Global water use - towards a sustainable future?

What means sustainability? One definition: 'a set of activities that ensures that the value of the services provided by a given water resource system will satisfy the objectives of future generations.' ('services' include maintenance of eco systems)

Major threats

Rapid population growth & multipliers

• increased pressure on water resources, quantity and quality (Fig)
• population distribution, 2000
• global precipitation
  
• water stress, globally
  

Climate change

• precipitation changes
  
• temperature changes
  
• rising sea levels typical current rate 2mm/y

Groundwater mining

Worldwide contamination of water resources

Land use change

• trees and shrubs have been replaced by agricultural cops and grassland => lower interception and ET => increased runoff => erosion
• negative feedback: less precipitation or retention of snow
• sometimes vegetation is purposefully changed in order to increase yield, however surprises happen:
• in Australia, Eucalyphtus trees have been removed near the Murray River in order to increase recharge; as a result, salty groundwater has been put into motion -> increased discharge into rivers -> incease of river salt content (Fig)
• also irrigation contributes to salinization (Govmt website)
  
• desertification
• deserts cover about 37% of the land on the globe (= 4.5 billion ha), 30% are natural, 7% man-made
• deserts increase at a rate of 6 million ha/y
• factors contributing:
• deforestation, overcultivation, poorly designed irrigation schemes
• destabilization of the topsoil is key factor
•  by the year 2000, one third of all the land used by agriculture has either been totally lost or become drought ridden
•  feedbacks on the desertification process

Hydropolitics

• many countries in the world need to share river basins and groundwater resources
• examples:
• Jordan River (Fig)
• River Nile (Fig)

Water quality

Sources of pollution

• pollution is defined as exceedence of natural concentrations in inacceptable levels
• human health is usually used as a measure
• pollution can be found in all components of the hydrologic cycle
• point: sewage treatment plants, factories, accidents, gas stations, ....
• nonpoint: agriculture, urban runoff, septic systems

Major surface sources of pollution

• surface sources dominate pollution
• organic pollution, nitrate, phosphate
• traditionally dominated by human sewage, but agricultural manure, slurry, and silage liquor have become major sources in 1980s and 90s, 'zero grazing policy'
• organic polution can adversely affet color, smell, and turbidity (from suspended matter), pathogenic bacteria, and viruses
• loss of oxygen: biological oxygen demand (BOD), measured by incubating a water sample in the dark for 5 days
• crude sewage has a BOD of 600 mg/l O₂/5days, unpoluted water only 5mg/l, silage liquor from fermented fodder grass can have a BOD 3000 times higher than sewage!
• three key parameters for measuring organic pollution: BOD, dissolved O₂ (DO, a measure of actual water status at the time of sampling), and ammonia (NH₃ or NH₄⁺)
• excessive levels of nitrogen and phosphorus produced by bacterial decomposition of organic waste can lead to eutrophication (indicator: algae growth) -> oxygen loss -> anaerobic conditions -> mobilization of sensitive elements
• high levels of nitrate in drinking water => 'blue baby syndrom', cancer by formation of nitrosamones in the gut
• WHO limit: 10mg/l of nitrate as N₂
• fecal coliform bacteria, concentrations > 100 000 per 100ml found in 4% of the rivers in the developed world!
• fecal contamination (human + aninmal sources) can carry E coli, Rotavirus, the protozoan Cryptosporidium, the bacterium salmonella, parasitic worms; some of these microbiological problems cannot be treated with chlorine or ozone
•  In 1993, this pernicious parasite grabbed the nation's attention. Its presence in the Milwaukee public water supply gave more than 400,000 people acute and often prolonged diarrhea or other gastrointestinal symptoms. By the time the outbreak ended, 100 people had died. It was the largest episode of waterborne disease in the United States in the 70 years since health officials began tracking such outbreaks. (Overview of similar cases)
• major other components of pollution are organic compounds such as TCE and MTBE (solvents, gasoline additives)
• inorganic pollution
• heavy metals, salts, industrial chemicals
• suspended solids and sediment yields
• suspended sediments often seen as pollutants, affect light transmission, clog intakes, can be natural and anthropogenic
• high loads in regions with high water surplus, highly erodible soils/sediments
• associated problems: filling of reservoirs with sediments, reduction of fertilization, sinking deltas, adsorption of pollutants

contaminants stored in sediments, PCBs in the Hudson are mostly coming out of the sediments today
• example: threats to water quality of the Great Plains aquifers (Fig)
• water quality standards

Some ideas for solutions:

• single most important factor: education!

Find other water sources?

• of very limited use, many areas are already approaching their limits
• desalinization ? Cost 4-10 times of water from other sources.

Climate change

• imitation of CO₂ emissions, reduction of global warming
• research adaptation strategies

Perform rigorous environmental audits, environmental impact assessments, economic analyses

Integrated management of water resources

• take into account interests of all stakeholders across boundaries
• hydropolitics; conflict, treaties, and international law
• Jordan, Nile, Ganges-Brahmaputra, Rio Grande,....
• example: India-Bangladesh treaty, Farraka barrage (Fig, Fig)

Conservation!!

• global distribution of irrigation
  
• implemetation of water saving measures, reduction of leaks, water metering, new technology, recycling
• agriculture is the biggest user of water worldwide, any solution needs to start with this sector
• improvement of irrigation efficiency necessary
• irrigation techniques
• basin
• furrow (Fig)
• sprinkler, in particular: central pivot irrigation (Fig)
• drip (Fig)
• Efficiencies of selected irrigation techniques (Fig)

• discussion of advantages and disadvantages of the individual techniques
• erosion control
• ET loss
• labor required for irrigation
• robustness regarding water quality
• efficiency (water/plant)
• other labor costs (weed control, distribution of fertilizers)
• initial cost
• the choice of the irrigation method also depends on the kind of crops that have to be irrigated
• drip irrigation is primarily a technique for regions with very low water supply or bad water quality
• Menu of options for improving irrigation water productivity (Fig)
• Water productivity gains from shifting to drip from conventional surface irrigation in India (Fig)
• sensible selection of crops
• pollution control in agriculture
• pricing
• adjustment of cost of water to market value
• market competition will reduce use
• water trading

Resources

• Vital Water Graphics - United Nations Environment Programme
• Postel, S. (1999) Pillars of Sand
• Postel, S. (1997) Last Oasis: Facing Water Scarcity
• Milwaukee Cryptosporidium Infection