Ninth International Conference on Permafrost ... - IARC Research

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Recent Rise of Water Level in Lake Hovsgol in the Permafrost Zoneof Northern Mongolia: Trends and Causal FactorsKazuo TakedaObihiro University of Agriculture and Veterinary Medicine, Obihiro, JapanHiroji FushimiUniversity of Shiga Prefecture, Hikone, JapanTatuo KiraLake Biwa Environmental Research Institute, Ohtsu, JapanIntroductionLake Hovsgol is the largest freshwater lake in Mongolia(Table 1), located on the southern fringe of the east Siberianpermafrost zone that supports the so-called “light taiga,” orthe deciduous conifer forests dominated by larch (Larix spp.).Once the larch vegetation is destroyed due to increasing forestfires and the outbreak of pest insects, direct sunshine raisesground surface temperature, resulting in deeper thawing ofpermafrost in summer.According to observations at the station of the NationalAgency for Meteorological (1940–2006) in Hatgal village(on the southernmost shore of Lake Hovsgol) during 67years, the annual mean temperature has gone up at the rateof 3°C per century with mean annual precipitation of only200~400 mm/yr. Also noticed is that the water level of thelake has risen by 100 cm during the latest 37 years (MurunMeteorological Station 1970–2006).As for the cause of such recent rise in water level, it issometimes suggested that global climate change might beresponsible (Kumagai 1998, Kumagai et al. 2006). Namely,the inflow of thawed fossil water from permafrost layers andglaciers brought about by global warming is supposed to be themain source of increasing lake water. This hypothesis, however,lacks concrete evidence because of the absence of continuousreliable records of groundwater supply into the lake.This paper deals mainly with another causal factor relevantto the lake water level rise, viz. the bottleneck structure at thehead of the Egiyn Gol (= river), the sole outlet of the lake.Environmental information related to the water budget of thelake is presented based on field survey around the lake.Study MethodsField surveys were conducted at 12 sites (Fig. 1),including 57 observation points during 3 years since 2000.Items observed were depth of active later (at most sites),soil properties such as moisture content, and grain sizecomposition (at some limited number of sites). To find thedepth of the active layer, a temperature profile was measuredalong a vertical hole made by striking an iron rod into theground. The 0°C isotherm depth was then estimated byextrapolating the profile curve downward. This procedurewas done after late August, when the active layer depthapproached the seasonal maximum.About 1.5 km southward from Hatgal at Site L (Fig. 1), theEgiyn River starts draining lake water through a very narrowand shallow bottleneck route, produced by the deposits carriedby a tributary river. The structure of riverbeds of the two joiningstreams, so important for the control of the lake’s water budget,was carefully surveyed. Further, as some of groundwater, theflow rate of an inflow stream originating from Har usnii Springabout 700 m from the lake (Site C, Fig. 1) was measured.ResultsOn most alluvial beds deposited around the lake, groundsurface soil layers generally consisted of silt and clay,fairly rich in mixed round gravel, and relatively dry witha volumetric water content of 10–20%. The estimatedmaximum depth of the active layer in late summer mainlyamounted to 1.5–4.0 m under grasslands (pasture), while itwas mainly 1.4–2.0 m under larch forests. The water contentof surface soil under larch forests on north-facing slopeswas around 22%, whereas it was only 13% on slopes facingthe other three directions. However, once such a foreststand had been burned or clear-felled, the depth of activelayer increased up to 1.9–5.4 m, owing to increased solarirradiation on the exposed ground.At Site L, a large tributary river, Ulgen Sair, joins theuppermost stream of Egiyn River (Fig. 2). The stream bedof Ulgen Sair is far larger than the Egiyn stream, about 400m wide at the confluence, and is entirely filled with fullyeroded round gravel. Surface water flow does not exist undernormal weather, but in case of concentrated heavy rainfall,vast mounts of debris are carried down by flood water anddeposited on and around the confluence with the Egiyn River.For instance, in July 1971, the debris deposits following aheavy rainfall of 71 mm/day (at Hatgal) entirely buried theEgiyn stream, completely cutting off the outflow from the lake(Batsukh et al. 1976). Similar events took place twice in 2003Table 1. Physical dimensions of Lake Hovsgol (Kurata 1993).Location50°27′–51°37′N, 100°51′–101°47′EAltitude (m) 1,645Surface area (km 2 ) 2,770Maximum depth (m) 267Mean depth (m) 138Volume (km 3 )* 383Length of shoreline (km) 414Drainage basin area (km 2 ) 4,940Forest (km 2 )** (2,365)Pasture (km 2 )** (1,559)Mountain (km 2 )** (1,016)* Data (Kumagai 1998); ** Values measured in map.307
Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tE100 Nand 2006. Owing to such repeated flood disasters, it is difficultfor Egiyn River at Site L to maintain a clearly open channel.The outflowing rate at Site L calculated from the current speedmeasured at stream surface (1.89 m/sec) and the cross-sectionalarea water channel (26.44 m 2 ) amounted to 1.58 km 3 /yr.At Site C, the inflowing rate of stream to originate fromHar usnii Spring, where the water keeping 4.3~6.2°Cflows throughout the year, was measured as 6.05 m 3 /s andamounted to 0.19 km 3 /yr.DiscussionBased on the survey results, a depth of active layer wasdetermined, and thereby estimated the increase of waterinflow to the lake caused by additional thawing of permafrostdue to climate warming. For example, the additional increaseof the active layer in the forest area was determined to be 3.5m, assuming that the forest vanishes and it becomes deeperfrom 1.9 m to 5.4 m. Using Vw 40% as the volumetric watercontent in permafrost and Vw 20% after thawing, the amountof fossilized water to outflow to the lake was estimated to be1.66 km 3 , using the area of forest given in Table 1.However, such water does not flow out at the same time, butdoes so gradually for a long time. For example, it is knownthat the fossilized water keeps flowing out due to thawing ofpermafrost for several years after a forest fire. If it takes acentury for the forest to vanish and the fossilized water flowsout by the thawing of permafrost, the outflow of the wateris estimated to be only 0.02 km 3 /yr. The estimated amount isnot even so much in the forest area larger than the pasture orthe mountain (Table 1), because of the