On the use of finite‐difference and neural‐network models to evaluate the impact of underground water overexploitation

The purpose of this study is to include expert knowledge as one part of the modelling system and thereby offer the chance to create a productive interactive system between expert, mathematical model, ASM, and artificial neural networks (ANNs). An attempt to determine outflow‐influencing parameters in order to simulate spring flow is presented. The Bouteldja dune aquifer is fed by rains and streaming water on the sandy argillaceous relieves in the Est. The lateral passage to the gravel of the Bouteldja Plain is marked by numerous bogs that correspond to the piezometric level. These bogs have long been an environment for migratory birds and a natural reserve for many species. However, the continued exploitation of about 30 wells has negatively influenced the hydrodynamic equilibrium of the aquifer and has brought a diminution of the sources' capacity. In this study, we tried by using a hydrodynamic model and the neural network to ascertain the state of the resources and to identify the factors responsible for the decreasing flows of the three principal springs of the area (Bougles, Bourdim and Titteri) by using neural networks. The results obtained show a continued exhaustion of the reserve since 1986 with a large cone of depression. The ANNs show that the decrease in flows of the springs is not only due to the unfavourable climatic conditions, but also to the intensive exploitation of the aquifer. These results show that the groundwater reserves are decreasing over time, thus highlighting the need to take some urgent measures to stop this phenomenon. Copyright © 2006 John Wiley & Sons, Ltd.     

The enhancing effect on tidal signals of a submarine spring connected to a semi-infinite confined aquifer

Abstract

Submarine springs play an important role in submarine groundwater discharge (SGD). To investigate the effects of these springs on the propagation of tidal signals in coastal confined aquifers, this paper considers a general coastal aquifer system with a submarine spring on the seabed where the length of the aquifer's offshore extent is finite and its submarine outlet is covered by an impermeable outlet-capping. An approximate analytical solution is obtained for describing the tidal head fluctuations in the aquifer. Solution analyses indicate that the error of the approximate analytical solution is negligible when both distances from the spring hole to the coastline and to the submarine outlet-capping are much greater than the radius of the spring hole. Sensitivity tests are conducted to investigate the effects of hydraulic properties, tidal and spring geometric configuration parameters on the tidal signal propagation in the inland aquifer. For aquifers with infinite offshore length, or without submarine springs, existing solutions in the literature are obtained. The comparison of groundwater head fluctuations for the cases with and without a submarine spring demonstrate the enhancing effect of the submarine spring on tidal signal propagation in the inland aquifer. Three situations that fit our model assumptions are given for future potential applications. A hypothetical example is used to show the possibility of identifying a spring's location using the present analytical solution together with tidal signals observed from inland wells.

Editor D. Koutsoyiannis; Associate editor Y. Guttmann

Citation Xia, Y.Q., Li, H.L., Yang, Y., and Huang, W., 2012. Enhancing effect on tidal signals of a submarine spring related to a semi-infinite confined aquifer. Hydrological Sciences Journal, 57 (6), 1231–1248.     

Environmental mercury and arsenic sources in fossil hydrothermal systems, Northland, New Zealand

 Northland, New Zealand has been affected by natural hot water spring systems depositing elevated concentrations of mercury and arsenic over the past 5 million years. Due to the different erosion levels of these hot water systems, four principal types of mercury and arsenic occurrences are found: active hot springs; layered surface deposits (sinters) deposited by hot springs; highly fractured rock zones formed immediately beneath hot springs; and chemically altered and mineralized rock from the deeper roots of hot spring systems. Mercury occurs principally as cinnabar and as a minor impurity (<1 wt%) in phosphate minerals and iron sulfides, particularly marcasite. Mercury is irregularly distributed through limonitic cements formed during oxidation. Arsenic occurs as a minor impurity (<1 wt%) in phosphate minerals and iron sulfides, particularly marcasite. Arsenic is also variably dispersed through limonite, but not necessarily with mercury. Decomposition of marcasite constitutes the most significant source of mercury and arsenic pollution from the studied sites. Release of mercury and arsenic into the environment from marcasite, phosphates and limonite is enhanced by acidification of the sites (down to pH of 2), caused by oxidation of iron sulfides. Mercury and arsenic concentrations of up to 100 parts per billion should be expected in waters near the deposits; these concentrations are in excess of recommended drinking water levels. Received: 9 April 1999 · Accepted: 2 August 1999     

Benthic life in karst spring—The life cycle and secondary production of benthic macroinvertebrates under the effects of constant water temperature

Because of the thermal stability and the persistence over geological time scales of their aquifers, the permanent karst springs may act as a glacial refuge, as well as serve as “in vivo” laboratories for the testing of various ecological hypotheses. For these reasons, our main hypotheses were: i) to the constant water temperature benthic species will response by specific voltinism and life-cycle length will be different from those that the species usually have in non-spring habitats; ii) under the constant water temperature the particular species and whole community will have higher biomass turnover like in similar non-spring habitats. Investigation was performed in large cave karst spring “Vyvieranie” in the Western Carpathians. In total, 40 species of benthic macroinvertebrates were identified in the studied karst spring. The trajectory of the annual change of the benthic community structure clearly showed a returnable pattern at the species density and biomass level. The constant water temperature throughout the year was reflected by specific life-history trajectories in certain benthic species. While some species had fixed voltinism (e.g. Ephemerella mucronata, Isoperla sudetica), others indicated having a flexible life-cycle pattern. In the species with a flexible life cycle, the trajectory of larval development occurred in two different ways. In the first case, a constant water temperature extended larval development (e.g. Protonemura auberti, Leuctra albida). In the second case, the addition of a winter cohort was recorded (e.g. Gammarus fossarum, Rhyacophila tristis, Protonemura austriaca). The productivity of this benthic community was considerably higher than that previously found in other submountain limestone streams in the Western Carpathians.     

