4.4 Water Pollution Past Paper PDF

04 Water, aquatic food production systems, and societies To learn more about the 10. To what extent can whaling ever be sustainable? status of whales, go to 11. Visit the hotlinks opposite and answer the following questions. www.pearsonhotlinks....

04 Water, aquatic food production systems, and societies To learn more about the 10. To what extent can whaling ever be sustainable? status of whales, go to 11. Visit the hotlinks opposite and answer the following questions. www.pearsonhotlinks. a. Briefly describe the status of whales. co.uk, enter the book title or ISBN, and click on b. How many whales are there in the wild? weblink 4.3. To learn more about the number of whales Big questions in the wild, go to www. Having read this section, you can now discuss the following big questions: pearsonhotlinks.co.uk, enter the book title What strengths and weaknesses of the systems approach and the use of models have been revealed or ISBN, and click on through this topic? weblink 4.4. To what extent have the solutions emerging from this topic been directed at preventing environmental impacts, limiting the extent of the environmental impacts, or restoring systems in which environmental impacts have already occurred? How are the issues addressed in this topic of relevance to sustainability or sustainable development? In what ways might the solutions explored in this topic alter your predictions for the state of human societies and the biosphere some decades from now? Points you may want to consider in your discussions: How far does a systems approach help our understanding of aquatic food production systems? Compare and contrast the environmental impact of capture fisheries and aquaculture. To what extent can fisheries be managed sustainably? Outline the likely pressures on, and potential solutions for the world fisheries in decades to come. 4.4 Water pollution Significant idea Water pollution, both groundwater and surface water, is a major global problem whose effects influence human and other biological systems. Big questions As you read this section, consider the following big questions: What strengths and weaknesses of the systems approach and the use of models have been revealed through this topic? To what extent have the solutions emerging from this topic been directed at preventing environmental impacts, limiting the extent of the environmental impacts, or restoring systems in which environmental impacts have already occurred? How are the issues addressed in this topic of relevance to sustainability or sustainable development? In what ways might the solutions explored in this topic alter your predictions for the state of human societies and the biosphere some decades from now? Knowledge and understanding There are a variety of freshwater and marine pollution sources. Types of aquatic pollutant include floating debris, organic material, inorganic plant nutrients (nitrates and phosphates), toxic metals, synthetic compounds, suspended solids, hot water, oil, radioactive pollution, pathogens, light, noise, and biological entities (invasive species). 248 M04_ESS_SB_IBGLB_0420_U04.indd 248 29/07/2015 16:48  4.4 A wide range of parameters can be used to directly test the quality of aquatic systems (e.g. pH, temperature, suspended solids/turbidity, metals, nitrates, and phosphates). Biodegradation of organic material uses oxygen and can lead to anoxic conditions and subsequent anaerobic decomposition, which in turn leads to formation of methane, hydrogen sulphide, and ammonia (toxic gases). Biochemical oxygen demand (BOD) is a measure of the amount of dissolved oxygen required to break down the organic material in a given volume of water through aerobic biological activity. BOD is used to indirectly measure the amount of organic matter in a sample. Some species can be indicative of polluted waters and are used as indicator species. A biotic index indirectly measures pollution by assaying the impact on species in the community according to their tolerance, diversity, and relative abundance. Eutrophication can occur when lakes, estuaries and coastal waters receive inputs of nutrients (nitrates and phosphates) which result in an excess growth of plants and phytoplankton. Dead zones in both oceans and fresh water can occur when there is not enough oxygen to support aquatic life. Water pollution management strategies include: – reducing human activities producing pollutants (e.g. alternatives to current fertilizers and detergents) – reducing release of pollution into the environment (e.g. treatment of wastewater to remove nitrates and phosphates) – removing pollutants from the environment and restoring ecosystems (e.g. removal of mud from eutrophic lakes and reintroducing plant and fish species). Water pollution There are a variety of freshwater and marine pollution sources. Freshwater and marine pollution sources include run-off, sewage, industrial discharge, solid domestic waste, transport, recreation and tourism, and energy waste. Sources of marine pollution include rivers, pipelines, atmosphere, oil spills, deliberate and accidental discharges from ships, sewage from cruise ships, aquaculture farms, power Types of aquatic stations, and industry. pollutant include floating debris, organic Storm water that washes off the roads and roofs can be a worse source of pollutants material, inorganic than sewage. Such water may contain high levels of heavy metals, volatile solids, and plant nutrients (nitrates organic chemicals. Studies of water quality during in floods of the Silk Stream in and phosphates), toxic metals, synthetic London recorded that between 20–40 per cent of storm water sediments were organic compounds, suspended and mostly biodegradable. Highway run-off has 5–6 times the concentration of heavy solids, hot water, oil, metals as roof run-off. Annual run-off from 1 km of a single carriageway of the M1 (a radioactive pollution, highway in the UK) included 1.5 