Five lake types have been identified to date:
The most oligotrophic of these are characteristic of the heads of basins with barely soluble lithological compositions, located in Sayan range, highest elevations of Altai range (in the Altai Tavan Bogd National Park in Bayan-Ulgii and Khovd provinces), and also in Khangai range. Khuvsgul Lake and a group of lakes located to its west, such as Deed Tsagaan, are found on the southern slopes of the Sayan range. In Altai: Khoton, Khurgan, Dayan and Tolbo, Tal and Duruu lakes. In the north watersheds of Khangai: Bayan Lake (Zavkhan), surrounded by sand dunes, and Terkhiin Tsagaan (Arkhangai), created by the damming of Khoid Terkh river by the lava formations which originated in the Khorgo volcano. Sharga Lake, also worthy of inclusion in this group, is found in Bulgan. These oligotrophic lakes tend to be deep and have highly transparent waters.
The mesotrophic or eutrophic lakes are generally found at lower elevations, fed by waters with high nutrient loads. The Buir (Dornod), Duuz (Sukhbaatar), Ogii (Arkhangai), Khar-Us, Dalai and Khar (Khovd), and Achit (Bayan-Ulgii) lakes fall into this category. These are shallow lakes with more or less turbid waters due to phytoplankton growth.
The substrates of these lakes tend to be composed of sand or gravel, although the most eutrophic ones have accumulations of organic silts. There is scant vegetation but species richness is high (sp. pl., Myriophyllum, Polygonum, Najas and Lemna trisulca). The littoral invertebrate community is generally made up of cyclopoids and chydorids, accompanied at times by Gammarus. Plankton with calanoids.
Khuvsgul Lake from the summit of Khisaa, characteristic of type 1.
These water bodies follow a similar distribution to the previous ones, but with much greater abundance. The ones in the mountains are normally oligotrophic and have similar limnological characteristics to the large lakes. Those found in taiga zones or steppes are more productive and their waters can be mesotrophic (greenish waters), or even eutrophic (green waters), and also dystrophic (yellowish, brown or reddish waters).
Depth is variable, but generally less than 3 m (except in the largest lakes of this type). The substrates tend to be sandy and/or silty, and often constitute true peat bogs. Many are surrounded by meadows and permafrost. Vegetation tends to be abundant except in the most eutrophic ones, in which the low transparency of the water limits the growth of underwater macrophytes. Littoral belts of Carex (sometimes also Scirpus lacustris or Phragmites), Hippuris, Myriophyllum and Polygonum tend to be present and, on the bottom, Elodea, Potamogeton and charophytes are found. Other species may enrich the community, among these Ranunculus, Caltha, Nymphaea, Lemna trisulca, Utricularia and filamentous algae. The helophytes tend to be affected by grazing. The less eutrophic ones have very rich invertebrate communities, with Gammarus, Sida, several species of anomopods (particularly chydorids), several species of cyclopoids, ostracods and insect larvae. In the most eutrophic ones, the community is considerably simpler, resulting in a clear predominance of Gammarus. Plankton is generally made up of anomopods and calanoids (at times several species of these coexist).
Khunt Lagoon in Zavkhan, characteristic of type 2.
This group includes large and relatively deep lakes whose endorheic regimes explain their high salt content. They are distributed throughout low-lying and steppe zones. Uvs Lake (Uvs province), with the largest surface area in Mongolia, belongs to this group, in addition to others whose more modest size makes them no less worthy of mention: Khyargas, Uureg, Airag and Durgun (also in Uvs), Buun Tsagaan (Bayankhongor), Sangiin Dalai (Khuvsgul), Ganga (Sukhbaatar), Telmen and Tsegeen (Zavkhan) and Khoh (Dornod), the latter located at the lowest elevation in Mongolia. Some of these lakes have clean, oligotrophic waters, such as Khyargas, Uureg, Airag, Durgun, Buun Tsagaan, Sangiin Dalai and Telmen that are practically free of vegetation with, at most, some Potamogeton gr. pectinatus remains accumulated on the shore. The rest are mesotrophic or eutrophic, with greenish or grey-greenish waters and similarly scarce vegetation, also consisting of P. gr. pectinatus sometimes accompanied by charophytes and Enteromorpha. The littoral invertebrate community includes Gammarus, chydorids, cyclopoids, ostracods and insect larvae. Plankton with daphnids, moinids, cyclopoids and calanoids.
