Some limitations in using <Superscript>222</Superscript>Rn to assess river–groundwater interactions: the case of Castel di Sangro alluvial plain (central Italy)

²²²Rn was used to assess river–groundwater interactions within Castel di Sangro alluvial aquifer (Italy). The effectiveness of results obtained through this indicator was verified by also analyzing δ¹⁸O, major ions and temperature in both surface and groundwater, and carrying out piezometric head monitoring and discharge measurements. Hydrogeological investigations suggested that the river infiltrates into the aquifer in the south-eastern aquifer portion, while groundwater discharges into the river in the north-eastern portion. The latter phenomenon is supported by ²²²Rn data. Nevertheless, flow-through conditions cause the modelled discharge along this river reach, estimated by ²²²Rn data in a degassing-corrected two-component mixing model, to be greater than the measured discharge. Concerning river infiltration into the aquifer, δ¹⁸O, major ions and temperature data show that the river contribution is negligible in terms of aquifer recharge. Thus, the observed increase in ²²²Rn concentration in that portion of the aquifer is due to the enrichment process caused by infiltration of rainwater (²²²Rn free) which flows from the local divide area. Hence, in the study site, the use of only ²²²Rn to predict river–groundwater interactions causes some estimation inaccuracies and it must be coupled with other hydrochemical and hydrogeological parameters to gain a thorough understanding of such interactions.     

Analysis of the exchange of groundwater and river water by using Radon-222 in the middle Heihe Basin of northwestern China

In arid regions of western China, water resources come from mountain watersheds and disappear in the desert plain. The exchange of surface water and groundwater takes place two or three times in a basin. It is essential to analyze the interaction of groundwater with surface water to use water resources effectively and predict the change in the water environment. The conventional method of analysis, however, measures only the flow of a stream and cannot determine groundwater seepage accurately. As the concentration of Radon-222 (²²²Rn) in groundwater is much higher than in surface water, the use of ²²²Rn was examined as an indicator for the analysis of the interaction between surface water and groundwater. Measurement of the ²²²Rn concentration in surface water was conducted to detect groundwater seepage into a stream in the middle Heihe Basin of northwestern China. Furthermore, the simultaneous groundwater flow into and out of a stream from the aquifers was quantified by solving the ²²²Rn mass balance equation, in which the losses of gas exchange and radioactive decay of ²²²Rn are considered. Meanwhile, river runoff was gauged to determine the exchange rates between surface water and groundwater. The result shows that ²²²Rn isotope can be used as a good environmental tracer with high sensitivity for the interaction between surface water and groundwater, especially in the fractured aquifer system, karst aquifer system and discharge basins.     

Long-term spatio-temporal hydrochemical and 222Rn tracing to investigate groundwater flow and water–rock interaction in the Gran Sasso (central Italy) carbonate aquifer

In the Gran Sasso fissured carbonate aquifer (central Italy), a long-term (2001–2007) spatio-temporal hydrochemical and ²²²Rn tracing survey was performed with the goal to investigate groundwater flow and water–rock interaction. Analyses of the physico-chemical parameters, and comparisons of multichemical and characteristic ratios in space and time, and subsequent statistical analyses, permitted a characterisation of the hydrogeology. At the regional scale, groundwater flows from recharge areas to the springs located at the aquifer boundaries, with a gradual increase of mineralisation and temperature along its flowpaths. However, the parameters of each group of springs may significantly deviate from the regional trend owing to fast flows and to the geological setting of the discharge spring areas, as corroborated by statistical data. Along regional flowpaths, the effects of seasonal recharge and lowering of the water table clearly cause changes in ion concentrations over time. This conceptual model was validated by an analysis of the ²²²Rn content in groundwater. ²²²Rn content, for which temporal variability depends on seasonal fluctuations of the water table, local lithology and the fracture network at the spring discharge areas, was considered as a tracer of the final stages of groundwater flowpaths.     

