Hydrology BC ENV 3025
Global water use - towards a
sustainable
future?
Agenda 21 of the UN conference on Environment
and
Development in Rio in 1992 specified the need to protect the
quality
and
supply of freshwater resources by an integrated approach to
protect the
quality and supply of freshwater resources by an integrated
approach to
the development, management, and use of water in a sustainable
way.
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
Climate change
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- trees and shrubs have been replaced by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 (Murray
River)
- 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 (Fig)
- 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 (Fig)
- 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:
Reduce population growth!
- 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