Boundaries

This ecoregion encompasses the endorheic basins of the Irgyz and Turgai rivers, along with a number of small interconnected lakes and intermittent channels. In the west the border follows the Mugodzhary Mountains [Mughalzhar Tauy], which divides the Irgyz [Yrghyz] River from the Or’ River drainage (a tributary of the Ural [Zhayyq] River) and Emba [Zhem] River. In the north the Turgai Tableland [Turghay Ustirti] divides the headwaters of the Irgyz and Turgai rivers from the Tobol (Irtysh tributary) headwaters (Ob [602]). The border crosses the Turgai Dolina Valley [Torghay Zhylghasy] and runs south along the western slopes of the Kazakhskiy Melkosopochnik Upland [Qazaqtyng Usaqshoqylyghy], which is the divide between the Tughay and Ishim drainage (Ob [602]). Further south and southeast the Ulutau Mountains [Ulytau] (western region of the Kazakhskiy Melkosopochnik Upland = Qazaqtyng Usaqshoqylyghy) forms the border between this ecoregion and the Sarysu River drainage (in the Lower and Middle Syr Darya [626]). In the south the ecoregion meets the Peski Priaral’skiy Karakumy Desert [Aral Mangy Qaraqumy] (Aral Sea Drainages [629]). The southernmost part of the ecoregion lies between the Peski Bol’shiye Barsuki Desert [Ulken Borsyq Qumi] and Chagray Plateau [Shaghyray Ustirti].

Topography

The Irgyz River rises in the eastern spurs of the Mugodzharskiye Mountains, and is confluent with the Turgai near its estuary. The length of the river is 180 km, and its drainage area is apporoximately 25,000 km². The Turgai River rises on the western outskirts of the Central Kazakhstan Melkosopochnik Upland at about 450 m altitude, and falls into Lake Chelkar-Tengiz having passed through a number of lakes. An elaborate network of tributaries lies in the upper part of the basin. In the confluence they form the Kara-Turgai River, which after the confluence with the Sary-Turgai is called Turgai.

Freshwater habitats

Rivers of the ecoregion are full-flowing in spring and shallow in other seasons of the year. In the upper and middle reaches the Irgiz flows through an ancient valley with well-developed terraces. Downstream from the town of Irgiz the river channel is poorly pronounced, so lakes and marshes occur in the floodplain. Upstream from the confluence with the Turgai River sandhills comprise the coasts along the river. After the spring flood the upper (up to the confluence with the Karabutak River) and lower reaches of the Irgiz split into a number of stretches separated by dried parts of the river channel. In the summer water of the Irgiz becomes brackish due to evaporation.

For much of its course the Turgai River flows through the Turgai Hollow. In this area it has a wide floodplain that is swampy in some areas. In spring the Turgai overflows and its water level rises by 4—8 m. When the floodplain overflows the river forms branches, oxbows, and numerous lakes.  The duration of flooding is 20—25 days. In summer the water level of the river declines abruptly, but a small flow is observed throughout the year.

The waters of the Turgai River and its tributaries are very diverse in terms of chemical composition. Only the upper Turgai River contains freshwater throughout the whole year. In the lower reaches, beginning from the middle of the summer, it becomes brackish. The water of the Sary-Turgai River is fresh, but it quickly becomes saline in the Kabarga and Bistamak rivers after the spring flood.

Lakes of the Irgyz-Turgai system in the southwestern part of Kazakhstan differ from each other by geological age, limnological history, hydrological and physicochemical regime, organic matter accumulation processes, specificity of food supply, and species composition of fishes.

Terrestrial habitats

The ecoregion comprises two terrestrial ecoregions – Kazakh semi-desert and Kazakh steppe. The Kazakh semi-desert is an ecotone between steppe in the northern part of the ecoregion and desert to the south. Much of this landscape consists of plains and melkosopochnik, dominated by bunch-grass steppes and dwarf semi-shrub deserts. Some of the rare plant species in the semi-desert include Artemisia lessingiana, Stipa richterana, Ferula feruloides, and Brachanthemum kasakorum. Kazakh steppe occurs in the northern part of the ecoregion. It is dominated by turf graminoids such as species in the genus Stipa.

Description of endemic fishes

There are no endemic species in this ecoregion.

Ecological phenomena

The inconsistent water level from year to year is a characteristic of the lakes of the Irgyz-Turgai system. This depends on the climate and timing of spring, and also the complete or partial drying of some lakes in dry years. Some shallow lakes (depth 3 m) become nearly completely overgrown by underwater and surface vegetation, and exhibit high hydrogen sulphide content in their ground and water. Such lakes, in a majority of which only Carassius species survive, are so-called \"suffocation\" or \"carassius\" lakes. Other deeper lakes (depth up to 5-7 m) have a sand bottom, lack massive vegetation cover on the bottom, and have low hydrogen sulphide content. These lakes contain a relatively varied composition of ichthyofauna, and are called ”pike” lakes. These lakes, apart from Carassius species, include pike, perch, ide, and sometimes, ruff.

Justification for delineation

The ecoregion covers the endorheic basins of two rivers, Irgyz and Turgai, with a number of small interconnected lakes. It is located in a plain with numerous, almost stagnant, water bodies. Some river sections and lakes are periodically desiccated. The fauna demonstrates clear Siberian links, but is very depauperate. It is unclear why there has not been a single species of fishes of the Caspian Aral complex noted in this ecoregion. A thorough morphological comparison of the Irgyz-Turgai forms with the Aral and Siberian forms is needed to clarify the zoogeographical affinities of the ecoregion.

Level of taxonomic exploration

Fair