Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 6 8 2009 10.5194/bg-6-1371-2009 http://www.biogeosciences.net/6/1371/2009/ http://www.biogeosciences.net/6/1371/2009/bg-6-1371-2009.html http://www.biogeosciences.net/6/1371/2009/bg-6-1371-2009.pdf 1371 1388 2009-08-04 SURFATM-NH3: a model combining the surface energy balance and bi-directional exchanges of ammonia applied at the field scale E. Personne erwan@bcgn.grignon.inra.fr B. Loubet B. Herrmann M. Mattsson J. K. Schjoerring E. Nemitz M. A. Sutton P. Cellier UMR Environment et Grandes Cultures/INRA – AgroParisTech, 78850 Thiverval Grignon, France Agroscope Reckenholz-Tänikon Research Station ART, Reckenholzstrasse 191, 8046 Zürich, Switzerland Plant and Soil Science Laboratory, University of Copenhagen, Faculty of Life Sciences, Thorvaldsensvej 40, 1871 Frederiksberg C, Copenhagen, Denmark Centre for Ecology and Hydrology, Edinburgh Research Station, Bush Estate, Penicuik, Midlothian, EH26 0QB, UK A new biophysical model SURFATM-NH3, simulating the ammonia (NH₃) exchange between terrestrial ecosystems and the atmosphere is presented. SURFATM-NH3 consists of two coupled models: (i) an energy budget model and (ii) a pollutant exchange model, which distinguish the soil and plant exchange processes. The model describes the exchanges in terms of adsorption to leaf cuticles and bi-directional transport through leaf stomata and soil. The results of the model are compared with the flux measurements over grassland during the GRAMINAE Integrated Experiment at Braunschweig, Germany. The dataset of GRAMINAE allows the model to be tested in various meteorological and agronomic conditions: prior to cutting, after cutting and then after the application of mineral fertilizer. The whole comparison shows close agreement between model and measurements for energy budget and ammonia fluxes. The major controls on the ground and plant emission potential are the physicochemical parameters for liquid-gas exchanges which are integrated in the compensation points for live leaves, litter and the soil surface. Modelled fluxes are highly sensitive to soil and plant surface temperatures, highlighting the importance of accurate estimates of these terms. The model suggests that the net flux depends not only on the foliar (stomatal) compensation point but also that of leaf litter. SURFATM-NH3 represents a comprehensive approach to studying pollutant exchanges and its link with plant and soil functioning. It also provides a simplified generalised approach (SVAT model) applicable for atmospheric transport models. Anderson, N., Strader, R., and Davidson, C.: Airborne reduced nitrogen: ammonia emissions from agriculture and other sources, Environ. International, 29, 277–286, 2003. Bates, R. G. and Pinching, G. D.: Dissociation constant of aqueous ammonia at 0 to 50°C from m.f studies of the ammonium salt of a weak acid, Am. Chem. Soc. J., 72, 1393–1396, 1950. Bobbink, R.: Effect of nutrient enrichment in Dutch chalk grassland, J. Appl. Ecol., 28, 28–41, 1991. Bouwman, A. F., Lee, D. S., Asman, W. A. H., Dentener, F. J., and van der Hoek, K. W.: A global high-resolution emission inventory for ammonia, Global Biogeochem. Cycles, 11, 561–587, 1997. Burkhardt, J., Flechard, C. R., Gresens, F., Mattsson, M., Jongejan, P. A. C., Erisman, J. W., Weidinger, T., Meszaros, R., Nemitz, E., and Sutton, M. A.: Modelling the dynamic chemical interactions of atmospheric ammonia with leaf surface wetness in a managed grassland canopy, Biogeosciences, 6, 67–83, 2009. Carsel, R. F. and Parrish, R. S.: Developping