Nico Goldscheider

Review: From multi-scale conceptualization to a classification system for inland groundwater-dependent ecosystems

Aquifers provide water, nutrients and energy with various patterns for many aquatic and terrestrial ecosystems. Groundwater-dependent ecosystems (GDEs) are increasingly recognized for their ecological and socio-economic values. The current knowledge of the processes governing the ecohydrological functioning of inland GDEs is reviewed, in order to assess the key drivers constraining their viability. These processes occur both at the watershed and emergence scale. Recharge patterns, geomorphology, internal geometry and geochemistry of aquifers control water availability and nutritive status of groundwater. The interface structure between the groundwater system and the biocenoses may modify the groundwater features by physicochemical or biological processes, for which biocenoses need to adapt. Four major types of aquifer-GDE interface have been described: springs, surface waters, peatlands and terrestrial ecosystems. The ecological roles of groundwater are conditioned by morphological characteristics for spring GDEs, by the hyporheic zone structure for surface waters, by the organic soil structure and volume for peatland GDEs, and by water-table fluctuation and surface floods in terrestrial GDEs. Based on these considerations, an ecohydrological classification system for GDEs is proposed and applied to Central and Western-Central Europe, as a basis for modeling approaches for GDEs and as a tool for groundwater and landscape management.RésuméLes aquifères fournissent eau, nutriments et énergie, selon des mécanismes variés, à beaucoup d’écosystèmes aquatiques et terrestres. Les écosystèmes dépendant des eaux souterraines (EDES) sont de plus en plus reconnus pour leur valeur écologique et socio-économique. Les connaissances actuelles sur les processus contrôlant le fonctionnement éco-hydrologique des EDES continentaux sont passées en revue, de façon à identifier les facteurs-clés qui conditionnent leur viabilité. Ces processus ont lieu à la fois à l’échelle du bassin versant et de l’émergence. Les types de recharge, la géomorphologie, la structure et la géochimie des aquifères contrôlent la disponibilité en eau nutritive des nappes. La structure de l’interface système souterrain-biocénoses peut modifier les caractéristiques des nappes du fait des processus physico-chimiques et biologiques, auxquels les biocénoses doivent s’adapter. Quatre types majeurs d’interface aquifère-EDES sont décrits : sources, eaux de surface, tourbières et écosystèmes terrestres. Le rôle écologique des eaux souterraines est conditionné par les caractéristiques morphologiques pour l’interface sources-EDES, par la structure de la zone hyporhéïque pour les eaux de surface, par la structure et le volume du sol organique pour l’interface tourbières-EDES et par la fluctuation de la surface libre et par les écoulements de surface dans les EDES terrestres. Sur la base de ces considérations, un système de classification éco-hydrologique pour les EDES est proposé et appliqué à l’Europe du Centre et du Centre-Ouest, comme fondement pour des modélisation des EDES et comme outil de gestion des eaux souterraines et des paysages.ResumenLos acuíferos proporcionan agua, nutrientes y energía con varios esquemas para muchos ecosistemas acuáticos y terrestres. Los ecosistemas dependientes del agua subterránea (GDEs) son cada vez más reconocidos por sus valores ecológicos y socioeconómicos. Se realiza una revisión del conocimiento actual de los procesos que gobiernan el funcionamiento ecohidrológico de los GDEs interiores, para evaluar los principales factores que limitan su viabilidad. Estos procesos ocurren tanto en escala de cuenca como de la emergencia. Los esquemas de la recarga, la geomorfología, la geometría interna y la geoquímica de los acuíferos controlan la disponibilidad del agua y el estado de los nutrientes del agua subterránea. La estructura de interfaz entre el sistema de agua subterránea y la biocenosis pueden modificar las características del agua subterránea por procesos fisicoquímicos y biológicos, para los cuales la biocenosis necesita adaptarse. Cuatro tipos principales de la interfaz de acuíferos GDEF han sido descriptos: manantiales, aguas superficiales, turberas y ecosistemas terrestres. Los roles ecológicos del agua subterránea están condicionados por las características morfológicas para los manantiales GDEs, por la estructura de la zona hiporreica para las aguas superficiales, por la estructura orgánica del suelo y por el volumen de los GDEs con turberas, y por la fluctuación de los niveles freáticos y las inundaciones de superficie en los GDEs terrestres. Basado en estas consideraciones se propone un sistema de clasificación ecohidrológico para los GDEs y es aplicado para el centro – oeste y el centro de Europa., como una base para modelar enfoques para los GDEs y como una herramienta para el manejo del agua subterránea y el paisaje.摘要含水层能够为许多水生和陆地生态系统提供水以及各种类型的营养和能量。依赖地下水的生态系统(GDEs)的生态及社会经济价值越来越被认可。本文综述了控制内陆GDEs生态水文功能的过程研究现状,从而评价限制其发展的主要驱动力。这些过程发生在流域及更大尺度上。含水层的补给类型、地形地貌、内部几何形状以及地球化学控制着水资源可利用量和地下水的营养状况。地下水系统及生物群落之间的界面结构可通过物理化学和生物过程改变地下水特征,并需要生物群落的适应。本文对四个主要类型的含水层—GDE界面进行描述;泉、地表水、沼泽、陆地生态系统。地下水的生态作用由形态学特征约束,对泉水GDEs而言,由伏流区结构约束,对地表水,由有机土壤结构和体积约束,对沼泽GDEs,由地下水位波动约束,对陆地GDEs由地表洪水约束。基于这些因素,本文提出一个GDEs生态水文分类系统,并应用到欧洲中部和中西部,从而为建立GDEs模型打下基础,为地下水及景观管理提供工具。ResumoOs aquíferos fornecem água, nutrientes e energia com vários padrões para muitos ecossistemas aquáticos e terrestres. Os ecossistemas dependentes das águas subterrâneas (EDAS) são crescentemente reconhecidos pelos seus valores ecológicos e socioeconómicos. Revê-se o conhecimento actual dos processos que determinam o funcionamento eco-hidrológico dos EDAS interiores de forma a avaliar os factores principais que condicionam a sua viabilidade. Estes processos ocorrem tanto à escala da bacia hidrográfica como à escala da emergência. Os padrões de recarga, geomorfologia, geometria interna e geoquímica dos aquíferos controlam a disponibilidade de água e o estado nutritivo das águas subterrâneas. A estrutura da interface entre o sistema de águas subterrâneas e as biocenoses pode modificar as características das águas subterrâneas por processos físico-químicos ou biológicos para os quais as biocenoses precisam de se adaptar. Descreveram-se quatro tipos principais de interface aquífero-EDAS: nascentes, águas superficiais, turfeiras e ecossistemas terrestres. O papel ecológico das águas subterrâneas está condicionado pelas características morfológicas no caso dos EDAS associados a nascentes, pela estrutura da zona hiporreica para as águas superficiais, pela estrutura e volume do solo orgânico no caso dos EDAS associados a turfeiras e pela flutuação do nível freático e das cheias de águas superficiais no caso dos EDAS terrestres. Com base nestas considerações, propõe-se um sistema de classificação ecohidrológica para os EDAS e faz-se a sua aplicação à Europa Central e Centro-ocidental como uma base para as abordagens de modelação de EDAS e como uma ferramenta para a gestão das águas subterrâneas e da paisagem.

