Large Springs Research Articles

Hydrogeological and historical aspects of the water supply of Benevento town since Roman times

The research analyses the historical evolution of the water supply systems of the city of Benevento (southern Italy) during centuries. We focused on three main historical periods, namely the Roman, Lombard and Papal times, and the recent-present times. During this long historical time, the water supply amount and quality have changed many times, and this has probably affected the well-being and growth of the city. The best water quality characterized the Roman times, when large karst springs were tapped, feeding the town for centuries. In this period, the town experienced the largest population expansion. On the other hand, the most depressed period was the Papal times, coinciding with the isolation of the city, as it was an enclave of the Pontifical State. During this period, the water supply from external sources was not guaranteed and therefore it primarily derived from the local, low-quality water resources. Only after the unification of Italy, and also after the Second World War, the water supply systems have been improved, and new aqueducts have brought again high-quality waters to Benevento coming from karst aquifers. Nowadays, the drinking water management of Benevento is still a matter of debate. In the near future, the water from a dam-reservoir (Campolattaro dam, Tammaro River) will be exploited to guarantee the water needs of the city, and water-supply systems will undergo further changes . The knowledge about the historical evolution of the water supply of Benevento represents an essential requirement for consciously analyzing the future planning and management of water resources.

Strategies for Sustainable Water Management

Groundwater in the Rania basin, Iraqi Kurdistan region, has been under intensive exploitation in the last two decades, where quantity and quality are both affected. Hence, any attempt to protect the aquifers has become an urgent need. Saruchawa, Qulai Rania, and Qulai Kanimaran are the three large springs, among dozens of others in the area, that are heavily relied on as the sole or main source of water supply. Hydrochemical analysis, the first and most practical step to evaluating the water quality, was carried out through 60 water samples collected from 13 springs and 17 wells in both dry and wet seasons (October 2018 and May 2019). Laboratory results show a high calcium bicarbonate concentration with weak acids’ dominance. Protection zones are delineated for these springs using aquifer susceptibility to contamination and analysis of the recession part of the spring curves. The equivalent relationship between the protection factor (Fp) produced by the Epikarst, protective cover, infiltration condition, and Karst network development mapping method and the groundwater protection zone (S) is considered. Qulai Rania and Kanimaran Springs are mapped to be in S2 (a highly vulnerable area), whereas Saruchawa Spring is located in S1 (very highly vulnerable). Based on the second method results (recession curve analyses), all three selected springs fall under the (D-type) vulnerability category. As a result, the immediate protection zone was going to be surrounded by the inner protection zone, and both are enclosed within the outer protection zone, which covers the remainder of the catchment area.

Design and Rate Control of Large Titanium Alloy Springs for Aerospace Applications

During the separation between satellite and launch vehicles, large steel springs are often used as compression separation spring sets in a catapult separation system. Replacing the steel springs with titanium alloy springs could reduce weight by about 50%. Although titanium alloy springs have been widely used in the aerospace field due to their excellent performance, there are few reports on the design of high-precision titanium alloy springs. The current spring design standards mainly focus on steel springs with helix angles between 5° and 9°, which are not applicable to titanium springs. Moreover, the change in spring rate with ambient temperature should also be considered. In this paper, β-C titanium alloy was used to design and prepare large compression separation springs, replacing steel springs in the catapult separation system. The design of titanium alloy springs took into account the big helix angle. The relationship between helix angle and the number of active coils was calculated. The parameters of titanium alloy springs were determined by the shear stress of the spring at working length. The effects of aging temperature and aging duration on the mechanical properties and modulus of β-C alloy were studied. By adjusting the aging process, the β-C alloy spring rate was controlled to meet the design requirements. The effect of ambient temperature on the mechanical properties and modulus of β-C titanium alloy were also investigated. It was found that as the ambient temperature increased, the rate of the β-C alloy spring gradually decreased.

Complex hydrology and variability of nitrogen sources in a karst watershed.

