years for a single inch to be formed. This can be attributed to several factors such as climate, topography living organisms and most important is the parent material. The parent material result from the breakdown of rocks or from the deposits by water sources such as streams, the sea, gulfs winds and or of organic plant residues. It is very important that for soil fertility there has to be active biological activity in the soil. These biological activities will help in several ways like, to recycle nutrients, decompose organic matter making nutrients readily available to be taken up by plants, to stabilize the soil humus and at the same time moderate soil ph. (Gaskel, 2012). Any fertile soil has to have sufficient nutrients as earlier mentioned and therefore in order to support the development of aerobic bacteria that encourage availability of nutrients in the soil, it is important to ensure maintenance of good soil conditions for good soil aeration. Organic matter Organic matter in the soil refers to any material from plants or an animal that is taken back to the soil through decomposition. However most of these organic matters originate from plant tissues. These organic matters in the soil are composed of various elements such as microorganisms and stable organic matters. Soil organic matter being the most important and most misunderstood component of the soil has major importance. The major difference between organic matter and organic material is that the material is anything that was once alive and is added to the soil while matter is that which is already stable in the soil and has reached the furthest extent of decomposition (Kumada, 1987). For organic material to become organic matter decomposition must take place to form humus. The organic matter in the soil is of several importance’ including the supply of nutrient. It acts as a reservoir that can be released to the soil. It also has a high water holding capacity holding up to 90 percent of its weight in water. The matter will release most of the water that it absorbs to plants that being an advantage. Other than that organic matter causes soil to crump and form aggregates improving the soil structure. Another property though not very well known is the ability to reduce soil erosion to a certain extent. Several ways are also recommended if need be to maintain and improve soil organic matter levels (Benites, 2005). Behavior of metals in soil The general description of metals could be stated as any element that has a silver luster and can conduct heat and electricity well. Metals can be defined and classified into different categories. The categories include transition metals, trace metals, micronutrients, toxic and heavy metals. As much as these have been used to classify the metals, many of the definitions are arbitrary and many at times we find that these terms have been used widely in literature review and in reports on various studies loosely and fail to meet the real definitions of the terms. The metals in reference with this particular paper include Lead, chromium, arsenic, nickel, zinc, copper, mercury and silver. Metals that are subject to movement in the aqueous phase of soils can be subject to movement with soil water and may be transported to round water through the vadose zone. Metals are non-biodegradable and therefore to reduce the harmful effect of metals such as chromium, and mercury, they can be turned around into other oxidation states so as to minimize their mobility and mobility and toxicity. When metals become absorbed through either absorption or precipitation, there will be prevention of movement of metals to the ground water. In the soil metal interactions, when the metals are introduced at the surface of the soil, unless the metal retention capacity of the soil is overloaded then downward transportation does not occur instantly. Transportation does not also occur instantly unless the metal interaction with the associated waste matrix enhances mobility (Shaila Sharmin, 2010). Metal mobility may be enhanced by changes in soil environmental conditions over time such as degradation of organic soil matrix, pH changes or soil solution composition due to natural weathering processes or soil solution composition. In the soil environment metals can be found to exist in one or more several pools which may include. They may either be present in the structure of primary or secondary minerals, precipitated as pure or mixed solids, associated with insoluble organic matter, absorbed on inorganic soil constituents or occupying their various exchange sites or they may be dissolved in the soil solution. In most cases the metals will exist in all the above pools except being present in the structure of secondary or primary minerals when they have been introduced into the environment through various human activities. When defining metal behavior, a phase known as multiphase equilibrium cannot be left unconsidered. Metals in soil solutions are subject to mass transfer by leaching to ground water and out of the system. It should be noted that metals participate in chemical reactions within the solid states. At any given time metals concentration in the soil is always governed by a couple of processes that are seemingly interrelated. Some of the interrelations maybe through inorganic and organic complexes, reactions involving the reduction of oxygen, and absorption and reabsorption reactions. The existence of molecules is always in two forms which is either I the form of free metal ions in various soluble complexes (units in which central metal ion is bonded with molecules in patterns) with inorganic or organic ligands or associated with mobile inorganic and organic colloidal material. The transportation through the soil matrix can be significantly affected by the presence of complex species in the soil solution. Any metal added to the soil will normally be retained at the soil surface and the movement extent of a metal in the soil system will always be intimately related to solution of surface chemistry of the soil. Ground Water Remediation Ground water is believed to be clean and has been used by many people to justify their needs the highest group of people paying tribute to this being the farmers. Numerous activities by human beings mainly lead to pollution of these waters and therefore the process of ground water remediation is usually aimed at removing the pollutants from the ground water for it to