Uranium in groundwater — Fertilizers versus geogenic sources

Due to its radiological and toxicological properties even at low concentration levels, uranium is increasingly recognized as relevant contaminant in drinking water from aquifers. Uranium originates from different sources, including natural or geogenic, mining and industrial activities, and fertilizers in agriculture. The goal of this study was to obtain insights into the origin of uranium in groundwater while differentiating between geogenic sources and fertilizers. A literature review concerning the sources and geochemical processes affecting the occurrence and distribution of uranium in the lithosphere, pedosphere and hydrosphere provided the background for the evaluation of data on uranium in groundwater at regional scale. The state of Baden-Württemberg, Germany, was selected for this study, because of its hydrogeological and land-use diversity, and for reasons of data availability. Uranium and other parameters from N=1935 groundwater monitoring sites were analyzed statistically and geospatially. Results show that (i) 1.6% of all water samples exceed the German legal limit for drinking water (10 μg/L); (ii) The range and spatial distribution of uranium and occasional peak values seem to be related to geogenic sources; (iii) There is a clear relation between agricultural land-use and low-level uranium concentrations, indicating that fertilizers generate a measurable but low background of uranium in groundwater.

Sources and processes affecting the spatio-temporal distribution of pharmaceuticals and X-ray contrast media in the water resources of the Lower Jordan Valley, Jordan

The closed basin of the Lower Jordan Valley with the Dead Sea as final sink features high evapotranspiration rates and almost complete reuse of treated wastewater for irrigation farming. This study focuses on the water transfer schemes and the presence, spreading, and potential accumulation of pharmaceutical residues in the local water resources based on findings of a five-year monitoring program. Overall 16 pharmaceuticals and 9 iodinated X-ray contrast media were monitored in groundwater, surface water, and treated wastewater. A total of 95 samples were taken to cover all geographical settings and flow paths from origin (wastewater) to target (groundwater). Nine substances were detected in groundwater, with concentrations ranging between 11 ng/L and 33,000 ng/L. Sometimes, detection rates were higher than in comparable studies: Diatrizoic acid 75%, iopamidol 42%, iopromide 19%, iomeprol 11%, carbamazepine and iohexol 8%, ibuprofen 6%, and fenofibrate and iothalamic acid 3%. Concentrations in groundwater generally increase from north to south depending on the application of treated wastewater for irrigation. Almost all substances occurred most frequently and with highest concentrations in treated wastewater, followed by surface water and groundwater. As exception, diatrizoic acid was found more frequently in groundwater than in treated wastewater, with concentrations being similar. This indicates the persistence of diatrizoic acid with long residence times in local groundwater systems, but may also reflect changing prescription patterns, which would be in accordance with increasing iopamidol findings and surveys at local hospitals. Trend analyses confirm this finding and indicate a high probability of increasing iopamidol concentrations, while other substances did not reveal any trends. However, no proof of evaporative enrichment could be found. The high spatial and temporal variability of the concentrations measured calls for further systematic studies to assess the long-term evolution of organic trace substances in this reuse setting.

Temperature-driven meltwater production and hydrochemical variations at a glaciated alpine karst aquifer: implication for the atmospheric CO2 sink under global warming

About two hydrological years of continuous data of discharge, temperature, electrical conductivity and pH have been recorded at the Glarey spring in the Tsanfleuron glaciated karst area in the Swiss Alps, to understand how glaciated karst aquifer systems respond hydrochemically to diurnal and seasonal recharge variations, and how calcite dissolution by glacial meltwater contributes to the atmospheric CO2 sink. A thermodynamic model was used to link the continuous data to monthly water quality data allowing the calculation of CO2 partial pressures and calcite saturation indexes. The results show diurnal and seasonal hydrochemical variations controlled chiefly by air temperature, the latter influencing karst aquifer recharge by ice and snowmelt. Karst process-related atmospheric CO2 sinks were more than four times higher in the melting season than those in the freezing season. This finding has implication for understanding the atmospheric CO2 sink in glaciated carbonate rock terrains: the carbon sink will increase with increasing runoff caused by global warming, i.e., carbonate weathering provides a negative feedback for anthropogenic CO2 release. However, this is a transient regulation effect that is most efficient when glacial meltwater production is highest, which in turn depends on the future climatic evolution.