Streams draining karst areas with rapid groundwater transit times may respond relatively quickly to nitrogen reduction strategies, but the complex hydrologic network of interconnected sinkholes and springs is challenging for determining the placement and effectiveness of management practices. This study aims to inform nitrogen reduction strategies in a representative agricultural karst setting of the Chesapeake Bay watershed (Fishing Creek watershed, Pennsylvania) with known elevated nitrate contamination and a previous documented groundwater residence time of less than a decade. During baseflow conditions, streamflow did not increase with drainage area. Headwaters and the main stem lost substantial flow to sinkholes until eventually discharging along large springs downstream. Seasonal hydrologic conditions shift the flow and nitrogen load spatially among losing and gaining stream sections. A compilation of nitrogen source inputs with the geochemistry and the pattern of enrichment of δ15N and δ18O suggest that the nitrogen in streams and springs during baseflow represents a mixture of manure, fertilizer, and wastewater sources with low potential for denitrification. The pH and calcite saturation index increased along generalized flow paths from headwaters to springs and indicate shorter groundwater residence times in baseflow during the spring versus summer. Given the substantial investment in management practices, fixed monitoring sites could incorporate synoptic water sampling to properly monitor long-term progress and help inform management actions in karst watersheds. Although karst watersheds have the potential to respond to nitrogen reduction strategies due to shorter groundwater residence times, high nitrogen inputs, effectiveness of conservation practices, and release of legacy nutrients within the karst cavities could confound progress of water quality goals.

Karst Aquifer Characterization by Means of Its Karstification Degree and Time Series Analysis (Case: Ngerong Spring in Rengel Karst, East Java, Indonesia)

The purpose of this study is to define the characteristics of the karst aquifer, which is approximated by the parameters of (1) degree of karstification (Dk) and (2) time series analysis (cross-correlation and auto-correlation). This research focuses on the Ngerong Spring, the largest spring in Rengel Karst, East Java, Indonesia. Pendant rain gauge RG-3M and HOBO U20L-02 water-level data loggers were installed over one year with a recording interval of 15 minutes. Furthermore, after one year of time-series discharge data was obtained, the discharge recession coefficient was applied to make the recession formula. It was then used to estimate the karstification degree scale from 1 to 10. The aquifer memory system and the spring response to rainfall events were analyzed by auto-correlation and cross-correlation. The results of this study indicate that the karstification degree (Dk) of the Ngerong Spring system is 4.8-5.0, with one laminar and one turbulent flow subregime type. The aquifer system comprises a subregime with turbulent and laminar flow, where the substantial role in groundwater discharge plays the subregime with laminar flow. Meanwhile, time series analysis shows that the capacity of aquifer storage in the Ngerong Spring is large enough. It has a memory effect for 26.41 days, followed by a rapid response to rainfall events within 8 hours. Compared with several other karst sites in Java, the Ngerong Spring aquifer has the youngest development level with the best storage and the slowest release.

Development of a deployable mechanism for a conical optical baffle for a small satellite

Baffles in optical systems on a satellite, such as imaging payloads and star trackers, involve structures with large empty volumes that take up significant payload volume. Limiting the volume of optical systems is essential, considering the demand for small satellite platforms and rideshare launch missions. A baffle structure with empty volume can be configured to stow in a packed configuration during launch and deploy to its operational configuration once the satellite is in orbit. An analytical model for deployable conical baffles is developed to trade off various design parameters. A simple and reliable deployment mechanism with large torsion springs is designed and developed for an optical baffle. A prototype baffle is developed with representative materials, and functional testing is carried out. The deployment tests were carried out to measure the shocks and deployment accuracy. The baffle in its stowed configuration performed satisfactorily and indicated no damages when subjected to vibration testing. Further, the deployment mechanism performed adequately at a low temperature of -40°C and at 0.062 mPa during the cold functional test in a thermovac chamber. The baffle is a precursor to the flight model, which will be launched as a part of a hyperspectral imager, CyanoSat of CSIRO.

