Hydrogeological controls of variable microbial water quality in a complex subtropical karst system in Northern Vietnam

Karst aquifers are particularly vulnerable to bacterial contamination. Especially in developing countries, poor microbial water quality poses a threat to human health. In order to develop effective groundwater protection strategies, a profound understanding of the hydrogeological setting is crucial. The goal of this study was to elucidate the relationships between high spatio-temporal variability in microbial contamination and the hydrogeological conditions. Based on extensive field studies, including mapping, tracer tests and hydrochemical analyses, a conceptual hydrogeological model was developed for a remote and geologically complex karst area in Northern Vietnam called Dong Van. Four different physicochemical water types were identified; the most important ones correspond to the karstified Bac Son and the fractured Na Quan aquifer. Alongside comprehensive investigation of the local hydrogeology, water quality was evaluated by analysis for three types of fecal indicator bacteria (FIB): Escherichia coli, enterococci and thermotolerant coliforms. The major findings are: (1) Springs from the Bac Son formation displayed the highest microbial contamination, while (2) springs that are involved in a polje series with connections to sinking streams were distinctly more contaminated than springs with a catchment area characterized by a more diffuse infiltration. (3) FIB concentrations are dependent on the season, with higher values under wet season conditions. Furthermore, (4) the type of spring capture also affects the water quality. Nevertheless, all studied springs were faecally impacted, along with several shallow wells within the confined karst aquifer. Based on these findings, effective protection strategies can be developed to improve groundwater quality.     

The use of nitrate, bacteria and fluorescent tracers to characterize groundwater recharge and contamination in a karst catchment, Chongqing, China

The Qingmuguan subterranean river system is located in the suburb of Chongqing, China, and it is the drinking water source that local people downstream rely on. The study aims to provide a scientific basis for groundwater protection in that area, using a hydrogeological framework, tracer tests, hydrological online monitoring, and hydrochemical and microbiological investigation, including heterotrophic plate count (HPC) and the analysis of denitrifying bacteria (DNB) and nitrobacteria (NB). The tracer tests proved simple and direct connections between two important sinkholes and the main springs, and also proved that the underground flows here are fast and turbulent. DNB and NB analyses revealed that the main recharge to the underground river in the dry season is the soil-leached water passing through the fissures of the epikarst, while in the rainy season, it is the surface water flow through sinkholes. The hydrochemical and microbiological data confirmed the notable impact of agriculture and sewage on the spring water quality. In the future, groundwater protection here should focus on targeted vulnerability mapping that yields different protection strategies for different seasons.     

Karstological study of the new Kunming airport building area (Yunnan, China)

In Kunming area (6.8 mio population), two big interventions are in progress: construction of a new airport, the 23 km² area of which will extend across karst terrain northeast of the city, and extensive uptake of water from karst aquifers for drinking and agricultural use. In the study, an interdisciplinary approach was utilized to demonstrate the need for holistic karstology studies prior to performing extensive interferences in the karst environment. This study included survey of surface karst features and microscopic analyses of rock samples in the area of the new airport location, accompanied by hydrogeological studies and microbiological analyses of two karst drinking water sources in its vicinity (Qinglongdong, Huanglongdong). Results showed the specific characteristics of the subsoil stone forest that indicated a high level of karstification. The direction and characteristics of groundwater flow from the sinking Qiaotou Stream at the margin of the new airport area toward the Huanglongdong Spring were defined with a single tracer test. Additional information about hydrogeological characteristics of the karst aquifer was obtained by individual measurements of physical and chemical parameters of the springs and sinking stream. Selected chemical and bacteriological parameters showed substantial pollution of both springs due to various types of human activities in the catchments. The results of the study pointed to the necessity of taking immediate measures for the springs’ protection and showed the importance of interdisciplinary research when planning anthropogenic activities in the karst.     

