A seasonal behavior of surface soil moisture condition in a reclaimed tropical peatland
A seasonal behavior of surface soil moisture condition in a reclaimed tropical peatland
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开垦热带泥炭地表层土壤水分状况的季节变化
DOI：
10.1080/00380768.2012.723222
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发表时间：
2012
影响因子：
2
通讯作者：
Tatsuya Nagai
中科院分区：
文献类型：
--
作者：
Ippei IIYAMA;Kazutoshi OSAWA;Tatsuya Nagai
土壤湿度条件对于调节排水泥炭地中土壤碳的释放至关重要，因为通过与土壤层脱水相关的供氧可以促进需氧微生物活动，而在过于干燥的条件下可能会抑制需氧微生物活动。为了表征开垦的热带泥炭地的土壤湿度状况，我们从 2010 年 3 月至 2011 年 11 月对泰国洛坤府的一片油棕田进行了 20 个月的 5 cm 深度体积含水量 (θ5 cm)、地下水位 (GWL) 和降雨量监测。我们还测量了一系列基质势（h）的土壤保水曲线和不饱和导水率（k），以利用白金汉-达西通量定律模拟现场监测的水分状况。 2010年旱季，θ5cm始终低于0.35m3m-3，GWL深度低于30cm。 2010年旱季转雨季期间，地面GWL在1个月左右的时间里呈现峰谷起伏，θ5 cm逐渐减小，趋于饱和。在雨季，当GWL停留在地表附近或高于地表时，θ5cm平均仍为现场饱和值0.58 m3m–3，小于实验室饱和值0.63 m3m–3，表明存在大量截留气相。测量的θ5 cm-GWL关系中的滞后行为也支持表土层在润湿过程中拒绝吸收水。基于实测k(h)和土壤保水曲线的模拟θ5 cm表明，旱季表层土壤容易干燥的主要原因是干燥条件下的低k(h)值，而θ(h)曲线的斜率适中，使得土层能够保持水分，以维持从下降的GWL到地表的液态水供应。改变 k(h) 和蒸发率 (E) 大小时的敏感性分析表明，k(h) 函数比 E 值更具确定性，使地表更容易干燥。由于全年监测中，GWL深度低于30cm的时间有187天，而全年有120天出现地表积水，因此可以得出结论，一年中研究地点主要出现极端干燥或饱和水分条件，因此，地表附近土壤有机质处于有利于好氧分解的有利水分条件的时间可能有限。
Soil moisture condition is essential to regulate the release of soil carbon from a drained peatland since aerobic microbial activities can be encouraged through oxygen supply associated with dewatering the soil layer while they may be discouraged under too dry conditions. Aiming to characterize the soil moisture condition in a reclaimed tropical peatland, we monitored the volumetric water content at 5 cm depth (θ5 cm), groundwater level (GWL) and rainfall for 20 months from March 2010 to November 2011 in an oil palm field in Nakhon-Si-Thammarat, Thailand. We also measured the soil water retention curve and the unsaturated hydraulic conductivity (k) for a series of matric potential (h) to simulate the moisture condition monitored in the field by using the Buckingham-Darcy's flux law. During the dry season in 2010, theθ5 cmconsistently stayed lower than 0.35 m3m–3with the GWL lower than a depth of 30 cm. In the transition from the dry season to the rainy season in 2010, the GWL rose to the land surface with peaks and dips across the time for about one month with theθ5 cmincreasing toward saturation. During the rainy season where the GWL stayed near or above the land surface, theθ5 cmremained the field-saturated value of 0.58 m3m–3on average, less than the laboratory-saturated value of 0.63 m3m–3, suggesting the development of a significant amount of entrapped air-phase. Hysteretic behavior in the measuredθ5 cm–GWL relation also supported that the top soil layer refuses to absorb water in wetting processes. The simulatedθ5 cmbased on the measuredk(h) and soil water retention curves demonstrated that the ease with which the top soil dries during a dry season was due mainly to the lowk(h) value in the dried condition, while the slope of theθ(h) curve was so moderate that the soil layer could retain moisture for maintaining liquid water supply to the surface from the dropped GWL. Sensitivity analyses while varying the magnitude of bothk(h) and evaporation rate (E) suggested that thek(h) function was more deterministic than the value ofEin making the land surface easily dried. As the GWL stayed lower than 30 cm in depth for a total of 187 days out of the year monitored, while surface-ponding conditions took place for 120 days of the year, it was concluded that either the extremely dried condition or the saturated-moisture condition had dominantly occurred in the study site through a year and, thus, there may only be a limited time when soil organic matter near the land surface is in favorable moisture conditions for aerobic decomposition.