The Hydrological Cycle, Water Pollution, and Ocean Currents: An In-Depth Exploration
The Hydrological Cycle
Water is evaporated from the oceans and continents by the direct action of solar energy, or indirectly through transpiration from plants. Evaporated water condenses and forms clouds. Due to gravity, they release the water as precipitation. Water falling over the land surface then flows over the ground surface (surface runoff) and other infiltration becomes part of the groundwater. Groundwater moves generally very slowly and is fed from springs (groundwater runoff).
Influence of Light, Temperature, and Salinity in Ocean Waters
Light
Light only penetrates the outermost layer of the oceans (100m and even 200 m), known as the photic zone. The area below, the aphotic zone, is huge, since the average depth of the ocean is about 4,000 m. In the photic zone, due to the influence of light, plant life can exist, while in the aphotic zone, the absence of light precludes their development.
Salinity
Salinity is the amount of dissolved salts in seawater. Seawater contains an average of 3.5% of salts. This percentage varies from other seas. Rain, the contribution of continental water, and melting ice are reducing the salinity by dilution (e.g., Baltic Sea). By contrast, the formation of ice, volcanism, and evaporation tend to increase it (e.g., Red Sea and Dead Sea).
Temperature
The temperature varies with depth and latitude. Salinity, along with temperature, determines the density of seawater, which is critical in the distribution of ocean currents.
Numerical Pattern in Paragraphs 1 and 2
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Exploitation of Coastal Aquifers
Well 1 draws water from the aquifer at which the water table has dropped. The aquifer is important because, although the extraction is still active, since its lower end is within the saturated zone of water. Well 2 is an example of the exploitation of a coastal aquifer. Since groundwater extraction exceeds its ability to recharge, the resulting vacuum is filled by seawater (seawater intrusion) that produces its salinity. The water is no longer useful for domestic and agricultural use and may even alter ecosystems such as wetlands.
Eutrophication: Causes, Consequences, and Prevention
Eutrophication occurs in stagnant waters such as lakes, ponds, reservoirs, etc. and is caused by an excess of nutrients such as nitrates and phosphates. This leads to an excessive growth of algae and aquatic plants and a large accumulation of their remains in the background, which involves the development of decomposer microorganisms. The decomposition of organic matter by aerobic bacteria at the bottom depletes the oxygen present in the deeper zone, a phenomenon that will be compounded if there is water in thermal stratification, favoring the occurrence of anaerobic bacteria responsible for the fermentation of the excess organic matter. Fermentation processes emit substances such as H2S, NH3, and CH4, responsible for the characteristic odor. The waters become muddy and lose oxygen and thus aquatic life. The way to prevent eutrophication is to reduce the supply of nutrients, particularly phosphorus, by:
- Using detergents without phosphates.
- Using fertilizers rationally.
- Pretreating water before being discharged.
- Limiting the growth of algae.
Wastewater Treatment Plant (WWTP) Processes
Wastewater treatment is a set of physical, chemical, and biological processes that take place in the wastewater treatment plant (WWTP) to return water characteristics as close to clean water as possible. In the processing carried out, there are three levels: water line, sludge line, and gas line.
Water Line
- Pretreatment: The elimination of solids by screens and sieves.
- Primary treatment: The separation of solid materials in suspension by various physical-chemical processes: sedimentation, coagulation, flotation, etc.
- Secondary treatment: Removes organic matter and remains suspended, not withdrawn earlier, by microbial processes. These processes are performed in digestion tanks, stabilization ponds, filters, drip, etc.
- Tertiary treatment: Elimination of viruses, heavy metals, and dissolved organic matter. The processes used include centrifugation, reverse osmosis, etc.
Sludge Line
After all these treatments, sewage sludge originates, in which treatment involves the following processes: thickening to reduce the volume, stabilization to reduce organic matter through aerobic processes, which produces biogas (methane) that can be used as fuel for the treatment plant itself, and dehydration, which can be mechanical or thermal.
Gas Line
The resulting gas can be reused as energy in the sewage plant itself, and any gas not used is usually burned in a fire torch.
Water Pollution: Concept and Origin
Water pollution is the addition of foreign matter such as microorganisms, chemicals, waste, wastewater, etc., or energy, like heat and radioactivity, that impair water quality and make it useless for the intended uses. The origin of the pollution can be:
- Natural: Without the intervention of human action (plant residues, animal dung, volcanic activity, etc.).
- Anthropogenic: Due especially to industrial and mining activities, farms or livestock, urban agglomerations, and civil engineering works.