Mise-a-la-masse method,tracer tests and cave detection analysis of underground-river karst-conduit distribution and structure: a case study of the Dafengdong conduits in Guizhou Province,China

In karst areas, groundwater movement is dominated by conduit flow; thus, understanding the distribution and structure of karst conduits has great significance for water research, groundwater protection and engineering construction. With the Dafengdong (Guizhou Province, China) underground river karst as an example, a mise-a-la-masse method, tracer tests and cave detection were conducted to study the distribution and structure of karst conduits. Combined with information on the geological and hydrogeological conditions, the geological factors that form karst conduits were determined. It can be concluded that: (1) Under the influence of faults, karst conduits usually develop towards or along faults; (2) multiple karst conduits form easily on both sides of tectonic fracture zones; (3) both lithology and geological structure affect the formation of blue holes, and when the directions of karst conduits change, blue holes easily form in weak parts of the structure; (4) at springs where two aquifers intersect, with strong chemical dissolution of the lower karst aquifer and mechanical collapse of the upper aquifer, blue holes also form easily; and (5) integrated mise-a-la-masse method, tracer tests and cave detection can accurately discern the distribution and structure of karst conduits. Geological factors can be used to preliminarily delineate the distribution and structure of karst conduits in similar areas based on hydrogeological conditions. Such methods hold great significance for groundwater extraction and protection and engineering construction in karst areas.

     

Characterization of karst conduits by tracer tests for an artificial recharge scheme

Challenged by rapidly changing climate in combination with an increase in anthropogenic pressures, karst groundwater resources in the Old Town of Lijiang (OTLJ), SW China, are diminishing. Higher frequency and longer duration of dried-up periods have been observed at the Heilongtan Park (HP) Springs in recent years. Thus, there is an urgent need for an artificial recharge scheme, aimed at replenishing groundwater in the aquifer and increasing the outflow of the springs to ensure effective water resources management. Evaluation of the scheme feasibility, prior to its implementation, is important. In this study, tracer tests were conducted between the recharge area and receiving springs in order to gain insight into the transport mechanisms of karst groundwater and the structural characteristics of the aquifer. Multiple underground flow paths, exhibiting high conductivity between the recharge area and HP Springs, were revealed by the interpretation of tracer breakthrough curves. Three springs considered as the leakages of the scheme were identified. Moreover, the outflow of springs at HP and OTLJ were predicted to be increased by the artificially recharged water after 9.2 and 12.5 days, respectively. Quantitative analysis of tracer recoveries demonstrates that the springs to be recharged and the springs considered as leakages, respectively, share 45 and 55% of the increased outflow. The feasibility of the scheme has been confirmed by the tracer tests. This report provides references for the evaluation of artificial groundwater recharge and protection strategies, particularly in large and poorly investigated karst spring fields.

     

岩溶泉域降雨径流水文过程的模拟——以重庆金佛山水房泉为例

通过地貌、水文地质、土壤、植被、地下洞穴管道等实地调查,以及示踪试验确定水房泉泉域范围和地下水文系统特征,并通过代表性点的土壤入渗试验、降雨和流量监测以及DEM数据等获得泉域水文模型所需的面积、结点高程、入渗率、糙率、管道长度、含水层孔隙度、出流系数等参数。选择SCS径流曲线模型估算地表产流,利用SWMM模型模拟泉域对场降雨的径流响应过程。通过运行模型,与实测流量比较,结果显示模拟曲线与观测流量曲线吻合较好,用于校正和验证的两场降雨产流的模拟误差分别为9.5%和12%,表明SWMM可应用于岩溶区以管道流为主要排水系统的含水介质的模拟。     

Dynamics and interaction of organic carbon, turbidity and bacteria in a karst aquifer system

The dynamics of organic carbon (OC), turbidity, faecal indicator bacteria and physicochemical parameters was studied in a karst system near Yverdon, Switzerland. Online measurements and sampling were done at a swallow hole draining an agricultural surface (the input), and two groups of springs (the outputs) that often show bacterial contamination. A fluorescent tracer that was injected into the swallow hole during low-flow conditions first arrived at the springs 10–12 days after injection; the total recovery rate was 29%. Previous tracer tests during high-flow conditions gave shorter travel times. After a major rainfall event, a primary turbidity peak was observed at the springs. It coincides with the rising limb of the hydrograph, indicating remobilisation of autochthonous particles from the aquifer. A secondary turbidity peak occurs several days later, suggesting the arrival of allochthonous particles from the swallow hole. Wider peaks of OC and bacteria were observed simultaneously. Applying methods from molecular microbiology (PCR-DGGE) allowed characterisation of the bacterial communities at the swallow hole and the springs. The results demonstrate that the swallow hole is an important source of groundwater contamination, while its contribution to aquifer recharge is insignificant. OC appears to be a better indicator for bacterial contamination than turbidity.     

