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Hövsgöl ILTER

Satellite image of Hovsgol LTER sites

The Hövsgöl International Long-Term Ecological Reserch Site (Hövsgöl ILTER) was established in 1997 by the Government of Mongolia. The Hovsgol GEF/WB Project, largely funded by the Global Environmental Facility (GEF) and implemented by the World Bank (WB), operated here from 2002 to 2006. Current work at Hövsgöl ILTER is conducted through PIRE Mongolia, an international collaboration of The Academy of Natural Sciences, the University of Pennsylvania, the Mongolian Academy of Sciences, the National University of Mongolia and the Mongolian University of Science and Technology. This project, which is supported by the National Science Foundation's PIRE Program, will continue through 2012.

Study Sites

The Hövsgöl ILTER consists of six parellel catchments entering Lake Hövsgöl along its eastern shore. They are drained by perennial streams that typically originate from upland wetlands fed by permafrost melt. The streams and watersheds are broadly similar in many respects, but differ in forest cover, livestock levels and grazing pressures.

Hövsgöl ILTER Catchments
Catchment Watershed Pasture Livestock1 Grazing Level2
1) Livestock levels are expressed in "sheep units"
2) overgrazing : moderate grazing : light grazing as percentages of pasture area
Turag 231 km2 73 km2 3300 08% : 83% : 09%
Shagnuul 76 km2 45 km2 3000 30% : 68% : 02%
Noyon 118 km2 48 km2 400 18% : 73% : 05%
Sevsuul 140 km2 40 km2 400 06% : 56% : 38%
Dalbay 161 km2 31 km2 500 31% : 54% : 15%
Borsog 69 km2 17 km2 <100 00% : 01% : 99%

Watersheds

Noyan Valley, Hovsgol ILTER

Vegetation in the Hövsgöl ILTER is largely a mixure of taiga (boreal forest) and steppe (grassland). On average, forest cover about 55% of the catchments, but forest coverage is generally lower in the northern catchments. For example, forests account for 37% of the coverage at Turag and 70% at Dalbay.

North-facing slopes and ridgetops are typically covered with taiga while steppe forms on south-facing slopes and valley floors. Riparian vegetation and wetlands account for much smaller proportions of the watersheds.

Siberian larch (Larix sibirica) accounts for 90-95% of the trees in the taiga. Natural regeneration rates are low and seedling establishment is strongly influenced by surface soil moisture; regeneration is highest in soils moist enough to support moss. The fire regime is not well understood, but fires are more frequent in spring, when the fuel base is driest.

Turag Valley

Grasses (e.g., Koeleria macrantha and Poa attenuata), sedges (e.g., Carex pedicularis) and forbs (e.g., Artemisia commutata) account for most of the steppe vegetation; mosses can be abundant in moister habitats. Intensive grazing typically reduces the abundance of mosses, sedges and grasses and favors a variety of xerophytic and unpalatable species, including wormwood or agi (Artemisia frigida), naytuul (Potentilla acaulis) and ganga (Thymus gobicus). In addition to altering species composition, Intensive grazing dramatically reduces plant biomass, percent cover and plant litter (necromass). Soil fertility (as expressed by percent humus, exchangable calcium and nitrate nitrogen) also declines.

Perhaps the most alarming consequences of intense grazing are the changes to soil moisture and permafrost degradation. Increases in soil surface temperatures, reductions in soil moisture and increased depths before reaching the active layer (the zone of liquid water lying above the permafrost) are all strongly associated with reduced soil cover by mosses and litter. In other words, overgrazing at Hövsgöl may be leading to long-term degradation of pastures and possibly desertification. The extended growing season and net increases in evapotranspiration will likely accelerate this trend.

Streams

stream at Hovsgol ILTER

The streams in the Hövsgöl ILTER are typically perennial during the growing season and frozen during the winter. Discharge in these streams is highly responsive to local rainfall events but less so in the more heavily forested watersheds (e.g., Borsog). Climate change may have a substantial impact on the flow in these streams. A longer growing season that's not accompanied by a corresponding increase in precipitation will result in an net increase in evapotranspiration, especially during the late Spring. Consequently, future spring flows may decline significantly or even cease.

As with Lake Hövsgöl, the ILTER streams are ultra-oligotrophic and phosphorus-limited. On the other hand, the streams are stained brown with colored dissolved organic matter. Moderate levels of ammonia enrichment and increases in dissolved chloride are associated with greater grazing intensities. There is also an inverse relationship between concentrations of nitrogen and carbon in steppe soils and the concentrations of total carbon, nitrogen and calcium in the streams; valleys experiencing lower grazing intensities tend to have richer soils but less enriched streams. These differences appear to be related to differences in nutrient concentrations in surface runoff and to differences in erosion within the riparian zone.

Several species of fish from Lake Hövsgöl, including lenok or Asian trout (Brachymystax lenok), Arctic grayling (Thymallus arcticus arcticus), Hövsgöl grayling (Thymallus nigrescens), roach (Rutilus rutilus) and perch (Perca fluviatilis) migrate into the ILTER streams in late May and early June to spawn. The salmonids (lenok and graylings) were generally more abundant in the Turag, Noyon and Sevsuul, where medium-sized gravel (the preferred spawning substrate) was most available. However, many of the most suitable substrates were situated in upper reaches that frequently experienced low flows during the peak spawning season. Overall biomass was highest in Borsog and Dalbay, where roach and perch were the most abundant.

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