CORE126 - Water Resources PDF

CORE126 – EARTH SCIENCE Reading Material 1st Semester 2024-2025 Water Sources Learning Competencies: The learners are able to… 1. Describe how water is distributed on earth. 2. Identify the various...

CORE126 – EARTH SCIENCE Reading Material 1st Semester 2024-2025 Water Sources Learning Competencies: The learners are able to… 1. Describe how water is distributed on earth. 2. Identify the various water resources on earth. 3. Explain how different activities affect the quality and availability of water for human use. 4. Suggest ways of conserving and protecting water resources. Water Water is a simple compound, made of two atoms of hydrogen and one atom of oxygen bonded together. More than any other substance on the Earth, water is important to life and has remarkable properties. Without water, life could probably not even exist on Earth. When looking at Earth from space, the abundance of water on Earth becomes obvious. On land, water is also common: it swirls and meanders through streams, falls from the sky, freezes into snowflakes, and even makes up most of you and me. In this section, we’ll look at the distribution of water on Earth, and also examine some of its unique properties. About 71% of the Earth’s surface is covered with water, most of which is found in the oceans. In fact, 97.5% of Earth's water, nearly all of it, is in the Earth’s oceans. This means that just 2.5% of Earth's water is fresh water, water with low concentrations of salts. Most freshwater is found as ice in the vast glaciers of Greenland and the immense ice sheets of Antarctica. That leaves just 0.4% of Earth’s water that is freshwater that humans can easily use. Most liquid freshwater is found under the Earth’s surface as groundwater, while the rest is found in lakes, rivers, and streams, and water vapor in the sky. Availability of Water on Earth Just 2.5% of the Earth’s water is freshwater, and most is frozen in glaciers and ice sheets. About 96% of all liquid freshwater can be found underground. The remaining small fraction is on the surface or in the air. Knowing how water cycles through the environment can help in determining how much water is available in different parts of the world. The Earth’s water cycle is the global mechanism by which water moves from the air to the Earth (precipitation) and eventually back to the atmosphere (evaporation). Page 1 of 6 ALBEUS |ADNU STEM © 2023 CORE126 – EARTH SCIENCE Reading Material 1st Semester 2024-2025 The principal natural components of this cycle are precipitation, infiltration into the soil, runoff on the surface, groundwater discharge to surface waters and the oceans, and evapotranspiration from water bodies, the soil, and plants. “Blue water”- the water in rivers, lakes, and aquifers- can be distinguished from “green water” - which feeds plants and crops, and which is subsequently released into the air. This distinction may help managers focus on those areas which green water feeds and passes through, such as farms, forests, and wetlands. How does water move from the atmosphere to the ground and back? About 10% of the Earth’s freshwater that is neither frozen nor underground is found in the atmosphere. Precipitation, in the form of rain or snow, for instance, is an important form of available freshwater. About 40% of precipitation has previously evaporated from the oceans; the rest from land. The amount of precipitation varies greatly around the world, from less than 100 mm a year in desert climates to over 3,400 mm a year in tropical settings. The drier the climate, the higher the proportion of precipitation that returns to the atmosphere and the lower the proportion that replenishes groundwater. In temperate climates, about a third of precipitation returns to the atmosphere through evaporation, a third filters into the ground and replenishes groundwater and the remainder flows into water bodies. A large part of the freshwater that returns to the atmosphere passes through soil and plants. Reliable figures are available only for some regions. Soil moisture is important for plant growth. Finding out how much moisture soil contains is important for such activities as farming and “river flow forecasting”, and for understanding climate and natural and water systems. Satellite data are increasingly complementing measurements of soil moisture taken on the ground to provide a broader and more up-to-date picture to decision-makers. Fresh Water in the Surface Page 2 of 6 ALBEUS |ADNU STEM © 2023 CORE126 – EARTH SCIENCE Reading Material 1st Semester 2024-2025 About three-quarters of the world’s freshwater is frozen in ice sheets and