NWIPB OpenIR
青藏高原高寒草甸生态系统的水分收支与生态系统水分利用效率的研究
其他题名Studies on water budget and water use efficiency over an alpine meadow on the Qinghai-Tibetan Plateau
戚培同
学位类型硕士
导师古松
2008-06-06
学位授予单位中国科学院西北高原生物研究所
学位授予地点西北高原生物研究所
关键词蒸散 波文比 涡度相关技术 小型蒸渗仪 高寒草甸 水分利用效率
摘要有“世界屋脊”之称的青藏高原被誉为地球的“第三极”,它是欧亚大陆上发育大江大河最多的地域,亦有亚洲“水塔”之称,其在全球生态系统水循环和水量平衡中的重要性可见一斑。高原上又以高寒草甸生态系统的分布面积最广,占60%以上。在这种特殊的生态环境中,导致了高寒草甸生态系统蒸散的特殊性。由于涡度相关系统普遍存在能量不闭合现象,这对准确评价生态系统的水分收支和水分利用效率带来了很大困难。本研究于2005年和2006年夏季的7~8月,利用小型蒸渗仪、波文比与涡度相关技术三种方法对青藏高原高寒草甸生态系统昼间的蒸散量进行对比研究,定量分析三种方法所得结果的差异,并试图分析其影响因子,为利用和正确评价涡度相关技术测定该生态系统的碳水收支提供了理论依据。同时利用2002年的通量数据分析高寒草甸生态系统的水分利用效率,初步探讨了生态系统的水分利用效率状况。结果表明: 1、海北高寒草甸生态系统的能量闭合程度为0.73,即涡度相关系统观测的能量通量(LE + H)明显低于能量平衡法观测的有效能量(Rn - G),然而二者存在较好的相关性,相关系数达0.92。海北站高寒草甸生态系统的能量不闭合状况主要是由于该地区特殊的环境条件以及涡度相关系统自身的原因而导致湍流通量的观测值偏低。 2、观测期间,三种不同方法测定的蒸散量之间具有较好的相关性,涡度相关系统与小型蒸渗仪测定的蒸散量相关系数达0.96,与波文比法的结果相关系数为0.95。然而,波文比法计算的蒸散量最大,比涡度相关系统的观测值高43%;小型蒸渗仪法的测定值次之,比涡度相关法的观测值高19%;涡度相关法测算的蒸散值最小。通过小型蒸渗仪对涡度相关系统测定的潜热通量进行校正可以初步得出结论,利用涡度相关技术测定该高寒草甸生态系统的潜热通量,可能会过小评价该生态系统的蒸散量。 3、本研究中波文比法计算的蒸散量远高于涡度相关系统,主要是因为本研究的试验地位于青藏高原,下垫面接受的太阳辐射多,温度梯度较大。而夏季天气多变,降水较多,土壤含水量高,昼间空气常处于不稳定状态,水汽压垂直梯度较小,可能是导致波-文比系统误差增大的原因。 4、本研究对环境因子中的VPD、太阳辐射、风速和气温与LE 观测结果的相关分析表明:净辐射、气温和VPD对LE 的影响比较明显,相关系数分别为0.95;0.71和0.80,说明LE 主要受太阳辐射控制。风速与LE 相关性并不是很大,相关系数仅为0.31。 5、高寒草甸生态系统水分利用效率的高值出现在生长旺盛季的7-8月,水分利用效率的日变化趋势基本都是上午和傍晚较高,中午较低,呈“U”形变化趋势。日变化幅度较大,上午和傍晚明显高于中午,一天之中有两个峰值,分别为7:00-9:00和17:00-19:00。
其他摘要The Qinghai-Tibetan Plateau, be known as the “roof of the world” and “third pole”, is the source of most major rivers on the Eurasian continent, it is also called the “water tower of Asia”. Alpine meadow is the most extensive vegetation type on the Qinghai-Tibetan Plateau (covering more than 60% of plateau). Water cycle and balance in alpine meadow plays an important role in determining water cycle of ecosystems in the world. In this unique environment, the characteristics of alpine meadow lead to the particularity of ecosystem evapotranspiration. However, it is difficult to accurately evaluate the water budget and water use efficiency of alpine meadow because ther imbalance was prevalent in this study site (the sum of sensible and latent fluxes estimated by eddy covariance technique (EC) method is often less than the difference between the net radiation and the soil heat flux). To examine the evapotranspiration (LE) by EC, the daytime evapotranspiration was measured using EC, mini-lysimeter and Bowen ratio-energy balance (BREB) methods in this alpine meadow on the Qinghai-Tibetan Plateau in July and August 2005 and 2006. We examined the differences among the three methods, and try to analyze the factors affecting energy imbalance. The results maybe provide a theoretical foundation for further studying carbon/water budget in this meadow by using EC. At the same time, we also examined the water use efficiency using the data of 2002 in this alpine meadow. The major results can be summarized as follows: 1. The energy imbalance with a slope of 0.73 was found in this study in the alpine meadow. The energy flux (LE + H) by EC was markedly lower than observed available energy (Rn - G), but there is a better correlation, the correlation coefficient is 0.92. The possible reason is that the unique environmental conditions in alpine meadow and the problem with EC technique resulted in the lower value of EC. 2. The energy imbalance with a slope of 0.73 was found in this study. Results showed a significant correlation between the E measured with the three methods, with the correlation coefficient of 0.96 between the EC and the mini-lysimeter methods, and 0.95 between the EC and the BREB methods. However, the value of E measured by the BREB was the largest, which was 43% higher than that by the EC; whilst the E measured with mini-lysimeter had the medium value, which was 19% higher than that by EC. The results indicate that evapotranspiration may be underestimated using the EC in this alpine meadow ecosystem. 3. Evapotranspiration calculated with BREB was much higher than that by EC, one of the possible reasons for this might be strong solar radiation reached on the meadow surface, large vertical air temperature gradient, and less vertical vapor pressure gradient in alpine meadow on the Qinghai-Tibet Plateau. 4. The effect of environmental parameters on the LE was examined, indicating that the net solar radiation, temperature and VPD were the dominant factors affecting LE, the correlation coefficient is 0.95, 0.71 and 0.80, respectively, the correlation coefficient is only while is 0.31 between LE and wind speed. 5. The maximum value of water use efficiency (WUE) appeared in the vigorous growing season (July and August), and large diurnal variation in WUE with U-shape was found in this meadow, low WUE was at noon, and relatively high value in morning (7:00-9:00) and afternoon (17:00-19:00).
页数69
语种中文
文献类型学位论文
条目标识符http://210.75.249.4/handle/363003/3206
专题中国科学院西北高原生物研究所
推荐引用方式
GB/T 7714
戚培同. 青藏高原高寒草甸生态系统的水分收支与生态系统水分利用效率的研究[D]. 西北高原生物研究所. 中国科学院西北高原生物研究所,2008.
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