近35年官厅水库消落带消涨特征及分区

水库消落带作为重要的生态交错带,是深入分析生态要素内在作用机制的特殊区域。以华北内陆大型水库——官厅水库为研究对象,选择1979—2013年Landsat MSS/TM/ETM+/OLI影像作为数据源,分析35年来官厅水库消落带的消涨特征、时空分布差异及其变化趋势,在此基础上进行消落带淹水时长和淹水频次的分区研究,揭示消落带生态结构的形成过程。研究结论如下:(1)近35年来,官厅水库水位落差较大,达8.19m,水位变化分为3个特征时期:1979—1996年,涨落周期约为4—5a的间歇涨落期;1996—2007年,水位持续下降达7.12m的持续萎缩期;2007—2013年,涨落周期为2 a,且年际变化差稳定在0.75m的频繁涨落期。(2)35年来,官厅水库水位消涨形成118.31km~2的消落带,对应3个特征时期形成消落带的面积依次为80.20km~2,76.81 km~2和19.89km~2。间歇涨落期形成的消落带主要分布在永定河河口及平坦的康西草原一带;持续萎缩期的消落带有明显向西北河岸带扩张的趋势;频繁涨落期的消落带以库心区域水位回升为主,面积仅19.89 km~2。(3)1979—2013年,基于淹水累计时长的分区中,消落带整体上表现为淹水累计时长随边岸向库区中心逐渐递增的趋势,25.85%的消落带淹水时长不足5a,71.77%的消落带淹水时长大于16 a,但随着淹水时长减少,消落带区域植物旱化现象突出,同时植被群落盖度和多样性降低。淹水频次分区中,相同淹水频次的区域在空间上离散分布,一次淹水区面积为32.79km~2,在消落带中所占比例优势明显,但累计淹水时长差异同样显著,分别为2 a和26 a,淹水最为频繁的消落带共经历了9次淹水过程;分区中的土壤有机质含量差异表明,淹水频次越高越有利于土壤有机质的积淀。

Analysis of fluctuation characteristics and subzone in hydro-fluctuation belt in the Guanting Reservoir during 1979-2013

As an important transition ecozone, hydro-fluctuation belt is known to be the key area to find the function mechanism between all kinds of ecological factors. We selected the Guanting Reservoir, a large inland reservoir in North China, as the research area. Based on the monthly and annual water level statistic characteristics during 1979-2013 and synchronous Landsat MSS/TM/ETM⁺/OLI image acquired in wet and dry seasons, we first analyzed the spatial and temporal distribution characteristics and its variation trend. Thus based on the water level fluctuation history, using transect sample and overlay analysis, we quantitatively discussed the flooding frequency and duration in hydro-fluctuation belt; moreover, based on the flooding times and years, we explored subzone in hydro-fluctuation belt. It was found that:(1) during1979-2013, the water level in the Guanting Reservoir dropped significantly up to 8.19m. The changing process of hydro-fluctuation belt could be divided into three stages:the intermittent fluctuation period during 1979-1996 with a 4-5-year fluctuation cycle; the shrinking period from 1996 to 2007, whose water level continued to drop to 7.12m; and the frequent fluctuation period during 2007-2013 with a 2-year fluctuation cycle and its inter-annual variability settled to 0.75m.(2)For the last 35years, 118.31km² area of hydro-fluctuation belt was formed because of water level fluctuation. The areas that formed during the three characteristic periods were 80.20km², 76.81 km², and 19.89 km², respectively. The hydro-fluctuation belt that formed in the intermittent fluctuation period was located in the Yongding River Estuary and the flat Kangxi prairie influenced by inflow water and terrain. In the shrinking period, the hydro-fluctuation belt showed an obvious trend of extension to the northwest riparian zone and was formed by water level rising during the frequent fluctuation period. (3)From 1979 to 2013, 25.85% of riparian flooded duration was less than 5 years, and 71.77% of riparian flooded duration was greater than 16 years, which show the obvious characteristics of wetland in the Guanting Reservoir. Furthermore, with the decrease of flooding time, the drought phenomenon of plant was outstanding, and the community coverage and diversity decreased. In the partition of flood frequency, the region with the same flood frequency was distributed discretely in space. Moreover, differences of soil organic matter content in partitions that show higher flooding frequency distribution present a discontinuous status, and regional soil organic matter content shows that precipitation was conducive to soil organic matter.