Water issues - US

Water quantity

precipitation distribution in the US is very uneven (Fig), demand and supply are not matched very well
1990 total water withdrawals in the US, qualitatively (Fig)
source, use and disposition of water in the US (Fig)(Fig)
water use in the US will probably not drop significantly in the near future

increasing damage through extreme climate events and increased settlement of river banks

the El Nino pattern (Fig) is a example how small climate perturbations affect the water cycle (Fig)
future climate change will have major impacts on water resources

a large number of aquifers, in particular in dry regions are mined (pumping rate > recharge rate) (Fig)
example: depletion of the Ogallala aquifer, in some areas water level is dropping by 1m/y, recharge only mm's/y (Fig)
results: groundwater mining, land subsidence (Fig)(Fig), sea water intrusion (Fig)
example: Houston TX (Fig)(Fig)

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

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 (NH₃or 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
high levels of nitrate in drinking water => 'blue baby syndrom', cancer by formation of nitrosamones in the gut
WHO limit: 10ml/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)

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

Fig J 8.16

), PCBs in the Hudson are mostly coming out of the sediments today

agriculture is the biggest user of water in the US, any solution needs to start with this sector

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