黄河下游灌区土壤碳储量及碳密度分布

Storage and Spatial Distribution of Soils Carbon in Lower Reaches of the Yellow River Irrigation District

土壤碳（C），特别是土壤有机碳（SOC），对于提高作物产量和减少温室气体排放具有重要影响，深入理解 SOC 空间分布特征对于未来区域生态环境和农业的可持续发展也具有重要作用。黄河下游引黄灌区是我国重要的粮、棉生产基地，具有50年以上的引黄灌溉历史，长期引黄灌溉对区域土壤C储量和分布的改变毋庸置疑。以往关于土壤C的估算多集中于较大尺度，受采样数据量和大区域环境因素复杂变异影响，结果经常出现较大差异，并且对于大型水利灌溉对土壤 C 分布的长期影响研究较少，尤其对于我国黄河下游引黄灌区土壤 C 分布的研究稀缺。本文通过收集黄河下游鲁、豫灌区相关统计资料，灌区土壤、水文资料等，分7层（0～5 cm、5～10 cm、10～20 cm、20～40 cm、40～60 cm、60～80 cm、80～100 cm）采集0～1 m剖面土壤样品，利用GIS空间差值、空间统计方法，分析不同土层、土地利用、土壤类型碳储量和碳密度（CD）空间分布特征，为研究区长期引黄灌溉条件下生态农业的发展提供依据。结果表明研究区（面积54153 km2）1 m土层总碳（TC）储量为1045.13 Tg，SOC储量达815.76 Tg，其0～20 cm，20～40 cm，40～60 cm，60～80 cm和80～100 cm分别占23.44%，20.06%，18.95%，18.83%，18.72%。估算1 m土层耕地和荒地SOC储量分别约为610 Tg和18.99 Tg，而草地和林地仅为25.97 Tg和16.41 Tg；不同土壤成土类型之间，半水成土所占的比例最大（约77.82%），初育土最小（约5.49%）。1 m土层平均总碳密度（TCD）为（19.37±1.48） kg·m^-2，而平均有机碳密度（SCD）为（15.12±1.14） kg·m^-2，其变化范围从荒地的（14.98±0.91） kg·m^-2到林地的（16±1.15） kg·m^-2，同一或不同土地利用类型各层储量变化略有不同，主要是受人类活动、植被凋落物输入以及地下水环境等影响。不同的土壤类型间SCD则介于盐碱土（14.76±0.81）kg·m^-2与半淋溶土（15.22±1.01）kg·m^-2之间，黄河泥沙沉积和地表、地下水循环决定研究区成土环境和成土过程，不同土壤类型C储量值受其影响较大。研究区平均SCD高于全国（9.60 kg·m^-2）和全球（10.6 kg·m^-2）平均水平，但相比其他地区，SCD垂直变异低。

Soil carbon, particularly the organic form （SOC）, exerts an important role in crop production and the mitigation of greenhouse gas emissions. So a better understanding of SOC storage and the variability in SOC distribution will contribute a lot to＆amp;nbsp;sustainable development of regional ecological environments and agriculture. As an important grain and cotton production base, the Yellow River irrigated district has irrigation history of more than 50 years, and there is no doubt that long-term irrigation has changed in regional soil C storage and distribution. Previous study on soil C estimates are more conducted in larger scale, and the results often appear quite different due to the amount of sampling and the complexity of the regional variation in environmental factors, moreover there are less studies concerning to long-term influence of large-scale irrigation on soil C distribution, particularly in the lower Yellow River irrigated district. In this study, we collected relevant statistical data, soil and hydrological data and so on, taken samples from 7 layers of soil with a depth of 1 m （0~5 cm、5~10 cm、10~20 cm、20~40 cm、40~60 cm、60~80 cm、80~100 cm）, using GIS spatial interpolation and spatial statistical methods, aimed at generalizing C storage and soil carbon density （CD） distribution characteristics in different depth or under different land uses and different soil types, so as to providing the basis for the development of ecological agriculture under long-term irrigation conditions in the study area. The study results are as follows：total carbon storage （TC） to 1 m soil depth was 1 045.13 Tg, and soil organic carbon storage （SOC） amounted to 815.76 Tg, with proportions of 23.44%, 20.06%, 18.95%, 18.83%, and18.72%held at soil depths of 0~20 cm, 20~40 cm, 40~60 cm, 60~80 cm, and 80~100 cm respectively. Estimated SOC in cultivated and uncultivated lands were approximately 610 Tg and 18.99 Tg respectively, while grassland and forested land held just 25.97 Tg and 16.41 Tg respectively. C storage in different depth layer changes slightly under the same or different land uses, mainly due to human activities, vegetation litter inputs and influence of groundwater environment. Among different kinds of soil type, semihydromorphic soils accounted for the largest proportion （about 77.82%） of total storage, while entisoils accounted for the smallest （about 5.49%）. Average total carbon density （TCD） was （19.37±1.48） kg·m^-2 to 1 m depth, while average soil organic carbon density （SCD） was （15.12±1.14） kg·m^-2, and ranged from （16±1.15） kg·m^-2in forested land to （14.98±0.91） kg·m^-2 in waste land. As to different kinds of soil type, SCD ranged from （14.76±0.81） kg·m^-2 of saline-alkali soil to （15.22±1.01） kg·m^-2of semi-luvisols. The SCD of different soil types was largely affected by formation environment and formation process of soil which was determined by Yellow River silt deposition and surface and groundwater circulation. Average SCD was higher than both the national average （9.60 kg·m^-2） for China and the planet as a whole （10.6 kg·m^-2）. However, SCD vertical variability was less apparent compared to other geographical regions.