Tracking changing X-ray contrast media application to an urban-influenced karst aquifer in the Wadi Shueib, Jordan

Sewage input into a karst aquifer via leaking sewers and cesspits was investigated over five years in an urbanized catchment. Of 66 samples, analyzed for 25 pharmaceuticals, 91% indicated detectable concentrations. The former standard iodinated X-ray contrast medium (ICM) diatrizoic acid was detected most frequently. Remarkably, it was found more frequently in groundwater (79%, median: 54 ng/l) than in wastewater (21%, 120 ng/l), which is supposed to be the only source in this area. In contrast, iopamidol, a possible substitute, spread over the aquifer during the investigation period whereas concentrations were two orders of magnitude higher in wastewater than in groundwater. Knowledge about changing application of pharmaceuticals thus is essential to assess urban impacts on aquifers, especially when applying mass balances. Since correlated concentrations provide conclusive evidence that, for this catchment, nitrate in groundwater rather comes from urban than from rural sources, ICM are considered useful tracers.

Erratum: Impact of managed aquifer recharge on the chemical and isotopic composition of a karst aquifer, Wala reservoir, Jordan

Storm-water harvesting and storage via managed aquifer recharge (MAR) is a promising approach to combat water scarcity in semi-arid regions, but poses a challenge for karst aquifers and regions with highly variable water availability. The infiltration of low-mineralized surface water and its impact on highly mineralized groundwater of a karst aquifer was investigated at Wala reservoir in Jordan over a period of approximately 10 years. The results show significant groundwater-level rise in a wellfield, in response to the yearly average infiltration of about 6.7 million m3. This corresponds to about 60 % of the yearly average abstraction of about 11.7 million m3, confirmed by mixing calculations with tritium. A decreasing trend in infiltration due to sedimentation is observed. Mean groundwater residence times of several thousand years, derived from carbon-14 dating, indicate a large storage capacity of the aquifer. The heterogeneous distribution of the residence times is caused by strong groundwater withdrawals and artificial recharge along with karst-specific aquifer characteristics. Temporal groundwater salinity fluctuations in the wellfield are observed after the first MAR infiltration. Enhanced groundwater flow along the wadi course was demonstrated, which is an important aspect with regards to future MAR projects in similar wadis of the region.

Evaluation of β-d-glucuronidase and particle-size distribution for microbiological water quality monitoring in Northern Vietnam.

In many karst regions in developing countries, the populations often suffer from poor microbial water quality and are frequently exposed to bacterial pathogens. The high variability of water quality requires rapid assays, but the conventional cultivation-based analysis of fecal indicator bacteria, such as Escherichia coli (E. coli), is very time-consuming. In this respect, the measurement of the enzymatic activity of E. coli could prove to be a valuable tool for water quality monitoring. A mobile automated prototype device was used for the investigation of β-d-glucuronidase (GLUC) activity at a remote karst spring, connected to a sinking surface stream, in Northern Vietnam. To assess the relationship between GLUC activity, discharge dynamics and contamination patterns, multiple hydrological, hydrochemical, physicochemical and microbiological parameters, including discharge, turbidity, particle-size distributions, and E. coli, were measured with high temporal resolution during ten days of on-site monitoring. A complex contamination pattern due to anthropogenic and agricultural activities led to high E. coli concentrations (270 to >24,200 MPN/100ml) and a GLUC activity between 3.1 and 102.2 mMFU/100ml. A strong daily fluctuation pattern of GLUC activity and particle concentrations within small size classes (<10μm) could be observed, as demonstrated by autocorrelations. A Spearmans rank correlation analysis resulted in correlation coefficients of rs=0.56 for E. coli and GLUC activity and rs=0.54 for GLUC activity and the concentration of 2-3μm particles. On an event scale, correlations were found to be higher (rs=0.69 and 0.87, respectively). GLUC activity and E. coli displayed a general contamination pattern, but with significant differences in detail, which may be explained by interferences of e. g. viable but non-culturable cells. Although further evaluations are recommended, GLUC activity is a promising, complementary parameter for on-site and near real-time water quality monitoring.