Multi-tracer investigation of river and groundwater interactions: a case study in Nalenggele River basin,northwest China

Environmental tracers (such as major ions, stable and radiogenic isotopes, and heat) monitored in natural waters provide valuable information for understanding the processes of river–groundwater interactions in arid areas. An integrated framework is presented for interpreting multi-tracer data (major ions, stable isotopes (²H, ¹⁸O), the radioactive isotope ²²²Rn, and heat) for delineating the river–groundwater interactions in Nalenggele River basin, northwest China. Qualitative and quantitative analyses were undertaken to estimate the bidirectional water exchange associated with small-scale interactions between groundwater and surface water. Along the river stretch, groundwater and river water exchange readily. From the high mountain zone to the alluvial fan, groundwater discharge to the river is detected by tracer methods and end-member mixing models, but the river has also been identified as a losing river using discharge measurements, i.e. discharge is bidirectional. On the delta-front of the alluvial fan and in the alluvial plain, in the downstream area, the characteristics of total dissolved solids values, ²²²Rn concentrations and δ¹⁸O values in the surface water, and patterns derived from a heat-tracing method, indicate that groundwater discharges into the river. With the environmental tracers, the processes of river–groundwater interaction have been identified in detail for better understanding of overall hydrogeological processes and of the impacts on water allocation policies.     

Variations of Hydrodynamics and Submarine Groundwater Discharge in the Yellow River Estuary Under the Influence of the Water-Sediment Regulation Scheme

The “Water-Sediment Regulation Scheme” (WSRS) is critically important to the hydrologic evaluation of the Yellow River estuary since a huge pulse of water and sediment are delivered into the sea during a short period. We used the natural geochemical tracers radium (²²³Ra, ²²⁴Ra, ²²⁶Ra) and radon (²²²Rn) isotopes as well as other hydrological parameters to investigate the mixing variations and submarine groundwater discharge (SGD) in the Yellow River estuary under the influence of the 2013 WSRS. Dramatically elevated radium and radon isotopic activities were observed during this WSRS compared with activities measured during a non-WSRS period. Radium “water ages” indicated that the offshore transport rate nearly tripled when the river discharge increased from 400 to 3400 m³/s. We calculated the SGD flux in the Yellow River estuary based on a radium mass balance model as well as radium and radon time-series models. The SGD flux was estimated at 0.02~0.20 m/day during a non-WSRS period and 0.67~1.22 m/day during the 2013 WSRS period. The results also indicate that large river discharge tends to lead more intense SGD along the river channel direction with a large amount of fresh SGD.     

Tracing of residual multiple DNAPL sources in the subsurface using 222Rn as a natural tracer at an industrial complex in Wonju, Korea

Depth-discrete tracing of residual dense non-aqueous phase liquid (DNAPL) sources in the subsurface is of great importance in making decisions related to contaminated groundwater remediation. Temporal variations in the natural tracer ²²²Rn and contaminant concentrations in groundwater contaminated with multiple chlorinated contaminants, such as trichloroethene, carbon tetrachloride, and chloroform, were examined to trace residual multiple DNAPL contaminants at an industrial complex in Wonju, Korea. The ²²²Rn activities and multiple DNAPL concentrations in the groundwater fluctuated irregularly according to the groundwater recharge. The natural tracer ²²²Rn in groundwater present in the soil layer, originating from the underlying crystalline biotite granite, had a wide range from 29,000 to 179,000 Bq/m³, and total concentrations of chlorinated solvents ranged from 0.06 to 17.77 mg/l, indicating the ambiguous results of ²²²Rn for tracing the residual DNAPL sources. In this paper, a method is presented to locate zones with a high probability of containing depth-discrete residual multiple DNAPL sources using ²²²Rn and considering relative contaminant concentrations. The results demonstrate that the combination of the ²²²Rn activities as a natural tracer and the relative contaminant concentrations is able to be used as a useful tool for tracing residual DNAPLs.     

Use of geochemical tracers for estimating groundwater influxes to the Big Sioux River,eastern South Dakota,USA

Understanding the spatial distribution and variability of geochemical tracers is crucial for estimating groundwater influxes into a river and can contribute to better future water management strategies. Because of the much higher radon (²²²Rn) activities in groundwater compared to river water, ²²²Rn was used as the main tracer to estimate groundwater influxes to river discharge over a 323-km distance of the Big Sioux River, eastern South Dakota, USA; these influx estimates were compared to the estimates using Cl^? concentrations. In the reaches overall, groundwater influxes using the ²²²Rn activity approach ranged between 0.3 and 6.4 m³/m/day (mean 1.8 m³/m/day) and the cumulative groundwater influx estimated during the study period was 3,982–146,594 m³/day (mean 40,568 m³/day), accounting for 0.2–41.9% (mean 12.5%) of the total river flow rate. The mean groundwater influx derived using the ²²²Rn activity approach was lower than that calculated based on Cl^? concentration (35.6 m³/m/day) for most of the reaches. Based on the Cl^? approach, groundwater accounted for 37.3% of the total river flow rate. The difference between the method estimates may be associated with minimal differences between groundwater and river Cl^? concentrations. These assessments will provide a better understanding of estimates used for the allocation of water resources to sustain agricultural productivity in the basin. However, a more detailed sampling program is necessary for accurate influx estimation, and also to understand the influence of seasonal variation on groundwater influxes into the basin.     