joint probablility distributions of soil water retention characteristics, Water Resour. Res., 24, 755–769, 1988. Choudhury, B. J. and Monteith, J. L.: A four-layer model for the heat budget of homogeneous land surfaces, Q. J. Roy. Meteorol. Soc., 114, 373–398, 1988. Cowan, I. R.: Transport of water in soil plant atmosphere system, J. Appl. Ecol., 2, 221–239, 1965. David, M., Loubet, B., Cellier, P., Mattsson, M., Schjoerring, J. K., Nemitz, E., Roche, R., Riedo, M., and Sutton, M. A.: Ammonia sources and sinks in an intensively managed grassland using dynamic chambers, Biogeosciences Discuss., 6, 1625–1655, 2009a. David, M., Roche, R., Mattsson, M., Sutton, M. A., Dämmgen, U., Schjoerring, J. K., and Cellier, P.: The effects of management on ammonia fluxes over a cut grassland as measured by use of dynamic chambers, Biogeosciences Discuss., 6, 1599–1623, 2009b. Dragosits, U., Theobald, M. R., Place, C. J., Lord, E., Webb, J., Hill, J., ApSimon, H. M., and Sutton, M. A.: Ammonia, emission, deposition and impact assessments at the field scale: a case of study of sub-grid spatial variability, Environ. Pollut., 1, 147–158, 2002. Dyers, A. G. and Hicks, B. B.: Flux-profile relationship in the constant flux layer, Q. J. Roy. Meteorol. Soc., 96, 715–721, 1970. Emberson, L. D., Simpson, D., Tuovinen, J.-P., Ashmore, M. R., and Cambridge, M. H.: Towards a model of ozone deposition and stomatal uptake avore Europe. EMEP/MSC – W Note 6/2000. Norwegian Meteorological Institute, Oslo, http://www.emep.int/publ/reports/2000/dnmi_note_6_2000.pdf, 2000. Erisman, J. W. and Wyers, G. P.: Continuous measurements of surface exchange of SO₂ and NH₃: implications for their possible interaction in the deposition process, Atmos. Environ., 27, 1937–1949, 1993. Fangmeier, A., Hadwiger-Fangmeier, A., Van der Eerden, L., and Jäger, H. J.: Effects of atmospheric ammonia on vegetation – a review, Environ. Pollut., 86, 43–82, 1994. Farquhar, G. D., Firth, P. M., Wetselaar, R., and Wier, B.: On the gaseous exchange of ammonia between leaves and the environment: determination of the ammonia compensation point, Plant Physiol., 66, 710–714, 1980. Flechard, C., Fowler, D., Sutton, M. A., and Cape, J. N.: Modelling of ammonia and sulphur dioxide exchange over moorland vegetation, Q. J. Roy. Meteorol. Soc., 125, 2611–2641, 1999. Fowler, D., Cape, J. N., and Unsworth, M. H.: Deposition of atmospheric pollutants on forest, Phil. Trans. Roy. Soc. London B., 324, 247–265, 1989. Freibauer, A.: Regionalised inventory of biogenic greenhouse gas emissions from European agriculture, Eur. J. Agron., 19, 153–160, 2003. Ganzeveld, L. N., Lelieveld, J., Dentener, F. J., Krol, M. C., and Roelofs, G.-J.: Atmosphere-biosphere trace gas exchanges simulated with a single-column model, J. Geophys. Res., 107(D16), 4297, doi:10.1029/2001JD000684, 2002. Genermont, S., Cellier, P., Flura, D., Morvan, T., and Laville, P.: Measuring ammonia fluxes after slurry spreading under actual field conditions, Atmos. Environ., 32, 279–284, 1998. Grünhage, L. and Haenel, H-D.: PLATIN (PLant-ATmosphere-Interaction) I~: A model of plant-atmosphere interaction for estimating absorbed doses of gaseous air pollutants, Environ. Pollut., 98, 37–50, 1997. Guyot G.: Physics of the environment and climate, John Wiley, Chichester, 632 pp., 1998. Hensen, A., Nemitz, E., Flynn, M. J., Blatter, A., Jones, S. K., Sørensen, L. L., Hensen, B., Pryor, S., Jensen, B., Otjes, R. P., Cobussen, J., Loubet, B., Erisman, J. W., Gallagher, M. W., Neftel, A., and Sutton, M. A.: Inter-comparison of ammonia fluxes obtained