tonnes of suspended sediment, 4 kg of lead, 126 kg of pathogens, light, noise, oil and 18 g of hazardous polynuclear aromatic hydrocarbons. and biological entities (invasive species). Water quality Standard water quality tests on drinking water, rivers, and other sites can be performed with portable equipment that enables detection of nitrate, nitrite, free chlorine, chloride, fluoride, hardness, and heavy metals such as lead. Water-quality tests on rivers include biochemical oxygen demand (BOD), chemical oxygen demand (COD), turbidity, ammonia, and dissolved oxygen. There are two main ways of measuring water quality, by direct and indirect measures. Direct measures take samples of the water and measure the concentrations of different 249 M04_ESS_SB_IBGLB_0420_U04.indd 249 29/07/2015 16:48  04 Water, aquatic food production systems, and societies A wide range of A report in 2014 confirmed that nearly 60 per cent of China’s underground water was parameters can be polluted. The country’s land and resources ministry found that of 4778 testing spots in used to directly test 203 cities, 44 per cent had ‘relatively poor’ underground water quality; the groundwater the quality of aquatic in another 15.7 per cent tested as ‘very poor’. Water quality improved year on year at systems, including 647 spots, and worsened in 754 spots. pH, temperature, Water of very poor quality cannot be used as source of drinking water. The Chinese suspended solids government is only now beginning to address the noxious environmental effects of (turbidity), metals, its long-held growth-at-all-costs development model. While authorities have become nitrates, and more transparent about air quality data since 2013, information about water and soil phosphates. pollution in many places remains relatively well guarded. In 2013, about a third of China’s water resources were groundwater based, and only 3 per cent of the country’s urban groundwater could be classified as ‘clean’. About 70 per cent of groundwater in the north China plain – 400 000 km2 of some of the world’s most densely populated land – was considered unfit for human consumption. Few Chinese urban dwellers consider tap water safe to drink – most either boil their water or buy it bottled. In 2014, a chemical spill poisoned the water supply of Lanzhou (a city of 2 million people in north-west China) with the carcinogen benzene. While Beijing’s noxious smog has become internationally infamous, drought and water pollution may pose even greater threats to the city. Beijing’s annual per capita water availability is about 120 cubic metres, about a fifth of the UN’s cut-off line for ‘absolute scarcity’. chemicals that it contains. If the chemicals are dangerous or the concentrations are too great, the water is polluted. Measurements like this are known as chemical indicators of water quality (Table 4.14). Indirect methods involve examining the fish, insects, and other invertebrates that live in the water. If many different types of creature can live in a river, the water quality is likely to be very good; if the river supports no fish life at all, the quality is obviously much poorer. Measurements like this are called biological indicators of water quality. Student measuring water quality 250 M04_ESS_SB_IBGLB_0420_U04.indd 250 29/07/2015 16:49  4.4 Indicator Method What the results show Table 4.14 Chemical indicators of water quality dissolved test kit, meter, or sensor; oxygen 75% oxygen saturation = oxygen usually measured as percentage healthy, clean water saturation; follow instructions to 10–50% oxygen saturation = measure oxygen saturation polluted water 30 none indicative of the level of and small Tubifex pollution. 253 M04_ESS_SB_IBGLB_0420_U04.indd 253 29/07/2015 16:49  04 Water, aquatic food production systems, and societies An indicator species is one whose presence, absence or abundance can be used as an indicator of pollution. It doesn’t have to be water pollution – some species can be used to indicate air pollution, soil nutrient levels and abiotic water characteristics: lichen (Usnea alliculata) indicates very low levels of sulfur dioxide in air nettles (Ullica dioica) indicate high phosphate levels in soil red alga (Corauina officinalis) indicate saline rock pools (absent from brackish ones). A biotic index indirectly measures pollution by Trent Biotic Index assaying the impact The Trent Biotic Index is based on the disappearance of indicator species as the level on species within the community according of organic pollution increases in a river. This occurs because the species are unable to to their tolerance, tolerate changes in their environment such as decreased oxygen levels or lower light diversity, and relative levels. Those species best able to tolerate the existing conditions become abundant – abundance. which can lead to a change in diversity. In extreme environments (e.g. a highly polluted river) diversity is low, although numbers of individuals of pollution-tolerant species may be high. Diversity decreases as pollution increases. The Trent Biotic Index has a maximum value of 10. The indices are in the form of marks out of 10 and give a sensitive assessment of pollution level: 10 indicates clean water and zero indicates highly polluted water. Here is how it works. 1. Sort your sample, separating the animals according to group (taxonomic Order). 2. Count the number of groups. 