Presentation on theme: "Students will understand global water resources, use, and pollution, including: o Ocean Circulation patterns; agricultural, industrial, and domestic use;"— Presentation transcript:
Students will understand global water resources, use, and pollution, including: o Ocean Circulation patterns; agricultural, industrial, and domestic use; surface and groundwater issues; conservation; desalination o Sewage treatment o Relevant laws and treaties
Of course, even though the oceans have different names, they are not really separate. Water is able to move freely between oceans. They are all connected in one global ocean. There is a large-scale pattern to the way that seawater moves around the world ocean. This pattern is driven by changes in water temperature and salinity that changes the density of water. It is known as the Global Ocean Conveyor or thermohaline circulation. It affects water at the ocean surface, as well as the deep ocean. It moves water around the world.
There are other factors that influence ocean currents as well. Factors such as: Global distribution of continents, which influence Wind speed and direction, which is driven by Pressure systems, which are influenced by Coriolis Force The surface current known as the Gulf Stream is one such current. It acts to bring warm equatorial water up the Atlantic coast, and over to Europe, moderating the temperature there.
Only freshwater sources are “potable”, and able to be used by humans for drinking and irrigation, and other organisms. Groundwater sources include the “reservoirs” of water found beneath the Earth. There are two distinct layers found beneath the ground level. The zone of aeration The zone of saturation Surface waters include: Oceans, and inland seas Rivers, lakes and streams Reservoirs Within the zone of aeration, water may be found, along with air spaces. In the zone of saturation, all spaces between “peds” are filled with water. The zone of saturation forms the water table.
Groundwater is stored underground in porous rock layers such as sandstone, called aquifers. Aquifers may be unconfined, or confined beneath an “impermeable” layer, known as a caprock, and above another impermeable layer. When we drill into this permeable aquifer, because of the pressure, it flows up under its own volition. An artesian well flows under its own pressure. They can be formed naturally, or they can be drilled.
Nearly 50% of the people in the US depend upon underground aquifers for their drinking water. Texas has aquifers, but because it is a very hot area, geographically, these aquifers lose a great deal of water during summer (drought) times. They rely upon “recharge”, from the rains that come seasonally. Many times, withdrawal exceeds recharge. This is known as overdraft. Water moving down through these porous layers is cleaned naturally. However, because of the increase in pollutants due to agriculture and industry, the natural ability of aquifers to clean the water has decreased. MTBE has leaked from underground gasoline tanks into the groundwater supply. It is a carcinogen, and one of the biggest pollutants found in groundwater.
Fertilizers and pesticides are common pollutants of groundwater in farming communities. Herbicides Insecticides Fungicides Nitrates and phosphates found in fertilizers, often exceed safety standards in rural water supplies and can lead to health problems. Farm waste is also a pollutant in our water supply. The residence time is the amount of time water stays in an aquifer. This can be a very long time. The longer the water is confined, the longer they are exposed to some contaminants. Water can be pumped up, filtered, and then pumped back down, but this is extremely expensive.
Much of the water used in industry is used for “cooling” purposes, such as what we learned about nuclear energy plants. As we already saw, thermal pollution, as well as direct chemical and particulate pollution by industry is a definite stressor of the aquatic environment. This is an obvious effluent from an industrial source in Texas. What type of pollution is this, since you know the source? POINT POLLUTION
CategoryExamplesDangersSources Infectious AgentsBacteria, viruses, parasitic worms, and protozoa DiseasesAnimal wastes Wastes demanding oxygen Organic wastes (animal manure) Dying populations of fish Sewage, animal feed lots, paper mills Inorganic chemicalsAcids, lead, arsenic, selenium, salts Unsafe drinking water, skin cancer, liver and kidney damage, harm to aquatic life Surface runoff, household cleaners Organic chemicalsOil, gasoline, plastic, pesticides, detergents Nervous system damage, cancer, harmful to fish and wildlife Surface runoff, household cleaners Plant NutrientsNitrates, phosphates, and ammonium Excessive algal growth, dangers to unborn babies and children Sewage, manure, runoff SedimentSoil, saltReduce photosynthesis, disrupt food webs, carry pesticides Land erosion HeatExcessive heatLowers oxygen levels in water, thermal shock of organisms Water cooling of electric, and nuclear plants
Most of the serious health-related water pollution problems are caused by animal manure…including humans. The presence of over 500 types of disease-causing bacteria, viruses, and parasites can travel from human or animal wastes into a water supply. Luckily, through treatment, we can prevent the spread of disease this way. In rural communities, many people have septic tanks installed to manage their wastewater. These are “domestic septic systems”. These have improved public health in rural areas. In a septic system, wastewater drains into a septic tank. Substances such as grease and oil rise to the top while the solids sink to the bottom. Here, they decompose through the activity of bacteria. The resulting liquid is channeled out through drain pipes that are surrounded by gravel (for absorption and cleaning). Most of the pathogens (which are anaerobic) are killed when exposed to the oxygen in the soil. The water percolates, and evaporates. Sometimes, the effluent must be pumped out and taken to a treatment plant manually.
