The role of permafrost in water exchange of a black spruce forest in Interior Alaska

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• 作者：Hiroki Iwata^a ; ^{hiwata@alaska.edu} ; Yoshinobu Harazono^a ; ^b ; Masahito Ueyama^b
• 关键词：Eddy covariance ; Energy balance ; Evapotranspiration ; Seasonal freeze&ndash ; thaw cycle ; Snowmelt
• 刊名：Agricultural and Forest Meteorology
• 出版年：2012
• 期刊代码：2_01681923
• 类别：abs
• 出版时间：15 August, 2012
• 卷：161
• 期：Complete
• 页码：107-115
• 文件大小：672 K

摘要

Water exchange in a black spruce forest on ice-rich permafrost in Interior Alaska was examined over seven years to clarify its seasonal and interannual variations. Partitioning of available energy to latent heat flux was strongly constrained by leaf area and thaw depth of the soil. Water balance on a monthly timescale showed that evapotranspiration was greater than precipitation in the early growing season. It is likely that evapotranspiration was supported by soil thawing and snowmelt water stored in microtopographic hollows during this period. Precipitation increased in the latter half of the growing season, whereas evapotranspiration decreased along with a decrease in net radiation and the leaf maturation and the senescence of understory deciduous vegetation. This resulted in an increase of stored water in the soil, which can be utilized by vegetation in the following growing season. The presence of ice-rich permafrost helps the accumulation of water in the soil by blocking deep percolation of water. Cumulative evapotranspiration during the snow-free period did not show noticeable interannual variability, in contrast to a significant variation in precipitation. Cumulative evapotranspiration was primarily controlled by the available energy. Water resources for this black spruce forest remained sustainable under the current climate due to net water gain in the late growing season, combined with the presence of ice-rich permafrost. From a comparison to other black spruce forests with non-permafrost soil, we found that whether ice-rich permafrost exits or not is an important factor for determining the magnitude in the interannual variation of evapotranspiration in boreal forests.