Isotopic constraints on water source mixing, network leakage and contamination in an urban groundwater system

Water supply in developing countries is prone to large water losses due to leaky distribution networks and defective sewers, which may affect groundwater quality and quantity in urban areas and result in complex subsurface mixing dynamics. In this study, a multi-stable isotope approach was used to investigate spatiotemporal fluctuations of surface and sub-surface water source partitioning and mixing, and to assess nitrogen (N) contamination in the urban water cycle of As-Salt, Jordan. Water import from the King Abdullah Canal (KAC), mains waters from the network, and wastewater are characterized by distinct isotopic signatures, which allowed us to quantify city effluents into the groundwater. Temporal variations in isotopic signatures of polluted groundwater are explained by seasonally fluctuating inflow, and dilution by water that originates from Lake Tiberias and enters the urban water cycle via the KAC. Isotopic analysis (N and O) and comparison between groundwater nitrate and nitrate from mains water, water imports and wastewater confirmed that septic waste from leaky sewers is the main contributor of nitrate contamination. The nitrate of strongly contaminated groundwater was characterized by highest δ15NNO3 values (13.3±1.8‰), whereas lowest δ15NNO3 values were measured in unpolluted groundwater (6.9‰). Analogously, nitrate concentration and isotopic ratios were used for source partitioning and qualitatively confirmed δDH2O and δ18OH2O-based estimates. Dual water isotope endmember mixing calculations suggest that city effluents from leaky networks and sewers contribute 30-64% to the heavily polluted groundwater. Ternary mixing calculations including also chloride revealed that 5-18% of the polluted groundwater is wastewater. Up to two thirds of the groundwater originates from mains, indicating excessive water loss from the network, and calling for improved water supply management.

Modelling groundwater over-extraction in the southern Jordan Valley with scarce data