Water Quality Parameters: BOD and COD
A parameter is a numerical expression of some variable of a system. The status of water pollution can be expressed through a series of physical, chemical, or biological parameters.
Biological Oxygen Demand (BOD)
BOD is a measure of the amount of oxygen that microorganisms need to oxidize organic matter. It is expressed in ppm or mg/L of oxygen. The most common is referred to the period of five days (BOD5) at 20°C, measured by subtracting the initial oxygen from the oxygen present after five days of incubation. The higher the BOD5, the greater the organic pollution (e.g., unpolluted rivers: 3 mg/L; domestic wastewater: 300 mg/L).
Chemical Oxygen Demand (COD)
COD is the oxygen dissolved in water that is spent on oxidized matter by chemical agents in an acidic medium. The recommended value must be = 20 mg of oxygen/L.
Consequences of Oil Spills at Sea
An oil spill in the sea forms a viscous mass on its surface, a “black tide,” whose effects are particularly harmful to:
- Fish that live near the surface (respiratory dysfunctions)
- Seabirds (lose their waterproof feathers and the layer of air that insulates them from the cold)
- Marine invertebrates
- Marine mammals
- Planktonic organisms (unlit phytoplankton does not photosynthesize)
- Benthic organisms
These oil spills, upon reaching the coast, produce very serious disturbances in coastal ecosystems:
- Cliffs and rocky areas
- Reef formations
- Wetlands and estuaries
In addition, they cause severe economic damage to:
- Fisheries
- Marine fish farms
- Aquaculture
- The quality of beaches for public use in areas of tourism and recreation
The oil contains carcinogenic substances that can accumulate in bivalve mollusks.
Water Balance
The water balance (Bh) represents the inputs and outputs of water on continents and oceans. (Bh = additions of water – water losses). The losses are due to evaporation and evapotranspiration, and inputs are due to precipitation, which on land leads to surface runoff or groundwater. Globally, that is, considering the Earth’s oceans and large bodies of water like the Pacific or Atlantic, the water balance is balanced. In a balanced water budget:
global water balance = water inlets – loss of water = 0
In other cases, the water balance is not balanced, mainly due to bad weather. For example, in the Mediterranean Sea, water loss by evaporation exceeds (is greater than) earnings of water due to river inputs and rainfall. This means its water balance is negative.
Water Plan: Concept and Importance
The main problem with freshwater in the world is its scarcity. In most countries, according to climatic criteria, seasonality, and pollution, there is a severe shortage of drinking water. Good examples are large areas of Africa, Asia, the Middle East, etc. In other regions, there is a constant demand for water as a function of population growth, intensification of agricultural systems, irrigation and industrial expansion, coupled with the progressive deterioration of watersheds, because of very different causes. For all these reasons, the need for Hydrological Plans is growing today.
Hydrological Plans are a set of guiding principles involved in water management to ensure that the interests of agricultural, industrial, urban, and environmental co-exist as a sustainable model.
Measures for Rational and Efficient Water Use
General Measures
- Protect streams, rivers, and aquifers from contamination.
- Protect forests to stabilize water flows and the water cycle.
- Regulate the exploitation of aquifers.
- Encourage recycling.
Savings Measures by Sector
Agriculture
- Use non-wasteful irrigation systems, for example, sprinkler irrigation and drip irrigation, especially in arid systems.
Industry
- Encourage industries with low water consumption and clean processes, and encourage the use of recycled water in closed circuits.
Urban Areas
- Encourage savings through public awareness, the use of low-energy appliances, the purification of wastewater for reuse in the irrigation of parks and gardens, and other technical solutions.
Technical Measures
- Regulate watercourses by constructing dams and reservoirs.
- Use groundwater through wells, drilling, and pumps.
- Transfer water under the National Water Plan to move water from surplus river basins to other deficient ones.
Legislation
- Regulate water intake, waste control, the economic system, and the exploitation of aquifers. In Spain, this is the Water Law of 1985.
Key Elements of an Aquifer
Pit
The upper surface of the saturated zone by groundwater. It is not a static area, but its height varies with the amount of water accumulated in the subsoil, and therefore with the season, following heavy rainfall, and so on.
Well
In a free aquifer, water must be removed by pumping.
Aquifer
An underground geological formation that is porous and permeable, saturated with water, allowing its displacement and removal.
Influence of Ocean Currents on Climate
In the North Atlantic, the Gulf Stream, a stream of warm water and surface, strongly influences the thermal characteristics of the Atlantic coast of Europe, with milder temperatures, especially in winter, while areas at the same latitude on the Atlantic coast of North America have lower temperatures.