3. Note which indicator species are present, starting from the top of the list in Table 4.16. Table 4.16 Indicator species Total number of groups present for the Trent Biotic Index 0–1 2–5 6–10 11–15 16+ Indicator present Number of species Trent Biotic Index stonefly nymphs >1 – 7 8 9 10 (Plecoptera) >1 – 6 7 8 9 mayfly nymphs >1 – 6 7 8 9 (Ephemeroptera) >1 – 5 6 7 8 cassias fly larvae >1 – 5 6 7 8 (Trichoptera) >1 4 4 5 6 7 Gammarus all above absent 3 4 5 6 7 shrimps, crustaceans all above absent 2 3 4 5 6 (Asellus) To learn more about the Trent Biotic Index Tubifex / chironomid all above absent 1 2 3 4 – for Chesapeake Bay larvae (2006–08), go to www. pearsonhotlinks.co.uk, all above absent organisms not 0 1 2 – – enter the book title requiring dissolved or ISBN, and click on oxygen may be weblink 4.5. present 254 M04_ESS_SB_IBGLB_0420_U04.indd 254 29/07/2015 16:49  4.4 4. Take the highest indicator species on the list and read across the row, stopping at the column with the appropriate number of groups for your sample. So, if your highest indicator animal belongs to the Trichoptera, you have more than one species and a total of 7 groups, the Trent Biotic Index for your sample is 6. Eutrophication Eutrophication can occur when lakes, estuaries and coastal Eutrophication refers to the nutrient enrichment of streams, ponds, and groundwater. waters receive inputs It is caused when increased levels of nitrogen or phosphorus are carried into water of nutrients (nitrates bodies. It can cause algal blooms, oxygen starvation and, eventually, the decline of and phosphates), which biodiversity in aquatic ecosystems. result in an excess growth of plants and (a) (b) phytoplankton. You should be able to explain the process and impacts of eutrophication. (a) Overgrowth of algae due to eutrophication, Cambridgeshire, UK. (b) Close-up of surface algal bloom due to eutrophication. CONCEPTS: Equilibrium In eutrophication, increased amounts of nitrogen and/or phosphorus are carried in streams, lakes, and groundwater causing nutrient enrichment. This leads to an increase in algal blooms as plants respond to the increased nutrient availability. As the algae, die back and decompose, further nutrients are released into the water. This is an example of positive feedback. However, the increase in algae and plankton shade the water below, cutting off the light supply for submerged plants. The prolific growth of algae and cyanobacteria, especially in autumn as a result of increased levels of nutrients in the water and higher temperatures, results in anoxia (oxygen starvation in the water). The increased plant biomass and decomposition lead to a build up of dead organic matter and to changes in species composition. Some of these changes are the direct result of eutrophication (e.g. stimulation of algal growth in water bodies), while others are indirect (e.g. changes in the diversity of fish species due to reduced oxygen concentration). Eutrophication is very much a dynamic system – as levels of nitrates and phosphorus in streams and groundwater change, there is a corresponding change in species composition. 255 M04_ESS_SB_IBGLB_0420_U04.indd 255 29/07/2015 16:49  04 Water, aquatic food production systems, and societies sunlight 5. Death of the ecosystem: oxygen levels reach a point where no life is possible. Fish and other organisms die. 1. Nutrient load up: excessive nutrients from fertilizers are flushed from the land into rivers or lakes by rainwater. algae layer 3. Algae blooms, oxygen is depleted: algae blooms, preventing sunlight reaching other plants. The plants die and oxygen in the water is depleted. decomposers 2. Plants flourish: these pollutants cause aquatic plant growth of algae, duckweed and other 4. Decomposition further plants. depletes oxygen: dead plants are broken nutrient down by bacteria material decomposers, using up even Figure 4.23 The process of more oxygen in the water. eutrophication time A number of changes may occur as a result of eutrophication (Figure 4.23). Turbidity (murkiness) increases and reduces the amount of light reaching submerged plants. Rate of deposition of sediment increases because of increased vegetation cover. This reduces the speed of water and decreases the lifespan of lakes. Net primary productivity is usually higher compared with unpolluted water and may be seen by extensive algal or bacterial blooms. Dissolved oxygen in water decreases, as organisms decomposing the increased biomass respire and consume oxygen. Diversity of primary producers changes and finally decreases; the dominant species change. Initially, the number of primary producers increases and may become more diverse. However, as eutrophication proceeds, early algal blooms give way to cyanobacteria. Fish populations are adversely affected by reduced oxygen availability, and the fish community becomes dominated by surface-dwelling coarse fish, such as pike and perch. Other species migrate away from the area, if they can. In freshwater aquatic systems, a major effect of eutrophication is the loss of the submerged macrophytes (aquatic plants). Macrophytes are thought to disappear because they lose their energy supply (sunlight penetrating the water). Sunlight is intercepted by the increased biomass of phytoplankton exploiting the high nutrient conditions. In principle, the submerged macrophytes could also benefit from increased nutrient availability, but they have no opportunity to do so because they are shaded by the free- floating microscopic organisms. Natural eutrophication The process of primary succession (Chapter 2, pages 114–119) is associated with gradual eutrophication as nutrients are trapped and stored by vegetation, both as 256 M04_ESS_SB_IBGLB_0420_U04.indd 256 29/07/2015 16:49  4.4 living tissue and organic matter in soil or lake sediments. Nutrient enrichment occurs Algae and cyanobacteria through addition of sediment, rainfall and the decay of organic matter and waste are tiny organisms products. Starting from an oligotrophic (nutrient-poor) state with low productivity, a occurring in fresh typical temperate lake increases in productivity fairly quickly as nutrients accumulate. water and saltwater. Algae belong to the eukaryotes – single- Anthropogenic eutrophication celled or multicellular organisms whose cells Human activities worldwide have caused the nitrogen and phosphorus content of contain a nucleus. The many rivers to double and, in some countries, local increases of up to 50 times have cyanobacteria belong been recorded. to the prokaryotes – single celled