Hydrochemical evidence for mixing of river water and groundwater during high-flow conditions, lower Suwannee River basin, Florida, USA

 Karstic aquifers are highly susceptible to rapid infiltration of river water, particularly during periods of high flow. Following a period of sustained rainfall in the Suwannee River basin, Florida, USA, the stage of the Suwannee River rose from 3.0 to 5.88 m above mean sea level in April 1996 and discharge peaked at 360 m³/s. During these high-flow conditions, water from the Suwannee River migrated directly into the karstic Upper Floridan aquifer, the main source of water supply for the area. Changes in the chemical composition of groundwater were quantified using naturally occurring geochemical tracers and mass-balance modeling techniques. Mixing of river water with groundwater was indicated by a decrease in the concentrations of calcium, silica, and ²²²Rn; and by an increase in dissolved organic carbon (DOC), tannic acid, and chloride, compared to low-flow conditions in water from a nearby monitoring well, Wingate Sink, and Little River Springs. The proportion (fraction) of river water in groundwater ranged from 0.13 to 0.65 at Wingate Sink and from 0.5 to 0.99 at well W-17258, based on binary mixing models using various tracers. The effectiveness of a natural tracer in quantifying mixing of river water and groundwater was related to differences in tracer concentration of the two end members and how conservatively the tracer reacted in the mixed water. Solutes with similar concentrations in the two end-member waters (Na, Mg, K, Cl, SO₄, SiO₂) were not as effective tracers for quantifying mixing of river water and groundwater as those with larger differences in end-member concentrations (Ca, tannic acid, DOC, ²²²Rn, HCO₃). Received, March 1999 / Revised, July 1999 / Accepted, July 1999     

Spatial Distribution of Dissolved Radon in the Choptank River and Its Tributaries: Implications for Groundwater Discharge and Nitrate Inputs

The Choptank River, Chesapeake Bay’s largest eastern-shore tributary, is experiencing increasing nutrient loading and eutrophication. Productivity in the Choptank is predominantly nitrogen-limited, and most nitrogen inputs occur via discharge of high-nitrate groundwater into the river system’s surface waters. However, spatial patterns in the magnitude and quality of groundwater discharge are not well understood. In this study, we surveyed the activity of ²²²Rn, a natural groundwater tracer, in the Choptank’s main tidal channel, the large tidal tributary Tuckahoe Creek, smaller tidal and non-tidal tributaries around the basin, and groundwater discharging into those tributaries, measuring nitrate and salinity concurrently. ²²²Rn activities were <100 Bq m^?3 in the main tidal channel and 100–700 Bq m^?3 in the upper Choptank River and Tuckahoe Creek, while the median Rn activities of fresh tributaries and discharging groundwater were 1,000 and 7,000 Bq m^?3, respectively. Nitrate-N concentrations were <0.01 mg L^?1 throughout most of the tidal channel, 1.5–3 mg L^?1 in the upper reaches, up to 13 mg L^?1 in tributary samples, and up to 19.6 mg L^?1 in groundwater. Nitrate concentrations in tributary surface water were correlated with Rn activity in three of five sub-watersheds, indicating a groundwater nitrate source. ²²²Rn and salinity mass balances indicated that Rn-enriched groundwater discharges directly into the Choptank’s tidal waters and suggested that it consists of a mixture of fresh groundwater and brackish re-circulated estuarine water. Further sampling is necessary to constrain the Rn activity and nitrate concentration of discharging groundwater and quantify direct discharge and associated nitrogen inputs.     