glaciers. Most remains inaccessible, located in the Arctic, Antarctica or Greenland. Land- based glaciers and permanent snow and ice, however, supply water in many countries, releasing water in amounts that vary seasonally and over longer time periods. Because of climate change, glaciers are now being more closely monitored. Surface waters, including lakes, ponds, reservoirs, rivers, streams and wetlands hold only a small volume of the Earth’s total fresh water (0.3%). Still they represent about 80% of the renewable surface water and groundwater that is available in a given year. These water bodies perform many functions in the environment, and provide people with the prime source of drinking water, energy and recreation, as well as a means of irrigation and transport. Lakes and other reservoirs counteract fluctuations in river flow from one season to the next because they store large amounts of water. Lakes contain by far the largest amount of fresh surface water. But the hydrology of only about 60% of the largest lakes has been studied in detail, leaving much to be learned. River basins are a useful “natural unit” for the management of water resources, though they often extend across national borders. International river basins have drainage areas covering about 45% of the Earth’s land surface (excluding the polar regions). Some of the largest basins are the Amazon, which carries 15% of all water returning to the oceans, and the Congo-Zaire Basin, which carries one-third of all river water in Africa. River flows can vary greatly from one season to the next and from one climatic region to another. In tropical regions, large flows are witnessed year-round, whereas in drylands, rivers are often ephemeral and only flow periodically after a storm. Drylands make up about 40% of the world’s land area and have only 2% of all water runoff. Past data records for river flow and water levels help to predict yearly or seasonal variations, though it is difficult to make accurate longer-term forecasts. Some records in industrialized countries go back up 150 to 200 years. By contrast, many developing countries started keeping records only recently and data quality is often poor. Wetlands, including swamps, bogs, marshes, and lagoons, cover 6% of the world’s land surface and play a critical role in the conservation of water resources. Many wetlands were destroyed or converted to other uses during the last century. Those that remain can play an important role in supporting ecosystems, preventing floods, and increasing river flows. Fresh Water Underground Ninety-six percent of liquid fresh water can be found underground. Groundwater feeds springs and streams, supports wetlands, helps keep land surfaces stable, and is a critical water resource. About 60% of the water that is taken from the ground is used for farming in arid and semi-arid climates, and between 25% and 40% of the world’s drinking water comes from underground. Hundreds of cities around the world, including half of the very largest, make significant use of groundwater. This water can be especially useful during shortages of surface water. Groundwater aquifers vary in terms of how much water they hold, their depth, and how quickly they replenish themselves. Much of the water underground is replenished either very slowly or not at all, and is thus termed “non-renewable”. The largest aquifers of non-renewable water are found in North Africa, the Middle East, Australia, and Siberia. There is some debate about Page 3 of 6 ALBEUS |ADNU STEM © 2023 CORE126 – EARTH SCIENCE Reading Material 1st Semester 2024-2025 how and when to use this water. Many aquifers that contain non-renewable groundwater resources are shared by more than one country and need to be managed in common for the benefit of all administrative entities concerned. If the infiltration of precipitation recharges the aquifer, the groundwater is considered “renewable” and can be used for irrigation, domestic and other purposes. While most renewable groundwater is of a high quality and does not require treatment, it should be analyzed before it is used to avoid possible health impacts. However, few countries measure the quality of underground water or the rate at which it is being withdrawn. Monitoring is being improved in Europe and India, but remains minimal in many developing countries, and is deteriorating in many industrialized ones. This makes it hard to manage underground water resources sustainably. Raw Water Treatment Process Water is collected from nature. For our consumption, it should undergo a treatment process and be distributed for human use. Raw Water Treatment Process