Illuminating the complexity of hydrogeological regimes in fault-influenced, anticlinal karst aquifers: Insights into the recharge patterns in tectonically complex karst catchments

For many countries, karst aquifers are a significant source of potable water; thus, understanding their hydrogeological behavior is of great importance. However, in tectonically complex karst areas, knowledge of their hydrogeological behaviors has remained largely limited due to the high heterogeneity, often necessitating the use of costly and time-consuming techniques. In this study, spring discharge hydrographs, water balance estimates, hydrochemical and stable isotopic analyses, geomorphological surveys, and a consideration of the geological and structural setting of the study area were used to investigate the hydrogeological function of karst aquifers drained by two large permanent springs: the Bibitalkhone (Bt) and Sabzab (Sa) springs, located in a highly faulted catchment in the Zagros Mountains (southwest Iran). The results obtained from these different approaches suggested that fault-controlled, external waters from neighboring karst aquifers are responsible for more than two-thirds of the total discharge recorded at both springs. In this study, this predominantly conduit-type recharge is referred to as “regional (or external) autogenic recharge”. A smaller portion of the springs’ discharge (∼25% and ∼5% of the Bt and Sa springs’ discharge, respectively) originates from internal waters associated with the springs’ host aquifer, which is supplied by rainfall and infiltrates into the subsurface via joints and fractures. This type of recharge is largely diffuse and is referred to here as “local (or internal) autogenic recharge”. A relatively large portion of the Sa Spring’s discharge (∼35%) originates from a nearby dam reservoir, which can leak into the host spring aquifer through joints and fractures. This type of recharge is described as “local (or internal) allogenic recharge” and is primarily diffuse. The results of this study demonstrate that the karst aquifers in the downstream catchments can supply a stable and continuous source of potable groundwater that can meet the region’s annual consumption, agricultural, and industrial demands. This study will provide insights into the hydrogeological regimes of fault-influenced aquifers, contributing to the sustainable development and proper management of water resources in tectonically complex karst catchments.

Assessing the persistence, mobility and toxicity of emerging organic contaminants in Croatian karst springs used for drinking water supply

Emerging organic contaminants (EOCs) are a vast group of often (very)persistent, (very)mobile and toxic (PMT/vPvM) substances that are continuously released worldwide, posing environmental and human health risks. Research on occurrence and behavior of EOCs in karst is in its infancy, thus policy measures and legislative control of these compounds in groundwater are still lacking. The Dinaric karst aquifers are an essential source of drinking water for almost half of Croatia's territory. Intense karstification, complex heterogeneous characteristics, and high fracture-cavernous porosity result in rapid, far-reaching groundwater flow and large karst springs, but also high intrinsic vulnerability due to low contaminant attenuation. To prioritize future monitoring and establish appropriate thresholds for EOCs detected in Croatian karst drinking water resources, in silico tools based on quantitative structure-activity relationships were used in PBT (persistence, bioaccumulation, and toxicity) and PMT/vPvM analyzes, while toxicological assessment helped identify potential threats to human health. In 33 samples collected during two sampling campaigns in 2019 at 16 karst springs and one lake used for water supply, we detected 65 compounds (EOCs and some legacy chemicals), of which 7 were classified as potentially PBT or vPvB compounds (PFOS, PFHxS, PFHpA, PFOA, PFNA, boscalid, and azoxystrobin), while only 2 compounds were assessed as not PMT/vPvM. This finding underlines that most of detected EOCs potentially endanger karst (ground)water ecosystems and important drinking water sources in Croatia. Comparison of maximum concentrations with existing or derived drinking water guideline values revealed how 2 of 65 detected compounds represent a potential risk to human health at lifelong exposure (sulfadiazine and hydrochlorothiazide), while 5 chemicals warrant additional human health impacts studies and groundwater monitoring. Although most compounds do not individually pose a significant risk to human health at current environmental levels, their potential synergistic and long-term effects remain unknown.

