Cave Stream Research Articles

Solution weathering rate and origin of karst landforms and caves in the quartzite of Auyan-tepui (Gran Sabana, Venezuela)

The paper reports the results of SiO 2 analyses in the Aonda Cave system, located on the Auyán-tepui, one of the widest table-mountains of the Gran Sabana (South Venezuela), characterised by karst landforms developed in siliceous rock. Chemical analyses underline the very low concentration of SiO 2 of the surface water. Percolation and cave drip waters have a SiO 2 concentration of about 1 mg/l. The mean silica load of the cave stream is 184 mg/s, mainly derived from surface solution removal in the allogenic recharge area. In the Aonda Cave system, the mean SiO 2 dissolved load is 40 mg/s, in part from surface solution (15%) and mainly from underground processes (85%). The low solubility of SiO 2 in slightly acidic water implies the importance of the time factor in the formation of cave systems. With the present dissolution rate, about 10 Ma would be necessary to form the known karst system. This estimation can be significant only if we assume that climate has been stable in the last few tens of millions of years. Furthermore, this age can be taken as a minimum estimate, while, according to the geomorphic evolution of the area, the origin of the Aonda Cave system could be reasonably dated back to at least 20–30 Ma, that is, to the Oligocene.

Flank Margin Cave Development in Telogenetic Limestones of New Zealand

Coastal limestone outcrops, typically with advanced levels of diagenetic maturity (i.e., are telogenetic carbonates), were ex­amined on NorthIsland (Raglan Harbour, Kawhia Harbour, Napier, and Waipu Cove) and SouthIsland (Pohara, Paturau River, Punakaiki, Kakanui, and Kaikoura), New Zealand, to de­termine if flank margin caves, produced by mixing dissolution, were present. In coastal settings, caves in carbonate rock can be the outcome of pseudokarst process, primarily wave erosion, as well as karst processes not associated with freshand sea-water mixing suchas epikarst features and conduit-flow stream caves. Flank margin caves were successfully differentiated from other cave types by the following criteria: phreatic dissolutional mor­phologies at the wall rock and chamber scales; absence of high-velocity, turbulent-flow wall sculpture and sediment deposits; and lack of integration of adjacent caves into a continuous flow path. The active tectonics of New Zealand creates a variable sea-level situation. The relatively short time of sea-level stability lim­its the size of the New Zealand flank margin caves compared to tectonically-stable environments, suchas the Bahamas, where glacioeustasy alone controls sea-level stability. Uplift events can be identified as slow and steady when the flank margin caves are uniformly elongated in the vertical direction, and episodic when the flank margin caves show widening and tube develop­ment at discrete horizons that cut across rock structure. New Zealand flank margin caves contain information on uplift dura­tion and rates independent of other commonly used measures, and therefore can provide a calibration to other methods.

Stygofauna biodiversity and endemism in four alluvial aquifers in eastern Australia

Short-range endemism is common in groundwater fauna (stygofauna), placing many species at risk from anthropogenic impacts such as water abstraction and pollution. Few of the alluvial aquifers in eastern Australia have been sampled for stygofauna. Fauna from two aquifers in Queensland and two in New South Wales was sampled to improve ecological knowledge of stygofauna and the potential threats posed to it by development. Our surveys found stygofauna in all four aquifers, with most taxa collected from bores with low electrical conductivity (<1500 µS cm–1). Taxon richness decreased with distance below the water table. The most taxon-rich bores in each region occurred where the water table depth was <10 m, were associated with the alluvium of tributaries of large regulated river systems, and were near phreatophytic trees. It is possible that tree roots constitute a habitat and source of organic matter in alluvial aquifers as they do in cave streams. It is important to document the biodiversity of particular regions and aquifers so that species can be conserved in the face of increasing groundwater use. For effective resource management, future research should strive to understand the tolerances and ecological requirements of groundwater communities and the ecosystem services they provide.