基于水化学、同位素特征的济南岩溶地下水补给来源研究

文章利用水化学、2H、18O同位素、87Sr/86Sr比值、13C和14C同位素对济南岩溶地下水补给来源、地热水补给来源进行研究。结果表明,岩溶冷水水化学类型以HCO3-Ca、HCO3·SO4-Ca型为主、地热水以SO4-Ca型为主。在旱季,间接补给区对泉群地下水补给比率在66.00%~73.58%之间,直接补给区仅占到26.42%~34.00%,旱季泉水的主要来源为间接补给区岩溶地下水。地热水受到了更新世以来的降水补给,是不同时期降水补给所形成的混合地下水,接受补给区域应为高程较高的张夏或者炒米店-三山子组地层,补给高程在350~550 m之间。      

示踪试验在岩溶大泉修复中的应用——以丽江黑龙潭为例

为查明云南丽江黑龙潭泉域九子海洼地补给区地下水与周边泉水的连通关系,提供泉水修复的科学依据,采用人工化学示踪方法,选取碘化钾作为示踪剂,开展了一次大型地下水示踪试验。根据试验数据计算地下水渗流速度,并分析黑龙潭泉域地下水系统结构特征。结果表明:九子海洼地补给区地下水与黑龙潭泉群和古城泉群具有显著的连通关系,与清溪泉群和白浪花泉群不存在连通关系,九子海至黑龙潭和古城的地下水渗流速度分别为405.86~1 077.84 m·d-1、349.96~629.09 m·d-1。九子海洼地为黑龙潭泉域地下水系统的主要补给区,同时也可作为黑龙潭泉水修复的有效注水点,接受补给后,主要通过深层岩溶管道向南运移至黑龙潭—古城方向,其中黑龙潭泉群为系统的排泄天窗。      

Application of inverse modeling in a study of the hydrogeochemical evolution of karst groundwater in the Jinci Spring region,northern China

This study explores the hydrogeochemical evolution of karst groundwater in the Jinci Spring region, Shanxi Province, northern China. During 2015, karst groundwater samples collected from 24 sampling points along several profiles that follow the groundwater flow direction were subjected to hydrochemical analysis. Reaction paths and mineral phases for the hydrogeochemical modeling were determined based on the analysis results and in conjunction with the regional geology and hydrogeology. The PHREEQC hydrogeochemical modeling software was used to perform mass balance and reaction path modeling of the hydrogeochemical evolution of the spring region. The modeling results showed that from the recharge area through the runoff area to the drainage area, the hydrogeochemical processes occurring in the karst water vary widely between the northeastern, central, and southwestern parts of the spring region, and across the piedmont discharge area. Additionally, hydrodynamic fields and geological structures were found to have significant control over the hydrogeochemical reactions occurring within the spring region’s karst groundwater.     

The study of hydrodynamic behaviour of a complex karst system under low-flow conditions using natural and artificial tracers (the catchment of the Unica River,SW Slovenia)

In this study a multi-tracer test with fluorescent tracers was combined with time series analyses of natural tracers to characterize the dynamics of the solute transport through different recharge pathways and to study hydraulic behaviour of a binary karst system under low-flow conditions. Fluorescent tracer testing included the introduction of uranine, amidorhodamine G, or naphthionate at three injection points. Sampling and monitoring took place at two karst springs (Malenščica, Unica) and at two underground rivers (Pivka, Rak) recharging the Unica River at the Polje of Planina, SW Slovenia. Other monitored parameters included precipitation, spring or underground river discharge, water temperature, and electrical conductivity. Water samples were collected and analyzed for total organic carbon, Mg²⁺, SO₄ ²⁻, and NO₃ ⁻ in the laboratory. In the study area, results of the tracer test suggest that contaminant transport in karst may be retarded for several weeks during low-flow conditions followed by increases in contaminant concentrations after subsequent rainfall events. Based on interpretation of tracer concentration breakthrough curves, low apparent dominant flow velocities (i.e., between 5.8 and 22.8 m/h through the well developed karst conduits, and 3.6 m/h through the prevailing vadose zone with a dominant influence of a diffuse recharge) were obtained. Together with analyses of hydro-chemographs the artificial tracing identified different origins of water recharging the studied aquifer. During prolonged low-water conditions the Malenščica spring is mainly recharged from the karst aquifer and the Unica spring by the sinking Pivka River. After more intensive rainfall events allogenic recharge from Cerknica prevails in the Malenščica spring, while the Unica spring drains mainly the allogenic water from the Pivka Valley. These findings of alternating hydraulic connections and drainage areas due to respective hydrological conditions are important and should be considered when monitoring water quality, implementing groundwater protection measures, and optimizing future water exploitation.     