continue its suitable uses. The groundwater is able to saturate the pore space in the subsurface. Contaminants found in the ground water cover a wide range of parameters. These together with the pollutants can be eliminated from the ground water using a number of ways which are biological, chemical and physical treatment technologies. And this are discussed below. The first form of biological treatment is known as Bio augmentation. This involves the application of specifically selected bacteria into a waste water treatment system. The uses of this application are several. It can be used through lagoons, through activated sledge plants, sequencing batch reactors and also through rotating biological contractors. The chemicals used for waste treatment plant are safe except for few that may be a little toxic. The process of bio augmentation will help to increase the reactive enzyme concentration within the bioremediation system and afterwards may increase the contaminant degradation rates over the no augmented rates initially after inoculation. The other method being bioventing. This is also a remediation technology. It is a process that stimulates the natural in situ biodegradation of contaminants in soil and is done by providing air or oxygen to existing soil microorganisms. This process uses low air flow rates to provide only enough oxygen that is able to support the activities microbes in the vados zone. This method is applicable to any aerobically degradable chemical and it has been successfully used to remediate soils that have been found to be contaminated by petroleum hydrocarbons, non-chlorinated solvents, some pesticides, wood preservatives and other organic chemicals. However there are some factors that may limit its applications. These factors include i. low permeability soils that end up reducing bioventing performance ii. air near the structure of concern that is to be extracted to escape move away from the chances of having vapor building up in basements within the radius of influence of air injection wells. iii. Monitoring of off-gases at the soil surface may at times be necessary. iv. Aerobic biodegradation of many chlorinated compounds may not be effective enough and v. Low soil moisture content that may result to bio degradation. Availability of oxygen will generally control the rate of aerobic in situ in the whole process of bioremediation. Bioventing is most at times the most suitable method for supplying oxygen to unsaturated soil zone and more often it couples soil venting with bioremediation. Studies have shown that bioventing can be successfully applied to compounds. These compounds can range from light hydrocarbons to high hydrocarbons. Other than venting alone, the promotion of biological activities through nutrients and moisture addition and optimization of the bioventing flow rates, can be greater achieved through the reduction of contaminants. Another in situ remediation technology is the use of indigenous microorganisms to biodegrade organic constituents in saturated zones better known as biosparging. The saturated zone is injected with oxygen and nutrients to increase the biological activities of microorganisms. It helps to reduce the concentrations of petroleum constituents that are dissolved in ground water, those that are within the capillary fringe and those absorbed to soil below the water table. Biospluring is a method that combines two applications. It involves the use of a vacuum-enhanced pumping of fee product. It uses the mechanism of a slurp tube that extends into the free product layer. The combination should be lighter than water so as to recover free-product from the ground water and soil and to the bio remediate soils. The pump draws liquid and gas from the soils up in the tube. The free product is then brought to surface and then separated from water and air. The other method of water remediation is through physical means and the most commonly used form is the pump and treats. Ground water is pumped to the surface and is then coupled with either biological or chemical treatments in order to get rid of impurities. Air can also be blown directly into ground water. The contaminants will be eliminated from the ground water with the air as the bubbles rise. This is through the physical contact and they are then carried up into the unsaturated zone. Vapors are removed from the soil as it moves through to the unsaturated zone through a process called soil vapor extraction. The other physical methods include dual phase vacuum extraction that uses high vacuum systems to remove both contaminants and soil vapor, monitoring-well oil skimming. Ground and surface waters It is very clear that ground water and surface water are fundamentally interconnected. These two sources feed each other and therefore can never contaminate each other. We can better understand this by taking a look at the water cycle. When it rains or when snow falls, some water will run off to the land and the streams, rivers, lakes and oceans which we better refer to as surface water, at the same time some water will also return to the atmosphere by evaporation or by transportation. The water running through the ground surface will infiltrate the soil where it can continue to move down and become ground water or alternatively can move down and then sideways or backup to become surface water. Some water will also be absorbed by the plant roots. As water moves down and sideways or backup to become surface water, the rate of movement will always vary. Ground water very slowly moves toward low areas including streams and lakes where it gets discharged and here it ends up becoming surface water again. The cycle will be completed only on evaporation. Ground water itself becomes affected in two major ways that is in terms of its quality and quantity. Overdraft is a problem and occurs when the ground water is removed faster than recharge can replace it which may intern result into a permanent loss of a portion of its storage capacity and a gradual change that can cause water of unusable quality to contaminate good water. In terms of quality the water quality can be negatively affected by the pathogens and organic compounds. Ground water quality As opposed to what most of us think, water quality is not a matter of taste, clarity or odor. Different properties may however be important depending on the other usages other than drinking such as water meant for industrial purpose use. This