organisms Phosphorus without a membrane- bound nucleus. The Phosphorus is a rare element in the Earth’s crust. Unlike nitrogen, there is no reservoir cyanobacteria used to of gaseous phosphorus compounds available in the atmosphere. In natural systems, be called blue–green phosphorus is more likely to be a growth-limiting nutrient than nitrogen. algae (a term you may still come across) Domestic detergents are a major source of phosphates in sewage effluents. Estimates but they have been of the relative contribution of domestic detergents to phosphorus build-up in Britain’s reclassified as bacteria. watercourses vary between 20 per cent and 60 per cent. As phosphorus increases in a The first members of freshwater ecosystem, the amount of plankton increases and the number of freshwater the cyanobacteria to be discovered were indeed plants decreases. blue–green in colour, but since then new members Nitrogen of the group have been Nearly 80 per cent of the atmosphere is nitrogen. In addition, air pollution has found that are not this increased rates of nitrogen deposition. The main anthropogenic source is a mix distinctive colour. of nitrogen oxides (NOx), mainly nitrogen monoxide (NO), released during the combustion of fossil fuels in vehicles and power plants. Despite its abundance, The mining of phosphate- nitrogen is more likely to be the limiting nutrient in terrestrial ecosystems (as opposed rich rocks has increased to aquatic ones), where soils can typically retain phosphorus while nitrogen is leached the mobilization of away. phosphorus. A total of 12 × 1012 g yr –1 are Nutrients applied to farmland through fertilizers may spread to the wider environment mined from rock deposits. by: This is six times the rate at which phosphorus drainage water percolating through the soil, leaching soluble plant nutrients is locked up in ocean washing of excreta, applied to the land as fertilizer, into watercourses sediments from which the rocks are formed. erosion of surface soils or the movement of fine soil particles into subsoil drainage About three-quarters of systems. the world’s production of phosphorus comes from In Europe, large quantities of slurry from intensively reared and housed livestock is the USA, China, Morocco, spread on the fields. Animal excreta are very rich in both nitrogen and phosphorus and Russia. and, therefore, their application to land can contribute to problems from polluted run- off. Evaluating the impact of eutrophication There are three main reasons why the high concentrations of nitrogen in rivers and groundwater are a problem. First, nitrogen compounds can cause undesirable effects in the aquatic ecosystems, especially excessive growth of algae. Second, the loss of fertilizer is an economic loss to the farmer. Third, high nitrate concentrations in drinking water may affect human health, and have been linked to increased rates of stomach cancer. 257 M04_ESS_SB_IBGLB_0420_U04.indd 257 29/07/2015 16:49  04 Water, aquatic food production systems, and societies Case study Eutrophication of Lake Erie Aerial view of lake 227 in 1994. The green colour is caused by cyanobacteria stimulated by the experimental addition of phosphorus for the 26th consecutive year. Lake 305 in the background is unfertilized. Natural eutrophication normally takes thousands of years to progress. In contrast, anthropogenic or cultural eutrophication is very rapid. During the 1960s, Lake Erie (on the USA–Canada border) was experiencing rapid anthropogenic eutrophication and was the subject of much concern and research. Eutrophication of Lake Erie caused algal and cyanobacterial blooms, which caused changes in water quality. The increase in cyanobacteria at the expense of water plants led to a decline in biodiversity. With fewer types of primary producer, there were fewer types of consumer, and so the overall ecosystem biodiversity decreased. Cyanobacteria are unpalatable to zooplankton, thus their expansion proceeds rapidly. The cyanobacterial blooms led to oxygen depletion and the death of fish. In addition, algal and bacterial species can cause the death of fish by clogging their gills and causing asphyxiation. Many indigenous fish disappeared and were replaced by species that could tolerate the eutrophic conditions. Low oxygen levels caused by the respiration of the increased lake phytomass killed invertebrates and fish. The death of macrophytes on the lake floor increased the build up of dead organic matter in the thickening lake sediments. Rotting bacterial masses covered beaches and shorelines. Researchers at the University of Manitoba set up the Experimental Lakes Area (ELA) in 1968 to investigate the causes and impacts of eutrophication in Lake Erie. Between June 1969 and May 1976, it was the main focus of experimental studies at the ELA. Aerial view lake 226 in August Over a number of years, seven 1973. The green colour is due different lakes (ELA lakes 227, 304, to cyanobacteria growing on 302, 261, 226, 303, and 230) were phosphorus added to the lake treated in different ways. Lakes 227 on the nearside of the dividing and 226 were especially important curtain. in showing the effect of phosphorus in eutrophication. Studies of gas exchange and internal mixing in lake 227 during the early 1970s clearly demonstrated that algae in lakes were able to obtain sufficient carbon dioxide, via diffusion from the atmosphere to the lake water, to support eutrophic blooms. The blue–green algae (now called cyanobacteria) were found to be able to fix nitrogen that had diffused naturally into the lake from the air, making nitrogen available for supporting growth. 