邵武-河源断裂带活动性及分段评价

邵武-河源断裂带是东南沿海地震亚区的西界。这条闽、赣、粤3省边界活动性断裂带包含3条形态各异、特征不同的较大断裂带,北段为邵武(福建)-石城断裂带,中段为瑞金-寻乌断裂带,南段为龙川(广东)-河源断裂带。3条断裂带并非首尾衔接,而是呈右列式多字型排列,长约750km,在江西境内近400km(占全长53%)。本文侧重研究江西境内的构造特征、地震、温泉和地裂缝展布特征,探讨其活动性以及对地壳稳定性的影响。笔者认为,邵武-河源活动性断裂带引起大震的可能性非常小,但分散小震有可能发生.     

四川雅安周公2井地热水环境同位素的初步研究

四川雅安周公2井高温热矿水位于井深1800m以下,为赋存于三叠系雷口波组、嘉陵江组及二叠系茅口组碳酸盐岩地层中的岩溶水,盖层为侏罗系及上三叠统的碎屑岩层.初步测试关闭时井下压力3Mpa, 井口水温达75℃,流量约5000t/d.通过对热矿水的14C及U系法定年及其周围山区地表水氢氧同位素一次性采样及分析,研究结果表明,周公2井热矿水系大气降水成因,补给区可能为其西部及西南部山区,即荥经河、荥河、冷水河以及周公河流域,海拔高程大体在1500~2500m左右.盆地上部主要为第四系-侏罗系赋存于砂砾岩中的孔隙水,而盆地深部的热矿水则是山区降水沿断裂裂隙及岩溶管道垂直入渗经深循环至盆地底部,两者并无水力联系.     

Analyzing the formation cause of Xidatan drinking mineral springs in island permafrost area on north slope of the Kunlun Mountains

The replenishment source of Xidatan drinking mineral springs in island permafrost area on north slope of the Kunlun Mountains are mainly the melting water from the modern glaciers bottom, snow and ice melting water, atmospheric precipitation, and surface water in Yuzhu Peak area on the Kunlun Mountains. This scenario is based on the survey of hydrogeology, water-conducting and water-controlling faults, and water chemistry, and on the EH-4 high-frequency electronic deep exploration. The original water recharges the deep groundwater at fracture zone of active normal faults F3 and F4 , then groundwater enriches at normal faults F2 and F2-1,2 , and then run northward. A water-rich triangle area is formed when groundwater reach the active reverse fault F1 . Groundwater then discharges through fracture zone of F1 , which is the major cause of the Xidatan mineral springs formation.     

近30年中国东北地区玉米种植体系的时空动态分析(英文)

Understanding crop patterns and their changes on regional scale is a critical requirement for projecting agro-ecosystem dynamics. However, tools and methods for mapping the distribution of crop area and yield are still lacking. Based on the cross-entropy theory, a spatial production allocation model(SPAM) has been developed for presenting spatio-temporal dynamics of maize cropping system in Northeast China during 1980–2010. The simulated results indicated that(1) maize sown area expanded northwards to 48°N before 2000, after that the increased sown area mainly occurred in the central and southern parts of Northeast China. Meanwhile, maize also expanded eastwards to 127°E and lower elevation(less than 100 m) as well as higher elevation(mainly distributed between 200 m and 350 m);(2) maize yield has been greatly promoted for most planted area of Northeast China, especially in the planted zone between 42°N and 48°N, while the yield increase was relatively homogeneous without obvious longitudinal variations for whole region;(3) maize planting density increased gradually to a moderately high level over the investigated period, which reflected the trend of aggregation of maize cultivation driven by market demand.     

春小麦地和大气观测场土壤贮水量对比分析

通过青海省互助县1997~2002年大气观测场和春小麦地测定的0~50 cm土壤贮水量变化规律的对比分析得出:同一气候背景下,地形地势相同的不同场地不同植被0~50 cm土壤贮水量变化特征基本一致。大气观测场11月至次年2月(一般为土壤封冻期)土壤贮水量保持在25~27 mm间,变化较平稳,6~7月处于谷值阶段,为24 mm,3月至4月初和9月处于峰值阶段,为28 mm,年变化似呈"M"形。春小麦地在土壤封冻期未测定,3月至4月初处于最大峰值阶段,为33 mm,7月处于谷值阶段,为21 mm,9月达次峰值阶段,为25 mm,年变化似呈"M"形。在同一气候背景下,大气观测场中子仪测定和春小麦地烘干法测定的0~50 cm贮水量经过相关性检验,建立回归关系式后可相互代替应用。