Cave Stream Research Articles

Cave Biodiversity of Cumberland Gap National Historical Park

Recognized as an important pathway between the east coast and the interior of the United States, much of the Cumberland Gap has been protected as part of the Cumberland Gap National Historical Park (CUGA). CUGA also contains extensive karst habitats, including Gap Cave, one of the longest caves in Virginia. With the aim of better understanding the cave biodiversity of CUGA, we conducted biological surveys in park caves and compiled records of other animals from CUGA caves, including bat monitoring data extending back more than 35 years. Results of that work include: (1) collecting five new cave-obligate species (troglobionts) from CUGA caves, increasing the number of troglobionts known from CUGA from 11 to 16; (2) increasing the total records of troglobionts in CUGA caves from 17 to 39; (3) finding an undescribed isopod (now described as Lirceus zigleri) in the Gap Cave stream; (4) noting six species of bats, including two federally endangered species—Indiana bats (Myotis sodalis) and northern long-eared bats (Myotis septentrionalis)—from CUGA caves; and (5) recognizing that Gap Cave once hosted one of the largest known populations of Indiana bats in Virginia. We present an annotated list of the animals found in the caves of the park. The caves of the Cumberland Gap National Historical Park provide critical habitat to two groups of species with distinct conservation concerns: poorly known troglobionts that exhibit extreme endemicity and bats under threat from white-nose syndrome disease.

Sexual dimorphism in subterranean amphipod crustaceans covaries with subterranean habitat type.

Sexual dimorphism can evolve in response to sex-specific selection pressures that vary across habitats. We studied sexual differences in subterranean amphipods Niphargus living in shallow subterranean habitats (close to the surface), cave streams (intermediate), and cave lakes (deepest and most isolated). These three habitats differ because at greater depths there is lower food availability, reduced predation, and weaker seasonality. Additionally, species near the surface have a near-even adult sex ratio (ASR), whereas species from cave lakes have a female-biased ASR. We hypothesized (a) a decrease in sexual dimorphism from shallow subterranean habitats to cave lake species because of weaker sexual selection derived from changes in the ASR and (b) an increase in female body size in cave lakes because of stronger fecundity selection on account of oligotrophy, reduced predation, and weaker seasonality. We measured body size and two sexually dimorphic abdominal appendages for all 31 species and several behaviours related to male competition (activity, risk-taking, exploration) for 12 species. Species with an equal ASR that live close to the surface exhibited sexual dimorphism in all three morphological traits, but not in behaviour. The body size of females increased from the surface to cave lakes, but no such trend was observed in males. In cave lake species, males and females differed neither morphologically nor behaviourally. Our results are consistent with the possibility that sexual and fecundity selection covary across the three habitats, which indirectly and directly, respectively, shape the degree of sexual dimorphism in Niphargus species.

Rapid evolution of salt glacier caves on a mountain diapir in a semiarid climate

Salt caves occur mostly in hyperarid and arid climates and are typically a few thousand years old. There is little data on the evolution of salt caves in semiarid climates, and no data on caves developed in salt glaciers, i.e., salt masses spreading under their own weight, similar to ice glaciers. The age of salt caves and the incision rates of cave streams were studied on a salt glacier of the Jahani diapir in a semiarid climate, Zagros Mts., Iran. Wood fragments from 3 caves sampled 0–11.3 m above the present streambed were dated by AMS 14C. The cave passages accessible today were developed during the last ~600 years at the Jahani. The cave level 5–6 m above the present streambed was formed 1520–1660 CE or slightly earlier, then the stream incised upward and reached its highest level between 1690 and 1920 CE or slightly earlier. Then, the downward incision started. This indicates that caves in semiarid climates evolve extremely rapidly. The maximum vertical incision rate of the cave stream on the semiarid Jahani diapir is 20–110 mm/yr, which is faster than 0.4–25 mm/yr in caves in hyperarid climates. The incision rate of the cave stream at the Jahani exceeds the denudation rate of the thick cap soil surface, being comparable to the denudation rate of salt exposures. The persistence of the steep longitudinal profiles of the integrated salt caves at the Jahani is probably caused by the transport of very coarse sediment. Aggradation was probably caused either by blocking of cave passages by earthquakes or by more intense erosion of the cap soil. The salt glacier at the Jahani is moving slowly (<10 mm/yr); claims that this glacier is the fastest on Earth (velocity in the range of m/yr) are based on a study that did not follow geodetic standards and are in strong disagreement with the age of the caves and other lines of evidence.