Is 222Rn a suitable tracer of stream–groundwater interactions? A case study in central Italy

River water infiltration into an unconfined porous aquifer (∼73% gravels, ∼12% sands, ∼15% silts and clays) in the Petrignano d’Assisi plain, central Italy, was traced combining isotopic techniques (²²²Rn) with hydrochemical and hydrogeologic techniques in order to characterize the system under study. The ²²²Rn gave information about the river water residence times within the aquifer and hydrochemical data, in a two-component mixing model, which allowed estimating the extent of mixing between surface waters and groundwater in wells at increasing distances from the river. The mixing measured in the well closer to the riverbank indicated a higher contribution of river water (up to 99%) during the groundwater recession phase and a moderate contribution (up to 64%) during the recharge phase. A model describing ²²²Rn concentrations in groundwater as the result of both parent/daughter nuclide equilibrium and mixing process (²²²Rn mixing/saturation model) was used to describe observed Rn concentrations and mixing index trends with the aim of evaluating water mean infiltration velocities along the transect. The stream bank infiltration velocities obtained by the model ranged from 1 m day⁻¹ during groundwater recharge periods, when river water infiltration is lower, to 39 m day⁻¹ during recession phases, when river water infiltration is larger.     

The relationship of soil 210Po and 210Pb geochemical dispersion patterns to uranium mineralization

²¹⁰Po and ²¹⁰Pb measurements of soils delineated uranium anomalies at three out of four test sites in Ontario, Canada. Measurements were made of ²¹⁰Po in solutions produced by both complete digestion and partial leaching of soil samples. Direct plating of ²¹⁰Po onto metal plates was followed by measuring the alpha activity. Subsequent plating of ²¹⁰Po in-grown from ²¹⁰Pb in solution several months later confirmed the anomalies.The ²¹⁰Po and ²¹⁰Pb anomalies at three of the test sites coincided with ²²⁶Ra and ²²²Rn anomalies. Samples from the fourth uranium occurrence associated with a known ²²²Rn anomaly failed to show either a ²²⁶Ra anomaly on the one hand, or ²¹⁰Po or ²¹⁰Pb anomalies on the other. This suggests that the ²¹⁰Po and ²¹⁰Pb anomalies were probably produced by the decay of ²²⁶Ra contained within secondary dispersion haloes.Although anomalies due to the ²¹⁰Po and ²¹⁰Pb products of ²²²Rn have now been documented, prospecting methods based on their use as direct tracers of the migration paths of ²²²Rn require much further development.     

Statistical analysis of the radon-222 potential of rocks in Virginia,U.S.A.

More than 3,200 indoor radon-222 (²²²Rn) measurements were made seasonally in an area of about 1,000 square kilometers of the Coastal Plain and Piedmont physiographic provinces in Virginia, U.S.A. Results of these measurements indicate that some geological units are associated, on the average, with twice as much indoor²²²Rn as other geological units, and that indoor²²²Rn varies seasonally. The Kruskal-Wallis test was used to test whether indoor²²²Rn concentrations for data gathered over the winter and summer seasons differ significantly by rock unit. The tests concluded that indoor²²²Rn concentrations for different rock units were not equal at the 5-percent significance level. The rocks associated with the highest median indoor²²²Rn concentration are specific rocks in the Mesozoic Culpeper basin, including shale and siltstone units with Jurassic diabase intrusives, and mica schists in the Piedmont physiographic province. The pre-Triassic Peters Creek Schist has the highest ranking in terms of indoor²²²Rn concentration. The rocks associated with the lowest indoor²²²Rn concentrations include coastal plain sediments, the Occoquan Granite, Falls Church Tonalite, Piney Branch Mafic and Ultramafic complex, and unnamed mafic and ultramafic inclusions, respectively. The rocks have been ranked according to observed²²²Rn concentration by transforming the average rank of indoor²²²Rn concentrations to z scores.     

The relationship of soil Po and Pb geochemical dispersion patterns to uranium mineralization

²¹⁰Po and ²¹⁰Pb measurements of soils delineated uranium anomalies at three out of four test sites in Ontario, Canada. Measurements were made of ²¹⁰Po in solutions produced by both complete digestion and partial leaching of soil samples. Direct plating of ²¹⁰Po onto metal plates was followed by measuring the alpha activity. Subsequent plating of ²¹⁰Po in-grown from ²¹⁰Pb in solution several months later confirmed the anomalies.The ²¹⁰Po and ²¹⁰Pb anomalies at three of the test sites coincided with ²²⁶Ra and ²²²Rn anomalies. Samples from the fourth uranium occurrence associated with a known ²²²Rn anomaly failed to show either a ²²⁶Ra anomaly on the one hand, or ²¹⁰Po or ²¹⁰Pb anomalies on the other. This suggests that the ²¹⁰Po and ²¹⁰Pb anomalies were probably produced by the decay of ²²⁶Ra contained within secondary dispersion haloes.Although anomalies due to the ²¹⁰Po and ²¹⁰Pb products of ²²²Rn have now been documented, prospecting methods based on their use as direct tracers of the migration paths of ²²²Rn require much further development.     

