A methodology for assessing the maximum expected radon flux from soils in northern Latium (central Italy)

Northern Latium (Italy) is an area where the Rn risk rate is potentially high because of the extensive outcropping of Neogene U-rich volcanics and the presence of major active tectonic lineaments. The lack of data on Rn risk rates in that area, which is undergoing major urban and industrial development, has prompted this study. It proposes a methodology to evaluate the maximum potential diffusive Rn flux from soils based on the measurement of ²²⁶Ra, ²³²Th and ⁴⁰K activities by γ-ray spectrometry, and the measurement of main soil parameters influencing the Rn emanation. This methodology provides a simple, reliable and low-cost tool for drawing up radon flux maps useful to both public planners and private individuals, who want to operate safely in the study area. The proposed methodology may also be applied to other geographic areas outside the prescribed study area.     

地表UV-B辐射增强对土壤-冬小麦系统N2O排放的影响机理研究

为了解UV-B增强条件下农田N₂O响应规律,采用室外盆栽实验,研究了地表UV-B辐射增强20%对土壤-冬小麦系统N₂O排放的影响及其影响机理.结果表明,在小麦返青期,UV-B辐射增强处理对该系统N₂O的排放影响不显著;在小麦的拔节期,UV-B辐射增强处理显著降低了土壤-小麦系统N₂O的排放,并减少了该系统的呼吸速率.UV-B辐射增强对N₂O的影响机理主要表现在对小麦植株N代谢过程的影响,如显著增加     

DNAPL source depletion: linking architecture and flux response

The relationship between dense non-aqueous phase liquid (DNAPL) mass reduction and contaminant mass flux was investigated experimentally in four model source zones. The flow cell design for the experiments featured a segmented extraction well that allowed for analysis of spatially resolved flux information. This flux information was coupled with image analysis of the NAPL spatial distribution to investigate the relationship between flux and the up-gradient NAPL architecture. Results indicate that in the systems studied, the relationship between DNAPL mass reduction and contaminant mass flux was primarily controlled by the NAPL architecture. A specific definition of NAPL architecture was employed where the source zone is resolved into a collection of streamtubes with spatial variability in NAPL saturation along each streamtube integrated and transformed into an effective NAPL content for each streamtube. The distribution of NAPL contents among the streamtubes (NAPL architecture) controlled dissolution dynamics. Two simplified models, a streamtube model and an effective Damkohler number model, were investigated for their ability to simulate dissolution dynamics.     

Dissolution kinetics of high explosives particles in a saturated sandy soil

Solid phase high explosive (HE) residues from munitions detonation may be a persistent source of soil and groundwater contamination at military training ranges. Saturated soil column tests were conducted to observe the dissolution behavior of individual components (RDX, HMX, and TNT) from two HE formulations (Comp B and C4). HE particles dissolved readily, with higher velocities yielding higher dissolution rates, higher mass transfer coefficients, and lower effluent concentrations. Effluent concentrations were below solubility limits for all components at superficial velocities of 10-50 cm day(-1). Under continuous flow at 50 cm day(-1), RDX dissolution rates from Comp B and C4 were 34.6 and 97.6 microg h(-1) cm(-2) (based on initial RDX surface area), respectively, significantly lower than previously reported dissolution rates. Cycling between flow and no-flow conditions had a small effect on the dissolution rates and effluent concentrations; however, TNT dissolution from Comp B was enhanced under intermittent-flow conditions. A model that includes advection, dispersion, and film transfer resistance was developed to estimate the steady-state effluent concentrations.     

Characteristics of an Ozone Deposition Module

An ozone deposition module is being developed to allow the estimation of stomatal fluxes of ozone into a number of vegetation types. This model is designed to be linked into a regional chemical-transport model for use within the European Monitoring and Evaluation Programme (EMEP), to provide information on possible risks to vegetation across Europe. This paper investigates some characteristics of this deposition module, for sites in very different climate zones. The model results suggest that both stomatal and non-stomatal fluxes are comparable in magnitude.     

