The series "Biology of Inland Waters" contains up to now publications on the Lakes Baikal and Kizaki, the Ethopian Rift Valley, the Black Sea, the Upper Parana River, and the Danube Delta. Now it has been replenished with a report about Lake Hövsgöl. This ancient large lake is also called the "Mongolian Baikal" and situated just 200 km east of its "Russian sister", belonging to the Baikal rift system too. After Lake Baikal, Lake Hövsgöl is the second largest freshwater lake by volume in Central Asia, containing approximately a hundredth of the world's unfrozen surface freshwater reserve. In Mongolia, the lake is the largest one by volume, however the number two after the salt lake Uvs Nuur according to surface area.
Detailed studies of the lake began in the first years of 1970s. 1989 they were published by scientists of both Mongolia and the former Soviet Union in a large book, with the Russian title "atlas osera xubsugul". Unfortunately, these reports and also most of the previous and the following papers about the lake are written in Russian or Mongolian language and not available abroad.
The recent investigations are the outcome of joint multinational research expeditions (mainly with scientists from Mongolia, USA, Russia and Japan). Altogether 51 authors have provided contributions to this book, most from abroad (41). It contains many new results, including the description of new species, and has the following topics: (i) Geology and climate (geological history, geography, permafrost and geocryological conditions, climate, recent rise in water level, soils); (ii) Physics and chemistry of the water; (iii) Biodiversity in the drainage area and in the lake (landcover vegetation, phyto-and zooplankton, Bacillariophyceae of Lake Hövsgöl National Park, Gammaridae, Ostracoda, Gastropoda, Bivalvia, bottom invertebrates, Tipuloidea, Trichoptera, wood-boring beetles (Cerambycidae), fish and fish parasites); (iv) Ecology (characteristics of an autotrophic chain and some biological and chemical parameters, distribution of zoobenthos and Chironomidae, near-shore bird populations, birds of Lake Hövsgöl and adjoining territories). Additionally, there are an appendix with the names of rotifers and aquatic plants and both a subject and a taxonomic index.
It is not only curious, but also important to know, that the name of the lake and its spelling can vary considerably. This seems to be symptomatic of nearly all geographic names in Mongolia. There are at least a dozen of names and transcriptions, e.g., Kossogol, Hövsgöl, Chöwsgöl, Hubsugul, to call only those being most common. Because of this great deal of inconsistency in the use of Mongolian geographic names in the popular and scientific literature a chapter 'conventions' was added.
Hövsgöl is an alpine lake (sea level 1645 m a.s.l., altitude in the watershed up to 3491 m) with a surface area of 2760 km 2 . The drainage area is small, restricted to the graben itself and almost twice as large. The lake has a mean theoretical retention time of 300-600 years. The surface water temperatures are low with a maximum of 11 °C in July/August.
The water of Lake Hövsgöl is of the alkaline type, the dominating cations are Ca 2+ and Mg 2+ with 32 and 11 mg/L, among the anions HCO 3 -is prevalent. The low concentrations of Cl -and Na + indicate pristine water -with 0.6 and 3.5 mg/L both only half of those in Lake Baikal. The water is also very poor in respect of nutrients. Concentrations of soluble reactive phosphorus and nitrate nitrogen range from 0.6-2.8 µg/L and 5.5-25 µg/L, respectively. Thus, the lake can be classified as ultra-oligotrophic. Nevertheless, during the investigation period the phytoplankton numbers reached abundances of several Millions of individuals per Litre, mainly small celled Chlorophyta and Bacillariophyta. A pecularity of the phytoplankton community is the gigantism: in Lake Hövsgöl some widespread taxa are much larger than their cosmopolitan counterparts -a phenomenon, that has been noted in other ancient lake systems too (e.g. Baikal). Chlorophyll-a content did not exceed 1 µg/L and Secchi disc water transparency changed between 14 and 23 m. However, all data refer to measurements in the months July and Internat. Rev. Hydrobiol.