Boundaries

The ecoregion is defined by the lowland section of the Amur [Heilong Jiang = Heilungkiang] River down to, but not including, the estuary. It also includes the Ussuri [Wusuli Jiang] River drainage and Khanka Lake basin.

In the west, the Yam-Alin’, Dusse-Alin’, and Bureinskiy Khrebet ranges divide the Lower Amur drainage (Urmi and Amgun’ rivers) from the Bureya drainage and the Zeya River headwaters (ecoregion 617). In the north, the border with the Coastal Amur ecoregion [615] runs along the coast of the Sea of Okhotsk along the Byuko, Yam-Alin’, Kivun, and Mevachan ranges down to Nikolayevsk-na-Amure, which is located at the mouth of the Amur River. The eastern border of the ecoregion runs along the dividing ranges of the Sikhote-Alin’ Mountains: (from north to south) Sredinnyy Khrebet, Golyye Gory, Bolshoy Yang, Khodzyal, Khrebet Strel’nikova, Dal’niy Khrebet, and Ol’ginskiy Khrebet. The southernmost extremity of the ecoregion is formed by the Khanka Lake basin, which is located between the Arsen’yevka [Daubikhe] River (headwaters of the Sungari) and Muling He drainage areas. Khanka Lake (with 16 tributaries) lies on the Khankayskaya Plain. The southern and western border follows the Khrebet Przhevalskogo Range and the northeastern slopes of the Nangang Mountains. The lake is connected to the Ussuri River [Wusuli Jiang] by the only outflow, the Sungacha [Bol’shoy Sungach = Song’acha He] River.

Topography

The Lower Amur River is regarded by geomorphologists as an area of lacustrine alluvial hollows. The hollows are strongly eroded river valleys with a well-developed floodplain, 50-80 km wide. The elevation of these hollows from top to bottom has fluctuated from 10-20 m to 80-100 m. The largest floodplain lakes are Bolon’, Evoron, Khummi, Bol’shoye Kizi, Kadi, Udyl’, Chlya, and Orel’. Each of them has a system of interconnected smaller lakes and channels. The longest section of the Amur where it flows among mountains is located 200 km downstream from Komsomol’sk, among spurs of the Sikhote Alin on the right and ridges on the left. Over the entire area the Amur flows through a narrow valley with one channel. The elevation in the ecoregion ranges from sea level to over 2000 m.

Freshwater habitats

The Amur River is mostly rainfed. Floods often occur in summer when rivers overflow and flood the extensive floodplain areas. On the Amur River, where water level fluctuates between 12-14 m, overflows attain 10-30 km in width.

The Ussuri River, the largest tributary of the Lower Amur River, is formed by a confluence of the Ulakhe and Daubikhe rivers. The length of the river is 590 km, and its catchment area is 187,000 km². Its tributaries originate on the southwestern slopes of the Sikhote Alin Ridge, and have a pronounced mountain character. In many areas the river forms meanders and anabranches; groups of islands appear in the river channel.

The Amgun River, the largest lower tributary of the Amur River, is formed from the confluence of the Kholuk and the Ayakit rivers that rise from the Upper Amgun Highland. The length of the river is 665 km, and catchment area is 54,900 km². Boths sources of the Amgun are mountainous rivers. Downstream from their confluence the Amgun River retains its high flow velocity. The river channel is clogged by snags, and forest overslaughs are formed in shallow areas. Downstream, the river channel meanders, and flow velocities decline. In the lower reaches the Amgun River flows over an extensive lowland where it floods during tides and forms many large islands and anabranches, particularly in the estuary.

Khanka Lake differs from the flood lakes of the Lower Amur in that it is located in its own hollow, and is not dependent on flood events of the main course of the river. It is the largest freshwater lake in the Russian Far East. It is very shallow despite its large surface area (4,000 km²). The average depth of the lake is between 4 and 5 m, and maximum depth is 6.5 m, although it has been commonly said to be 10 m. The water level changes periodically, with amplitudes reaching 210 cm. Surface area may vary between 3,700 to 4,400 km², and water volumes may vary about 40%. There are 26 inflowing rivers to the lake, 9 draining from China and 17 draining from Russia. The Song’acha River is the only outflow river from the lake, and is subsequently connected with the Ussuri River and the Amur River system. Khanka Lake possesses a number of adjacent lakes that are connected to Khanka Lake during periods of high water. The largest lakes of this kind is the Small (Malaya) Khanka located in China. It is separated from the Large Khanka by a sand spit that rises up to 10 m high in some places.

Khanka Lake has its own hydrological regime. Steady southern winds create a system of surface currents. Almost the entire water column is mixed by strong winds during the ice-free period. Peculiar physical-chemical characteristics of the lake include its low transparency (up to only 0.15-0.30 m by Secchi disc) and high concentration (up to 200 g in cubic m) of mineral suspended matter. In winter turbidity gradually declines, up to 0.7 m by Secchi.

The construction of the Zeiskaya Hydroelectric Power Station in the 1970s affected the water levels and river flow in the Middle and Lower Amur. This led to changes in the river’s chemical composition, particularly in winter. Higher summer temperatures and the critical decline in summer water levels also negatively affected the river ecosystem and fish habitats, in particular.