Regional Analysis of Tracer Tests in the Karstic Basin of the Gacka River (Croatian Dinaric Karst)

Tracer testing is the only method in karst hydrogeology that can definitively determine whether a particular site belongs to a watershed of a particular karst spring. Therefore, it is an essential technique for delineating groundwater basins in karst areas. The availability of tracer test results is often limited due to the complicated and relatively expensive application of this approach, especially for large regional watersheds. The Croatian part of the Dinaric karst region extends for several hundred kilometers along the Adriatic coast and consists almost entirely of highly karstified carbonate rocks. The groundwater basins in these areas almost never match the surface morphology of the terrain. In practice, all available results of previous surveys are often used to define watersheds, regardless of the methodology and age of their implementation. This is also true for the earlier delineations of the Gacka River watershed, a regional karst basin in the Croatian Dinaric karst. However, tracer testing methods, especially the accuracy of tracer determination and monitoring, have improved significantly during this time. In order to assess the reliability of past tracing results in this significant karst basin, we reviewed reports of previous tracer tests. More recent tests, in particular the most recent multitracer injection test with continuous tracer detection on the major springs, produced high-quality data that allowed us to assess the reliability of the findings from prior research. A number of large karst springs with partially overlapping subcatchments feed the Gacka River. After discarding unreliable tracing data, we reevaluated the subcatchments of the main springs as well as the characteristics of the regional groundwater flow patterns throughout the basin, which is particularly important for water quality protection measures of the springs. The Gacka River basin is used as a case study to emphasize the importance of thoroughly assessing the reliability of previous tracing data before using them in regional analyses.

Emerging organic contaminants in springs of the highly karstified Dinaric region

Emerging organic contaminants (EOCs) have become of increasing interest due to concerns about their impact on humans and the wider environment. Karst aquifers are globally widespread, providing critical water supplies and sustaining rivers and ecosystems, and are particularly susceptible to pollution. However, EOC distributions in karst remain quite poorly understood. This study looks at the occurrence of EOCs in the Croatian karst, which is an example of the “classical” karst, a highly developed type of karst that occurs throughout the Dinaric region of Europe. Samples were collected from 17 karst springs and one karst lake used for water supply in Croatia during two sampling campaigns. From a screen of 740 compounds, a total of 65 compounds were detected. EOC compounds from the pharmaceutical (n = 26) and agrochemical groups (n = 26) were the most frequently detected, while industrials and artificial sweeteners had the highest concentrations (range 8–440 ng/L). The number of detected compounds and the frequency of detection demonstrate the vulnerability of karst to EOC pollution. Concentrations of 5 compounds (acesulfame, sucralose, perfluorobutane sulfonate, emamectin B1b, and triphenyl phosphate) exceeded EU standards and occurred at concentrations that are likely to be harmful to ecosystems. Overall, most detections were at low concentrations (50 % <1 ng/L). This may be due to high dilution within the exceptionally large springs of the Classical karst, or due to relatively few pollution sources within the catchments. Nevertheless, EOC fluxes are considerable (10 to 106 ng/s) due to the high discharge of the springs. Temporal differences were observed, but without a clear pattern, reflecting the highly variable nature of karst springs that occurs over both seasonal and short-term timescales. This research is one of a handful of regional EOC investigations in karst groundwater, and the first regional study in the Dinaric karst. It demonstrates the need for more frequent and extensive sampling of EOCs in karst to protect human health and the environment.

Arthur Marble Aquifer and Te Waikoropupu Springs, New Zealand: flow contributions and nitrate sources