Roles of hydrogeochemical evaluations in estimating protection zones of Koçpınar springs in Aksaray, central Anatolia, Turkey

The present study indicates estimation of protection zones of KoçpLnar springs in Aksaray area by means of hydrogeochemical methods. Relevant hydrogeochemical studies were carried out to achieve this objective. KoçpLnar springs emerge on strike-slip Hasanda<L fault set (HFS) along the Tuzgölü (Salt Lake) fault zone (TFZ) in central Anatolia. The outcrops of volcanic origin exhibit different hydrogeological properties in the study area. The hydrogeochemical evaluations of KoçpLnar springs represent good results about the available main groundwater flow systems that exist in this area. Marbles of Palaeozoic age form the main aquifer that recharges KoçpLnar springs. The CO₂ gas content of the spring waters is significantly high. Based on the ion concentrations, the water of this spring has mainly two hydrochemical facies: Ca-Mg-HCO₃ and Na-HCO₃. Although, the hydrochemical analyses showed that waters of these springs meet the drinking and irrigation water standards, the area around the springs is continuously being contaminated by both domestic and agricultural wastes. Therefore, detailed hydrogeological, hydrochemical and isotopic investigations were carried out to accurately estimate the protection zones of KoçpLnar springs. These studies showed that three main protection zones could be proposed against external pollution effects around the spring's area.     

金沙江河谷巧家段地下水化学特征

金沙江河谷巧家段地形切割强烈,最大相对高差可达2 719 m,水文地质条件差异大,河谷区内泉水出露众多。对河谷区内38组泉水水化学组分进行分析的结果表明:地下水化学类型较简单,主要为HCO3- Ca、HCO3- Ca?Mg、HCO3- Mg?Ca型;地下水溶解性总固体(TDS)浓度变化较大,总体上TDS浓度自河谷斜坡补给-径流区至谷底排泄区,具有逐步增高的趋势;孔隙水TDS浓度明显高于岩溶水;地下水宏量组分HCO3-、Ca2+、Mg2+、SO42-与TDS具有正相关关系。据水化学组分变化分析谷底第四系地层中出露大泉的形成条件,其为孔隙水与岩溶水相混合形成。      

Geochemical characterization of surface water and spring water in SE Kashmir Valley,western Himalaya: Implications to water–rock interaction

Water samples from precipitation, glacier melt, snow melt, glacial lake, streams and karst springs were collected across SE of Kashmir Valley, to understand the hydrogeochemical processes governing the evolution of the water in a natural and non-industrial area of western Himalayas. The time series data on solute chemistry suggest that the hydrochemical processes controlling the chemistry of spring waters is more complex than the surface water. This is attributed to more time available for infiltrating water to interact with the diverse host lithology. Total dissolved solids (TDS), in general, increases with decrease in altitude. However, high TDS of some streams at higher altitudes and low TDS of some springs at lower altitudes indicated contribution of high TDS waters from glacial lakes and low TDS waters from streams, respectively. The results show that some karst springs are recharged by surface water; Achabalnag by the Bringi stream and Andernag and Martandnag by the Liddar stream. Calcite dissolution, dedolomitization and silicate weathering were found to be the main processes controlling the chemistry of the spring waters and calcite dissolution as the dominant process in controlling the chemistry of the surface waters. The spring waters were undersaturated with respect to calcite and dolomite in most of the seasons except in November, which is attributed to the replenishment of the CO₂ by recharging waters during most of the seasons.     

济南泉域排泄区岩溶地下水水化学特征

文章通过分析研究济南泉域排泄区地下水水化学成分特征及形成过程,结合岩溶地下水的补径排条件,揭示了不同位置、不同深度循环的水质存在差异的原因。为保护泉水、优化泉域内地下水的开采方案提供了依据。     

Influence of coal mining on regional karst groundwater system: a case study in West Mountain area of Taiyuan City,northern China

Karstic limestone formations in the West Mountain area are important water resources for Taiyuan City in Shanxi Province, northern China, which is also known for its large-scale coal mining production. In this study area, groundwater is not only exploited for water supply purposes but also drained because of coal mining. The process of coal mining changes both the quantity of the karst springs and the quality of karst groundwater system because of overexploitation and overdrainage. In this paper, the influence of coal mining on the groundwater is analyzed from a qualitative and quantitative perspective. The hydrochemical analysis results reflect the relationship of the recharge, runoff, and drainage; the features of the medium; and water-rock interactions. Based on a qualitative understanding of the geological deposition and characteristics of the groundwater flow system, three-dimensional groundwater flow models are established and applied to several scenarios to explore the quantitative influence and allow better protection of the groundwater environment and better utilization of water resources.     