To deal with the challenge of groundwater over-extraction in arid and semi-arid environments, it is necessary to establish management strategies based on the knowledge of hydrogeological conditions, which can be difficult in places where hydrogeological data are dispersed, scarce or present potential misinformation. Groundwater levels in the southern Jordan Valley (Jordan) have decreased drastically in the last three decades, caused by over-extraction of groundwater for irrigation purposes. This study presents a local, two-dimensional and transient numerical groundwater model, using MODFLOW, to characterise the groundwater system and the water balance in the southern Jordan Valley. Furthermore, scenarios are simulated regarding hydrological conditions and management options, like extension of arable land and closure of illegal wells, influencing the projection of groundwater extraction. A limited dataset, literature values, field surveys, and the ‘crop water-requirement method’ are combined to determine boundary conditions, aquifer parameters, and sources and sinks. The model results show good agreement between predicted and observed values; groundwater-level contours agree with the conceptual model and expected flow direction, and, in terms of water balance, flow volumes are in accordance with literature values. Average annual water consumption for irrigation is estimated to be 29 million m3 and simulation results show that a reduction of groundwater pumping by 40% could recover groundwater heads, reducing the water taken from storage. This study presents an example of how to develop a local numerical groundwater model to support management strategies under the condition of data scarcity.RésuméPour relever le défi de la surexploitation des eaux souterraines dans les milieu arides et semi-arides, il est nécessaire d’établir des stratégies de gestion basées sur la connaissance des conditions hydrogéologiques. Cela peut être difficiles dans les endroits où les données hydrogéologiques sont dispersées, rares ou présentent une désinformation potentielle. Les niveaux des eaux souterraines dans le Sud de la Vallée du Jourdain (Jordanie) ont diminué de façon drastique au cours des trois dernières décennies, en raison de la surexploitation des eaux souterraines à des fins d’irrigation. Cette étude présente un modèle numérique bidimensionnel et transitoire des eaux souterraines à l’échelle locale, utilisant MODFLOW, afin de caractériser le système aquifère et le bilan hydrique dans la vallée méridionale du Jourdain. En outre, des scénarios sont simulés en ce qui concerne les conditions hydrologiques et les options de gestion, comme l’extension des terres arables et l’arrêt d’exploitation de puits illégaux, influençant la projection de l’exploitation des eaux souterraines. Un ensemble de données limité, des valeurs de la littérature, des enquêtes de terrain, et la ‘méthode d’évaluation de la demande d’eau des cultures’ sont combinés pour déterminer les conditions aux limites, les paramètres de l’aquifère, et les termes sources et puits. Les résultats du modèle montrent une bonne cohérence entre les valeurs prédites et observées; les contours piézométriques sont concordants avec le modèle conceptuel et les directions d’écoulement attendues, et, du point de vue du bilan hydraulique, les volumes écoulés sont conformes aux valeurs de la littérature. La consommation annuelle moyenne en eau pour l’irrigation est estimée à 29 millions m3 et les résultats des simulations montrent qu’une réduction des pompages d’eau souterraine de 40% pourrait permettre de récupérer les niveaux piézométriques, limitant ainsi les prélèvements d’eau stockée. Cette étude présente un exemple de la façon de développer un modèle numérique des eaux souterraines à l’échelle locale pour soutenir les stratégies de gestion en condition de rareté de données.ResumenPara enfrentar el desafío de la sobreextracción de agua subterránea en ambientes áridos y semiáridos, es necesario establecer estrategias de gestión basadas en el conocimiento de condiciones hidrogeológicas. Esto puede ser difícil en lugares donde los datos