using the relaxed eddy accumulation technique, Biogeosciences Discuss., 5, 3965–4000, 2008. Herrmann, B., Mattsson, M., Jones, S. K., Cellier, P., Milford, C., Sutton, M. A., Schjoerring, J. K., and Neftel, A.: Vertical structure and diurnal variability of ammonia exchange potential within an intensively managed grass canopy, Biogeosciences, 6, 15–23, 2009. Hicks, B. B., Baldocchi, D. D., Meyers, T. P., Hosker Jr., R. P., and Matt, D. R.: A preliminary multiple resistance routine for deriving dry deposition velocities from measured quantities, Water Air Soil Pollut., 36, 311–330, 1987. Husted, S. and Schjorerring, J. K.: Apoplastic pH and ammonium concentration in leaves of Brassica napus L., Plant Physiol., 109, 1453–1460, 1995. Husted S., Schjorerring, J. K., Nielsen, K. H., Nemitz, E., and Sutton, M. A.: Stomatal compensation points for ammonia in oilseed rape plants under field conditions, Agr. Forest. Meteorol., 105, 371–383, 2000. Hyde, B. P., Carton, O. T., O'Toole, P., and Misselbrook, T. H.: A new inventory of ammonia emissions from Irish agriculture, Atmosph. Environ., 37, 55–62, 2003. Jarvis, P. G.,: The interpretation of the variation in leaf water potential and stomatal conductance found in canopies in the field, Phil. Trans. Roy. Soc. London. (B), 273, 375–391, 1976. Jones H. G.: Plants and Microclimate. A quantitative approach to environnemental plant physiology, Cambridge University Press, 428 pp., 1992. Krupa, S. V.: Effects of ammonia (NH3) on terrestrial vegetation : a review, Environ. Pollut., 124, 179–221, 2003. Li, C., Zhuang, Y., Cao, M., Crill, P., Frolking, S., Moore, B., Salas, W., Song, W., and Wang, X.: Comparing a process-based agro-system model to the IPCC methodology for developing a national inventory of N₂O emissions from arable lands in China, Nutrient Cycling Agrosystems, 60, 159–175, 2001. Loubet, B.: Modélisation du dépôt sec d'ammoniac atmosphérique à proximité des sources, PhD Thésis, 329 pp., Paul Sabatier University, Toulouse, France, 2000. Loubet, B., Milford, C., Sutton, M. A., and Cellier, P.: Investigation of the interactions between sources and sinks of atmospheric ammonia in an upland landscape using a simplified dispersion exchange, J. Geophys. Res., 106(D20), 24183–24195, 2001. Loubet, B., Milford, C., Hill, P. W., Tang, Y. S., Cellier, P., and Sutton, M. A.: Seasonal variability of apoplastic NH4+ and pH in an intensively managed grassland, Plant Soil, 238, 97–110, 2002. Loubet, B., Cellier, P., Milford, C., and Sutton, M. A.: A coupled dispersion and exchange model for short-range dry deposition of atmospheric ammonia, Q. J. Roy. Meteorol. Soc., 132, 1733–1763, doi:10.1256/qj.05.73, 2006. Loubet, B., Milford, C., Hensen, A., Daemmgen, U., Erisman, J.-W., Cellier, P., and Sutton, M. A.: Advection of NH3 over a pasture field, and its effect on gradient flux measurements, Biogeosciences Discuss., 6, 163–196, 2009. Lumley, J. L. and Panofsky, H. A.: The structure of Atmospheric Turbulence. Wiley-Interscience, New York, 239 pp., 1964. Massman, W. J.: A review of the molecular diffusivities of H₂O, CO₂, CH₄, CO, O₃, SO₂, NH₃, N₂O, NO and NO₂ in air, O₂ and N₂ near STP, Atmos. Environ., 32, 1111–1127, 1998. Mattsson, M. and Schjoerring, J. K.: Dynamic and steady-state responses of inorganic nitrogen pools and NH3 exchange in leaves of Lolium perenne and Bromus erectus to changes in root nitrogen supply, Plant Physiol., 128, 742–750, 2002. Mattsson, M. and Schjoerring, J. K.: Senescence-induced changes in apoplastic and bulk tissue ammonia concentrations of ryegrass leaves, New