Rock Pigeon Cave, Colorado: development and mineralogy

The late Cretaceous Mancos Shale in western Colorado contains several vadose caves developed entirely within the shale. The largest of these, Rock Pigeon Cave, is over 300 m in length and contains a seasonal stream. The cave, and others like it, is hypothesized to develop as a result of the oxidation of disseminated pyrite in the shale by descending meteoric water with resulting sulfate ions reacting with the carbonate component of the shale to produce gypsum. The gypsum pries apart the shale, increasing its secondary porosity, and allows flowing water to remove shale particles via corrasion. As these particles are removed, they are transported down-gradient to an outlet, allowing continuous openings (cave passages) to develop. Extensive sulfate mineralization is observed within the cave and takes several forms: soft globular deposits on rocks at water level, a white to tan crust on shale surfaces, dry crusts on the passage floor following evaporation of pools, and needle and hair-like extrusions on passage walls. Powder X-ray diffraction (XRD) indicates that these deposits are a mixture of thenardite and blodite with lesser amounts of gypsum, hexahydrite, and konyaite. Na+, Mg2+, and SO4 2- ions in the entering stream are the source of the sulfate minerals at stream level and on the wetted slopes above. These come out of solution as the cave stream and pools evaporate with sulfates precipitating as saturation is reached. Fibrous, needle-like sulfates on walls above the wetted zone are a result of crystallization by evaporation: fluids containing sulfate ions are extruded and evaporate at the rock/air interface. Other minerals, e.g., deposits containing goethite and jarosite, are seen on passage walls as reaction products from oxidation of pyrite in the shale.

First insight in cyanobacterial and algal communities from cave stream (Stopić Cave, Serbia)

First insight in cyanobacterial and algal communities from cave stream (Stopić Cave, Serbia)

Divergent Geochemical Pathways of Carbonate Aquifer Evolution in a Classic Karst Terrain: (1) Polygenetic Cave Development Identified Using Longitudinal Groundwater Geochemistry

Carbonic acid and sulfuric acid speleogenesis describe a dichotomy between epigenetic and hypogenetic caves and carbon and sulfur cycling in karst, but do not acknowledge the global spectrum of cave formation. This paper, part one of a two-part investigation, tests and revises speleogenetic models from a classic karst landscape using dissolved ion concentrations δ13CDIC, and δ34S in water samples collected at four sites across the Bluespring and Lost River karst basins in the Mitchell Plateau, Indiana, USA. Analyses revealed elevated sulfur in both karst basins but differently sourced; H2S (δ34S = −14.2‰) evolved from petroleum seeps in Bluespring Caverns accounted for up to 61% of sulfur in the cave stream, while evaporite beds (δ34S = [+14.50‰, +17.91‰]) of the St. Louis Limestone contributed up to 100% of sulfur at Orangeville Rise, a terminal spring of the Lost River karst basin. These results have implications for carbon–sulfur cycle linkages, particularly the potential acceleration of carbon flux from sulfuric acid dissolution in otherwise epigenetic settings. We suggest a new paradigm for speleogenesis in the North American midcontinent—speleogenesis in the Mitchell Plateau and similar settings is not epigenetic or hypogenetic, but instead polygenetic with competing chemical processes varying across space and time.

Is the relationship between body length and body mass consistent across habitats? A case study on Niphargus (Crustacea: Amphipoda)

Body size is one of the main characteristics of any organism and influences various aspects of individual’s biology. In animal ecology, it represents a key functional trait that can be quantified using different measures and is often used as a proxy for different organismal functions. The way we quantify body size is critical in any study using this measure alone or to scale other organismal traits. It is especially important in groups that act as model systems across different fields of biological research. One of such groups are amphipods, which are at focus in many ecological studies where appropriate quantification of body size is needed. Here, we explored the relationship between body length and body mass in the largest freshwater amphipod genus Niphargus, and evaluated whether the two measures lead to different conclusions in a putative ecological study of species coexistence. We selected 16 species inhabiting two different subterranean habitats, cave lakes and cave streams. The relationship between log-transformed body mass and body length was linear in all species, but body mass increased steeper among species from cave lakes than from cave streams, reflecting the stouter body shape of the former. In the simulated ecological study, the comparisons of the two measures showed that they may yield different results: in 10 % of cases, body length detected differences between species when body mass did not and vice versa (13 %). Usage of body length or body mass can thus lead to different conclusions. We recommend avoiding direct transformations between body length and body mass in ecological studies. Whenever needed, such transformations should be done with caution using habitat-specific body mass – body length ratios.