hidrogeológicos son dispersos, escasos o presentan posibles informaciones erróneas. Los niveles de agua subterránea en el valle del Jordán meridional (Jordania) han disminuido drásticamente en las últimas tres décadas, causado por la sobreexplotación de aguas subterráneas con fines de riego. Este estudio presenta un modelo numérico de aguas subterráneas local, bidimensional y de régimen transiente, utilizando MODFLOW, para caracterizar el sistema de aguas subterráneas y el balance hídrico en el valle del Jordán meridional. Además, se simulan escenarios sobre condiciones hidrológicas y opciones de gestión, como la extensión de tierras de cultivo y el cierre de pozos ilegales, que influyen en la proyección de la extracción de aguas subterráneas. Un conjunto de datos limitado, valores obtenidos de la literatura, evaluaciones en terreno y el “método de necesidades de riego de los cultivos” se combinan para determinar las condiciones de borde, los parámetros del acuífero y las recargas y extracciones. Los resultados del modelo muestran una buena relación entre los valores pronosticados y observados; los mapas de contornos concuerdan con el modelo conceptual y la dirección esperada del flujo y, en términos de balance hídrico, los volúmenes de flujo están en conformidad con los valores de la literatura. El consumo promedio anual de agua para riego es estimado en 29 millones de m3 y los resultados de la simulación muestran que una reducción del 40% de la captación de agua subterránea podría recuperar los niveles de agua subterránea, reduciendo el agua proveniente del almacenamiento. Este estudio presenta un ejemplo de cómo desarrollar un modelo numérico local de aguas subterráneas para apoyar estrategias de gestión bajo la condición de escasez de datos.摘要为了应对干旱、半干旱环境下地下水超采的挑战,有必要建立基于掌握水文地质条件的管理策略。这可能在水文地质数据零散、匮乏和有潜在错误信息的地方非常困难。(约旦)约旦河谷南部地下水位过去三十年来大幅下降,由地下水超采用于灌溉引起。本研究展示了一个局部的、二维和瞬时数值地下水模型,利用MODFLOW来描述约旦河谷南部的地下水系统和水平衡。此外,针对水文条件和管理选择,如影响地下水开采规划的可耕地扩展、非法井的关闭,对各种方案进行了模拟。有限的数据集、文献价值、野外调查及 “作物需水方法”联合在一起确定边界条件、含水层参数以及汇和源。模型结果显示,预测的值和观测的值非常吻合;地下水位等高图与概念模型和预计的水流方向一致,在水平衡方面,流量与文献值一致。平均每年灌溉水消耗量估计为2900万立方,模拟结果显示,地下水抽取减少40%就能恢复地下水水头,减少储存的使用量。本研究展示了怎样建立一个局部的地下水模型以支持数据匮乏条件下管理策略的例子。ResumoPara lidar com o desafio do excesso de extração de águas subterrâneas em ambientes áridos e semiáridos, é necessário estabelecer estratégias de gerenciamento baseadas no conhecimento das condições hidrogeológicas. Isso pode ser difícil em locais onde os dados hidrogeológicos são dispersos, escassos ou apresentam desinformação potencial. Os níveis freáticos no sul do Vale do Jordão decresceram drasticamente nas últimas três décadas, devido ao excesso de extração de águas subterrâneas para irrigação. Esse estudo apresenta um modelo numérico de águas subterrâneas local, bidimensional e transiente, utilizando o MODFLOW, para caracterizar o sistema de águas subterrâneas e o balanço hídrico no sul do Vale do Jordão. Ademais, os cenários são simulados em relação às condições hidrológicas e opções de gerenciamento, como extensão da terra arável e fechamento de poços ilegais, influenciando a projeção da extração de águas subterrâneas. Um conjunto de dados limitados, valores de literatura, pesquisas de campo, e o ‘método de requerimento de água das culturas’ são combinados para determinar as condições de contorno, parâmetros do aquífero, bem como as fontes e sumidouros. Os resultados do modelo apresentaram boa concordância entre os valores estimados e observados; as isolinhas do nível das águas subterrâneas coincidiram com o modelo conceitual e com a direção de fluxo esperada, e, em termos do balanço hídrico, os volumes de fluxo estão em conformidade com os valores da literatura. O consumo anual médio de água para irrigação foi estimado como 29 milhões de m3 e os resultados da simulação demonstraram que uma redução de 40% no bombeamento das águas subterrâneas poderiam recuperar os níveis freáticos, reduzindo a água retirada do armazenamento. Esse estudo apresenta um exemplo de como desenvolver um modelo numérico local de águas subterrâneas para apoiar estratégias de gerenciamento sob a condição de escassez de dados.