Phytol., 160, 489–499, 2003. Mattsson, M., Herrmann, B., David, M., Loubet, B., Riedo, M., Theobald, M. R., Sutton, M. A., Bruhn, D., Neftel, A., and Schjoerring, J. K.: Temporal variability in bioassays of the stomatal ammonia compensation point in relation to plant and soil nitrogen parameters in intensively managed grassland, Biogeosciences, 6, 171–179, 2009a. Mattsson, M., Herrmann, B., Jones, S., Neftel, A., Sutton, M. A., and Schjoerring, J. K.: Contribution of different grass species to plant-atmosphere ammonia exchange in intensively managed grassland, Biogeosciences, 6, 59–66, 2009b. Milford, C., Theobald, M. R., Nemitz, E., and Sutton, M. A.: Dynamics of ammonia exchange in response to cutting and fertilizing in an intensively-managed grassland, Water Air Soil Pollut., Focus, 1, 167–176, 2001a. Milford, C., Theobald, M. R., Nemitz, E., and Sutton, M. A.: Dynamics of ammonia exchange in response to cutting and fertilising in an intensively-managed grassland, in: Air-Surface Exchange of Gases and Particles (2000), edited by: Fowler, D., Pitcairn, C. E. R., and Erisman, J.-W., Kluwer, Academic Publishers, 2001b. Milford, C., Theobald, M. R., Nemitz, E., Hargreaves, K. J., Horvath, L., Raso, J., Dämmgen, U., Neftel, A., Jones, S. K., Hensen, A., Loubet, B., Cellier, P., and Sutton, M. A.: Ammonia fluxes in relation to cutting and fertilization of an intensively managed grassland derived from an inter-comparison of gradient measurements, Biogeosciences, 6, 819–834, 2009. Monteith, J. L. and Unsworth, M. H.: Principles of environmental physics, 2nd edn., Arnold Press, London, 291 pp, 1990. Nemitz, E., Sutton, M. A., Gut, A., San Jose, R., Husted, S., and Schjørring, J. K.: Sources and sinks of ammonia within an oilseed rape canopy, Agric. Forest Meteorol., 105, 385–404, 2000a. Nemitz, E., Sutton, M. A., Schjoerring, J. K., Husted, S., and Wyers, G. P.: Resistance modelling of ammonia exchange over oilseed rape, Agric. Forest Meteorol., 105, 405–425, 2000b. Nemitz, E., Milford, C., and Sutton, M. A.: A two-layer canopy compensation point model for describing bi-directional biosphere/atmosphere exchange of ammonia, Q. J. Roy. Meteorol. Soc., 127, 815–833, 2001. Nemitz, E., Hargreaves, K. J., Neftel, A., Loubet, B., Cellier, P., Dorsey, J. R., Flynn, M., Hensen, A., Weidinger, T., Meszaros, R., Horvath, L., Dämmgen, U., Frühauf, C., Löpmeier, F. J., Gallagher, M. W., and Sutton, M. A.: Intercomparison and assessment of turbulent and physiological exchange parameters of grassland, Biogeosciences Discuss., 6, 241–290, 2009. Nikolov, N. and Zeller, K.: Modeling coupled interactions of carbon, water and ozone exchange terrestrial ecosystems and atmosphere. I: Model description, Environ. Pollut., 124, 231–246, 2003. Pinder, R. W., Pekney, N. J., Davidson, C. I., and Adams, P. J.: A process-based model of ammonia emissions from dairy cows: improved temporal and spatial resolution, Atmos. Environ., 38, 1357–1365, 2004. Polcher, J., McAvaney, B., Viterbo, P., Gaertner, M.-A., Hahmann, A., Mahfouf, J.-F., Noilhan, J., Phillips, T., Pitman, A., Schlosser, C. A., Schulz, J.