官厅水库消落带土壤有机质空间分布特征

消落带土壤由于在水陆交替的特殊生境和复杂的地球化学共同作用下形成,具有独特的理化性质和生态功能。各营养盐含量在时间和空间上具有较高的变异性,土壤中有机质的分布及迁移和转化均受到复杂的影响。针对官厅水库流域上游妫水河段消落带,选择典型消落带落水区,对该区土壤有机质含量的时空分布特征进行研究。结果表明:1)研究区消落带土壤有机质含量较为贫瘠,变化范围在1.64-26g/kg之间,平均值仅为13.16g/kg,变异系数达50.59%。说明消落带由于季节性干湿交替的特殊水文条件的影响,土壤养分的分布具有较高的空间异质性。淹水频繁区有机质含量平均值为15.74g/kg,高于长期出露区的10.12g/kg,且变异系数为41.38%,小于长期出露区的54.98%。说明淹水频繁区对土壤养分的持留能力更强,且周期性的淹水条件使得研究区近岸具有相似的生境类型,不同采样点土壤有机质含量的差异相对较小。2)不同植物群落下,芦苇和香蒲群落土壤有机质含量最高,平均值为17.08g/kg;含量最低的是以小叶杨和白羊草为主的中旱生植物带,平均值为9.12g/kg;其次是酸模叶蓼、大刺儿菜为优势物种的湿生植物带,土壤有机质含量平均值为15.49g/kg。3)不同土壤层次有机质含量差异较大,总体变化趋势均由表层向下逐渐减少,各层之间体现出显著差异性(P0.05)。研究区土壤C/N变化范围在1.64-18.95,平均值为8.95。说明研究区土壤碳氮比相对较低,有机质的腐殖化程度较高,且长期出露区土壤有机质更容易发生分解,C的累积速度远小于N。土壤C/N垂直分布大致呈先增大后减小趋势,在30cm处达到最大值,而后随着土壤深度的增加逐渐减小。4)消落带土壤有机质分布的影响因素分析中,土壤有机质与全磷呈极显著正相关,相关系数为0.62(P0.01);与土壤全氮和C/N呈显著正相关(R=0.57,0.60;P0.05)。这说明研究区土壤全磷、全氮、C/N和有机质明显具有相同的变化趋势,和有机质存在相互影响。其次,土壤有机质和湿度在呈显著负相关(R=-0.51;P0.05),表明研究区土壤湿度对有机质含量具有显著的影响。气候因子中,温度对研究区土壤有机质的分布具有显著的影响,相关系数为-0.51(P0.05)。植被因子中,植被覆盖度和土壤有机质含量呈显著正相关,相关系数为0.64,表明植被因子也是影响土壤有机质分布的重要因素之一。

Spatial distribution characteristics of organic matter in the water level fluctuation zone of Guanting Reservoir

The soil in the water level fluctuation zone (WLFZ) has specific particularly physical and chemical properties as well as ecological functions because it is generated in a special hydrological environment. The nutrient content of the soil has a high level of variability in time and space. Therefore, the distribution, migration and transformation of organic matter (OM) are under complex influences. In the present study, a typical WLFZ in Guanting Reservoir, and the temporal and spatial distribution characteristics of OM content in the soil, were analyzed. Results showed that the OM content of WLFZ soil in Guanting Reservoir was fairly low, and changed in the range of 1.64-26g/kg, with an average value of 13.16g/kg. The coefficient of variation was 50.59%, which showed that the distribution of soil nutrients in the WLFZ had higher heterogeneity, because of the dry-wet alternate hydrological conditions and human activities. The OM content of the frequent flooding area was 15.74g/kg on average, which was higher than the contrasting long-term exposed area at 10.12g/kg. The coefficient of variation was 41.38% in the frequent flooding area, which was lower than in the control zones that were 54.98%. This indicated that the soil nutrient retention ability in the frequent flooding area was stronger, and differences of soil OM between different sampling points were relatively small. Under different plant communities, the OM content of Phragmites australis and Typha angustifolia emergent communities was the highest, with an average value of 17.088g/kg; the lowest content was in Populus simonii and Bothirochloa ischaemum mesoxerophytes communities, which had an average value of 9.12g/kg. The Polygonum Lapathifolium and Cirsium setosum hygrophyte communities were second highest, with an OM average value of 15.49g/kg. In different soil depths, the OM content varied, with an overall decreasing trend from the surface downward. The OM of each soil layer showed significant differences (P < 0.05). The soil C/N changed in the range of 1.64-18.95, with an average value of 8.95. This demonstrated that the C/N of the study area was relatively low, the OM had a high degree of humification, organic nitrogen tended to accumulate, there was greater potential of soil anaerobic decomposition to produce CH₄ and CO₂. In the vertical distribution, C/N first increased and then decreased as the depth of the soil profile changed, and reached the maximum value at 30cm deep. Soil OM and total phosphorus, total N, and C/N were significantly positively correlated, with coefficients of 0.62 (P < 0.01), 0.57, and 0.60 (P < 0.05), respectively. This showed that the soil OM, total phosphorus, total N, and C/N had similar change trends, and experienced interaction. Soil OM and moisture were negatively correlated (R=-0.51) at the 0.05 significant P-value, indicating that soil moisture in the study area had a significant impact on the OM content. Temperature had a significant influence on the distribution of soil OM in the study area, the correlation coefficient was -0.508, significance level P=0.031. Vegetation cover and soil OM content was significantly positively related, indicating that the vegetation factor was also an important factor affecting the distribution of soil OM.