Context‐dependent evolution of high trophic position drives functional disparity in subterranean crustaceans

Abstract Species performance depends on the concerted interplay of their functional traits. Natural selection acts on the performance of the species and influences entire suits of interdependent functional traits, thereby driving the evolution of functional diversity (FD) within a clade. In a given habitat, interdependent functional traits are expected to integrate into only a few adaptive combinations. When a clade diversifies in different habitats, the FD within habitats (herein called α‐FD) diversifies in response to local selections, while between the habitats, alternative adaptive combinations of interdependent traits that are specific to the habitat emerge. This multivariate selection leads to two hypotheses. First, realized α‐FD within one habitat represents only a small fraction of the variation of functional traits, and second, realized FDs across habitats (hereafter called β‐FD) are equal to or greater than would be in the absence of the interdependence of functional traits. We tested these hypotheses using 185 species of the highly diverse subterranean amphipod genus Niphargus living in three habitats: river interstitial, cave lakes, and cave streams. We (i) explored integration of functional traits related to locomotion and feeding biology and tested (ii) if realized α‐FD within each habitat is lower than it would be without trait interdependence, and (iii) if realized β‐FD in pairwise comparisons of habitats is higher than it would be without trait interdependence. In all three habitats, the length of the appendages as a proxy of the locomotion speed was positively correlated with the trophic position of the species. On the contrary, the body shape correlations were habitat dependent: species in high trophic positions were slender, stout or invariant in shape in interstitial, cave streams and cave lakes, respectively. Using null models, we show that only a fraction of functional trait combinations was realized in each habitat, whereas β‐FD between habitats was equal to or greater than the null expectations. The results indicate preserved potential for diversification in species within and between habitats. This potential can be realized through hybridization and can drive diversification in adaptive radiations. Moreover, this perspective on the evolution of FD is compatible with several central ecological and evolutionary concepts, such as adaptive landscape or ecological niche theory. Read the free Plain Language Summary for this article on the Journal blog.

Cave sediment sequesters anthropogenic microparticles (including microplastics and modified cellulose) in subsurface environments

Anthropogenic microparticles (of synthetic, semisynthetic, or modified natural compositions) are globally pervasive, yet little is known about their distribution and storage in the subsurface despite their potential threats to belowground environments. We therefore assessed their amounts and characteristics in water and sediment from a cave in the United States. During a flood, water and sediment samples were collected at 8 sites every ~25 m along the cave passageways. Both sample types were evaluated for anthropogenic microparticles, while water was assessed for geochemistry (e.g., inorganic species) and sediment was evaluated for particle sizes. Additional water samples were collected during low flow at the same sites for further geochemical analysis to determine water provenance. We found anthropogenic microparticles in all samples that were mainly fibers (91 %) and clear (59 %). Both suspected (identified visually) and confirmed (identified with Fourier transform infrared spectroscopy; FTIR) anthropogenic microparticle concentrations were positively correlated between the compartments (r ≥ 0.83, p ≤ 0.01), but quantities in sediment were ~100 times those in water. These findings indicate that sediment sequesters anthropogenic microparticle pollution in the cave. Microplastic concentrations were similar among all sediment samples, but only one water sample at the main entrance contained microplastics. Treated cellulosic microparticle abundances in both compartments generally increased along the cave stream's flowpath, which we suspect is due to both their flood and airborne deposition. Water geochemical and sediment particle size data collected at a branch indicated at least two distinct water sources to the cave. However, anthropogenic microparticle assemblages did not differ between these sites, implying minimal variation in sourcing across the recharge area. Our results reveal that anthropogenic microparticles intrude karst systems and are stored in sediment. Karstic sediment consequently represents a potential source of “legacy” pollution to the water resources and fragile habitats found in these globally distributed landscapes.