258 M04_ESS_SB_IBGLB_0420_U04.indd 258 29/07/2015 16:49  4.4 ELA lake 226 was the site of a very successful experiment. The lake was divided into two relatively Algae may be a nuisance equal parts using a plastic divider curtain. Carbon and nitrogen were added to one half of the lake, but they do not produce while carbon, nitrogen and phosphorus were added to the other half of the lake. For 8 years, the side substances toxic to receiving phosphorus developed eutrophic cyanobacterial blooms, while the side receiving only carbon humans or animals. and nitrogen did not. The experiment suggested that in this case phosphorus was the key nutrient. A Cyanobacteria, on the multibillion dollar phosphate control programme was soon instituted within the St Lawrence Great Lakes other hand, produce Basin. Legislation to control phosphates in sewage, and to remove phosphates from laundry detergents, substances that are was part of this programme. extremely toxic causing By the mid-1970s, North American interest in eutrophication had declined. Nevertheless, the nutrient- serious illness and death pollution problem remains the number one water-quality problem worldwide. if ingested. This is why cyanobacteria are a Loss to farmers very worrying problem in water sources or Eutrophication can result in an economic loss for farmers. Farmers are keen to use reservoirs used for leisure NPK (nitrogen, phosphorus, and potassium) fertilizers because these products increase facilities. crop growth, improve farmers’ income and may help increase crop self-sufficiency in a country. However, the removal of these nutrients from the soil reduces these benefits. Arable soils often contain much inorganic nitrogen: some is from fertilizer unused by Use of nitrogen fertilizers the previous crop but most is from the decomposition of organic matter caused by has increased by 600 autumn ploughing – ploughing releases vast quantities of nitrogen. However, unless a per cent in the last 50 new crop is planted quickly, much of this is lost by leaching. Another influence is climate years and up to 30 per cent of nitrogen used in – there is normally more decomposition in the autumn when warm soils get wet. In still- agriculture ends up in our growing grass pasture, the nitrate is absorbed but when fields are bare soil, the nitrate is fresh water. prone to leaching. This problem is especially severe where a wet autumn follows a dry summer. Much soil organic matter may be decomposed and leached at such a time. Health concerns The concern for health relates to increased rates of stomach cancer (caused by nitrates in the digestive tract) and to blue baby syndrome (methaemoglobinaemia), caused by insufficient oxygen in the mother’s blood for the developing baby. However, critics argue that the case against nitrates is not clear – stomach cancer could be caused by a variety of factors and the number of cases of blue baby syndrome is statistically small. However, in parts of Nigeria, where nitrate concentrations have exceeded 90 mg dm–3, the death rate from gastric cancer is abnormally high. Case study Eutrophication in England and Wales The amount of nitrates in tap water is a matter of general concern. The pattern of nitrates in rivers and groundwater shows marked regional and temporal variations. In the UK, it is concentrated towards the arable areas of the east, and concentrations are increasing. In England and Wales, over 35 per cent of the population derive their water from the aquifers of lowland England and over 5 million people live in areas where there is too much nitrate in the water. The problem is that nitrates applied on the surface slowly make their way down to the groundwater zone – this may take up to 40 years. Thus, increasing levels of nitrate in drinking water will continue to be a problem well into the 21st century. The cost of cleaning nitrate-rich groundwater is estimated at between £50 million and £300 million a year. Case study Eutrophication in Kunming City, China Dianchi Lake, near Kunming City in the Yannan Province of China, has huge problems with eutrophication. Untreated sewage has been drained into the lake since before the 1980s. Cyanobacteria (Microcystis spp.) have killed over 90 per cent of native water weed, fish, and molluscs, so destroying the fish industry. The lake is largely green slime but because water supplies have run short, lake water from Dianchi Lake has been used since 1992 to supply Kunming’s 1.2 million residents. The city opened its first sewage treatment plant in 1993, but this copes with only 10 per cent of the city’s sewage. Billions of dollars have been spent since the 1980s in attempts to clean up the lake, but with no real success. 259 M04_ESS_SB_IBGLB_0420_U04.indd 259 29/07/2015 16:49  04 Water, aquatic food production systems, and societies There are three main ways of dealing with Management strategies for eutrophication eutrophication: Water pollution management strategies include: altering human activity reducing human activities that produce pollutants (for example, using alternatives to regulating and current fertilizers and detergents) reducing pollutants reducing release of pollution into the environment (for example, treatment of waste at the point of water to remove nitrates and phosphates) emission clean-up and removing pollutants from the environment and restoring ecosystems (for example, restoration of removal of mud from eutrophic lakes and reintroduction of plant and fish species). polluted water. Altering human activities Public campaigns in Australia have encouraged people to: use zero- or low-phosphate detergents wash only full loads in washing machines wash vehicles on porous surfaces away from drains or gutters reduce use of fertilizers on lawns and gardens compost garden and food waste collect and bury pet faeces. Possible measures to reduce nitrate loss (based on the mid-latitude northern hemisphere) include the following. Avoid using nitrogen fertilizers during the wet season when soils are wet and fertilizer is most likely to be washed through the soil. Give preference to autumn-sown crops – their roots conserve nitrogen in the soil and use up nitrogen left from the previous year. Sow autumn-sown crops as early as possible and maintain crop cover through autumn and winter to conserve nitrogen. Do not