thin surface soil andabundance of gravel and rocks.0N5130kmMongoliaFigure 1. Distribution of the study sites around L. Hovsgol.The total amount of fossilized water in the drainage basinarea is considered to be too small to cause a significant rise inwater level, because the amount in the forest area is negligiblysmall compared with the outflow 1.58 km 3 /yr through EgiynRiver. Therefore, it is difficult to regard as the main causalfactor that the increase of water inflow to the lake caused byadditional thawing of permafrost due to climate warminginduces the rise in water level.On the other hand, the draining capacity of the soleoutflowing river—Egiyn River—is very unstable, since itsuppermost course suffers from vast amounts of sedimentcarried down by a large tributary stream at times of heavyrainfall, filling the river channel either partly or completely.A close negative correlation was found between the lake’swater level and the rate of outflow through this bottleneck inthe uppermost part of the Egiyn River.ReferencesFigure 2. Outflow River, Egiyn River, at the confluence with thetributary river, Ulgen Sair.Batsyk, N., Schymeev, V.P. et al. 1976. Surface water and waterbalance of Lake Khubusgul. In: N. Sodnom & N.E.Losev (eds.), Natural Conditions and Resources of theKhubusgul Region in the Mongolian Peoples Republic.Moscow: Nedra, 185-206 (in Russian and Japanese,translated by Dr. Naganawa).Kumagai, M. 1998. Lake Hovsgol in Mongolia. In: LakeBiwa Research Institute (ed.), Record of the 16 th IBRISymposium. Otsu: LBRI, 89-104 (in Japanese).Kumagai, M., Urabe, J. et al. 2006. Recent rise in waterlevel at Lake Hovsgol in Mongolia. In: C.E. Goulden,T. Sitnikova et al. (eds.), The Geology, Biodiversityand Ecology of Lake Hovsgol (Mongolia). Leiden:Backhuys, 77-91.Kurata, A. (ed.), 1993. Data Book of World LakeEnvironments: Compact-size Ed 1: Asia and Oceania.Kusatsu: ILEC & UNEP.Murun Meteorological Station 1970-2006. MeteorologicalData Observed at Lake Hovsgol during 1970–2006.National Agency for Meteorology 1940–2006.Meteorological Data observed at Moron and Hatgalduring 1940–2006.308
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NICOP 2008 Ninth <
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ContentsPreface ...................
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Mapping and Modeling the Distributi
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Satellite Observations of Frozen Gr
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xiiIce Wedge Thermal Regime in Nort
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xivPermafrost Response to Dynamics
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NICOP SponsorsUniversitiesUniversit
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Deep Permafrost Studies at the Lupi
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Effect of Fire on Pond Dynamics in
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Cryological Status of Russian Soils
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Acoustical Surveys of Methane Plume
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Permafrost Delineation Near Fairban
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Preparatory Work for a Permanent Ge
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A Provisional Soil Map of the Trans
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Martian Permafrost Depths from Orbi
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Time Series Analyses of Active Micr
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Impact of Permafrost Degradation on
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DC Resistivity Soundings Across a P
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Modeling Thermal and Moisture Regim
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A Provisional Permafrost Map of the
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Alpine Permafrost Distribution at M
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Cryogenic Formations of the Caucasu
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Modeling Potential Climatic Change
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A Hypothesis: A Condition of Growth
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Modeled Continual Surface Water Sto
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Freeze/Thaw Properties of Tundra So
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Discontinuous Permafrost Distributi
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Thermal Regime Within an Arctic Was
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Seasonal and Interannual Variabilit
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Twelve-Year Thaw Progression Data f
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Continued Permafrost Warming in Nor
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Landsliding Following Forest Fire o
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A Permafrost Model Incorporating Dy
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Seasonal Sources of Soil Respiratio
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Greenland Permafrost Temperature Si
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The Importance of Snow Cover Evolut
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The Account of Long-Term Air Temper
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The Combined Isotopic Analysis of L
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Adaptating and Managing Nunavik’s
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Human Experience of Cryospheric Cha
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HiRISE Observations of Fractured Mo
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A Soil Freeze-Thaw Model Through th
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Mapping and Modeling the Distributi
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First Results of Ground Surface Tem
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Historical Changes in the Seasonall
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Rock Glaciers in the Kåfjord Area,
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Snowpack Evolution on Permafrost, N
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Climate Change in Permafrost Region
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Maximizing Construction Season in a
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Pleistocene Sand-Wedge, Composite-W
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370Huang, B. 339Hugelius, G. 105, 1
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