Floods enhance the abundance and diversity of anthropogenic microparticles (including microplastics and treated cellulose) transported through karst systems

Microplastics (plastics <5 mm) are emerging contaminants that have been detected in virtually all environments. While microplastic research in terrestrial surface waters has been proliferating, microplastic contamination in subsurface environments remains understudied. Karst terrains may be particularly susceptible to microplastic pollution because the presence of large dissolution openings allows fast transport of water through these systems, facilitating the introduction of surface contaminants into subsurface habitats. Furthermore, few studies address the prevalence and movement of microparticles composed of semisynthetic and modified natural materials, despite their known ecotoxicity. Our study therefore aims to identify anthropogenic (i.e., synthetic, semisynthetic, and treated natural) microparticle extent, sourcing, and transport in subsurface karst environments. To do so, we examined a cave spring under variable flow conditions, finding that anthropogenic microparticles were present in all samples and were most frequently fibrous and clear. The mean anthropogenic microparticle concentration during baseflow was 9.2 counts/L but increased up to 81.3 counts/L during floods, indicating their enhanced mobilization when relatively dilute, acidic, and sediment-rich event water entered the cave. These results suggest that anthropogenic microparticles may originate from surface recharge or sediment resuspension within the cave. When we analyzed a subset of microparticles with Fourier transform infrared spectroscopy (FTIR), we found that cellulose of known (i.e., dyed) and suspected (i.e., clear) anthropogenic origin was the most abundant material type. We nevertheless confirmed the presence of microplastics in the cave stream under all flow conditions, with the most common polymer being polyethylene. Both the concentrations and relative fractions of microplastics were higher during floods compared to baseflow, indicating their increased transport during high flow events. We also observed that microplastic polymer types diversified as discharge increased. Our study gives new insight into how anthropogenic microparticle contamination is transported through karst landscapes that can help inform debris mitigation strategies to protect ecosystems and water resources.

Conservation and characterization of karst water using morpho-hydrogeological methods in Pindul Cave system, Gunungsewu Karst, Java, Indonesia

Pindul Cave system is one of the essential water resources in Wonosari Basin. Pindul Cave has a perennial flow and is used to cave tubing. Administratively, this research was conducted in Pindul Cave and its surrounding areas located in Karangmojo District, Gunungkidul Regency. The aim of this research are: (1) to analyze the underground flow system in Pindul Cave (2) to estimate the catchment area of Pindul Cave using morphology approach (3) to propose management action of the catchment area. The method used in this study using a survey method that is divided into several stages include the preparation stage, the fieldwork stage, and the post-field stage. The preparation stage includes site selection study, discharge measurement site selection, site selection, and injection of dye tracer. The fieldwork stage is ground check survey, discharge measurements, and tracer tests. The post-field stage is analyze breakthrough curve, and making the management action of catchment area. The results of this research are: (1) based on tracer test result show that, Pindul cave stream is supplied from 2 sources, namely those originating from the cave system and those originating from surface runoff; (2) the estimated catchment area of the Pindul Cave system using a morphological approach is 15,44 km2; (3) Propose management action for the catchment area of the Pindul Cave system are not mining in the upstream area, not throwing garbage in the upstream underground river, continuing to apply the rules with restrictions on visitors to Pindul Cave in accordance with the carrying capacity.

Karstic Aquifers—Simple or Hybrid Systems? Thermal Stories from Maaras Cave, Greece

Karst systems, such as caves, provide a unique opportunity to study the groundwater from the inside in contrast to spring studies, where hydrographs, chemographs, and thermographs show an integrated signal from the entire catchment and aquifer. Studies from karst springs show that recharge and conduit characteristics significantly influence how the temperature signal is transmitted and thus could inform on the structure of underground flow paths. Here, we present monitoring temperature data from a two-year-long study of a 10 km long river cave, Maaras, in northern Greece. Our data from five measuring stations along the cave stream show how different flow paths transform the temperature signal. The catchment area consists of a polje impacting the recharge conditions that change seasonally from diffuse to concentrated. Diffuse recharge stabilizes the temperature regardless of the conduit conditions. However, temperature fluctuations occur on four different time scales: seasonal, event-based, diurnal, and hourly, indicating different passage conditions. Interaction between the cave stream and the in-cave porous aquifer in the clastic sediments strongly impacts the alteration of the thermal signal through the cave: temperature fluctuations are damped, and the temperature is raised.