water must not be corrosive and must also not contain dissolved solids that might precipitate on the surface of machinery and other work equipment. As water continually evolves and moves through the hydraulic cycle, the chemical nature of it evolves respectively. Near coastlines precipitation is found to contain higher concentrations of sodium chloride as compared to industrial areas where precipitation is made acidic by the airborne sulphur and nitrogen compounds. The most important chemical change in ground water chemistry will occur in the soil. In the passage of soil from recharge to discharge area, ground water may dissolve substances it comes across during the movement. The utmost quality of ground water will entirely depend on the temperature and pressure conditions on the kinds or rock and soil formations through which it flows. Faster flowing water therefore is believed to absorb fewer contents as opposed to slow flowing water. At any given location, ground water will always tend to be harder and more saline than surface water. Also with increasing depth ground water more saline. It is true that contamination can render ground water unsuitable for use. However, despite this knowledge the overall extent of contamination has been a serious course for alarm across Canada and only a few cases of contamination have been subject to investigation. Soil management and ground water Ground water is a natural resource which is very essential and therefore concern about its quality and potential contamination has made the effects to protect ground water a national issue in the United States. Ground water exists in very natural state and therefore it can be effectively used without having to incur high costs of treatment and purification. It can also save on the costs that can be incurred in transporting it through long distances since it can be easily tapped. For rural residents, ground water proves to be the only available water supply as most of them rely on individual wells and public water supply. Due to its natural state and suitability for various uses it has therefore justified the widespread dependence on ground water. The consumption of ground water is twice as much as the rate of surface water. There is dare need to continue the protection of future ground water supplies since the consumption trend is bound to continue in the future. For us to appreciate the value of ground water it is crucial that we first of all understand it in its environmental context. Therefore we first look at the relationship between the recharge zone and the saturated zone that is; the relationship of soil to ground water. Water moves from the atmosphere to the earth’s surface, into the ground and eventually will go back into the atmosphere. The formation through which ground water moves is called aquifers. Ground water occupies spaces within rocks features or between particles of sand, gravel. Silt, or clay and does not consist of large underground lakes and streams and neither does it move rapidly in the aquifers. The quantity and quality of water that move down to the saturated zone through the soil will always determine the quality of ground water. For this recharge, (water that moves down through the soil to the unsaturated zone) to reach the water table it has to pass through the root zone and the unsaturated zone. Throughout this recharge process soil plays an important role as it will either hold water in its soil spores, release it to plants or to the atmosphere, or allow it to pass through the underlying materials. Since the quantity and quality reaching the recharge zone is controlled by the ground water, the efforts to protect ground water will have a prime focus on the recharge process. Ground water is a very sensitive and a highly interdependent system as it has distinct characteristics such as being diffuse, vulnerable, and potentially gets affected by all types of activities especially farming practiced by human beings as it was earlier mentioned that they will highly determine the soil state in terms of contamination. Human beings leave pollutants unattended to and therefore they can be carried down into water sources or water tables such as rivers through the recharge water. Farmers commonly use fertilizers with high chemical content and in case of a downpour they become incorporated into the soil and end up becoming ground water contaminants. Once in contact with the recharge water the chemicals form a region of contaminated water known as plume they may intern flow with the ground water, until it resurfaces and contaminates springs, wells, or other surface water bodies. Weathering of rocks Since we saw that contaminants reach the ground water by moving through the percolating water through the soil spores, it therefore has a major role to play also in the removal of contaminants in the soil so as to allow uncontaminated water to flow through the ground since it is a source for many people living in the urban areas. Soil contains a lot of contaminants most of them being chemical ones for example pesticides pathogens and nitrates. Shifting our attention to only the three examples above a number of methods can be employed to ensure soil is free from these contaminants. Most likely pesticides are known to leach through sandy soils since they contain a small percentage of organic matter. These soils do not have a close tie with pesticides and because of few microbes the breakdown process will be slow. To prevent contamination it is necessary to carefully manage pesticides by building up their organic matter. When soils are extremely coarse textured, waste water from septic systems may percolate very rapidly and pathogens may not therefore be allowed opportunity for movement (Estigarribia, 2006). They should be exposed to microbial active aerated soil since they cannot survive for long in such environments. Most microbes are not capable of breaking nitrates down since they are not bound to soil particles. The easiest way of removing nitrates from the soil is through absorption by plants as they require it as a form of nutrients and the other way to get rid of it is through careful fertilizer and irrigation management. Natural waters and trace elements In natural waters trace elements are characterized by concentrations not exceeding 1mg. When total dissolved solids are being calculated in rivers, lakes and waters, trace elements are never considered. The reason being that their