o Coagulation - Involves the addition of compounds that promote the clumping of fines into larger flocs so that they can be more easily separated from the water. In a colloidal suspension, particles will settle very slowly or not at all because the colloidal particles carry surface electrical charges that mutually repel each other. This surface charge is most commonly evaluated in terms of zeta potential, the electrical potential at the slipping plane. To induce coagulation, a coagulant (typically a metallic salt) with the opposite charge is added to the water to overcome the repulsive charge and "destabilize" the suspension. For example, the colloidal particles are negatively charged and alum is added as a coagulant to create positively charged ions. Once the repulsive charges have been neutralized (since opposite charges attract), van der Waals force will cause the particles to cling together (agglomerate) and form micro floc. o Flocculation - It transports the destabilized particles that will cause collisions with flocs. Flocculation and sedimentation are widely employed in the purification of drinking water as well as in sewage treatment, storm-water treatment and treatment of industrial wastewater streams. Typical treatment processes consist of grates, coagulation, flocculation, sedimentation, granular filtration and disinfection. o Sedimentation - Use gravity to remove suspended solids from water. Sedimentation in potable water treatment generally follows a step of chemical coagulation and flocculation, which allows grouping particles together into Page 4 of 6 ALBEUS |ADNU STEM © 2023 CORE126 – EARTH SCIENCE Reading Material 1st Semester 2024-2025 flocs of a bigger size. This increases the settling speed of suspended solids and allows settling colloids. o Filtration - Water flows through a filter designed to remove particles from within it. The filters are made of layers of sand and gravel, and in some cases, crushed anthracite. Filtration collects the suspended impurities in water, enhancing the effectiveness of disinfection. These filters are routinely cleaned by backwashing. o Disinfection - Water is disinfected before it enters the distribution system to ensure that any disease-causing microorganisms are destroyed. Chlorine is used because it is a very effective disinfectant, and residual concentrations can be maintained to guard against possible microbial contamination in the water distribution system. o Storage - Safe water storage means that once the water has been treated and is safe to use, it is stored in a container that protects the water from re- contamination. o Optional Processes: § Sludge Drying - Solids that are collected and settled out of the water by sedimentation and filtration are removed to drying lagoons. § Fluoridation - Water fluoridation is where community water supplies are treated with a concentration of the free fluoride ion. This is adjusted to an optimum level to reduce dental decay. § PH Correction - Lime is added to filtered water to adjust the pH and stabilize the naturally soft water. This minimizes corrosion in the distribution system, and within customers’ plumbing. Environmental Concerns that Affect Water Sources Sedimentation due to farming, forest-clearing, road-building, and mining. Pollution can harm water resources and aquatic ecosystems. o Organic chemicals - Fertilizers, Herbicides & Fungicides through leaches. o Pathogens - Harmful microorganisms due to introduction of sewage water to the environment. o Acid Rain - Alteration of pH in water. o Heavy Metals - from Mining Operations that are toxic in our water sources. Melting of glaciers due to climate change. Exploitation or over-withdrawal from a water source. Land subsidence Saltwater intrusion and result to groundwater degradation Sinking water tables can also make rivers less reliable Reference(s): Carlson, D.H., Carlson, Plummer, C.C., and Hammersley, L., 2011. Physical Geology: Earth Revealed. McGraw-Hill. 645 p. Desonie, D., 2015. CK-12 Earth Science High School. http://www.ck12.org/earth-science/ Junine, J.I., 2013. Earth Evolution of a Habitable World. Second Edition. Cambridge University Press. 304 p. Kirkland, K. 2010. Earth Science: notable research and discoveries. Facts on File, Inc., 212 p. Lutgens, F.K., Tarbuck, E.J. and Tassa, D., 2013. Essentials of Geology. 11th Edition. Pearson Prentice Hall, 554 p. Page 5 of 6 ALBEUS |ADNU STEM © 2023 CORE126 – EARTH SCIENCE Reading Material 1st Semester 2024-2025 Tarbuck, E.J. and Lutgens, F.K., 2008. Earth – An Introduction to Physical Geology. 9th Edition Pearson Prentice Hall, 703 p. Page 6 of 6 ALBEUS |ADNU STEM © 2023