三峡库区水位消涨对杉木溪消落带土壤性质的影响

为了准确揭示杉木溪消落带土壤养分及其空间分布对三峡库区水位消涨及其所带来的环境变化的响应,2014年研究了5个完整水位消涨周期的不同海拔梯度和土层深度土壤。沿海拔梯度分别在150、155、160、165、170、175 m处各设置1个样带,180 m处设置1个对照样带,每样带设置5个样方,在各样方内选取4个角及中心点共5个样点,用土壤采集器分别在0~5、5~10和10~15 cm土层分层采集土样。结果表明,在水位消涨的作用下,消落带土壤养分含量显著下降,有机质、全氮和全磷含量与非消落带土壤相比分别减少了14.55%、20.00%和26.12%,土壤p H值则显著增加。水位消涨还导致消落带土壤养分随海拔梯度呈显著的空间变化。其中,有机质、全氮和全钾含量以中部消落带土壤的含量最高,全磷含量则以中下部消落带土壤的含量最高,而土壤p H值随着海拔梯度的减少而增加。消落带和非消落带土壤养分在不同土层之间有着显著差异,有机质、全氮、全磷含量随土壤的加深而显著减少。在水位消涨的影响下,消落带表层土与下层土有机质和全氮含量的差异显著减少,而全磷和全钾含量的差异则有所增加。

Response of Soil Nutrient Levels and Spatial Distribution to Water-level Fluctuation on the Shanmu Riverbanks in the Three Gorges Reservoir Area

The Three Gorges Project has changed the natural rhythm and range of water level fluctuations in the reservoir area, forming a 440 km2 water-level fluctuation zone at elevations from 145-175 m. The rhythm of water-level variation has been reversed, from high in summer and low in winter to low in summer and high in winter. The rapid reversal in rhythm and range has significantly influenced soil properties in the fluctuation zone. To determine the response in soil nutrient levels and spatial distribution to these disturbances, a case study of soil along Shanmu River tributary of Three Gorges Reservoir was carried out in 2014, when five water-level fluctuation cycles had occurred after impoundment reached 175 m in 2009. Soil samples in the water-level fluctuation zone of Shanmu River were collected at seven elevations (150, 155, 160, 165, 170, 175 and 180 m) and at three soil depths (0-5 cm, 5-10 cm and10-15 cm). The samples were analyzed for pH, organic matter, total phosphorus, total nitrogen and total potassium. Results show that soil nutrients decreased significantly under the influence of water-level fluctuation; organic matter, total nitrogen and total phosphorus decreased by 14.55%, 20.00% and 26.12%, respectively, compared to soil outside the fluctuation zone, while soil pH increased significantly. Water level fluctuations also caused significant changes in the spatial variation of soil nutrients with elevation. The highest levels of organic matter, total nitrogen and total potassium occurred in the mid-elevation soils of the fluctuation zone, while total phosphorus content was the highest in the mid- to lower elevations. Soil pH increased as elevation decreased. Nutrient depth profiles also changed significantly. While soil organic matter, total nitrogen and total phosphorus decreased significantly with soil depth both inside and outside the fluctuation zone, water-level fluctuation decreased the differences in soil organic matter and total nitrogen between surface and bottom soils, but increased the difference in total phosphorus and potassium. The total phosphorus, potassium and pH of soil in the fluctuation zone were significantly related to the elevation, but soil organic matter and total nitrogen were not. With soil depth, there was a significant positive correlation with soil pH and a significant negative correlation with organic matter, total nitrogen and total phosphorus.