摘要
荒漠地区包气带中的Cl^-、NO_3^-与生态环境有密切联系,与地下水安全有直接联系。主要以荒漠地区包气带Cl^-、NO_3^-为研究对象,通过对Cl^-、NO_3^-在包气带及不同土壤类型中的分布特征进行研究,表明强烈的蒸散发作用使Cl^-、NO_3^-呈活塞式分布,同时植物对水分的吸收以及对NO_3^-的优先吸收使NO_3^-表现出不同的分布特征。土壤中的NO_3^-可能被植物优先吸收并遵循营养循环,使表层土壤中出现极大值,随后逐渐减小。靠近表层土壤出现NO_3^-峰值和较高的NO_3^-/Cl^-原子比率反映了蓝藻菌活跃的固N作用;相对较大的NO_3^-/Cl^-原子比率伴随着较低的Cl^-说明在干旱地区稀疏的植被覆盖条件限制了对NO_3^-的吸收作用。不同的土壤类型中,Cl^-、NO_3^-表现出不同的分布特征,在粘性土壤中,NO_3^-、Cl^-浓度随含水率的减小而减小。
Chloride and nitrate, as a conservative and a semi-conservative ion, have been used to examine the re- charge history, reconstruct the related climate change and vegetation transitions and so on in the cold-arid desert re- gion of northwest China. In general, they always transport with rainfall in the soil, even though the nitrate always takes part in plenty of bio-chemical reactions. And soils are crucial to the functioning of the Earth system, since they are at the interface between the atmosphere, lithosphere, hydrosphere and biosphere, and influence terrestrial net primary production, climate regulation, and water quality. So revealing the spatial distribution of the dissolved chlo- ride and nitrate is favor to prohibit the potential water contamination caused by nitrate leaching from upwards, and to understand the impacts on the desert ecosystem. The water content and nitrate and chloride concentrations with the NO3-/C1- were measured in different profiles and different soil types in verticality. It was found that the distributions of Cl-, NO3- tend to be piston oscillations as a result of the severe evapotranspiration. The average concentrations of C1- increase from 35 mg/L to 6 545 rag/L, with the maximum rising from 41 mg/L to 9 592 mg/L, correspondingly. Meanwhile, the average concentrations of NO3- range from 8 rng/L to 1 227 mg/L, and the average NO3-/C1- molar ra- tios are between 0.03 and 1.75. The relatively higher NO3- concentration in Wuwei and Minqin areas, especially in the profiles WW1, WW3, MQ1, may demonstrate the effects of the anthropogenic inputs. And the declines of the NO3-/Cl- molar ratios from east to west may be due to the decrease of the rainfall from southeast to northwest in the area. Plant＇ s taking-up of moisture and nitrate preferentially makes the nitrate distribute differently in vadose zone. The presence of peaks in the nitrate profiles is probably proportional to the preferential taking-up of nitrate and due to be coincidence with the nutrient profile, which leads the concentration of nitrate to decline sharply with the soil depth. The near surface peaks in NO3- with higher NO3-/Cl- molar ratios reflect active modem N-fixation by cyano- bacteria. The higher NO3-/Cl- molar ratios are consistent with the bulge shaped CI-, which probably indicates that rel- atively less vegetation coverage in the drought environment plays a limiting role in the uptake of nitrate. The charac- teristics of chloride and nitrate tend to be distinct in different soil types .The piston distribution of chloride and ni- trate in the sand soil, which has a great conductivity and inferior water binding capacity, attributes to the plant taking in the nitrate within its cycling in the soil along with intensive evapotranspiration, while the concentration of chloride and nitrate in the clay soil decreases with the moisture content.
出处
《干旱区地理》
CSCD
北大核心
2013年第3期409-415,共7页
Arid Land Geography
基金
国家创新群体科学研究基金项目(40421101)
科技部“973”项目的课题(2009CB421306)