Life history observations of the Illinois state endangered Enigmatic Cavesnail, Fontigens antroecetes (Hubricht, 1940) made under simulated cave conditions

The Enigmatic Cavesnail, Fontigens antroecetes (Hubricht, 1940), is a cave adapted hydrobioid snail listed as state endangered in Illinois. It is known from only one cave in Illinois, Stemler Cave, and from several caves in the eastern Ozark ecoregion of Missouri. Little is known about the snail’s reproductive habits, embryological development, or growth rates. I attempted to gain basic life history information by breeding Enigmatic Cavesnails under simulated cave conditions in the laboratory. Six adult snails were collected from Stemler Cave and held in aerated containers of cave water with one or two cobbles from the cave stream. Containers of snails were housed in incubators set at the average cave water temperature of 13 °C. The snails produced 49 embryos in captivity over the course of 34 weeks. Eggs were deposited singly, attached to the underside of rocks within small pits or crevices. Nearly 82% of embryos developed to hatching. Mean estimated development time of embryos was 70.7 days. Survival of hatchling snails was poor. Limited data available from surviving hatchling snails suggests slow growth rates. The process was replicated with nine Enigmatic Cavesnails collected from Cliff Cave in St. Louis County MO. Captive Cliff Cave snails produced 34 embryos over 46 weeks and varied from the Stemler population in their oviposition behavior, with a majority of eggs deposited on the top surface of rocks. Cliff Cave snail embryos also had longer mean estimated development times (82.17 days).

Caves in clastic rocks (Muğla, SW Türkiye)

Caves evolution is controlled by lithological properties, discontinuities, water, climate, and physico-mechanical properties of soluble rocks, vegetation and human impact. This study investigates the cave formation in Upper Miocene-Pliocene clastic rock in Menteşe town of Muğla. The lithology, physico-mechanical properties and hydrogeologic factors of host rocks and morphology of the caves in Asar Hill and Damlam stream valley were examined. The caves are 1.47-9.71 m long, 2.24-19.36 m wide and 1.38-27 m high. Four joint sets and bedding planes affect the clastics in the Asar Hill area. Mudstones (low plasticity clay, sandy clay) are in soft-very soft rock, while conglomerate is in moderate-hard rock class. The mudstone removal has started the formation of the caves. The vegetation roots act as groundwater circulation paths in the Damlam stream area. Water has eroded mudstone and muddy matrix of conglomerate following cracks and led to the formation of the caves. Water infiltration may have led to stalactite, flowstone and travertine formation in Damlam stream caves. Possible cave collapse could threaten life and property in the Asar Hill area, and may cause the destruction of internal structures of the caves in the Damlam stream. Thus, precautionary measures such as continuous monitoring and protection must be taken in both cave areas.

Empirical roughness coefficients for moderate floods in an open conduit cave: Fullers stream canyon, Culverson Creek Cave System, West Virginia

Open conduit modeling of cave stream floods can yield useful information about water velocities and shear stresses, which can in turn be used to estimate sediment transport capabilities. All such calculations require roughness coefficients for estimating energy losses and a priori knowledge of either discharge or flow depths to set model boundary conditions. However, the difficulties associated with observing in-cave floods generally preclude measuring discharge; roughness coefficients must be assumed based on channel properties. To overcome these challenges, we monitored stream flow depths in Fullers Cave, Greenbrier County, West Virginia using pressure transducers, and simultaneously measured stage and discharge in a karst window immediately upstream of the cave. Five pressure transducers were deployed opportunistically along a 93-meter-long reach in a 10+ meter high canyon averaging 1.5 to 3 meters wide. Stage-discharge relationships were determined for the karst window using an electromagnetic flow meter for floods with peak discharges of 1.66 m3 s-1 or less. The collected data was used to obtain the empirical Manning’s n roughness values, head losses, and energy gradients. Calculated floodwater velocities are comparable to values obtained from scallops on passage walls. Major energy losses were observed where breakdown partially occludes the passage. At peak flow, Manning n values average 0.053 for reaches typified as cobble-floored canyons, but n was 0.069 in the breakdown reach. Roughness values declined exponentially with increasing discharge, but friction slopes calculated using head losses show more complex relationships with discharge. Notably, n values back calculated using bed gradients differ from those calculated using measured head losses by as little as 12%, so the use of bed gradients in roughness estimations will generally yield reasonable approximations of flow conditions. Fullers Cave experiences significantly larger open conduit floods than we observed, so additional work is needed to estimate roughness coefficients for higher discharges. Our empirical roughness coefficients can be applied to similar cave passages in other caves and contexts, including modeling slot canyon-like channels, and our methods demonstrate a technique for measuring hard to obtain data. The addition of data for open conduit conduits significantly expands the range of environments that can be modeled using empirical data beyond pipe-full caves. Applications include studying flooding, sediment transport, and bedrock erosion process. All of these topics will be addressed in Fullers in the future.

