With the development of the binary structure of karst landforms, surface water is largely drained with rapid loss of nutrients. However, the pathway and mechanism of nutrient loss remain elusive. From a three-dimensional (vegetation-soil-epikarst system) perspective of a critical zone in karst area, this study conducted rainfall induced runoff and nitrogen loss monitoring during monsoon in karst shrub slopes. Isotope-based (D and 18O) hydrograph separation method was applied to partition the ratio of 'old' and 'new' water in main hydrological path. The main results were summarized as follows. Deep percolation and interflow were the dominant hydrological pathways, accoun-ting for 71% and 9% of total rainfall amount, respectively. In contrast, surface runoff occupied less than 2%. Both deep percolation and interflow were dominated with 85% and 61% of old water, respectively. The highest nitrate concentration occurred in deep percolation (1.97 mg·L-1), while the highest ammonium nitrogen concentration occurred in interflow (1.18 mg·L-1). Deep percolation contributed 89.4% of total nitrogen loss, which was significantly higher than that of surface runoff and interflow. Old water ratio showed a significant positive correlation with nitrate nitrogen concentration, ammonium nitrogen concentration, and total nitrogen loss, suggesting it might be the main agent driving nitrogen migration for the whole soil-epikarst system in karst hillslopes. The results would provide scientific basis for rational allocating water resources and developing nutrient loss control technology in karst region of southwestern China.喀斯特二元结构发育,地表水大量漏失,养分表现出快速流失的特点,然而养分流失的途径和机制尚不清楚.本研究从喀斯特关键带三维空间的视角,通过监测喀斯特灌丛坡地雨季典型降雨产流和氮素流失特征,基于氢氧稳定同位素技术对主要水文路径“新旧水”比例进行划分,并探讨氮素流失的主要途径和机制.结果表明:深层渗漏和壤中流是喀斯特灌丛坡地主要水文路径,两者分别占降雨量的71%和9%,地表径流仅占2%;深层渗漏、壤中流均以“旧水”为主,“旧水”比例分别为85%、61%;硝态氮浓度在深层渗漏中最高(1.97 mg·L-1),铵态氮浓度在壤中流中最高(1.18 mg·L-1),深层渗漏对氮素流失的贡献率达89.4%,显著高于地表径流和壤中流;“旧水”比例与硝态氮、铵态氮浓度和流失总量均表现出显著正相关关系,“旧水”可能是喀斯特坡地土壤-表层岩溶带系统携带氮素迁移的主要介质.以上研究能够为西南喀斯特地区坡地水资源合理配置和养分流失阻控技术研发提供理论支撑.
The microorganisms in permafrost could live in cold environment through the coadapted physicochemical process,which exists between microorganisms in permafrost and permafrost environment.In this paper,the relation between microbial number and soil physicochemical properties of permafrost at different depths at the headwaters of the urumqi River is analyzed by using fluorescence microscopy counting and oligo-culture techniques.Totally,20 samples from a 200-cm permafrost core were used as study materials.It is found that the number of cultivable bacteria has a significant positive correlation with soil water content,total carbon and total nitrogen concentrations,and a significant negative correlation with pH value.Meanwhile,the ratio of cultivable bacteria to total cell number decreases with depth.The results demonstrate that the number of cultivable bacteria in permafrost is closely correlated with soil physicochemical properties and depositional age.
By the methods of geostatistics, this paper studied the spatial structure and distribution pattern of surface soil (0 - 5 and 5 - 10 cm) moisture content in the depression area of karst region in northwest Guangxi under moist and arid conditions in the forepart of dry season. The results showed that in test area, surface soil moisture content had obvious spatial heterogeneity and anisotropy, presenting a significantly different plaque distribution pattern. Under moist condition, surface soil moisture content had a medium or stronger spatial relativity, with a range of about 33.15 and 15.75 m, respectively, and an obvious trend effect in 0 - 5 cm soil layer. Under arid condition, the spatial relativity was strong, and the spatial scale of resembling plaque had somewhat decrease, with the smallest range being 8.22 m. The moisture content under arid condition had a higher spatial variability, and thus, the sampling strategy should be based on the mean soil moisture content. The significant difference in the spatial variability and distribution pattern of surface soil moisture in test area was mainly due to the effects of physiognomy, soil mean moisture (precipitation), and topography.
Abstract In order to reveal the spatial distribution and pollution characteristics of heavy metals in surface water and sediment of Nanchang section of GanJiang River in JiangXi Province, potential ecological hazard index method and ground accumulation index method were used to evaluate the risk of heavy metals. The results show that: 1) The concentration of heavy metals in surface water of GanJiang River is much lower than the first standard limit of “Surface Water Environmental Quality Standard GB3838-2002”. 2) The average RI value of sediment in Nanchang section of GanJiang River is 144.21, and the total ecological risk level is very high. The RI of two sections of Bayi Bridge are 169.89 and 192.38, respectively, which have become potential ecological high-risk areas. 3) According to the method of accumulative index, the pollution degree of heavy metals in GanJiang River is as follows: Cu > Cd > Pb > As > Cr > Zn. Among them, Cu and Cd are the main pollutants. Relevant departments should take urgent measures to strengthen the environmental management and pollution control of GanJiang River.
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