西南某岩溶区地下水系统示踪试验与解析

以西南某典型岩溶区为例,解析示踪试验在岩溶管道连通性以及获取水文地质参数中的应用。选择落水洞为投放点,分别从落水洞西侧和东侧寻找地下水出露点作为接收点,判别落水洞地下径流的实际去向以及落水洞与接收点之间的水力联系。结合Qtracer2软件对示踪试验成果进行定量解析,确定示踪剂回收率、地下水平均流速、最快流速,估算出岩溶管道结构特征和水文地质参数。结果表明:落水洞与接收点JS01、JS03之间不存在直接水力联系;落水洞与接收点JS02存在水力联系且岩溶管道极为发育,含水介质不均匀,地下水运移路径较为通畅,为典型的紊流流态;落水洞地下径流的主要方向是由西向东,但在丰水期雨量较大期间,接收点JS04能够接收到荧光素钠,说明丰水期水位上涨后两者间会有水力联系,导致部分水量向落水洞西侧排泄。     

重庆金佛山泉水地球化学特征及其空间分布意义

2006年7月和9月在重庆金佛山地区选取22个地下水出露的泉点.对泉水的地球化学性质进行详细调查。利用野外和实验室测量手段得到了主要阴离子和阳离子浓度与物理化学参数。分析得知:研究区泉水的水化学类型为Ca-HCO_3和Ca、Mg-HCO_3;结合地质和地貌背景把它们分为6个泉群,分别讨论各泉群的空间分布意义;估算泉水方解石(SI_C)、白云石(SI_D)和石膏(SI_G)的饱和指数,即可反映地层岩性、地形和地下水的运移时间对水质的影响,该区地下水基本上是来自大气降水的下渗.没有深部含水层的上升混合.这些泉水的地球化学特征以及它们的空间分布规律能够很好地反映区内地质状况.该研究可以为金佛山地区地下水资源的调查和环境保护提供基础数据。     

明月峡背斜南部张关—排花洞岩溶水系统地下水径流模式解析

川东明月峡背斜地下岩溶发育的强烈非均质性造就了独特的地下水径流模式,孕育出区域复杂的岩溶工程水文地质问题,查明明月峡背斜南段地下水径流模式对指导区内隧道工程选址及建设具有重要意义。文章在已有研究基础上,以“张关—排花洞”岩溶水系统为研究区,通过系统厘清区内水文地质条件,深入剖析区内地下水水文地球化学特征及水动力条件,明确区内岩溶含水介质不均一性控制下的地下水小尺度径流规律。结果显示:研究区地下水在平面上表现为形似“扫帚状”的径流模式:在补给、径流区,三叠系下统嘉陵江组一段（T₁j1）、嘉陵江组三段(T₁j3)地层（强岩溶化）与嘉陵江组二段（T₁j2）、嘉陵江组四段 （T₁j4）地层（弱岩溶化）呈间互状分布的特点导致相邻地层之间水力联系较弱,以地层为单位形成多个相对独立的岩溶水子系统;在研究区排泄区,受控于势汇最强的T₁j3内部管道流对其他地层地下水持续的袭夺效应,地下水统一汇聚至排花洞暗河出口向御临河排泄,各岩溶水子系统最终整合为一个岩溶水系统。      

织金大龙井岩溶大泉形成机理研究

为了弄清大龙井岩溶大泉形成机理以及地下水补径排关系。通过调查大龙井地形地貌、补径排关系以及对水化学分析等研究大龙井岩溶大泉的形成机理,通过调查得知:大龙井岩溶大泉是形成于低山－丘陵地区的石灰岩地区。是山盆期和乌江期的强烈岩溶作用以及河谷的不断下切,加上上寨台地地表峰丛之间发育洼地、漏斗,中间区域的落水洞,大气降雨沿着落水洞进入地下,在重力作用下从南向北径流,在这过程中水流逐渐集中,岩溶空间形态也逐步扩大,最终水汇集于龙洞沟呈泉集中排泄出地面,形成大龙井岩溶大泉以及大龙井水系统。