Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 13 3 2009 10.5194/hess-13-327-2009 http://www.hydrol-earth-syst-sci.net/13/327/2009/ http://www.hydrol-earth-syst-sci.net/13/327/2009/hess-13-327-2009.html http://www.hydrol-earth-syst-sci.net/13/327/2009/hess-13-327-2009.pdf 327 341 2009-03-13 Impacts of changes in vegetation cover on soil water heat coupling in an alpine meadow of the Qinghai-Tibet Plateau, China W. Genxu wanggx@imde.ac.cn H. Hongchang L. Guangsheng L. Na Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu 610041, China College of Resources & Environment, Lanzhou University, Lanzhou 730000, China Alpine meadow is one of the most widespread grassland types in the permafrost regions of the Qinghai-Tibet Plateau, and the transmission of coupled soil water heat is one of the most crucial processes influencing cyclic variations in the hydrology of frozen soil regions, especially under different vegetation covers. The present study assesses the impact of changes in vegetation cover on the coupling of soil water and heat in a permafrost region. Soil moisture (θv), soil temperature (Ts), soil heat content, and differences in θv−Ts coupling were monitored on a seasonal and daily basis under three different vegetation covers (30, 65, and 93%) on both thawed and frozen soils. Regression analysis of θv vs. Ts plots under different levels of vegetation cover indicates that soil freeze-thaw processes were significantly affected by the changes in vegetation cover. The decrease in vegetation cover of an alpine meadow reduced the difference between air temperature and ground temperature (ΔTa−s), and it also resulted in a decrease in Ts at which soil froze, and an increase in the temperature at which it thawed. This was reflected in a greater response of soil temperature to changes in air temperature (Ta). For ΔTa−s outside the range of −0.1 to 1.0°C, root zone soil-water temperatures showed a significant increase with increasing ΔTa−s; however, the magnitude of this relationship was dampened with increasing vegetation cover. At the time of maximum water content in the thawing season, the soil temperature decreased with increasing vegetation. Changes in vegetation cover also led to variations in θv−Ts coupling. With the increase in vegetation cover, the surface heat flux decreased. Soil heat storage at 20 cm in depth increased with increasing vegetation cover, and the heat flux that was downwardly transmitted decreased. The soil property varied greatly under different vegetation covers, causing the variation of heat conductivity and water-heat hold capacity in topsoil layer in different vegetation cover. The variation of heat budget and transmitting in soil is the main factor that causes changes in soil thawing and freezing processes, and θv−Ts coupling relationship under different vegetation fractions. In addition to providing insulation against soil warming, vegetation in alpine meadows within the permafrost region also would slow down the response of permafrost to climatic warming via the greater water-holding capacity of its root zone. Such vegetation may therefore play an important role in conserving water in alpine meadows and maintaining the stability of engineering works constructed within frozen soil of the Qinghai-Tibet Plateau. Bakalin V. A. and Vetrova V. P.: Vegetation-Permafrost relationships in the zone of sporadic permafrost distribution in the Kamchatka Peninsula, Russian Journal of Ecology, 39(5), 318–326, 2008. Bubier, J. L., Frolking, S., Crill, P. M., and Linder, E.: Net ecosystem productivity and its uncertainty in a diverse boreal peatland, J. Geophys. Res., 104(D22), 27683–27693, 1999. Carey S. K. and Woo M. K.: Hydrology of two slopes in subarctic Yukon, Canada, Hydrol. Process, 13, 2549–2562, 1999. Cheng, G.: Problems on zonation of high altitude permafrost. Acta Geographica Sinica, 39(2), 185–193, 1984. Chen, R., Lu S. H., and Kang E. S.: A distributed water-heat coupled (DWHC) model for mountainous watershed: model structure and equations. Adv. Earth Sci., 21(8), 806–818, 2006.. Christensen T. R., Johansson T., and Kerman H. J.: Thawing sub-arctic permafrost: Effects on vegetation and methane emissions, Geophysi. Res. Lett., 31, L04501, 2004. Flerchinger, G. N.: The Simultaneous Heat and Water (SHAW) Model: User's Manu, Technical Report NWRC, 2000-10, 2000. Eugster,W., Rouse,W., Pielkesr, R. A.,Mcfadden, J. P., Baldocchi, D. D., Kittel, T. G. F., Chapin, F. S., Liston, G. E., Vidale, P. L., Vaganov, E., and Chambers, S.: Land-atmosphere energy exchange in Arctic tundra and boreal forest: available data and feedbacks to climate, Global Change Biol., 6 (suppl. 1), 84–115, 2000.. Jansson, P.