Uranium prospecting with Rn in frozen terrain

Published reports show that ²²²Rn contents of soil gas can increase under snow-covered or frozen soils. By utilizing these observations and results of field tests described here, it can be stated that U prospecting with ²²²Rn in frozen terrain is practicable.Rn profiles in frozen and snow-covered soils over U mineralization in the Bancroft area of Ontario outlined known radioactive zones more clearly than did scintillometer profiles.Tests in Gatineau Park, Quebec, in the proximity of a radioactive pegmatite dike showed that lake ice acts as a restrictive barrier to Rn movement from lake waters beneath. Water samples, collected and allowed to freeze in plastic bottles, retained dissolved Rn quite effectively thus permitting sample collection and storage under the most severe winter conditions. Rn sampling of through-ice lake waters is therefore a feasible prospecting tool.Samples of spring run-off (snow-melt) waters and slushy snow collected from within a known weakly radioactive zone near South March, Ontario, were shown to contain less Rn than found in the same stream waters in the summer. No pronounced Rn degassing event of frozen soils was apparent early in the spring thaw in percolating run-off waters draining from the zone. The usefulness of spring thaw hydrogeochemistry using Rn is discussed.     

Time lapse tracer and SP measurements to characterize the hydrodynamics of fractured granite aquifer: A case study

An attempt is made to identify and delineate the groundwater flow direction and rate in a fractured hard rock aquifer in Maheshwaram granite watershed in Andhra Pradesh using multiple tracers such as bromide, iodide and rhodamine-B under both natural and induced conditions. A main well in the center and three observation wells at 25 m in north-northwest, southeast and southwest directions respectively were constructed based on ²²²Rn anomalies and ⁴He measurements. Streaming potential survey was also carried out in the area before, during and after pumping test. The tracer tests indicated preferential groundwater flow in N-S direction. The groundwater flow velocity estimated based on arrival of tracer under natural and induced conditions are 0.52 m/d and 375 m/d respectively.     

Helium, radon and radiocarbon studies on a regional aquifer system of the North Gujarat-Cambay region, India

The study reports the age evolution of groundwater as it flows from the recharge area through a regional alluvial aquifer system in North Gujarat-Cambay region in western India. Radiocarbon (¹⁴C), ⁴He and ⁴He / ²²²Rn dating methods have been employed. Sediments from a drill core in the Cambay Basin were also analysed for uranium (U) and thorium (Th) concentrations and the measured values have been used to estimate the ⁴He and ²²²Rn production rate for groundwater age calculations. Additionally, factors controlling the distribution of ²²²Rn, ⁴He and temperature anomalies in groundwater, vis-à-vis their relation to the tectonic framework and lithology of the study area, have also been examined.The multi-isotope study indicated a reasonable correspondence in groundwater age estimates by the three methods employed. The groundwater ¹⁴C ages increased, progressively, in the groundwater flow direction: from the foothills of Aravalli Mountains in the east, and reached a value of ∼35 ka towards the region of lowest elevation, linking Little Rann of Kachchh (LRK)-Nalsarovar (NS)-Gulf of Khambhat (GK) in the western part of the study area. In this region, groundwater ages obtained for free flowing thermal wells and springs employing ⁴He and ⁴He / ²²²Rn systematics are in the order of million years. Such anomalous ages are possibly due to enhanced mobilisation and migration of ‘excess helium’ from hydrothermal circulation vents along deep-seated faults. Excluding such anomalous cases and considering all uncertainties, presently estimated ⁴He and ⁴He / ²²²Rn groundwater ages are in reasonable agreement with ¹⁴C age estimates in the Cambay Basin for helium release factor (Λ_He) value of 0.4 ± 0.3. The ⁴He method also indicated west-southwards progression of groundwater ages up to ∼100 ka beyond the Cambay Basin.Large ‘excess helium’ concentrations are also seen to be generally associated with anomalous groundwater temperatures (> 35 °C) and found to overlie some of the basement faults in the study area, particularly along the east and the west flanks of the Cambay Basin. Groundwater ²²²Rn activities in most of the study area are 800 ± 400 dpm/l. But, a thermal spring at Tuwa on the east flank of the Cambay Basin, having granitic basement at shallow depth, recorded the highest ²²²Rn activity (∼63,000 dpm/l).     