Yüksek Rakımlı Karstik Bir Mağara Deresinin (Güvercinkaya Mağarası: Çanakkale, Türkiye) Hidrokimyasal ve Bakteriyolojik Durumu ile Sucul Makroomurgasız Bulguları

Caves are laboratories for many disciplines that work in natural sciences including mineralogy, biology, hydrogeology, and archaeology. In this study, bi-monthly samplings were carried out from three sampling locations within and around the Güvercinkaya Cave, a high-altitude cave located in northwestern Turkey, to evaluate the hydrochemical and microbiological properties and the aquatic macroinvertebrates of the cave stream. Some parameters of the water including pH, electrical conductivity, temperature, oxidation-reduction potential, and dissolved oxygen were measured in-situ, while elemental (70 in total) and ionic composition of water were analyzed in the laboratory. Microbiological analyses of the cave stream were examined through analyses of total bacteria, total coliforms, fecal coliforms, fecal Streptococcus, and Escherichia coli. According to the Piper diagram of hydrochemical data, the cave stream had mainly Ca-Mg-HCO3 character, on the other hand, the Schoeller diagram indicated a common water source in Güvercinkaya cave due to the similar components of the main ionic components of the water. As a result of microbiological analysis, fecal contamination was determined, indicating active wildlife in the cave. Additionally, several aquatic macroinvertebrates taxa, Rhynchelmis limosella, Dugesia sp., Gammarus uludagi which have non-troglobiont character were found in the cave stream. Rhynchelmis limosella detected in this study is the first record for the Turkish fauna.

The Interplay of Environment and Biota in Assessing the Freshwater Quality in Karst

Karst aquifers are both a valuable resource for humankind and a habitat for unique biota. The quality of freshwater sources may be easily affected by natural (e.g., geology, climate, and vegetation) and anthropogenic (e.g., agriculture, livestock, and tourism) changes, particularly in karst landscapes with highly vulnerable groundwater reservoirs. We seasonally monitored nine representative freshwater sources (i.e., six springs, a well, a surface stream, and a cave stream resurgence) in the karst system of the Runcuri Plateau (KSRP) (Western Romanian Carpathians) during seven sampling campaigns in 2019–2021. We assessed how these natural and anthropogenic factors influenced the water quality based on the European and national standards for drinking water. The geological structure (i.e., tectonics and lithology) of the KSRP was reassessed, and the environmental variables of the freshwater sites were investigated in order to evaluate their impact on the physicochemical profile, the microbial contamination, and on the meiofauna presence. Multivariate statistics were performed to gain insights into the interplay among all these factors and to evaluate the self-purification capacity of the KSRP for chemical and microbial pollutants. The most relevant drivers shaping the microbial content of the freshwater sources were the altitude of the sampling sites, the normalized difference vegetation index (NDVI), and air temperature, followed by the physicochemical profile of the waters (i.e., calcium hardness, magnesium hardness, nitrites, nitrates, conductivity, phosphates, total dissolved solids, and iron concentrations). The meiofauna presence was influenced mostly by precipitation, air temperature, and NDVI. Our results reflected the effect of the geological structure and environment on water chemistry and biota assemblages. A pollutant attenuation trend was observed in discharging waters, even though the self-purification capacity of the studied karst system was not statistically supported. More investigations are needed to comprehend the processes developed in the black box of the KSRP.

