May 25, 2013 | 06:01 AM (BD Time)
25 May, 2013 Saturday
The drying of Iran's Lake Urmia
Lake Urmia in the northwestern corner of Iran is one of the largest permanent hypersaline lakes in the world and the largest lake in the Middle East. It extends as much as 140 km from north to south and is as wide as 85 km east to west during high water periods. The lake was declared a Wetland of International Importance by the Ramsar Convention in 1971 and designated a UNESCO Biosphere Reserve in 1976. The lake itself is home to a unique brine shrimp species, Artemia urmiana, and along with the surrounding wetlands and upland habitat, it supports many species of reptiles, amphibians and mammals. Lake Urmia provides very important seasonal habitat for many species of migrating birds. Around 200 species of birds have been documented on and surrounding the lake including pelicans, egrets, ducks, and flamingos. The watershed of the lake is an important agricultural region with a population of around 6.4 million people; an estimated 76 million people live within a radius of 500 km.
The lake's surface area has been estimated to have been as large as 6 100 km2 but since 1995 it has generally been declining and was estimated from satellite data to be only 2 366 km2 in August of 2011 (Landsat data).
The decline is generally blamed on a combination of drought, increased water diversion for irrigated agriculture within the lake's watershed and mismanagement. In addition, a causeway has been built across the lake with only a 1 500 m gap for water to move between the northern and southern halves of the lake. It has been suggested that this has decreased circulation within the lake and altered the pattern of water chemistry; however evidence suggests that the impact of the causeway on the uniformity of water
chemistry in the lake has been minimal. The unfolding ecological disaster threatens to leave much of the lake bed a salt-covered wasteland. Scientists have warned that continued decline would lead to increased salinity, collapse of the lake's food chain and ecosystem, loss of wetland habitat, wind blown "saltstorms," alteration of local climate and serious negative impacts on local agriculture and livelihoods as well as regional health.
Thousands of protesters took to the streets in the cities of Tabriz and Urmia in late August and early September 2011 saying that authorities have done too little to save the lake. Those around the lake fear a fate similar to that of the population surrounding the nearby Aral Sea, which has dried up over the past several decades. Disappearance of the Aral Sea has been an environmental disaster affecting people throughout the region with windblown salt-storms. The population surrounding Lake Urmia is much denser putting more people at risk of impact.
Lake Urmia is an endorheic or terminal lake meaning that water leaves the lake only by evaporation. As is generally the case, this leads to a saltwater body and in the case of Lake Urmia, salinity is quite high. The lake has dramatically decreased in volume over the past decade-and-a-half, further concentrating salts in the lake, raising salinity to more than 300 g/L or 8 times as salty as typical seawater. Aquatic biodiversity is limited by the lake's salinity and Lake Urmia does not support any fish or mollusk species and no plants other than phytoplankton within the lake.
Wetlands surrounding the lake support a variety of salt tolerant plant species. There is significant phytoplankton growth, with reports of some dense algae blooms occurring during years with low salinity. The most significant aquatic biota in the lake is a brine shrimp species, Artemia urmiana. This macro-zooplankton species is the key link in the lake's food chain, consuming algae and in turn being consumed by several bird species including the Lake's migratory flamingo population. The diverse bird population of Lake Urmia and its associated wetlands was documented in a series of surveys in the 1970s which recorded an impressive list of species.
Satellite altimeter data measured the lake's level in 1995 to be at its highest level of any time in the past 40 years. This is in agreement with Hassanzadeh and others (2011) who state a measured water level of roughly 1 278 m above sea level for the same time. Both measures show a steady decline from that year forward with the most recent satellite altimeter data indicating a drop of approximately 7 metres between 1995 and 2011 (21).
Because the lake is relatively shallow, this decline in water level translates to an equally dramatic decline in surface area (Figures 2 & 3). Satellite imagery extending back to the early 1960s shows the lake's area to have been somewhat smaller in 1963, growing to almost 6 000 km2 in 1969, and then remaining generally stable from the late 1960s to the mid-1990s. Since peaking in the mid-1990s, surface area has generally declined quite rapidly despite regular seasonal variation and a brief expansion during a wet period in the early 2000s.
Variability of the lake prior to the early 1960s does not appear to have been widely studied, however, a generalized plot of lake levels dating back to the early 1900s shows only one brief period in 1937 where the lake declined to below 1 273 m above sea level, and then for less than one year. The recent decline reached 1 273 m above sea level in 2008 and, based on satellite images of surface area, the trend has continued through seasonal ups and downs to where current water levels appear to be approaching 1.5 metres lower than at any time in over 100 years.
(United Nations Environment Programme)
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