Shallow lagoons with also highly mineralized and even saline but not hypersaline waters belong to this group. Their geographical distribution is much wider than that of the aforementioned lakes, since their occurrence is not restricted to low altitude areas; concretely this kind of lagoons have been found at high altitude in the Khangai and Altai mountain ranges.
Sangiin Dalai Lake, representative of group 3
These are very abundant in Mongolia and are distributed primarily in steppe and desert territories, although they can also be found in taiga zones and in the mountains (particularly in Altai). The substrates tend to be sandy-marly or clayey, and depths are less than 3 m. This group includes even ephemeral ponds. The waters are turbid due to the presence of clay, which form a stable colloidal suspension that lends brown, grey and milky colorations, and combinations of these. Heterotrophic metabolism dominates in these water bodies, as there is very little representation by primary producers such as phytoplankton and underwater macrophytes. The invertebrate community is dominated by crustacean species adapted to extreme conditions such as the drying up or complete freezing of the water body. Large branchiopods (anostracans, conchostracans and notostracans) are the most characteristic organisms, accompanied by anomopods, calanoids, cyclopoids, ostracods, coleopters and heteropters. The littoral fringe of the most highly mineralized lakes tends to whiten due to the presence of precipitated salts, giving rise to halophyte vegetation.
Tokhom Lagoon, representative of group 4
These are very shallow and endorheic water bodies which appear mainly on the steppes and deserts of the Dornod, Khentii, Dundgobi, Bulgan, Bayankhongor, Gobi-Altai, Khovd and Zavkhan provinces. Some have considerable dimensions although most of them are only flooded temporally. Water salinity is very high and significant temporal oscillations related to the phase of the hydrologic cycle are registered, such that salinity increases as water availability declines and salts become concentrated to form true brines. At times, sodium and bicarbonate ions predominate with very high pH values while, at the same time, this high salinity is not accompanied by the characteristic salty taste; this is the case of lakes such as Dovon in Zavkhan. These would be the lakes known as “soda lakes,” characteristic of very arid zones and which are of great scientific interest due to their unique microbial communities. Turbidity is variable, but generally it is due to suspended inorganic particles. At least three of the lakes that were visited are exploited as salt pans: Davst Lake (Bayankhongor), and Oigon and Davsnii lakes (Zavkhan). Davsnii Lake has a powerful and brilliant crystalline salt layer that regenerates spontaneously after mining extractions thanks to underground inflows of hypersaline water. The biota of these lakes is composed of athalassic species: algae and bacteria that form extremely interesting microbial mats that cover the lake beds, planktonic algae colouring the waters pink (Dunaliella), and crustaceans such as Artemia, Branchinectella, Moina salina, Arctodiaptomus salinus and Metadiaptomus asiaticus. Coleoptera, hemiptera and ephydrids are present among the insects. The dry portions of the lakes, or the lakes themselves when they become desiccated, display a dazzling, snow-white saline residue, at times adorned with magnificent decimeter-sized crystals of evaporitic minerals that are only stable in hyper-arid atmospheres. Within the white crystalline littoral blanket, are vividly colored salt marsh plants that form dense red lawns (Salicornia and similar).
Davsnii Lake in Zavkhan, representative of group 5
The study of aquatic invertebrates represents one of the most outstanding objectives of this project. To date, the following have been identified:
- Eleven anostraceans, of which Galaziella murae is a Mongolian endemism and new to Science, and another taxa still undescribed.
- Two notostracans branchiopods
- Five conchostracan branchiopods
- One haplopod branchiopod
- Three ctenopod branchiopods
- Sixteen daphnid branchiopods
- Five moinid branchiopods
- Six macrothricid branchiopods, probably one new to Science
- Five bosminid branchiopods
- Thirty-six chydorid branchiopods, of which Alona flossneri is a Mongolian endemism and new to Science
- Twenty-two calanoid copepods, one probably new to Science
- Twenty-seven cyclopoid copepods
- Four harpacticoid copepods
Triops (notostracan branchiopods) collected in a pond in the Bayan district (Tuv province).