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Most organism respond to the salinity of their environment in a manner analogous to blood
cells. Exposure to concentrations either too high or too low are problematic. Plant roots
for example, must maintain their salt concentration higher than their surroundings in order to
extract water from the soil. Plant cells avoid bursting under such conditions because they
are surrounded by a strong cell wall. Plants experience water stress in saline soils because
extracting water is more difficult. Irrigated agriculture invariably exacerbates soil salinity.
Natural sources of water contain some dissolved salts. Transpiration from plants and evaporation
from soils, lakes and rivers act as a distillation process in which pure water vaporizes and
the salts left behind become more concentrated in the smaller volume of liquid that remains.
Unless large amounts of water are periodically flushed through soils and discarded, irrigated
farmlands invariably become salt-inflicted. Mesopotamia is located at the confluence of
the Tigris and Euphrates rivers in what is now currently Iraq. It is considered the cradle
of civilization because societies that formed here somewhere between 4000 and 3500 BC, developed
sophisticated writing systems and used them in the context of complex governmental administration.
Supporting these societies were many agricultural advances including plant breeding, animal
domestication, crop rotations, water storage and irrigation. Centuries of irrigation with
inadequate drainage however, progressively added salt to the soil and eventually farmers
were forced to abandon large acreage and prosperity declined. Much of this area still suffers
from salinity problems.
The Salinas Valley of California, affectionately known as America's Salad Bowl, is a primary
source of salad greens, celery and broccoli consumed in the United States and Canada.
Water for irrigation primarily comes from pumping of groundwater. This and to a smaller
extent rising sea levels, have led progressively to greater intrusion of saltwater into the
local aquifers. Global warming will increase transpiration of plants and evaporation from
soils. Increased transpiration and evaporation, if not matched with additional precipitation
and proper disposal of drainage water, will accelerate soil salinization. Rising sea levels
and depletion or contamination of aquifers will diminish the availability of fresh water
for crops and humans alike, particularly in coastal regions.
In summary, number 1, changes in the patterns of precipitation will influence food production.
Number two, irrigated agriculture invariably exacerbates soil salinization.