ENSP101 Chapter 18 Water Pollution 18 1 Water Pollution While pollution from factory pipes has been vastly reduced in the past 40 years erosion from farm fields construction sites and streets has gotten worse since 1972 o Airborne mercury sulfur and other substances are increasingly contaminating lakes and wetlands o Concentrated livestock production and agricultural runoff threaten underground water a well as surface water systems o Increasing industrialization in developing countries has led to widespread water pollution in impoverished regions with little environmental regulation Water pollution is anything that degrades water quality o Factories power plants sewage treatment plants underground coal mines and oil wells are classified as point sources because they discharge pollution from specific locations such as drain pipes ditches or sewer outfalls o Nonpoint sources of water pollution are scattered or diffuse having no specific location where they discharge into a particular body of water Nonpoint sources include runoff from farm fields and feedlots golf courses lawns and gardens construction sites logging areas roads streets and parking lots Atmospheric deposition sedimentation of solids liquids or gaseous materials from the air The nearest sources for many of these chemicals are sometimes thousands of kilometers away Amounts of these pollutants can be quite large 18 2 Types and Effects of Water Pollutants The most serious water pollutants in terms of human health worldwide are pathogenic organisms human wastes o The main source of these pathogens is from untreated or improperly treated o Animal wastes from feedlots or fields near waterways and food processing factories with inadequate waste treatment facilities also are sources of disease causing organisms o Coliform bacteria bacteria that live in the intestines of humans and other animals used as a measure of the presence of feces in water or soil Most common E coli Bacteria are detected by measuring oxygen levels o Biochemical oxygen demand BOD a standard test for measuring the amount of dissolved oxygen utilized by aquatic microorganisms o An alternative method called the chemical oxygen demand COD uses a strong oxidizing agent to completely break down all organic matter in a water sample o A third method of assaying pollution levels is to measure dissolved oxygen DO content directly using an oxygen electrode The effects of oxygen demanding wastes on rivers depends to a great extent on the volume flow and temperature of the river water o The oxygen decline downstream is called the oxygen sag Water clarity is affected by sediments chemicals and the abundance of plankton organisms and is a useful measure of water quality and water pollution Oligotrophic condition of rivers and lakes that have clean water and low biological productivity are usually clear cold infertile headwater lakes and streams Eutrophic rivers and lakes rich in organisms and organic material o Some amount of eutrophication is a normal part of successional changes in most lakes o Eutrophication often results from nutrient enrichment sewage fertilizer runoff even decomposing leaves in street gutters can produce a human caused increase in biological productivity called cultural eutrophication o Cultural eutrophication can also result from higher temperatures more sunlight reaching the water surface or a number of other changes o Eutrophication has undesirable results blooms of algae increase in bacterial populations and in extreme cases plants and algae die and decomposers deplete oxygen in the water collapse of the aquatic ecosystem can result Eutrophication can cause toxic tides and dead zones o Red tide a population explosion or blood of minute single celled marine organisms called dinoflagellates Billions of these cells can accumulate in protected bays where the toxins they contain can poison other marine life o Have become increasingly common in slow moving rivers brackish lagoons estuaries and bays as well as near shore ocean waters where nutrients and wastes wash down our rivers o Extensive dead zones often form where rivers dump nutrients into estuaries and shallow seas o It appears that fish and other marine species die in these hypoxic zones not only because oxygen is depleted but also because of high concentrations of harmful organisms including toxic algae pathogenic fungi parasitic protists and other predators In many areas toxic inorganic chemicals introduced into water as a result of human activities have become the most serious form of water pollution Because metals are highly persistent they can accumulate in food webs and have a cumulative effect in top predators including humans o Most widespread toxic metal contamination Mercury released from coal burning power plants Problem mercury in fish o Mine drainage and leaching of mining wastes are serious sources of metal pollution in water Some soils contain high concentrations of soluble salts including toxic selenium and arsenic o Irrigation and drainage of desert soils can mobilize these materials on a larger scale and result in serious pollution problems o Salts such as sodium chlorine table salt that are nontoxic at low concentrations also can be mobilized by irrigation and concentrated by evaporation reaching levels that are toxic for many plants and animals Acids are released as by products of industrial processes such as leather tanning metal smelting and plating petroleum distillation and organic chemical synthesis o Coal mining is an especially important source of acid water pollution o Sulfur compounds in coal react with oxygen and water to make sulfuric acid o Coal and oil combustion also leads to formation of atmospheric sulfuric and o If acidification is severe enough aquatic life is limited to a few resistant nitric acids species of mosses and fungi o Increased acidity may result in leaching of toxic metals especially aluminum from soil and rocks making water unfit for drinking or irrigation as well Organic pollutants include drugs pesticides and other industrial substances o Many of these chemicals are highly toxic o Some can persist in the environment because they are resistant to degradation and toxic to organisms that ingest them o Contamination of surface waters and groundwater by these chemicals is a serious threat to human health o The 2 most important sources of toxic organic chemicals in water are improper disposal of industrial and household wastes and runoff of