BESC 201 11 6 2013 Lecture 28 Outline of Last Lecture I Water Systems Outline of Current Lecture II Human Activities Affect Waterways III Solutions to the Depletion of Freshwater IV Water Pollution and its Control Current Lecture 11 6 2013 Human Activities Affect Waterways Fresh water is unevenly distributed across Earth People are not distributed across the globe in accordance with the amount of fresh water Water supplies households industry and especially agriculture Consumptive Use removing water from an aquifer or surface water body and not returning it Primary consumptive use of water is for agricultural irrigation Nonconsumptive Use does not remove or only temporarily removes water from an aquifer or surface water body Water Mining withdrawing water faster than it can be replenished We build dikes and levees to control floods Flooding snowmelt of heavy rain swells the volume of water in a river so that water spills over the river s banks Dikes Levees long raised mounds of Earth along riverbanks to hold water in main channels These structures prevent flooding most of the time but they can sometimes worsen flooding because they force water to stay in channels and accumulate building enormous energy and leading to occasional catastrophic overflow events We have erected thousands of dams Dam any obstruction placed in a river or stream to block its flow Reservoirs artificial lakes that store water for human use Many aging dams are in need of costly repairs or have outlived their economic usefulness and these are candidates for removal These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Excessive water withdrawals are draining rivers and lakes Many major rivers regularly run dry before reaching the sea due to excessive water withdrawals This reduction in flow not only threatens the future of the cities and farms that depends on these rivers but also drastically alters the ecology of the rivers and deltas changing plant communities wiping out populations of fish and invertebrates and devastating fisheries Surface water depletion is most evident at the Aral Sea Groundwater depletion affects people and ecosystems Groundwater is more easily depleted than surface water because most aquifers recharge very slowly As aquifers are mined water tables drop deeper underground This deprives freshwater wetlands of groundwater inputs causing them to dry up Groundwater also becomes more difficult and expensive to extract and eventually it may run out When groundwater is overpumped in coastal areas salt water can intrude into aquifers from the ocean making water undrinkable As aquifers lose water they become less able to support overlying strata and the land surface above may sink or collapse Bottled water has ecological costs Chemical analyses show that bottled water is no safer or healthier than tap water Will we see a future of water wars Resource security can lead to conflict Many predict that water s role in regional conflicts will increase as human population continues to grow and as climate change alters precipitation patterns Solutions to the Depletion of Fresh Water Aim either to increase supply or reduce demand Increasing water supplies is to generate fresh water by desalination the removal of salt from seawater or other water of marginal quality Desalination is an energy intensive process that requires large inputs of fossil fuels or electricity Its ability to increase water supplies in most nations is limited We can decrease our demand for water Strategies for reducing fresh water demand include conservation and efficiency measures but its is politically difficult Agriculture Low pressure spray irrigation squirts water downward toward plants and drip irrigation systems target individual plants and introduce water directly onto the soil Choosing crops to match the land and climate in which they are farmed can also save huge amounts of water Households Installing low flow faucets showerheads washing machines and toilets Replacing exotic vegetation with native plants adapted to your region s natural precipitation patterns can also reduce watering demand Xeriscaping landscaping using plants adapted to arid conditions Industry and municipalities Recycling treated municipal wastewater for irrigation and industrial uses Water Pollution and its Control The largely invisible pollution of groundwater has been termed a covert crisis Water pollution comes from point sources and non point sources Pollution the release into the environment of matter or energy that causes undesirable impacts on the health or wellbeing of people or other organisms Water Pollution can cause diverse impacts on aquatic ecosystems and human health Most forms of water pollution are not conspicuous to the human eye so scientists and technicians measure water s chemical properties Point Sources discrete locations Non Point Sources pollution is cumulative arising from multiple inputs over larger areas Water quality in the United States today suffers most from non point source pollution resulting from countless common activities Water pollution takes many forms Toxic Chemicals Issuing and enforcing more stringent regulations of industry can help reduce releases of many toxic chemicals Pathogens and waterborne diseases Biological pollution by pathogens causes more human health problems than any other type of water pollution Oil Pollution Nearly 13 million metric ton of petroleum entering the world s oceans each year originates from natural seep in the ocean bottom Nutrient Pollution Causes eutrophication and hypoxia in surface waters Harmful algal blooms several species of marine algae that produce powerful toxins Red Tides some toxic algal species produce a red pigment that discolors the water Biodegradable Wastes Bacterial decomposition escalates as organic material is metabolized This lowers dissolved oxygen levels in the water Wastewater water affected by human activities Sediment High sediment concentrations impair aquatic ecosystems by interfering with the respiration of fish and invertebrates and smothering benthic organisms Thermal Pollution Water s ability to hold dissolved oxygen decreases as temperature rises so some aquatic organisms may not survive when human activities raise water temperatures Nets and plastic debris Plastic trash is accumulating in certain regions of the oceans where currents converge One such