Approximating groundwater age distributions using simple streamtube models and multiple tracers

We use a streamtube based decomposition and a recently developed, simple relationship between tracer concentrations and ages to estimate groundwater age distributions. The decomposition assumes that an age distribution can be approximated using a superposition of linearly independent streamtubes. Transport in each streamtube is modeled with inverse Gaussian functions, the parameters of which are inferred from radiometric tracer concentrations. Three simple sampling methods are considered for weakly and moderately heterogeneous aquifers and the method gives reasonable approximations in both systems. The method is sensitive to errors in the measured concentrations but some of these errors are easily identifiable and a range of plausible age distributions can still be found. The method was then tested in a highly heterogeneous system and reasonable estimates of the age distribution were also obtained. The simplicity of this method and its insensitivity to the heterogeneity structure suggest that this approach may be an effective tool for obtaining estimates of age distributions in natural systems.     

ROAD SALT ACCUMULATION IN HIGHWAY SNOW BANKS AND TRANSPORT THROUGH THE UNSATURATED ZONE OF THE OAK RIDGES MORAINE,SOUTHERN ONTARIO

Pathways and fate of road deicing salt (NaCl) applied during the 1994–1995 winter were studied for a 14-km section of a major highway that crosses the Oak Ridges Moraine in southern Ontario. Total salt applications over the winter ranged from 29 to 74 kg m⁻¹ of highway, and NaCl concentrations in snow banks adjacent to the roadway reached 9400 mg l⁻¹ during the later stages of snow cover development. This salt was released to the ground surface during snowmelt. Sodium chloride (NaCl) loadings to soil from snow cover during the final melt phase were relatively uniform along the study section (3–5 kg NaCl m⁻¹ of highway). However, the snowpack at all transects retained <50% of applied NaCl, and this shortfall probably reflected direct runoff and infiltration of saline meltwater from the road surface into the adjacent shoulder and right-of-way. Cation exchange with Ca²⁺ in near-surface soils most likely resulted in preferential retention of Na⁺ relative to Cl⁻, although total storage of NaCl in upper soil horizons by winter's end was <15% of deicing salt applications. An environmental tracer (¹⁸O) was used to trace movement of saline meltwater through the unsaturated zone underlying the highway. Average meltwater particle velocities at a site underlain by loam soils were 0.02 m d⁻¹, and ca. 280 mm of water was displaced below a depth of 1.86 m over a 78-day period in the spring and summer of 1995. Sodium ion and chloride ion concentrations in water sampled in late summer 1995 at depths >2 m exceeded 500 mg l⁻¹ and 1000 mg l⁻¹, respectively. Approximately 75% of the net flux of NaCl below the upper soil was retained in the 0–2.8 m depth interval at this site, and results from more permeable soils traversed by the highway indicate an even greater penetration of the annual NaCl application into the unsaturated zone along the moraine. This saline water likely recharges groundwater in this portion of the Oak Ridges Moraine.     

Study on ann-based multi-step prediction model of short-term climatic variation

In the context of 1905-1995 series from Nanjing and Hangzhou, study is undertaken of establishing a predictive model of annual mean temperature in 1996-2005 to come over the Changjiang (Yangtze River) delta region through mean generating function and artificial neural network in combination. Results show that the established model yields mean error of 0.45℃ for their absolute values of annual mean temperature from 10 yearly independent samples (1986-1995) and the difference between the mean predictions and related measurements is 0.156℃. The developed model is found superior to a mean generating function regression model both in historical data fitting and independent sample prediction.     

人工智能和专家系统在测绘科学中的应用

讨论了人工智能和专家系统应用于测绘科学的优越性,分析了其在测绘科学中应用的主要内容,对其发展趋势进行了探讨。     

光滑强度包络线模型及其工程应用

三角函数级数法是人工地震合成常用的计算方法之一,但是利用这种方法计算速度时程时,却存在一定的零线漂移现象,并且对位移时程产生很大的影响。本文详细地分析了产生误差的原因,在此基础上,建立了光滑强度包络线计算模型,较好地解决了这一问题。通过工程实例计算证明,该计算模型是正确可行的。     

不同饵料及添加剂对中国对虾幼体的影响

在连续两年春季中国对虾育苗期间,采用几种不同的饵料－人工饵料为主、活饵料和两种强化饵料分别培育中国对虾幼体,以存活率、体长、体重、抗感染力的缺氧耐受力等指标检验育苗效果。结果表明,人工饵料为主的喂养方式各项指标均显著劣于活饵料;强化与未强化的活饵料效果相近;强化的人工饵料在体长和耐缺氧方面显著优于人工饵料,存活率略低于后者,增重和抗感染方面与后者相近。     