This paper investigates sources of early signs of nitrate pollution in a karst aquifer and major karst spring. Te Waikoropupu Springs are the largest springs in New Zealand and amongst the largest in the Southern Hemisphere with a mean outflow of 13.4 m3/s. They discharge the clearest water ever recorded from a karst spring, but early warning of water quality deterioration is signalled by increasing nitrate concentrations. The springs discharge water from a partly artesian aquifer of 2.85 km3 volume in karstified Ordovician marble with a transmission time averaging 7.9 years. Reservoir porosity is unusually high for a crystalline carbonate rock, estimated as 6%. Water emerging at Main Spring (9.89 m3/s) and adjacent Fish Creek Springs (3.48 m3/s) is a mix of recharge from four main sources. The paper investigates by means of mass balance modelling the proportions of water coming from each source, the origins of nitrate contamination and the contribution of nitrification. Water losses into the bed of the upper Takaka River, about 17 km from the Springs, provide 13% of the mean flow at Main Spring, 34% of the flow at Fish Creek Springs, and 83% of the volume discharged at submarine springs. Infiltration from rain falling over farmed land in the middle valley is estimated to supply 10% of total outflow at Main Spring and Fish Creek Springs but to contribute 82% of the NO3-N output discharged at the springs. Nitrification accounts for 16% of the nitrate discharged. A 34% reduction of leachate concentration in the middle valley would be required to bring NO3-N values at Main Spring back to levels recorded in the 1970s.

The distribution, magnitude, and endemic species of US springs

Freshwater springs and other groundwater-dependent ecosystems represent important natural resources in landscapes, providing consistent, high-quality water to both freshwater and terrestrial organisms. However, spring and GDE conservation does not appear to be a prominent feature on the US conservation radar. Therefore, this study evaluated the distribution and size of springs in the US with the national water dataset: the US Geological Survey National Water Information System. Using all available measurements of spring discharge and the sampling dates for all springs with data in the dataset (10,279 springs), I compared the number and sizes of springs between states and, where time series were available, determined whether the springs were maintaining historic discharges. I evaluated data quality using the date of the last sampling, number of times sampled, and the length of time sampled for each spring. Finally, I searched the literature for spring endemic species and recorded the states in which they occurred. Within the database, springs were most abundant in western states, but average discharges were largest for states in the southeast and for Idaho and Alaska. Very large springs occurred in some western states, but the multitudes of tiny springs reduced the average discharges. The data were poorly resolved as many of the springs had been sampled only once, often 40–50 years ago. Time series were available only for 126 springs and half of these springs exhibited declines in discharge. Endemic species were mentioned in the literature for 24 states, particularly those in the lower half of the country, and so loss of spring integrity would threaten biodiversity in many states. Due to the poor resolution of the data, broad conclusions about the integrity of these important freshwater systems are difficult to impossible to make for most states using the national dataset. Therefore, I call for a concerted national effort to more broadly evaluate spring and GDE resources. Springs and GDEs are likely to become even more important in the future as climate changes and their roles as freshwater refuges, temperature buffers, and bellwethers become even more important.

Aquatic Macroinvertebrate Community Structure along a Continuum in a Spring Dominated River, Missouri, USA

The Current River is a cold-water, thermally constant Missouri Ozark stream and is one of the few remaining free-flowing rivers in the U.S. The Current River’s baseflow is largely fed by hundreds of springs, which include five first-magnitude springs. Little attention has been given to the influence of spring inflows on river temperature and spring influence on biodiversity. The objectives of this study were to demonstrate how large springs affect river macroinvertebrate communities, and to explore the relationships among macroinvertebrate diversity and habitat variables to estimate spring influences on community structure and diversity. Aquatic macroinvertebrates were collected from 42 riffle/run habitats of the Current River main-stem, tributaries, and springs during the winter season. Samples at each site were collected using a Slack-Surber sampler for macroinvertebrates with additional habitat variables collected: substrate size, embeddedness, periphyton, filamentous green algae, vegetation, depth, current velocity, temperature, dissolved oxygen, specific conductance, and pH. Beta diversity analysis was performed on consecutive pairs of site taxa richness values using the Wilson–Shmida calculation to determine the impact of main-stem confluences with either tributaries or springs, and invertebrate community relationships were explored using nonmetric multidimensional scaling (NMDS). Water temperature and taxa richness exhibited similar patterns, with higher temperatures being associated with lower taxa richness. Downstream of each large-magnitude spring, taxa richness sharply decreased, while taxa richness increased downstream of tributaries. Beta diversity usually declined downstream of the confluences with springs, but increased downstream of the tributaries. Data from large springs were closely grouped in NMDS, while tributaries and main-stem sites were more widely scattered. These data indicate spring inputs produce more homogenous conditions in the main-stem river compared to more heterogenous conditions produced by tributary inputs. Macroinvertebrate diversity along the Current River also does not follow predictions from the river continuum concept, but rather diversity peaks are downstream of springs. Our data clearly demonstrate the strong influence of large springs on macroinvertebrate communities in the Current River.