-P., Timbal, B., Verseghy, D., and Xue, Y.: A proposal for a general interface between land-surface schemes and general circulation models, Global Planet. Change, 19, 261–276, 1998. Raupach, M. R.: Stand overstorey processes, Phil. Trans. Roy. Soc. London. (B), 324, 175–190, 1989. Raupach, M. R., Finnigan, J. J., and Brunet, Y.: Coherent eddies and turbulence inside vegetation canopies. The mixing layer analogy, Bound. Lay. Meteorol., 78, 351–382, 1996. Riedo, M., Milford, C., Schmid, M., and Sutton, M. A.: Coupling soil-plant-atmosphere exchange of ammonia with ecosystem functioning in grasslands, Ecological Modelling, 158, 83–110, 2002. Schaap, M. G. and Bouten, W.: Forest floor in a dense Douglas fir stand, J. Hydrol., 193, 97–113, 1997. Schjoerring, J. K.: Plant-atmosphere ammonia exchange: Quantification, physiology regulation and interaction with environmental factors, D. Sc. Thesis, Roy. Veterinary and Agric. Univ. Copenhage, Danemark, 55 pp, 1997. Schjoerring, J. K., Husted, S., and Mattsson, M.: Physiological parameters controlling plant-atmosphere ammonia exchange, Atmos. Environ., 32, 491–498, 1998. Schjoerring, J. K., Husted, S., Mack, G., Nielsen, K. H., Finnemann, J., and Mattsson, M.: Physiological regulation of plant-atmosphere ammonia exchange, Plant Soil, 221, 95–102, 2000. Shuttelworth, W. J. and Wallace, S. J.: Evaporation from sparse crop – An energy combination theory, Q. J. Roy. Meteorol. Soc., 111, 477–507, 1985. Stevens, C. J., Dise, N. B., Gowing, D. J. G., and Mountford, J. O.: Loss of forb diversity in relation to nitrogen deposition in the UK : regional trends and potential controls, Global Change Biol., 12, 1823–1833, 2006. Stevens, C. J., Dise, N. B., Mountford, J. O., and Gowing, D. J. G.: impact of nitrogen deposition on the species richness of grasslands, Science, 303, 1876–1879, 2004. Sutton, M. A., Pitcairn C. E., R., and Fowler, D.: The exchange of ammonia between the atmosphere and plant communities, Adv. Ecol. Res., 24, 301–389, 1993. Sutton, M. A., Schjoerring, J. K., and Wyer, G. P.: Plant atmosphere exchange of ammonia. Phil. Trans. Roy. Soc. Lond. A., 351, 261–278, 1995. Sutton, M. A., Burkardt, J. K., Guerin, D., Nemitz, E., and Fowler, D.: Development of resistance models to describe measurements of bi-directional ammonia surface atmosphere exchange, Atmos. Environ., 32, 473–480, 1998a. Sutton, M. A., Milford, C., Dragosits, U., Place, C. J., Singles, R. J., Smith, R. I., Pitcairn, C. E. R., Fowler, D., Hill, J., ApSimon, H. M. , Ross, C., Hill, R., Jarvis, S. C., Pain, B. F., Phillips, V. C., Harrison, R., Moss, D., Webb, J., Espenhahn, S. E., Lee, D. S., Hornung, M., Ullyett, J., Bull, K. R., Emmett, B. A., Lowe, J., and Wyers., G. P.: Dispersion, deposition and impacts of atmospheric ammonia: quantifying local budgets and spatial variability, Environ. Pollut., 102, 349–361, 1998b. Sutton, M. A., Milford, C., Nemitz, E., Theobald, M. R., Hill, P. W., Fowler, D., Schjoerring, J. K., Mattsson, M. E., Nielsen, K. H., Husted, S., Erisman, J. W., Otjes, R., Hensen, A., Mosquera, J., Cellier, P., Loubet, B., David, M., Genermont, S., Neftel, A., Blatter, A., Herrmann, B., Jones, S. K., Horvath, L., Führer, E., Mantzanas, K., Koukoura, Z., Gallagher, M., Williams, P., Flynn, M., and Riedo, M.: Biosphere-atmosphere interactions of ammonia with grasslands: experimental strategy and results from a new European initiative, Plant Soil, 228, 131–145, 2001. Sutton, M. A., Nemitz, E., Erisman, J. W., Beier C., Butterbach Bahl, K., Cellier, P., de Vries, W., Cotrufo, F., Skiba, U., Di Marco, C., Jones, S., Laville, P., Soussana, J.