El Niño and La Niña Phenomena
The phenomenon represented is called La Niña. In eastern parts of the tropical ocean, the surface boundary layer and the thermocline are pushed off the coast due to the influence of trade winds blowing in these areas to the west. The moving water is replaced by deep cold water rich in nutrients, which are the basis for the development of major fish stocks. So in these areas, there are (or were) the most important fishing grounds in the world. The dry trade winds that blow from the continent make the climate of the regions adjacent to areas of outcrop very dry, so these are usually limited to desert areas, such as the Atacama Desert in southern Peru and northern Chile, meanwhile, it rains heavily in the coastal surface layer of the Pacific Ocean.
1. Marine Layer
The marine layer is less dense in terms of temperature and hydrological changes, which occur more because of the incessant energy exchanges between oceans and the atmosphere. Its power is not uniform and usually does not exceed 500 m in depth.
2. Thermocline
A layer that provides a quick drop in temperature and separates surface waters (less dense and less saline) from deep water (cooler, denser, and saline).
3. Deep Layer
A deep layer of cold water mass whose temperature varies between 5° and 1°C, depending on latitude. These temperatures remain nearly constant at the seabed, despite the climate across the surface.
4. Upwelling Area
This area occurs when trade winds move away from the coast to the limit of the surface layer and the thermocline, allowing the rise of deep, cold, and nutrient-rich water. For this reason, the upwelling zones are often very rich in fisheries and marine populations, as on the west coast of South America.
Water Flow in the Mediterranean Sea
The waters of the Mediterranean have a high salinity due to abundant evaporation, thus are denser and sink, flowing through the bottom to the Atlantic Ocean, part of which is a surface current in the opposite direction of less dense water.
Types of Aquifers and Wells
1. Piezometric Level
The height the groundwater would reach from a confined aquifer under pressure when it arises from a captive or natural source.
2. Confined Aquifer
An aquifer is an underground geological formation of porous and permeable water-saturated material, allowing its displacement and extraction. In confined aquifers, the water pressure is higher than atmospheric pressure.
3. Artesian Well
An artesian well is so-called because its mouth is situated beneath the level of groundwater, so water reaches the surface under natural pressure.
4. Well
Water does not reach the surface because its mouth is located above the level of groundwater. The water must be removed by pumping.
Major causes of pollution of aquifers. The main causes of pollution of groundwater discharges are point sources (domestic and industrial wastewater, landfill leachate and mines, etc..), And diffuse pollution ( nitrates and other products from agricultural fertilizers and pesticides). Aquifer: concept and elements. Helping a drawing explains the key elements of it. An aquifer is an underground geological formation, porous and permeable, allowing water saturated extracción.Los their displacement and main elements of an aquifer are: – aeration zone or subsurface area where water infiltrates vertically.
– Saturated zone where the rocks are saturated with water .- water level top of the zone of saturation. Often below the saturation zone are impermeable strata. Discuss the accompanying sketch saying what type aquifers represented (A1, A2 and A3). Explains the characteristics of the wells P1, P2 and P3, and precisely what to do for water in each. What is the relationship between the river and the aquifer A1?
– A1 is a free aquifer, which feeds the river. ” Therefore it is a winner effluent or river bed. – A2 aquifer is hung on the hillside. – A3 a confined aquifer. – P1 is an artesian well, water rises to a height of NP and spontaneously. — P2 is a dry well without water as it does not reach the water table. To obtain should be deepened. – P3 is a pit where it is necessary to use a pump to remove water as it would fill the well to the high water table. Explain the expression: a river has a certain capacity for self-purification. The purification is the natural process by which pollutants in the natural environment, such as the river, or natural alterations of the characteristics of its waters are processed tralized or eliminated by a series of physical, chemical and biological . Explain the consequences of oil spill at sea. The oil spill in the sea forms on its surface a “black tide” viscous mass whose effects are particularly harmful to fish that live near the surface (respiratory disorders), the seabirds (lose waterproofness and the layer of air that insulates them from the cold), marine invertebrates, marine mammals and planktonic organisms (phytoplankton unlit does not photosynthesize) and benthic. In addition, the oil is carcinogenic substances that can accumulate in bivalve molluscs. These oil spills reaching the coast produce very serious disturbances in coastal ecosystems: cliffs and rocky areas, reef formations, wetlands and estuaries. Also cause serious economic damage to fisheries, marine fish farms, aquaculture, quality of beaches for public use in areas of tourism and recreation.