PH results and coordination of spring waters in Gallaorol district, Uzbekistan

Samples of groundwater resources (spring waters) collected in Gallaorol district of Jizzakh region and their pH indicators were determined. Water samples were taken and examined from large springs in Gallaorol district. In addition, the coordinates of the location of the springs were determined using a special GPS (Global Positioning System) device, and coordination were presented. The results of chemical laboratory analysis showed that most of the spring waters showed a weak alkaline. The pH indicators of spring waters fully comply with the requirements of the State Standard of Uzbekistan “Hygienic requirements and quality control for domestic drinking water supply” (UzDSt 951:2011), as well as “Hygienic requirements for drinking water and quality control” (UzDSt 0950:2011).

Probable reasons for interruption of the flow of the Iskrets karst spring

The object of research is the Iskrets spring, one of the large and important karst springs in Bulgaria. A characteristic feature of its regime is the temporary interruptions of its outflow. The purpose of the research is to establish the probable causes and mechanism for these interruptions. After analyzing the hydrogeological situation and data from the results of continuous measurements of changes in water quantities, it is assumed that the main cause of this phenomenon is the processes of erosion, transport and deposition of cave alluvial sediments.

Hydrological features of Matese Karst Massif, focused on endorheic areas, dolines and hydroelectric exploitation

ABSTRACT This study presents an original mapping of hydrological karst features of the Matese massif (southern Italy), whose relevance is given by large basal springs supplying millions of people and the hydroelectric exploitation of the major endorheic areas. We mapped dolines and endorheic areas from 1- and 5-meter Digital Elevation Models (DEM) using Geographic Information System (GIS) tools and techniques. Instead, ponors, caves, and karst springs were mapped mainly based on cartographic and literature analyses. We identified 321 endorheic areas occupying 31% of the massif area and 489 dolines, distinguished in (i) solution (N = 433) and collapse dolines (N = 56), the latter located in the discharge zones of the massif and connected to ascendant flows of CO2- and H2S-rich groundwater. The map shows the hydrological features of a karst massif from a more detailed and new perspective, and it can be helpful in water management, groundwater resource protection, environmental safeguarding, and ecological development.

Population Density and Reproductive Seasonality of Tryonia cheatumi (Gastropoda: Cochliopidae), the Phantom Tryonia

We studied population density, population size, and reproductive seasonality of the Phantom Tryonia, Tryonia cheatumi (Pilsbry, 1935). This endangered freshwater snail is found only in the San Solomon Spring system, a cienega, or karst-based, arid-land freshwater spring system, in western Texas, USA. We sampled populations at seven locations in the system seasonally over a 2-yr period. San Solomon Spring, the system's largest spring and modified into a swimming pool, had the largest population of T. cheatumi, with an estimated 49 million individuals and a mean density as high as 23,626 ± 39,030 (individuals/m2 ± SD). There were seasonal differences in mean density (up to 25-fold) and median snail size at all sites, but consistent seasonal patterns of mean density or size were not observed. Median snail size among samples was not related to water temperature, and juveniles were present in most samples in all seasons. These results support continuous, aseasonal reproduction, as expected in thermally stable habitats, but differences in median size and mean density among seasons and sites suggest that other factors affect reproduction and seasonal variation in population size of T. cheatumi.