基于人工神经网络的地震活动性研究

人工神经网络通过神经元之间的相互作用来完成整个网络的信息处理,具有自学习和自适应等一系列优点,因而用它来进行地震活动性研究是可行的。针对地震活动性问题,初步建立了基于人工神经网络的计算分析系统,给出了应用实例。     

Characterizing the heterogeneity of karst critical zone and its hydrological function: An integrated approach

Spatial heterogeneity in the subsurface of karst environments is high, as evidenced by the multiphase porosity of carbonate rocks and complex landform features that result in marked variability of hydrological processes in space and time. This includes complex exchange of various flows (e.g., fast conduit flows and slow fracture flows) in different locations. Here, we integrate various “state‐of‐the‐art” methods to understand the structure and function of this poorly constrained critical zone environment. Geophysical, hydrometric, and tracer tools are used to characterize the hydrological functions of the cockpit karst critical zone in the small catchment of Chenqi, Guizhou Province, China. Geophysical surveys, using electrical resistivity tomography (ERT), inferred the spatial heterogeneity of permeability in the epikarst and underlying aquifer. Water tables in depression wells in valley bottom areas, as well as discharge from springs on steeper hillslopes and at the catchment outlet, showed different hydrodynamic responses to storm event rainwater recharge and hillslope flows. Tracer studies using water temperatures and stable water isotopes (δD and δ¹⁸O) could be used alongside insights into aquifer permeability from ERT surveys to explain site‐ and depth‐dependent variability in the groundwater response in terms of the degree to which “new” water from storm rainfall recharges and mixes with “old” pre‐event water in karst aquifers. This integrated approach reveals spatial structure in the karst critical zone and provides a conceptual framework of hydrological functions across spatial and temporal scales.     

Lessons from the 2018 drought for management of local water supplies in upland areas: A tracer-based assessment

Climate change, combined with industrial growth and increasing demand, could result in serious future water shortages and related water quality and temperature issues, especially for upland and humid areas. The extreme 2018 drought that prevailed throughout Europe provided an opportunity to investigate conditions likely to become more frequent in the future. For an upland rural catchment utilised by the distilling industry in North-East Scotland, a tracer-based survey combined discharge, electrical conductivity, stable water isotopes and temperature measurements to understand the impacts of drought on dominant stream water and industry water sources, both in terms of water quantity and quality (temperature). Results showed that water types (groundwater, ephemeral stream water, perennial stream water and water from small dams) were spatially distinct and varied more in space than time. With regards to the drought conditions we found that streams were largely maintained by groundwater during low flows. This also buffered stream water temperatures. Water types with high young water fractions were less resilient, resulting in streams with an ephemeral nature. Although our results demonstrated the importance of groundwater for drought resilience, water balance data revealed these storage reserves were being depleted and only recovered towards the end of the following year because of above average rainfall in 2019. Increased storage depletion under continued trends of extreme drought and water abstraction could be addressed via informed (nature based) management strategies which focus on increasing recharge. This may improve resilience to droughts as well as floods, but site specific testing and modelling are required to understand their potential. Results could have implications for management of water volumes and temperature, particularly for the sustainability of an historic industry, balancing requirements of rural communities and the environment.     

Particle transport in gravel-bed rivers: Revisiting passive tracer data

Data from tracer experiments were compiled and analysed in order to explore the role of geomorphological, hydrological and sedimentological constraints on fluvial gravel transport in gravel-bed rivers. A large data set from 217 transport episodes of tagged stones were compiled from 33 scientific papers. Our analyses showed that while magnitude of peak discharge is a major control on gravel transport and mobility, tracer travel distances show some scale dependence on the morphological configuration of the channel. Our results also highlight differences in the way tracers are displaced between step–pool and riffle and pool channels. The riffle–pool sequence seems to be a more efficient trap for travelling gravels than the step–pool pair. In addition, in step–pool channels there are clear differences in tracer transport between observations of first displacements after tracer seeding (unconstrained-stone conditions), and second and subsequent observations of tracer displacements (constrained-stone conditions). The comparison between tracer experiments under constrained conditions and those under unconstrained conditions also highlights the importance of bed state and structures in gravel mobility. The results of this study confirm that sediment transport in gravel-bed rivers is a complex process, whereby sedimentological and geomorphological controls are superimposed on the hydraulic forcing. © 2018 John Wiley & Sons, Ltd.