Inertial oscillations and particle flux interactions in a marine protected area in Gulf of Naples

The area between the island of Capri and Punta Campanella was investigated from June to November 2003. Punta Campanella separates the Gulf of Naples from the Gulf of Salerno and has been declared a marine protected area in 1997. The study area has a particular interesting topography, due to the presence of a sill situated at a depth of 80 m. Samples were collected by instruments carried on a mooring array (sediment trap, current meters, and temperature sensors) and by CTD cast (along transects perpendicular to the coast). We observed most important fluctuations in the temperature spectra (corresponding to the inertial oscillations period), in August. The total mass flux was 585.67 mg m^-2 d^-1 in the summer, while in early autumn the flux exhibited values one order of magnitude higher than in summer (1539.97 mg m^-2 d^-1). The main focus of this study was to understand the influence of the internal waves on the particle flux. During the autumn, in the particle flux collected, there is a strong resuspension component, and the observation that the enhanced inertial oscillations and increased sedimentation occur at the same time allows us to presume that the inertial oscillations could be one of the reasons for the resuspension process during the sampling period.     

Net ecosystem CO2 exchange over a larch forest in Hokkaido, Japan

Larch forests are distributed extensively in the east Eurasian continent and are expected to play a significant role in the terrestrial ecosystem carbon cycling process. In view of the fact that studies on carbon exchange for this important biome have been very limited, we have initiated a long-term flux observation in a larch forest ecosystem in Hokkaido in northern Japan since 2000. The net ecosystem CO₂ exchange (NEE) showed large seasonal and diurnal variation. Generally, the larch forest ecosystem released CO₂ in nighttime and assimilated CO₂ in daytime during the growing season from May to October. The ecosystem started to become a net carbon sink in May, reaching a maximum carbon uptake as high as 186 g C m⁻² month⁻¹ in June. With the yellowing, senescing and leaf fall, the ecosystem turned into a carbon source in November. During the non-growing season, the larch forest ecosystem became a net source of CO₂, releasing an average of 16.7 g C m⁻² month⁻¹. Overall, the ecosystem sequestered 141–240 g C m⁻² yr⁻¹ in 2001. The NEE was significantly influenced by environmental factors. Respiration of the ecosystem, for example, was exponentially dependent on air temperature, while photosynthesis was related to the incident PAR in a manner consistent with the Michaelis–Menten model. Although the vapor pressure deficit (VPD) was scarcely higher than 15 hPa, the CO₂ uptake rate was also depressed when VPD surpassed 10 hPa.     

Methane emission characteristics and its relations with plant and soil parameters under irrigated rice ecosystem of northeast India

Methane flux from rice varieties grown under two identical soils of Assam were monitored. In the first experiment, variety Jaya and GRT was grown in sandy loam soil of Lower Brahmaputra Valley Zone of Assam and the second experiment was conducted with variety Jyotiprasad and Bishnuprasad in sandy to sandy loam soils of Upper Brahmaputra Valley Zones of Assam. Methane flux recorded from variety Jyotiprasad and GRT was higher compared to variety Bishnuprasad and Jaya. The seasonal integrated flux recorded was 10.76 g m⁻², 9.98 g m⁻², 9.74 g m⁻² and 11.31 g m⁻² for variety GRT, Jaya, Bishnuprasad and Jyotiprasad, respectively. All the varieties exhibited two methane peaks one at maximum tillering stage and other at panicle initiation stage of the crop. Crop growth parameters such as leaf number, number of tillers and leaf area index (LAI) showed strong positive relationship with total methane flux. In both the experiments it was calculated that CH₄ emission was substantially influenced by crop phenology and growth. This study emphasise the relationship of different growth parameters with methane emission.     

鄱阳湖典型洲滩湿地植物根系对水分垂向通量的影响

为了定量揭示湿地植物根系的水文效应,采用全物理机制的土壤水分运移数值模型,以鄱阳湖吴城湿地国家自然保护区的茵陈篙群落为例,模拟分析根系引起的水文效应.结果表明,根系将增加土壤饱和含水量与土壤进气值,显著改变土壤水分特征曲线（SWRC）与土壤蓄水能力;在考虑根系影响SWRC下模拟率定的土壤含水量与观测数据的时空变化一致：模型10和50cm观测值与拟合值相关系数由不考虑根系效应下的0.83提高至0.85,10和50cm深度土壤含水量的实测值与模拟值的均方根误差分别减少61%和83%.同时这种率定方法下的模拟相比以往的研究地下水补给根系层水量提高34%;考虑典型的根系效应蒸散发量和累积地下水边界向上通量分别增加10%和150%.而在气候极端干旱条件下地下水向上补给量在根系效应下增加7%~56%,累计差异可达38~312cm,同时蒸散发量增加13%.在植被生长旺季时若地下水埋深较深,则根系效应对蒸散发量的影响会放大.因此在进行相关的湿地生态水文过程和湿地水与物质平衡研究中,建议充分评估湿地植物根系的水文效应,并视计算的工况条件,考虑其水文效应在整个水文过程中的影响.