제주도 강정마을의 물 문화에 대한 고찰

to lack of water. However, Gangjeong Village in Seogwipo-si has ‘Keunnae(Gangjeong River)’ and ‘Akeunnae(Akgeun River)’ that flow all year round, and large and small springs spring up, so it is blessed with natural conditions for rice farming. Therefore, Gangjeong Village was nicknamed ‘Ilgangjeong(Best Gangjeong)’. In Gangjeong, there are many stories about water that are hard to find in other areas of Jeju Island. In particular, Gangjeong-Rice and Gangjeong-Sweetfish are things that anyone from that village can be proud of. However, from the late 1980s, Gangjeong Village began to decline. With the construction of a water intake plant in Gangjeong and the development of groundwater, too much groundwater is being drawn up. As a result, the output of spring water sharply decreased and the price of rice plummeted, making rice farming less competitive. Now, Gangjeong-Rice and Gangjeong-Sweetfish, which were representative of Gangjeong, are left only as stories, and the work songs that were sung while farming rice remain only as lyrics. The stories about water in Gangjeong Village are the main ecological and cultural heritage of Jeju Island, where water was scarce. Before it is too late, it is necessary to restore the old appearance of Gangjeong and make it an Eco Museum. The water-themed ecological museum will serve as a foundation for preserving and transmitting the water cultural heritage of Ilgangjeong, raising the income of local residents by using local products, and will greatly contribute to restoring the divided village community

Characterizing Hydrological Functioning of Three Large Karst Springs in the Salem Plateau, Missouri, USA

Spring discharge hydrographs can provide information on karst aquifer connectivity and responses to precipitation. However, few studies have conducted time-series analyses of spring hydrographs over multi-decadal time scales. We examine daily discharge for three large karst springs and daily precipitation for adjoining weather stations during 1928–2019 in the Salem Plateau of southern Missouri, one of the major karst regions in the USA. For different time periods, we conducted baseflow index calculations and time-series (autocorrelation, spectral density, and cross-correlation with precipitation) analyses for discharge data, and Mann–Kendall (MK) trend analyses for discharge and precipitation data. Hydrograph separation indicates discharge is baseflow-dominated (86–94%) at all three springs. The memory effect is lower for Bennett Spring (with an auto-correlation lag time 29–41 days) than for Big Spring (60–92 days) and Greer Spring (77–112 days). Spectral density analysis indicates that annual signals dominate all three springs. Cross-correlation analysis shows a quicker response to precipitation at Bennett Spring (0–1 days) than at Big and Greer springs (1–2 days). MK trend analysis shows significant increases in discharge for all three springs over multiple decades, but not for the period 2007–2019. Increased discharge accompanies regional increases in precipitation, but may also reflect increased recharge associated with reversion of farmland to forest.

Deciphering complex groundwater age distributions and recharge processes in a tropical and fractured volcanic multi‐aquifer system

AbstractGroundwater recharge in highly fractured volcanic aquifers in the humid tropics remains poorly understood. In this region, rapid demographic growth and unregulated land use change are resulting in extensive surface water pollution and a large dependency on groundwater extraction. Here we present a multi‐tracer approach including δ18Oδ2H, 3H/3He dating, and noble gases (NG) within the most prominent multi‐aquifer system of central Costa Rica, with the objective to assess dominant groundwater recharge mechanisms and age distributions. We sampled wells and large springs across an elevation gradient from 868 to 2421 m asl. Our results indicate relatively young apparent ages ranging from 0.0 ± 3.2 up to 43.5 ± 7.6 years within the unconfined aquifer system. Helium isotopes (R/Ra up to 5.4) indicate a dominant signal from the upper mantle and preclude 3H/3He dating in 50% of the samples. Potential recharge elevations (based on NG and δ18O) ranged from ~1350 to 2670 m asl. NG‐derived recharge temperatures ranged from 11.0°C to 19.4°C. Recharge estimates varied from 129 ± 78 to 1605 ± 196 mm/yr with a mean value of 642 ± 117 mm/yr, representing 20.1 ± 4.0% of the total mean annual rainfall as effective recharge. The shallow unconfined aquifer is characterized by young and rapidly infiltrating water, whereas the deeper aquifer units have relatively older water (&gt;60 years). These results are intended to guide the delineation and mapping of critical recharge areas in mountain headwaters to enhance water security and sustainability in the most important headwater dependent systems of Costa Rica.