Screening of NaCl salinity sensitivity across eight species of subterranean amphipod genus Niphargus

Secondary salinization of freshwater is becoming a growing environmental problem. Currently, there is few data available on the effects of salinisation on subterranean crustaceans that are vital for the maintenance of groundwater ecosystem functioning. In this study, the sensitivity of subterranean Niphargus amphipods to NaCl was investigated. We expected that cave-dwelling species would be more sensitive as surface-subterranean boundary species. Eight ecologically different Niphargus species were tested: four live at the boundary between the surface and subterranean ecosystems (N. timavi, N. krameri, N. sphagnicolus, N. spinulifemur), three live in cave streams (N. stygius, N. scopicauda, N. podpecanus), and one species (N. hebereri) lives in anchialine caves and wells. The organisms were exposed to five concentrations of NaCl for 96 h and afterwards the immobility, mortality, and electron transfer system (ETS) activity (a measure for metabolic rate of animals) were evaluated. As expected, the most tolerant species was N. hebereri dwelling in naturally high-salinity habitat. However, contrary to our expectations, the species collected at the surface-subterranean boundary were more sensitive as cave stream species when their immobility and mortality were assessed. Interestingly, the majority of Niphargus tested were more NaCl tolerant as can be deduced from currently available data for subterranean and surface crustaceans. We could not observe a clear trend in ETS activity changes between groups of surface-subterranean boundary and cave streams species after exposure to NaCl stress, but it appears that osmotic stress-induced metabolic rate changes are species-specific. This study shows that amphipods Niphargus can be a valuable subterranean environmental research model and further ecotoxicity research is of interest.

Land-use impacts on the hydrology of the Hidden River groundwater subbasin, Horse Cave, Hart County, Kentucky

Hidden River Cave, located in the city of Horse Cave, Ky., forms one of the main tributaries of the Hidden River groundwater subbasin that spans multiple counties in south-central Kentucky. Hidden River Cave formed in Mississippian-aged carbonates and consists of a dendritic network of canyons and collapsed domes; a major trunk stream flows through the cave that supports myriad subsurface ecosystems and recharges the Mammoth Cave aquifer and the Green River, important water resources on which several communities depend. Poor land-use practices historically have contaminated the cave stream. As a result, the hydrology of the Hidden River groundwater subbasin has been extensively studied using fluorescent dye-tracing, and developments in groundwater resource management have improved cave conditions. However, land-use boundaries that intersect with areas of recharge still influence contaminant transport to groundwater. This study combined groundwater dye-tracing, high-resolution stage data collection, and supervised classification in a geographic information system (GIS) to assess land-use impacts on the hydrology of the Hidden River groundwater subbasin. Dye-tracing confirmed that stormwater infrastructure in Horse Cave discharges to Hidden River Cave, and, subsequently, the Hidden River groundwater subbasin. High-resolution stage data determined that the cave’s major trunk streams respond to precipitation within 40 minutes to 1.5 hours, while baselevel conditions, except after sustained precipitation, are met three to four days after precipitation ends. Supervised classification determined that development is concentrated in Horse Cave and has increased by approximately 7 % between 1989 and 2017. These results suggest opportunities for the implementation of karst-specific stormwater management regulations where such regulations are weak.

New insights into particle transport in karst conduits using comparative tracer tests with natural sediments and solutes during low‐flow and high‐flow conditions

AbstractColloidal particles are an important vector for the transport of contaminants in karst aquifers, characterized by a high degree of hydrologic variability. Understanding this heterogeneity and hydrogeological functioning is of particular importance for water management strategies. Until now, transport parameters for particles were mostly determined by injection of solutes or surrogates for natural sediments. But suspended particles are easier to analyse, less expensive and better represent natural conditions. Therefore, tracer tests with sediments represent natural transport and a conservative solute dye were conducted simultaneously in an active and partly accessible cave system in Vietnam during constant high‐flow and low‐flow conditions. Breakthrough curves (BTCs) for 10 different particle sizes classes ranging from 1 to 15 μm and the solute were recorded in situ at the two main resurgences of the cave stream at high temporal resolution. This study gives new insights into the transport processes of suspended particles and the highly dynamic exchange between mobile and immobile regions. Major findings include: (1) at low‐flow conditions, inflow from the surrounding aquifer matrix and the velocity distribution inside the karst conduits themselves lead to hydrodynamic focusing, mainly affecting particles; (2) this highly advective, preferential transport of particles in the centre of the karst conduits results in narrow BTC. The more dispersive transport of solutes results in a longer tailing; (3) at high‐flow conditions a more homogeneous distribution of the particles indicates a reversal of the conduit‐matrix interaction; (4) by comparing the results at different hydraulic conditions, the activation of additional flow paths with increasing discharge could be identified. This study also presents the first tracer test in the field resulting in pronounced double peaks for the particulate tracer but only a single, right‐skewed BTC for the simultaneously injected solute, including a conceptual model for particle transport.