Geoscience Reference
In-Depth Information
higher the water table (during wet periods) the
lower the storage capacity and vice versa (Carter
1997). Storage capacity also inl uences the
abundance of l ora and fauna available within a
given wetland, serves to replenish streams and
lakes during dry periods, and helps with ground-
water recharge.
In rural parts of the developing world without
piped water systems, communities are often
dependent on wetlands for household and agri-
cultural needs. For instance, beels are expansive
low-lying seasonally l ooded regions adjacent to
major l oodplains in eastern India and Bangla-
desh that provide water supplies and i shing
opportunities to resident populations for many
months of the year. When seasonal l oodwaters
recede, remnant deeper beels may still dot the
landscape and provide water resources while
their drier counterparts are used for agriculture.
Similarly, hoars (another local wetland term),
are found in northeastern parts of Bangladesh
and are much deeper bowl-shaped depressional
wetland features which may contain fresh water
almost year-round. They can be quite large and
during severe monsoonal l ooding may inundate
vast areas of adjacent land. In other instances
tanks or reservoirs built into depressions serve
as artii cially created wetlands all across South
Asia. They are used as sources of water by resi-
dent communities, serve bird and resident wild-
life and cattle populations, and often support
aquatic plant communities. Such natural and
artii cial wetland features provide vital fresh-
water resources to rural communities and their
signii cance cannot be emphasized enough.
From the earliest hydraulic civilizations of
Mesopotamia and Egypt, the development of
water as a resource for agriculture, urbanization,
and industrial use has led to signii cant altera-
tions to the l ow regimes of rivers. Through the
construction of storage and hydroelectric dams,
water-diversion schemes, river channelization
for navigation and l ood control, l oodplain and
deltaic wetlands have reduced dramatically in
extent. This chapter has already considered
some of the consequences of such wetland
reductions. Perhaps one of the most striking
examples of large-scale anthropogenic changes
to river regimes and wetland deltas comes from
the 1950s water diversion schemes built on the
Amu Darya and Syr Darya rivers that feed into
the Aral Sea (Fig. 11-6). The Aral Sea basin
covers 2.2 million km
2
across central Asia. A
landlocked sea in an arid region, it is fed prin-
cipally by the Amu Darya and Syr Darya, which
originate in the Pamir and Tien Shan mountains
and meander across a distance of 2500 km
before emptying into deltas along its southern
(Amu Darya) and northeastern (Syr Darya)
shores (World Bank Report 1998).
Today the Aral Sea is shared by the i ve
Central Asian countries of Uzbekistan, Kazakh-
stan, Tajikistan, Turkmenistan, and Kyrgyzstan,
which were all once part of the former Soviet
Union. Agricultural policies of nineteenth-
century Russia targeted the development of this
region for cotton and rice cultivation. The Soviet
period saw a further expansion of irrigation
through large-scale water diversion schemes and
a network of canals, which dramatically reduced
water l ows into the Aral, shrank its volume by
more than 75 percent, and increased salinity
levels from 10 g/L in 1960 to 100 g/L by 2004
(NATO 2005). Figure 11-6 illustrates this startling
reduction in area with an outline of the 1960
shoreline of the sea.
The consequences of such radical reductions
in water volume have altered the landscape of
the region and the coni guration of the sea itself.
The desiccation of the Aral Sea has resulted in
its breakup into several smaller water bodies.
The salinization of rivers, ground water and
agricultural land due to the mobilization of salts
from the expansion of irrigation and inefi cient
water use has had serious economic conse-
quences. The Amu Darya and Syr Darya deltas
were once important migratory stopping points
for birds and nourished vibrant i sheries. Today,
only a small fraction of these ecosystems remain,
yet their re-establishment through concerted
international cooperation could yield benei ts to
the local and regional ecology and economy.
Recent cooperative agreements between the
central Asian countries concerning integrated
water basin management and conservation
efforts provide some hope.