-E. and Karlberg, L.: COUP manual Coupled heat and mass transfer model for soil-plant-atmosphere systems, online available at: http://www.lwr.kth.se/varadatorprogram/CoupModel/, 2001. Jayawickreme, D. H., Van Dam, R. L., and Hyndman, D. W.: Subsurface imaging of vegetation, climate, and root-zone moisture interactions, Geophys. Res. Lett., 35, L18404, doi:10.1029/2008GL034690, 2008. Jorgenson, M. T., Racine, C. H., Walters, J. C.: Permafrost degradation and ecological changes associated with a warming in central Alaska, Clim. Change, 48, 551–579, 2001. Kang, E., Cheng, G. D., and Song, K. C: Simulation of energy and water balance in Soil-Vegetation-Atmosphere Transfer system in the mountain area of Heihe river basin, China. Science in China (Series D), 48(4), 538–548, 2005. Legates, D. R. and McCabe, G. J.: Evaluating the use of "goodness-of-fit" measures in hydrologic and hydro-climatic model validation, Water Resour. Res. 35(1), 233–241, 1999. Ma, Y., Yao, T., Wang, J., and Hu, Z.: The Study on the Land Surface Heat Fluxes over Heterogeneous Landscape of the Tibetan Plateau, Adv. Earth Sci., 21(12), 1215–1224, 2006. McGuire, A. D.: Environmental variation, vegetation distribution, carbon dynamics and water/energy exchange at high latitudes, Journal of Vegetation Science, 13(1), 301–314, 2002. Mayocchi, C. L. and Bristowa, K. L.: Soil surface heat flux: some general questions and comments on measurements, Agr. For. Meteor., 75, 43–50, 1995. Ministry of Agriculture of China Technical specifications of soil analysis, Beijing, Chinese Agriculture Press, 14–172, 1993. Nash, J. E. and Sutcliffe, J. V.: River flow forecasting through conceptual models, 1, discussion of principles, J. Hydrol., 10, 282–292, 1970. National Soil Survey Office (NSSO), Soil of China, China Agriculture Press, Beijing, China, 1998. NWRC SHAW (Vol.2.3.6), http://www.nwrc.ars.usda.gov/Models/SHAW.html, 2004. Oechel, W. C., Vourlitis, G. L., Hastings, S. J., Zulueta, R. C., Hinzman, L., and Kane, D.: Acclimation of ecosystem CO2 exchange in the Alaskan Arctic in response to decadal climate warming, Nature, 406, 978–980, 2000. Payero, J. O., Eale, C. M. U., Wright, J. L., and Allen, R. G.: Guidelines for validating Bowen Ratio data, Transactions of the ASAE, 46(4), 1051–1060, 2003. Rouse, W. R.: Progress in hydrological research in the Mackenzie GEWEX study, Hydrol. Proc., 14, 1667–1685, 2000. Sato, T.: Spatial and temporal variation of frozen ground and snow cover in the eastern Tibetan Plateau, J. Meteor. Soc. Jpn., 79, 519–534, 2001. Smith, M. W. and Riseborough, D. W.: Ground temperature monitoring and detection of climate change, Permafrost Periglac., 7(4), 301–310, 1996. Smith, M. W. and Riseborough, D. W.: Climate and the limits of permafrost: a zonal analysis, Permafrost Periglac., 13(1), 1–15, 2002. Gu, S., Tang, Y. H., Cui, X. Y., Kato, T., Du, M. Y., Li, Y. N., and Zhao, X. Q.: Energy exchange between the atmosphere and a meadow ecosystem on the Qinghai-Tibetan Plateau, Agr. For. Meteor., 129, 175–185, 2005. Turetsky, M. R., Kelman Wieder, R., and Vitt, D. H.: Boreal peatland C fluxes under varying permafrost regimes, Soil Biol. Biochem., 34, 907–912, 2002. Walker, D. A., Jia, G. J., and Epstein, H. E.: Vegetation-soil-thaw-depth relationships along a low-arctic bioclimate gradient, Alaska: synthesis of information from the ATLAS studies, Permafrost Periglac., 14, 103–123, 2003. Wang, G., Li, Q., Cheng, G. D., and Sheng, Y. P.: Climate change and its impact on the eco-environment in the source regions of Yangtze and Yellow Rivers in recent 40 years, J. Glac. Geocry., 23(4), 346–352, 2001a. Wang, G., Cheng, G. D., and Shen, Y. P.: Research on ecological environmental changes in Yangtze and Yellow Rivers source regions and their integrated protection (in Chinese), 213 pp., Lanzhou University Press, Lanzhou, China, 2001b. Wang, G., Ding, Y. J., Wang, J., and Liu, S. Y.: Land ecological changes and evolutional patterns in the source regions of the Yangtze and Yellow Rivers, Acta Geographic Sinica, 15(2), 163–173, 2004. Weller, G., Chapin, F. S., Everett, K. R., and Hobbie, J. E.: The arctic FLUX study: a regional view of gas release, J. Biogeogr., 22, 365–374, 1995. Wu, Q. and Liu, Y. Z.:: Ground temperature monitoring and its recent change in Qinghai-Tibet Plateau, Cold Reg. Sci. Technol., 38, 85–92, 2004. Wu, Q. B., Shi, B., and Liu, Y. Z.: Research on the interaction of permafrost and highway along Qinghai-Tiber highway, Science in China (Series D), 32(6), 514–520, 2002. Xu, X., Wang, J. C., and Zhang, L. X.: Permafrost physics (in Chinese), Science Press, Beijing, 310 pp. 2001. Yi, S., Arain, M. A., and Woo, M. K.: Modefications of a land surface scheme for improved simulation of ground freeze-thaw in northern environments, Geophys. Res. Lett., 33, L13501, doi:10.1029/2006GL026340, 2006. Zhang, Y., Ohata, T., and Kadata, T.: Land surface hydrological processes in the permafrost region of the eastern Tibetan Plateau, J. Hydrol., 283, 41–56, 2003. Zhang, Y., Munkhtsetseg, E., Ohata, T., and Kadata, T.: An observational study of ecohydrology of a sparse grassland at the edge of the Eurasian cryosphere in Mongolia, J. Geophys. Res., 110, D14103, doi:10.1029/2004JD005474, 2005. Zhou, Y., Guo, D. X., Qiu, G. Q., and Cheng, G. D.: Geocryology in China (in Chinese), Science Press, Beijing, China, 450 pp., 2000. Zhou, X. M.: Chinese Kobresia pygmaea meadow (in Chinese), Science Press, Beijing, China, 370 pp., 2001.