apply nitrogen when the field is by a stream or lake. Do not apply nitrogen just before heavy rain is forecast (assuming that forecasts are accurate). Use less nitrogen if the previous year was dry because less will have been lost. This is difficult to assess precisely. Regulating and reducing the nutrient source Prevention of eutrophication at source has the following advantages (compared with treating its effects or reversing the process). Technical feasibility – in some situations, prevention at source may be achieved by diverting a polluted watercourse away from the sensitive ecosystem, while removal of nutrients from a system by techniques such as mud-pumping is more of a technical challenge. Cost – nutrient stripping at source using a precipitant is relatively cheap and simple to implement. Biomass stripping of affected water is labour-intensive and therefore expensive. Products – restored wetlands may be managed to provide economic products such as fuel, compost or thatching material more easily than trying to use the biomass stripped from a less managed system. 260 M04_ESS_SB_IBGLB_0420_U04.indd 260 29/07/2015 16:49  4.4 Phosphate stripping Up to 45 per cent of total phosphorus loading to fresh water in the UK comes from sewage works. This input can be reduced by 90 per cent or more by carrying out phosphate stripping. The effluent is run into a tank and dosed with a precipitant, which combines with phosphate in solution to create a solid, which then settles out and can be removed. CONCEPTS: Environmental value systems Different users and organizations view eutrophication in different ways – farmers claim to need to use fertilizers to improve food supply; chemical companies argue they produce fertilizers to meet demand from farmers; water companies seek money from the government and the consumer to make eutrophic water safe to drink; the consumers see rising water bills and potential health impacts Managing eutrophication using of eutrophication. barley bales. The bales of barley straw are just visible (brown) beneath the water surface at the Clean-up strategies right-hand edge of the lake. Once nutrients are in an ecosystem, it is much harder and more expensive to remove them than it would have been to tackle the eutrophication at source. The main clean-up methods available are: precipitation (e.g. treatment with a solution of aluminium or ferrous salt to precipitate phosphates) removal of nutrient-enriched sediments; for example, by mud pumping removal of biomass (e.g. harvesting of common reed) and using it for thatching or fuel. Temporary removal of fish can allow primary consumer species to recover and control algal growth. Once water quality has improved, fish can be re-introduced. Mechanical removal of plants from aquatic systems is a common method for mitigating the effects of eutrophication. Efforts may be focused on removal of You should be able unwanted aquatic plants (e.g. water hyacinth) that tend to colonize eutrophic water. to evaluate pollution Each tonne of wet biomass harvested removes about 3 kg of nitrogen and 0.2 kg of management strategies phosphorus from the system. Alternatively, plants may be introduced deliberately to with respect to water pollution. mop-up excess nutrients. Case study Effluent diversion at Lake Washington, USA CHALLENGE In some circumstances, it may be possible to divert sewage effluent away from a water body. This was YOURSELF achieved at Lake Washington, near Seattle, USA. In 1955, Lake Washington was affected by cyanobacteria. Thinking skills ATL The lake was receiving sewage effluent from about 70 000 people. The sewerage system was redesigned to divert effluent away from the lake to the nearby sea inlet of Puget Sound. ‘It is easier and more cost- effective to control the causes of eutrophication rather than to deal with the symptoms (results) of eutrophication.’ Critically To learn more about experiments related to eutrophication, go to www.pearsonhotlinks.co.uk, examine this statement. enter the book title or ISBN, and click on weblink 4.6. 261 M04_ESS_SB_IBGLB_0420_U04.indd 261 29/07/2015 16:49  04 Water, aquatic food production systems, and societies Dead zones in both oceans and fresh water Dead zones and red tides can occur when there is Dead zones, red tides and their associated plagues of jellyfish seem to have occurred not enough oxygen to support marine life. naturally for centuries, but their appearance is becoming increasingly frequent. Red tides, for example, regularly form off the Cape Coast of South Africa, fed by nutrients brought up from the deep, and off Kerguelen Island in the Southern Ocean. Nowadays, though, most are associated with a combination of phenomena including overfishing, warmer waters, and the washing into the sea of farm fertilizers and sewage. Most of the larger fish in shallow coastal waters have already been caught. As the larger species disappear, so the smaller ones thrive. These smaller organisms are also stimulated by nitrogen and phosphorus nutrients running off the land. The result is an explosion of growth among phytoplankton and other algae, some of which die, sink to the bottom and decompose, combining with dissolved oxygen as they rot. Warmer conditions, and sometimes the loss of mangroves and marshes, which once acted as filters, encourage the growth of bacteria in these oxygen-depleted waters. A situation develops where there is not enough oxygen to support marine life. (A similar effect occurs with eutrophication in freshwater rivers.) The result may be a sludge-like soup, apparently lifeless – hence the name dead zones – but in fact teeming with simple, and often toxic, organisms. These may be primitive bacteria whose close relations are known to have thrived billions of years ago. Or they may be algae which colour the sea green or red-brown. In such places, red tides tend to form, some producing toxins that get into the food chain through shellfish, and rise up to kill bigger fish (if