Fluorescence-based multi-parameter approach to characterize dynamics of organic carbon, faecal bacteria and particles at alpine karst springs

Karst springs, especially in alpine regions, are important for drinking water supply but also vulnerable to contamination, especially after rainfall events. This high variability of water quality requires rapid quantification of contamination parameters. Here, we used a fluorescence-based multi-parameter approach to characterize the dynamics of organic carbon, faecal bacteria, and particles at three alpine karst springs. We used excitation emission matrices (EEMs) to identify fluorescent dissolved organic material (FDOM). At the first system, peak A fluorescence and total organic carbon (TOC) were strongly correlated (Spearmans rs of 0.949), indicating that a large part of the organic matter is related to humic-like substances. Protein-like fluorescence and cultivation-based determination of coliform bacteria also had a significant correlation with rs=0.734, indicating that protein-like fluorescence is directly related to faecal pollution. At the second system, which has two spring outlets, the absolute values of all measured water-quality parameters were lower; there was a significant correlation between TOC and humic-like fluorescence (rs=0.588-0.689) but coliform bacteria and protein-like fluorescence at these two springs were not correlated. Additionally, there was a strong correlation (rs=0.571-0.647) between small particle fractions (1.0 and 2.0μm), a secondary turbidity peak and bacteria. At one of these springs, discharge was constant despite the reaction of all other parameters to the rainfall event. Our results demonstrated that i) all three springs showed fast and marked responses of all investigated water-quality parameters after rain events; ii) a constant discharge does not necessarily mean constant water quality; iii) at high contamination levels, protein-like fluorescence is a good indicator of bacterial contamination, while at low contamination levels no correlation between protein-like fluorescence and bacterial values was detected; and iv) a combination of fluorescence measurements and particle-size analysis is a promising approach for a rapid assessment of organic contamination, especially relative to time-consuming conventional bacterial determination methods.