combined mass is not significant compared to the mass of elements such as Na+, K+, Ca2+, Mg2+ HCO3- Cl, and NO3. Of all elements almost all of them occur at trace levels in natural waters but they are however not necessarily qualified as trace elements in rocks. Due to technical advances in trying to determine concentrations in water, the geochemistry of trace elements in river waters as well as those of ground water and seawater is increasingly receiving alarming attention. Trace elements such as aluminum (whose concentrations are related to fish abundance in rivers) can play a major role in hydro systems. Many trace elements have been exploited from sites and over several years been used by human beings in various activities (Gamo., 2007). Trace elements are highly sensitive indexes of human impacts from local to global scale. It is generally accepted that for successful studies of impacts on pollution then it is very necessary to fully understand the behavior of trace metals in the geological processes and in particular during chemical weathering and transportation by waters. From the fact that trace elements are much more fractionated by weathering and transport process it is gives us a lead to also understand both the nature and the intensity of both the weathering and the transport process. Understanding of these does not only impact on the application for weathering studies but also for the possibility of better utilization of trace elements in aqueous environments. Ground water and surface water The surface water and ground water exist as components of the hydrologic system and they are not isolate since they interact in a variety of physiographic and climatic landscapes. If one gets contaminate then it is very obvious that the other one also will get contaminated. Hydrologic interactions between surface and subsurface waters occur by subsurface lateral flow through the unsaturated soil and by infiltration into or exfiltration from the saturated zones. In cases of fractured terrain, interactions occur through flow in solution channels. In response to such individual water any water that will enter the surface water body promptly in known as event flow, direct flow or quick flow. This kind of water is distinguished from water that enters a stream from slowly varying process and maintains stream flow between water input events (Winter., 1998). Most base flow is supplied from ground water flow but however some of the base flow may also come from drainage of lakes or wetlands or even from the slow drainage of relatively thin soils on upland hill slopes. Interflow is defined as the near surface flow of water within the soil profile that will at most time result into stream channels within the time frame of a storm hydrograph. It usually involves both saturated and unsaturated flows with the latter being in zones where there is limited vertical extent. The limited vertical extent may be caused by soil horizons coming to percolation. Ecological significance and Interactions of surface and ground water. Apart from the interstices of stream-channel and blank sediments, water also flows in the open stream channel. This ends up creating a mixing zone with the subsurface water. The region where the surface and subsurface water mix is known as the hyporheic zone. It is a region characterized by intensive biogeochemical activity. As water moves down the stream the type and rate of material transformation are affected by the subsurface exchanges. An important aspect of ground water and surface water interchange is that surface water existing in streams, lakes and wetlands repeatedly interchanges with nearby ground water. This means that, the length of time that water is in contact with mineral surfaces in its drainage basin extends after the water fast enters a water body (Winter, 1998). The integrity of ground water and fluvial systems is often threatened by human activities that result in to a number of negative effects such as reducing connectivity, altering exchange processes, and organic contaminations. Toxic contamination in surface water can be transferred to the ground water in influent reaches. Increased sewage loading leads to clogging. It causes sedimentation of an organic layer on river beds. The extent of these effects is directly related to the land use practices such as farming which always result to increased suspended particulate matter and sediments loading. However gradual clogging is a common occurrence in many streams and is occurs naturally as a result of siltation of fine material during low discharge. Conclusion It is evident from the above discussions that water is very essential and key to many people who depend on it for survival. Since the environment involves all surrounding, the quality and quality of water is seen to be affected by several factors such as the soil contents during its movements through the soil to reach to the aquifers. The elements in the soil and their quantity will determine the quality and quantity of ground water. The quality of water is also to an extent determined by human activities leading to a general ecological effect. For effective soil management farmers have a role to play in ensuring that they reduce the soil contamination by using fertilizers that are friendly with low nitrate contents. Metals as non-biodegradable components of the soil have to be controlled also in the process of soil management. Surface and ground water are inter connected and therefore contaminating on will eventually lead to contamination of the other affecting the water quality. Bibliography Benites, A. B. (2005). The Importance of Soil organic Matter. Rome: FAO. Estigarribia, D. (2006). Learning about Rocks Weathering and Erosion with Graphic Organizers. Newyork: Thr Rosen Publishing Group. Gamo., T. (2007). Geochemistry of the Environment. Tokyo: Baihu-Kan Co.Ltd. Gaskel, M. (2012, December 12). Vegetable Research and Information Centre. Retrieved from UC Peer Reviewed: http://anrcatalog.ucdavis.edu/pdf/7249.pdf Kumada, K. (1987). Chemiistry of soil Organic Matter. Tokyo: Japan Scientific Societies . Regina, A. U. (2006). Soil Parent Material is a key Determinant of the bacterial community structure in areable soils. FEMS Microbiology Ecology, 56(3), 430-443. Shaila Sharmin, Z. M. (2010). Fractionation profile and mobility pattern of trace metals in sediments of Nomi River, Tokyo, Japan. 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