there are any left), birds, and even seals and manatees. Red tides and similar blights do not necessarily last long, nor do they cover much of the surface of the sea. But they are increasing in both size and number: dead zones have now been reported in more than 400 areas. And increasingly they affect not only estuaries and inlets, but also continental seas such as the Baltic, the Kattegat, the Black and East China Seas and the Gulf of Mexico. All of these are traditional fishing grounds. The winners in these newly polluted, over-exploited, oxygen-starved seas are simple, primitive forms of life, whereas the losers are the species that have taken millenia to develop. The impacts of waste on the marine environment Over 80 per cent of marine pollution comes from land-based activities. When waste is dumped, it is often close to the coast and very concentrated. The most toxic waste material dumped into the ocean includes dredged material, industrial waste, sewage sludge, and radioactive waste. Dredging contributes about 80 per cent of all waste dumped into the ocean. Rivers, canals, and harbours are dredged to remove silt and sand build up or to establish new waterways. About 20–22 per cent of dredged material is dumped into the ocean. About 10 per cent of all dredged material is polluted with heavy metals such as cadmium, mercury, and chromium, hydrocarbons such as heavy oils, nutrients including phosphorus and nitrogen, and organochlorines from pesticides. When dredged material is dumped into the ocean, fisheries suffer adverse affects, such as unsuccessful spawning in herring and lobster populations. Over 60 million litres of oil run off America’s roads and, via rivers and drains, find their way into the oceans each year. Through sewage and medical waste, antibiotics and hormones enter the systems of seabirds and marine mammals. Mercury and other metals turn up in tuna, orange roughy, seals, polar bears, and other long-lived animals. In the 1970s, 17 million tonnes of industrial waste were legally dumped into the ocean. 262 M04_ESS_SB_IBGLB_0420_U04.indd 262 29/07/2015 16:49  4.4 In the 1980s, 8 million tonnes were dumped, including acids, alkaline waste, scrap metals, waste from fish processing, flue desulfurization sludge, and coal ash. The peak of sewage dumping was 18 million tonnes in 1980, a number that fell to 12 million tonnes in the 1990s. Alternatives to ocean dumping include recycling, producing less wasteful products, saving energy and changing the dangerous material into more benign waste. Oil pollution All over the world, oil spills regularly contaminate coasts. Oil exploration is a major activity in such regions as the Gulf of Mexico, the South China Sea and the North Sea. The threats vary. For example, there is evidence of widespread toxic effects on benthic (deep-sea) communities on the floor of the North Sea in the vicinity of the 500+ oil production platforms in British and Norwegian waters. Meanwhile, oil exploration in the deep waters of the North Atlantic, north-west of Scotland, threatens endangered deep-sea corals. There is evidence, too, that acoustic prospecting for hydrocarbons in these waters may deter or disorientate some marine mammals. Shipping is a huge cause of pollution. Ships burn bunker oil, the dirtiest of fuels, so more carbon dioxide is released and more particulate matter, which may be responsible for about 60 000 deaths each year from chest and lung diseases, including cancer. Most of these occur near coastlines in Europe, and East and South Asia. Some action is being taken. Oil spills should become rarer after 2010, when all single-hulled ships were banned. Efforts are also being made to prevent the spread of invasive species through the taking on and discharging of ships’ ballast water. And a UN convention may soon ban the use of tributyltin, a highly toxic chemical added to the paint used on almost all ships’ hulls, in order to kill algae and barnacles. Case study Deepwater Horizon oil spill The Deepwater Horizon oil spill is the largest in US history. In April 2010, an explosion ripped through the Deepwater Horizon oil rig in the Gulf of Mexico, 80 km off the coast. Two days later the rig sank, with oil pouring into the sea at a rate up to 62 000 barrels a day. The oil threatened wildlife along the US coast as well as livelihoods dependent on tourism and fishing. Over 160 km of coastline were affected, including oyster beds and shrimp farms. The extent of the environmental impact is likely to be severe and last a long time. A state of emergency was declared in Louisiana. The cost to BP, who operated the rig, may reach US$20 billion. BP’s attempts to plug the oil leak were eventually successful. Dispersants were used to break up the oil slick but BP was ordered by the US government to limit their use, as they could cause even more damage to marine life in the Gulf of Mexico. By the time the well was capped (in July 2010), about 4.9 million barrels of crude oil had been released into the sea. Radioactive waste Radioactive effluent also makes its way into the oceans. Between 1958 and 1992, the Arctic Ocean was used by the Soviet Union, or its Russian successor, as the resting place for 18 unwanted nuclear reactors, several still containing their nuclear fuel. Radioactive waste is also dumped in the oceans, and usually comes from the nuclear power process, medical and research use of radioisotopes, and industrial uses. Nuclear waste usually remains radioactive for decades. Following the explosion at the Daichi nuclear power in Japan in March 2011, radioactive material was carried by air and water across the Pacific towards North America. It reached Vancouver Island, Canada, in February 2015. 