**2. Sistan region**

164 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

the elderly, low birth weight and high death rates in newborns [37].

their chemical composition [22]. Size distribution is a key parameter to characterize the aerosol chemical, physical, optical properties and their effects on health. The lower and upper size limits of dust aerosols are from a few nanometers to ~100μm and aerosol properties change substantially over this size range. Several studies demonstrated that airborne Particulate Matter (PM) has an impact on climate [23], biogeochemical cycling in ecosystems [24], visibility [25] and human health [26-28]. Over recent years in the public health domain the PM concentration has become a topic of considerable importance, since epidemiological studies have shown that exposure to particulates with aerodynamic diameters of < 10 μm (PM10) and especially < 2.5 μm (PM2.5) induces an increase of lung cancer, morbidity and cardiopulmonary mortality [e.g. 29-35]. Thus air pollution appears to have an adverse effect on respiratory and cardiovascular systems [36], which might result in an acute reduction of lung function, aggravation of asthma, increased risk of pneumonia in

Some dust contaminants (soluble and chelatable metallic salts, pesticides, etc) affect human health when they are transported over densely populated areas [38], retained in residences and other occupied structures [39], and they also impact the nutrient loading of waters flowing from adjacent watersheds [40] and terminal bodies of water by direct and indirect deposition [41-42]. PM is a complex mixture of substances suspended in to the atmosphere in solid or liquid state with different properties (e.g. variable size distribution or chemical composition amongst others) and origins (anthropogenic and natural). Owing to this mixture of substances, the chemical composition of PM may vary widely as a function of emission sources and the subsequent chemical reactions which take place in the atmosphere [43-45].The chemical mass balance is the most commonly used method for assessing PM source contributions [46], while statistical methods, such as factor analysis and multi-linear regression [47], have also produced interesting results regarding dust source identification. Elemental and mineralogical analyses have also been used to identify the source regions of

dust deposited in Arctic ice caps [48] and on other depositional surfaces [49, 42].

of Iran, the rate of asthma in Sistan is, in general, higher than in other regions [54].

One spectacular example of such dust effects is the Hamoun (dry) lakes in the eastern part of Iran that has attracted scientific interest during recent years, since it constitutes a major dust source region in southwest Asia, often producing intense dust storms that cover the Sistan region in eastern of Iran and the southwest of Afghanistan and Pakistan and influencing the air quality, human health and ecosystems as well as aerosol loading and climate from local to regional scales [50-52, 12]. Particles from the Hamoun dust storms might also cover farm and grasslands to result in damage to crops and fill the rivers and water channels with aeolian material. Over recent years, tens of thousands of people have suffered from respiratory diseases and asthma during months of devastating dust storms in the Sistan basin, especially in the cities of Zabol and Zahak and the surrounding villages [53]. According to the Asthma Mortality Map

The aim of this Chapter is to: (1) assess the seasonal and annual variability of dust storms that originate from the Hamoun Basin, (2) identify the amount of dust loading from the dry lakes, (3) assess the contribution of the lake beds to regional dust emissions for specific locations, (4) assess the dust chemical and mineralogical composition to provide useful The Sistan basin (Helmand basin) lies between the Hindu Kush Mountains in Afghanistan and the mountain ranges flanking the eastern border of Iran and is the depository that receives the discharge of the Helmand (Hirmand) river in the lower Sistan Basin (Fig. 1). It is a large and remote desert basin**,** extremely arid and known for its windstorms, extreme floods and droughts. The closed basin receives the waters of the Helmand river, the only major perennial river in western Asia between the Tigris-Euphrates and Indus rivers [9]. The Helmand and its tributary streams drain the southern Hindu Kush Mountains of Afghanistan and flow into an otherwise waterless basin of gravel plains and sandy tracts before terminating in Sistan (also Seistan, British spelling), a depression containing the large inland delta of the Helmand river and a series of shallow, semi-connected playas at the western edge of the basin (Fig. 1).

**Figure 1.** Landsat-5 image showing the lower Hirmand Basin and Sistan region. [9].

In 1949 the United States initiated a new program for the improvement of underdeveloped areas of the world. The damming of the Helmand river in southern Afghanistan became one of the showcase projects of U.S. foreign aid in the "Third World" after World War II. Dams were built on the Helmand river and its main tributary (Arghandab river) during the 1950s. The main project goals were to provide hydroelectric power and increase agricultural productivity through irrigation and land reclamation. The Arghandab dam, located northwest of the city of Kandahar, was completed in 1952 with a height of 145 feet (44.2 meters) and storage capacity of 388,000 acre-feet (478.6 million cubic meters). The larger Kajakai dam on the Helmand was completed a year later with a height of 300 feet (91.4 meters) and length of 919 feet (280 meters) and storage

capacity of 1,495,000 acre-feet (1,844 million cubic meters). About 300 miles (482.8 kilometers) of concrete-lined canals were built to distribute the reservoir waters [9]. The Hirmand river is the longest river in Afghanistan (ca. 1150 km; catchment > 160,000 km2) and the main watershed for the Sistan basin, finally draining into the natural swamp of the Hamoun lakes complex [10].