Rn solution by the circulating fluids in a “hot dry rock” geothermal reservoir

The mechanism of²²²Rn release into fracture fluids by direct alpha-recoil, lattice and grain boundary/micro-crack diffusion is discussed. Experimental measurements of²²²Rn release into surrounding air and water phases have been made for crystalline rock specimens with well defined surface areas. The²²²Rn flux from an infinite plane surface and hence the effective diffusion length of²²²Rn in the rock matrix has been estimated.The²²²Rn flux from plane crystalline rock surfaces has been used in conjunction with a simple hydrological model of the reservoir to calculate the²²²Rn content of the return fluids of a geothermal doublet circulation system. For given production rate and piezometric difference between the injection and production wells, the²²²Rn content of the return fluid is dependent upon the distribution of flow path lengths and fracture apertures in the reservoir. Matching of the calculated and experimental²²²Rn contents of the return fluids has been used to select appropriate parameters for the reservoir model and hence to estimate the extent of the heat-transfer surface. The model estimates the fracture width of the flow paths, total swept surface area and fracture volume within the reservoir.     

222Rn solution by the circulating fluids in a “hot dry rock” geothermal reservoir

The mechanism of²²²Rn release into fracture fluids by direct alpha-recoil, lattice and grain boundary/micro-crack diffusion is discussed. Experimental measurements of²²²Rn release into surrounding air and water phases have been made for crystalline rock specimens with well defined surface areas. The²²²Rn flux from an infinite plane surface and hence the effective diffusion length of²²²Rn in the rock matrix has been estimated.The²²²Rn flux from plane crystalline rock surfaces has been used in conjunction with a simple hydrological model of the reservoir to calculate the²²²Rn content of the return fluids of a geothermal doublet circulation system. For given production rate and piezometric difference between the injection and production wells, the²²²Rn content of the return fluid is dependent upon the distribution of flow path lengths and fracture apertures in the reservoir. Matching of the calculated and experimental²²²Rn contents of the return fluids has been used to select appropriate parameters for the reservoir model and hence to estimate the extent of the heat-transfer surface. The model estimates the fracture width of the flow paths, total swept surface area and fracture volume within the reservoir.     

Radon-222 in medicinal groundwaters of Szczawno Zdrój (Sudety Mountains, SW Poland)

 Radon is a significant component of the groundwaters that discharge in the springs of Szczawno Zdrój and are recognized as medicinal. However, among the five exploited springs adjoining each other, it is only in Marta Spring that radon occurs in large concentrations (up to 325.6 Bq/dm³). Therefore, the authors have made an attempt to describe and clarify this fact. They found out from their own research and archival data that ²²²Rn dissolves in the waters of Marta Spring after acidulous waters of deep circulation have mixed with poorly mineralized shallow waters in their outflow zone. The genesis of the gas is determined by the content of its parent nuclide, ²²⁶Ra, in the sandstones in the vicinity of the intake. The volume of the rocks providing radon to the waters of this intake has been estimated at several hundred cubic metres. No seasonal fluctuations in radon concentration have been observed and ²²²Rn concentration changes do not seem to be influenced by changes in the concentration of other chemical components of the waters or by the discharge of the intake. The process of dissolving ²²²Rn in the medicinal groundwaters of Marta Spring is the last, the shortest, and the most local of the processes that form the chemical composition and the physical properties of these waters. Received: 7 January 2000 · Accepted: 12 August 2000     

Combined use of natural and artificial tracers to determine the hydrogeological functioning of a karst aquifer: the Villanueva del Rosario system (Andalusia,southern Spain)

Analysis of natural responses of karst springs provides information on the behavior of the aquifers they drain. Detailed monitoring and qualitative and quantitative analyses of natural responses, and environmental—total organic carbon (TOC), NO₃ ^?, Cl^? and intrinsic fluorescence—and artificial (fluorescent dye) tracers, in the water drained by Villanueva del Rosario spring (southern Spain), suggest the existence of a conduit flow system with rapid flows and very short transit times of water through the aquifer. This is in agreement with uranine and eosin breakthrough curves and with simple numerical models done using these data. However, due to the low capacity for natural regulation, not all the recharge effects are simultaneously transmitted to the spring water; given a single input, the system modulates and transfers hydrodynamic variations faster than variations of chemical composition and of water temperature. Additionally, time lags between maximum concentrations of natural and artificial tracers show that the global system response (including diffuse infiltration) is faster and more sensitive than that produced from infiltration concentrated at a single point on the surface (sinkholes).