263 M04_ESS_SB_IBGLB_0420_U04.indd 263 29/07/2015 16:49  04 Water, aquatic food production systems, and societies Plastic More alarming still is the plague of plastic. In 2006, the UN Environment Programme reckoned that every square kilometre of sea held nearly 18 000 pieces of floating plastic. Much of it was and still is in the central Pacific, where scientists believe as much as 100 million tonnes of plastic waste are suspended in two separate gyres (large rotating ocean currents) of garbage in the Great Pacific Garbage Patch. To read more about plastic pollution in the Great Pacific Garbage Patch, see pages 428–429. Dead albatross with plastic debris (in its stomach). Exercises 1. Define the term biochemical oxygen demand (BOD) and explain how this indirect method is used to assess pollution levels in water. 2. Describe and explain an indirect method of measuring pollution levels using a biotic index. 3. Figure 4.22 (page 253) shows changes in characteristics of a stream below an outlet of pollution. a. Describe the relative changes in Tubifex and stonefly nymphs along the course of the river. b. Suggest reasons for these changes. c. Compare and contrast the presence and abundance of stonefly nymphs and Tubifex worms. d. Explain the variations in BOD and dissolved oxygen. 4. Outline the processes of eutrophication. 5. Evaluate the impacts of eutrophication. 6. Describe and evaluate pollution management strategies with respect to eutrophication. 7. Outline the effects of eutrophication on natural and human environments. 264 M04_ESS_SB_IBGLB_0420_U04.indd 264 29/07/2015 16:49  4.4 8. The data below show the main sources of waste entering the sea. run-off and land-based discharge 44 per cent atmosphere 33 per cent maritime transportation 12 per cent dumping 10 per cent offshore production 1 per cent a. Choose a suitable method to present this data. b. Comment on the results you produce. Big questions Having read this section, you can now discuss the following big questions: What strengths and weaknesses of the systems approach and the use of models have been revealed through this topic? To what extent have the solutions emerging from this topic been directed at preventing environmental impacts, limiting the extent of the environmental impacts, or restoring systems in which environmental impacts have already occurred? How are the issues addressed in this topic of relevance to sustainability or sustainable development? In what ways might the solutions explored in this topic alter your predictions for the state of human societies and the biosphere some decades from now? Points you may want to consider in your discussions: To what extent can water pollution be considered as a system? Are the existing solutions to pollution likely to cope with current levels of water pollution? Which is the lesser evil – less food production or eutrophication? How are they linked? How is water pollution likely to change in the next decades? Give reasons for your answer. Practice questions 1 Study the model of the hydrological cycle below. evapotranspiration A interception storage stemflow and drip surface storage C B soil moisture storage through flow seepage aeration zone storage interflow groundwater recharge channel storage channel groundwater storage D run-off a Identify the flows A, B, C, and D. 265 M04_ESS_SB_IBGLB_0420_U04.indd 265 29/07/2015 16:49  04 Water, aquatic food production systems, and societies b Explain how the hydrological cycle may be changed in urban areas. c How can the use of groundwater be sustainable? 2 The graph below shows Japan’s whale catch between 1985 and 2010. 2600 2400 2200 2000 1800 1600 number of whales taken Fin (Antarctic) Sei (North Pacific) 1400 Sperm (N. Pacific & Coastal) Brydes (N. Pacific & Coastal) 1200 Minke (Coastal) Minke (North Pacific) 1000 Minke (Antarctic) 800 600 400 200 0 19 5 19 6 19 7 19 8 19 9 19 0 19 1 19 2 19 3 19 4 19 5 19 6 19 7 19 8 20 9 20 0 20 1 20 2 20 3 20 4 20 5 20 6 20 7 20 8 20 9 10 8 8 8 8 8 9 9 9 9 9 9 9 9 9 9 0 0 0 0 0 0 0 0 0 0 19 season (beginning in the second half of the year indicated) a Describe the trend in the number of whales caught by Japan between 1985 and 2010. b What is the main species of whale caught, and from where is it mainly taken? c Suggest why the number of whales killed fell so much in 1987, but then began to rise again. d Compare the total number of whales that Japan are taking to those that the Inuit populations of North America and Greenland are taking. 3 Study the table below which shows the results of a survey of a stream above and below an outlet from a sewage works. The figure below is a sketch map of the stream and the outlet. Site CSA* / Velocity / Temp Oxygen pH No. of No. of m2 m sec–1 / °C /% caddis bloodworms fly 1 2.1 0.2 18 0.1 6.0 12 0 2 2.3 0.2 17 0.2 6.0 15 0 3 2.2 0.3 18 0.1 7.0 11 0 4 3.8 0.3 23 0.3 6.5 0 16 5 3.9 0.6 22 1.8 7.0 0 1 6 4.1 0.8 22 1.7 7.5 1 0 7 3.9 0.7 20 1.6 6.5 2 0 8 4.0 0.7 22 1.5 7.0 7 0 266 M04_ESS_SB_IBGLB_0420_U04.indd 266 29/07/2015 16:49  4.4 1 site numbers 2 outlet 3 4 weir 5 6 7 50 m 8 scale a Define the terms water quality, pollution, and discharge. b Plot the results for variations in oxygen content along the course of the stream. How does the oxygen content change at sites 4 and 5? Explain why. c What is the trend in temperature levels between site 1 and site 8? d i What does pH measure? ii How do you account for the relatively small linear variations in the stream’s pH? 4 Study the figure below which shows sources of cultural eutrophication. ‘Downtown’ CBD nitrogen compounds produced by cars woodland and factories forest housing stream inorganic fertilizer run-off (nitrates + phosphates) road 8 9 7 arable farm sewage 6 (ploughed) treatment pastoral farm 1 (cows & sheep) plant 5 road sources 2 of suburban housing cultural road air pollution eutrophication retail outlet car park 4 factories lake 3 construction road site a Explain what is meant by the term cultural eutrophication? b Suggest two ways in which urban areas may contribute to eutrophication. c What are the natural sources of nutrients as suggested by the figure above? d Briefly explain the process of eutrophication. 267 M04_ESS_SB_IBGLB_0420_U04.indd 267 29/07/2015 16:49