Boundaries

This ecoregion includes the Argun’ [Ergun He] River drainage,  Uldz Gol River drainage, and lakes and marshes of the Barun-Torey and Zun-Torey depressions, which are now endorheic.

The southern border of the ecoregion follows the course of the Kerulen [Herlen Gol = Herlen He] River, which flows from the southern spurs of the Altan Ulugui Range [Altan Olgiy Nuruu]. In the east, the Bol’shoy Khingan Range [Da Hinggan Ling] divides the Middle Amur tributaries (ecoregion 617) and the Nen Jiang drainage (Songhua Jian ecoregion [620]) with the Khalkhin [Halhaiin] Gol, Haylar [Hailar He], and Gan He drainages (in the Argun’ River system). The northwestern border of the ecoregion follows the divide between the Shilka River and the Argun’ River drainages (Dutugtu Uul Range in the west and the Nerchenskiy Khrebet Range in the east).

Topography

The ecoregion occupies the most elevated part of the Amur basin (350-2500 m asl), which runs deep into the continent.

Freshwater habitats

The most peculiar features of the ecoregion are two big shallow lakes and a number of intermittent lakes and marshes in the Torey Depression. In general, rivers and lakes contain little water and lack high floods. By the end of summer some river sections become shallow. The  Torey lakes region, however, is characterized by an unusual system of underground water. As a result, it contains a number of small lakes that do not dry out even during the hottest and driest seasons, as well as a large pine-tree forest (400 km²) that grows on a waterless sandy valley. The beds of the Barun-Torey and Zun-Torey are periodically filled with water, with a total surface area of 800-900 km² and depths up to 4-6 m.

Terrestrial habitats

Much of the ecoregion is characterized by the flat and rolling grasslands of the Mongolian-Manchurian grassland ecoregion and Daurian forest steppe ecoregion that stretch west from the Da Hingann Mountains (WWF 2001). The Da Hinggan-Dzhagdy Mountains conifer forests and East Siberian taiga occur in the east.

Description of endemic fishes

Hemiculter varpachovskii, the only strict endemic species in the ecoregion, is a typical lacustrine cultrine cyprinid. It has been commonly considered to be conspecific with species that are mostly distributed in Lake Khanka and other parts of the Lower Amur drainage.

Other noteworthy fishes

The species Lefua pleskei needs a special revision and may represent a distinct taxon. A comparison should be made with eightbarbel loach (Lefua costata) from Lake Dalai Nor (43.3 N 116.6 E isolated, south of Inner Mongolia=Nei Mongol Zizhiqu [NOT Dalai Nor=Hulun Nur in the Argun drainage]).

Ecological phenomena

The lacustrine ecosystems of lakes Buir Nor [Buyr Nuur] and Dalai Nor [Hulun Nur] need further study; there may be a case of ecological parallelism (development of a pelagic fish assemblage) with Lake Khanka in the Lower Amur.

Justification for delineation

The ranges of the the Bol’shoy Khingan [Da Hinggan Ling], which stops monsoons, represent the orographic border of the upper part of the basin (so-called "Anikinskiy Porog" (Anikin Threshold). At the same time, the Argun’ ecoregion in the south is clearly different from the Shilka basin (618) in the north by the composition of the fish fauna. In general, the ecoregion is characterized by the predominance of limnophylous species.

Level of taxonomic exploration

Poor; most species distributed in the Argun’ drainage need taxonomic revision, especially in comparison with paired forms from the Lower Amur in the genera Acanthorhodeus, Hemiculter, Chanodichthys, Misgurnus, Thymallus.