-F., Loubet, B., Twigg, M., Famulari, D., Whitehead, J., Gallagher, M.W., Neftel, A., Flechard, C. R., Herrman, B., Calaca, P. L., Schjoerring, J. K., Daemmgen, U., Horvarth, L., Tang, Y. S., Emmett, B. A., Tietema, A., Penuelas, J., Kesik, M., Brueggemann, N., Pilegaard, K., Vesala, T., Campbell, C. L., Olesen, J. E., Dragosits, U., Theobald, M. R., Levy, P., Mobbs, D. C., Milne, R., Viovy, N., Vuichard, N., Smith, J. U., Smith, P., Bergamaschi, P., Fowler, D., and Reis, S.: Challenges in quantifying biosphere-atmosphere exchange of nitrogen species, Environ. Pollut., 150, 125–139, 2007. Sutton, M. A., Nemitz, E., Theobald, M. R., Milford, C., Dorsey, J. R., Gallagher, M. W., Hensen, A., Jongejan, P. A. C., Erisman, J. W., Mattsson, M., Schjoerring, J. K., Cellier, P., Loubet, B., Roche, R., Neftel, A., Hermann, B., Jones, S. K., Lehman, B. E., Horvath, L., Weidinger, T., Rajkai, K., Burkhardt, J., Löpmeier, F. J., and Daemmgen, U.: Dynamics of ammonia exchange with cut grassland: strategy and implementation of the GRAMINAE Integrated Experiment, Biogeosciences, 6, 309–331, 2009a. Sutton, M. A., Nemitz, E., Milford, C., Campbell, C., Erisman, J. W., Hensen, A., Cellier, P., David, M., Loubet, B., Personne, E., Schjoerring, J. K., Mattsson, M., Dorsey, J. R., Gallagher, M. W., Horvath, L., Weidinger, T., Meszaros, R., Dämmgen, U., Neftel, A., Herrmann, B., Lehman, B. E., Flechard, C., and Burkhardt, J.: Dynamics of ammonia exchange with cut grassland: synthesis of results and conclusions of the GRAMINAE Integrated Experiment, Biogeosciences Discuss., 6, 1121–1184, 2009b. Theobald, M. R., Dragosits, U., Place, C. J., Smith, J. U., Sozanska, M. Brown, L., Scholefield, D., Del Prado, A., Webb, A., Whitehead, P. G., Angus, A., Hodge, I. D., Fowler, D., and Sutton, M. A.: Modelling nitrogen fluxes at the landscape scale, Water Air Soil Pollut., 6, 135–142, 2004. Tulet, P., Crassier, V., and Rosset R.: Air pollution modelling at a regional scale, Environ. Modell. Softw., 15, 693–701, 2000. Tuzet, A. and Perrier, A.: Crop water budget estimation of irrigation requirement, ICID Bulletin., 44, 1–16, 1992. Tuzet, A., Perrier, A., and Oulid Aissa, A. K.: A prediction model for field drying of hay using a heat balance method, Agric. Forest Meteorol., 65, 63–89, 1993. Twine, T. E., Kustas, W. P., Noman, J. M., Cook, D. R., Houser, P. R., Meyers, T. P., Prueger, J. H., Starks, P. J., and Wesely, M. L.: Correcting eddy-covariance flux underestimates over a grassland, Agric. Forest Meteorol., 103, 279–300, 2000. Van Breemen, N. and Van Dijk, H. F. G.: Ecosystem effects of atmospheric deposition of nitrogen in The Netherlands, Environ. Pollut., 54, 249–274, 1988. Van der Hoek, K. W.: Estimating ammonia emission factors in Europe: summary of the work of the UNECE ammonia expert panel, Atmos. Environ., 32, 315–316, 1998. Van Hove, L. W. A., Koops, A. J., Adema, E. H., Vredenberg, W. J., and Pieters, G. A.: A study of the adsorption of NH₃ and SO₂ on leaf surfaces, Atmos. Environ., 23, 1479–1486, 1989. Varlet-Grancher, C., Gosse, G., Chartier, M., Sinoquet, H., Bonhomme, R., and Allirand, J.-M.: Mise au point : rayonnement solaire absorbé ou intercepté par un couvert végétal, Agronomie, 9, 419–439, 1989. Wesely, M. L.: Parameterization of surface resistances to gaseous dry deposition in regional-scale numerical models Atmos. Environ., 23, 1293–1304, 1989. Weyers, J. D. B. and Meidner, H.: Methods in stomatal research, Longman Scientific and Technical ed., 1990. Zhang, Y., Wu, S.-Y, Krishnan, S., Wang, K., Queen, A., Aneja, V. P., and Arya, S. P.: Modeling agricultural air quality: Current status, major challenges, and outlook, Atmos. Environ., 42, 3218–3237, 2008. Zhou, M. C., Ishidaira, H., Hapuarachchi, H. P., Magome, J., Kiem, A. S., and Takeuchi, K.: Estimating potential evapotranspiration using Shuttelworth-Wallace model and NOAA-AVHRR NDVI data to feed a ditributed hydrological model over the Mekong River basin, J. Hydrol., 327, 151–173, 2006.