Urban sprawl has demanded a greater solution than the small domestic septic system, adequate for larger numbers of people. There are typically three steps to treating municipal sewage: Primary Treatment: Raw sewage enters a treatment plant and the solids are separated from the liquids using a series of screens. Sand and gravel settle in one tank, along with about half of the solids. We call this sludge. The main purpose of primary treatment is to separate, and settle. Some municipalities only have primary treatment. The wastewater is chlorinated, and released into the environment at this point.
After manual separation, the sewage enters the secondary stage of treatment. The sludge, once settled, is moved to a holding tank for primary digestion (using bacterial decomposers), while the liquid portion is piped to a holding tank for aeration. This process is sometimes referred to as the activated sludge process, as a bacterial slurry bathes the solids, encouraging decomposition. The final settling tank contains the aerated wastewater, and any solids that didn’t initially settle.
The third stage, known as tertiary treatment, varies depending on the community and the composition of the wastewater. Typically, the third stage will use chemicals to remove phosphorous and nitrogen from the water, but may also include filter beds and other types of treatment. Chlorine added to the water kills any remaining bacteria, and the water is discharged. The sludge is left to decompose, and dry out. In this process, more methane is produced, and is often used by the wastewater treatment plant as an energy source. This dried sludge is often used as fertilizer compost, if it is free from pollutants such as heavy metals, which must be removed at great expense.
Desalination is also called distillation, and the process is responsible for removing many impurities from water…not just salt. The process is not new, and has been employed since ancient times, when early mariners learned how to turn sea water into potable water. The most important users of desalinated water are in the Middle East, (mainly Saudi Arabia, Kuwait, the United Arab Emirates, Qatar and Bahrain), which uses about 70% of worldwide capacity; and in North Africa (mainly Libya and Algeria), which uses about 6% of worldwide capacity. Large-scale desalination typically uses large amounts of energy and specialized, expensive infrastructure, making it more expensive than fresh water from conventional sources such as rivers or groundwater
The goal of the CWA (Clean Water Act) of 1972 was to return all of the surface waters in the US to “fishable, and swimmable”. It has improved most bodies of water significantly, however, not all the waters in the US meet this criterion. One of the most important contributions of the CWA was the allocation of federal and state money to build municipal sewage treatment facilities. Opponents: Farmers Industry State and Local Governments Limiting the amount of pesticides and fertilizers added to their soils, means lower crop yields, and less income as a result. Limiting the amount of industrial waste output, and use of clean-technology means increased cost, and less profit as a result. Must spend money implementing the CWA, none of which is reimbursed by the federal government
The Safe Drinking Water Act: The Great Lakes Water Quality Agreement The London Dumping Convention: Regulates water in municipal and commercial systems. Some people say that the regulations are too loose for rural communities and provide evidence of pesticides, herbicides and lead to back up their claims. We must remember that detecting these substances is quite different than having them at dangerous levels. An important international agreement between Canada and the US concerning water quality signed in 1972. This agreement has made huge strides into cleaning up this major water system. In 1990, this convention set up regulations for phasing out ocean dumping of industrial wastes, effluent, and plastics by 1995. The results of this convention are still being studied.