Terrestrial habitats

The Amur River flows through lowlands with few hills and swampy areas covered by herbaceous vegetation. Along the Ussuri extends an area of broadleaf and meadow plains. The headwaters of northern tributaries pass through mixed forest and taiga zones. In the catchment of the Lower Amur swampy areas are widespread.

Description of endemic fishes

The ecoregion contains no strict endemic species. Near-endemics include:

Cherskii’s thicklip gudgeon (Sarcocheilichthys czerskii) is a near-endemic form that requires further clarification on its taxonomy and distribution. It deserves special concern as a rare and poorly known species with a restricted range. This is a small gudgeon with relatively well-pronounced sexual dimorphism. Brightly colored males guard the nest.

Rhodeus amurensis is the smallest bitterling reliably known from the Lower Amur. It may be that Chinese authors do not identify the fish in water bodies of China. It is often confused with R. lighti or R. fangi.

Chanodichthys abramoides was taxonomically re-established by Bogutskaya and Naseka (2004); earlier it had been known in the Khanka Lake under the name Erythroculter dabryi shinkainensis. It is a lacustrine cultrin cyprinid. Its distribution in rivers needs clarification.

Dwarf catfish (Pelteobagrus mica, also noted as Pseudobagrus mica) is a small bagrid only known from the Lower Amur. It is never mentioned in Chinese literature, and is probably commonly misidentified.

Other noteworthy fishes

 

The genus Thymallus has recently undergone a deep revision; it was shown that T. grubii in the traditional sense involves a number of species. One new species was described from the Bureya River (see ecoregion 617), and two more were shown to exist in the Lower Amur and the coastal areas of the Sea of Japan. The species status of Lower Amur grayling (Thymallus sp. 1) is supported in the literature (Shed’ko 2001; Froufe et al. 2003; Knizhin et al. 2004), as is the status of yellowfin grayling (Thymallus sp. 2), which is partly sympatric with the Lower Amur grayling. However, it is not clear if either of these species is conspecific with Thymallus arcticus yaluensis (Mori 1928), which was described from the Yalu River at Kozan.

Khanka spiny bitterling (Acanthorhodeus chankaensis) traditionally includes many subspecies, but here is considered as A. chankaensis s. str. It may be endemic to the Amur basin, but the exact range is not clear due to taxonomic problems. It is a spiny bitterling with a small inferior transverse mouth and a markedly transformed lower jaw.

Lake minnow (Phoxinus percnurus) is a small minnow that prefers lakes, oxbow lakes, and channels with slow or no currents.

In the Khanka Lake, the nucleus of the fish assemblage of the lake is a group of pelagic cyprinids from the subfamily Cultrinae. They form a diverse system of pelagic fishes from purely planktivorous to purely predatory forms that spawn in the lake (Chanodichthys abramoides, predatory carp (C. erythropterus), Mongolian redfin (C. mongolicus), C. oxycephalus, Culter alburnus, sharpbelly (Hemiculter leucisculus), and Usurri sharpbelly (H. lucidus)).

Ecological phenomena

The Lower Amur supports mass migrations of sea-migrants of chum salmon (Oncorhynchus keta) and Kaluga (Huso dauricus). A great number of species migrate 1000 km up- and downstream without leaving the river, such as silver carp (Hypophthalmichthys molitrix), yellowcheek (Elopichthys bambusa), Amur sturgeon (Acipenser schrenckii), lenok (Brachymystax lenok), B. tumensis, and taimen (Hucho taimen). The lake systems of the Lower Amur are extremely important for phytophilous species, which migrate from the main course of the Amur into lakes through channels that form during flooding to find spawning-sites and yearling development areas. With the water level declines, these species leave lakes and return to the river. Human mediated changes of the flood regime have dramatically destroyed this life circle.

Khanka Lake is interesting because of its fish fauna composition. By preferred biotopes, the species are grouped as either purely lacustrine (52%, a high ratio if compared to the Lower Amur), or purely riverine (27% and 21% of those species inhabit mostly the lower reaches of rivers, river mouths, and lake shallows). By feeding preferences, most species are benthophagous. The number of planktophagous and predatory species is much lower, but these species are the most abundant in the lake. In better years, they comprised up to 80% of commercial yields.

Justification for delineation

In the west, the region is defined by the narrow Amur bed where the river cuts through the mountains of the Bureinskiy and Malyy Khingan ridges (47.75 N 130.97 E, at Ekaterino-Troitsk). Just below the rapids, the Amur enters a plain and divides into several branches, forming lakes and a wide floodplain. The lakes are especially developed in the lower section (Bolon’, Ommi, Evoron, Udyl, Orel, and others). The river here is low gradient and the lakes are shallow and possess heavy vegetation. Their size and pattern of interconnection and connection to the river vary greatly depending on water outflow.

In general, the ecoregion has outstanding biological diversity on the national and internationals levels.

Level of taxonomic exploration

Fair: cultrins and acheilognathins are especially poorly studied and need deep revisions.