Changes of Permanent Lake Surfaces, and Their Consequences for Dust Aerosols and Air Quality: The Hamoun Lakes of the Sistan Area, Iran 167

The Hamoun lakes are situated roughly at the termination of the Hirmand river's inland delta. The Hamoun lakes complex (Hamoun-e-Puzak, Hamoun-e-Sabori and Hamoun-e-Hirmand and Baringak) are located in the north of the Sistan region, which is also the largest fresh water ecosystem of the Iranian Plateau and one of the first wetlands in the Ramsar Convention [58]. Water in the Hamoun lakes is rarely more than 3 meters deep, while the size of the lakes varies both seasonally and from year to year. Maximum expansion takes place in late spring, following snowmelt and spring precipitation in the mountains. In years of exceptionally high runoff, the Hamoun lakes overflow their low divides and create one large lake that is approximately 160 kilometers long and 8–25 kilometers wide with nearly 4,500 square kilometres surface area. Overflow from this lake is carried southward into the normally dry Gaud-i Zirreh (Fig. 1), the lowest playa (463-meter altitude) in the Sistan depression. Furthermore, mountain runoff varies considerably from year to year; in fact, the Hamoun lakes have completely dried up at least three times in the 20th century [9]. The maximum extent of the Hamoun lakes following large floods is shown in Fig. 4, where a continuous large lake has been created covering an extended area of ~4,500 km2 with a volume of 13000 million m3 in Sistan and southwestern Afghanistan. This figure corresponds to spring of 1998 after snowmelt in the Afghanistan mountains that transferred large quantities of water into the Hamoun Basin. As a consequence, livelihoods in the Sistan region are strongly interlinked with and dependent on the wetland products and services, as well as on agricultural activities in the Sistan plain. Fishing and hunting represent an important source of income for many households and, therefore, the local and regional economy is strongly dependent on weather conditions, precipitation and land use – land cover changes. The political boundary between Iran and Afghanistan splits the Hamoun system, further complicating management possibilities in the area. Most (90%) of the watershed is located in Afghanistan and practically all of the wetlands' water sources originate there. The Iranian part is desert, and produces runoff only in rare cases of

In view of the Hirmand and the surrounding rivers that supply most of the sediments to the Hamoun lakes, a brief encapsulation of the relevant geology of the catchment area in Afghanistan is given. Afghanistan has a very complex geology, encompassing two major relatively young orogenies, Triassic and subsequent Himalayan, resulting in amalgamation of crustal blocks and formation of concomitant ophiolites and younger clastic and carbonate sedimentary rocks as well as basaltic lavas and, more recently, extensive alluvial and eolian detritus [59] . The Sistan region and Hamoun dry lake beds are mainly composed of Quaternary lacustrine silt and clay material as well as Holocene fluvial sand, silt and clay (Fig. 3). These materials have been carried to the basin by the rivers, while along their courses Neogene fluvial sand, eolian sand, silt and clay are the main constituents. Note also the difference in the soil-dust composition between two major desert areas, Registan and Dasht-i-Margo in Afghanistan. The former is composed of Neogene coarse gravels and the latter of Quaternary eolian sand. More details about the geology in the Sistan region can be

**3. Hamoun lakes** 

significant local rainfall [10].

found in [60].

Severe dust plumes usually extend from Sistan into southern Afghanistan and southwestern Pakistan obscuring the surface over much of the region (Fig 2). Severe droughts during the past decades, especially after 1999, have caused desiccation of the Hamoun lakes leaving a fine layer of sediment that is easily lifted by the wind [55], thus modifying the basin to one of the most active sources of dust in southwest Asia [56, 50, 57]. Therefore, the Hamoun dry-lake beds exhibit large similarities with the other two major dust source regions of the world that comprise of dried lakes and topographic lows, i.e. Bodele depression in Chad [3] and lake Eyre in Australia [4]. The strong winds blow fine sand off the exposed Hamoun lake beds and deposit it to form huge dunes that may cover a hundred or more villages along the former lakeshore. As a consequence, the wildlife around the lake has been negatively impacted and fisheries have been brought to a halt.

Fig. 2 (left panel) shows a severe dust storm over the Sistan region as observed from the Terra-MODIS satellite's true color image on 15 June 2004. The intense dust plumes form a giant U-shape extending from Sistan into southern Afghanistan and southwestern Pakistan that obscures the surface over much of the region. The pale color of the dust plume is consistent with that of dried wetland soils. The dust is blowing off the dry lake beds that become the Hamoun wetlands during wet years.

**Figure 2.** MODIS image of dust deflation over southern Afghanistan originating from the dry Hamoun lakes in Sistan on June 15, 2004.