The role of the epikarst in karst and cave hydrogeology: a review

The epikarst (also known as the subcutaneous zone) comprises highly weathered carbonate bedrock immediately beneath the surface or beneath the soil (when present) or exposed at the surface. Porosity and permeability are higher near the surface than at depth, consequently after recharge percolating rainwater is detained near the base of the epikarst, the detention ponding producing an epikarstic aquifer. Such an aquifer is found only where the uppermost part of the vadose zone is very weathered compared to the bedrock at depth. Sometimes this contrast in porosity and permeability does not occur either because the epikarst has been scraped off by glacial scour or because high porosity exists throughout the bedrock. In some conditions porosity may even diminish near the surface because of case-hardening. The epikarst is best developed in pure, crystalline limestones or marble where it is typically about 10 m thick. It then contains a suspended aquifer that is under-drained and sustains the distal tributaries of cave streams and small perennial flows emerging on hillsides (epikarstic springs). Slow leakage paths from the epikarst maintain seepage to many stalactites throughout the year. A distinction should be recognized between the location (and form) of the epikarst and the function of the epikarst, because the near surface zone in carbonate rocks does not always contain a suspended aquifer.

Solute and Colloid Transport in Karst Conduits under Low‐ and High‐Flow Conditions

Solute and colloid transport in karst aquifers under low and high flows was investigated by tracer tests using fluorescent dyes (uranine) and microspheres of the size of pathogenic bacteria (1 microm) and Cryptosporidium cysts (5 microm), which were injected into a cave stream and sampled at a spring 2.5 km away. The two types of microspheres were analyzed using an epifluorescence microscope or a novel fluorescence particle counter, respectively. Uranine breakthrough curves (BTCs) were regular shaped and recovery approached 100%. Microsphere recoveries ranged between 27% and 75%. During low flow, the 1-microm spheres displayed an irregular BTC preceding the uranine peak. Only a very few 5-microm spheres were recovered. During high flow, the 1-microm-sphere BTC was regular and more similar to the uranine curve. BTCs were modeled analytically with CXTFIT using a conventional advection dispersion model (ADM) and a two-region nonequilibrium model (2RNE). The results show that (1) colloids travel at higher velocities than solutes during low flow; (2) colloids and solutes travel at similar velocities during high flow; (3) higher maximum concentrations occur during high flow; and (4) the 2RNE achieves a better fit, while the ADM is more robust, as it requires less parameters.

Climate influence on geochemistry parameters of waters from Santana–Pérolas cave system, Brazil

A four-year study of water geochemistry and hydrology was performed in a relatively deep cave system (overlying bedrock thickness varies from 100 to 300 m) as part of two monitoring programs, from June 1990 to February 1992 and from March 2000 to March 2002. The pH, saturation index for calcite, Ca and SO 4 concentrations, and elemental ratios of Mg/Ca and Sr/Ca were measured in surface, well and drip waters throughout the system. Despite local hydrological and geological differences among sampling sites, the monitoring revealed significant synchronous intersite variations in these parameters that are related to seasonal changes in rainfall recharge, suggesting that element ratios of speleothems formed in deep caves are capable of recording short-term climate variations. Groundwater residence time appears to be the main factor affecting the water composition in the epikarst. Epikarstic waters are always undersaturated with respect to calcite but both saturation index (S.I.) and dissolved solids content increase substantially during drier periods because of longer residence times and longer interaction between meteoric water and limestone. By contrast, results from cave drips and rimstone pools indicate constant supersaturation for calcite and demonstrate that a major control on trace element ratios of waters in the deep vadose zone is the degree of prior calcite precipitation. This mechanism is more effective during drier periods when higher Mg/Ca and Sr/Ca values are observed in all drip and pool sites. However, variations do occur independently of the general trend of drip discharge, which suggest non-linear features in cave seepage water geochemistry. In addition, synchronous variations in SO 4 and Cl concentration indicate high connectivity between different water flow pathways characterized by similar response to interseasonal changes in vadose water level. Fluctuations in trace element ratios of cave streams appear to reflect increased contribution of waters flushed from the vadose fissure aquifer during very wet periods by a piston flow mechanism. Flushing episodes are also responsible for maintaining more positive saturation indices in streams even during periods of high river discharge. Our results suggest that trace elements are a potential proxy for past rainfall changes but they also reveal different scenarios for interpreting trace elements ratios of speleothems and freshwater tufa deposited in a deep cave systems located in tropical humid areas.

A comparison of the leaf shredding ability and influence on microbial films of surface and cave forms of Gammarus minus Say

Gammarus minus has both cave and surface forms that differ considerably in their morphology. We experimentally compared the ability of these two forms to consume leaves and influence the activity of the microbial films associated with leaves. Both forms of G. minus were effective leaf shredders, and were equally efficient at converting leaves to small particles. We found little relationship between amphipod size and the rate at which they shredded leaves. Both forms of G. minus stimulated the respiration rate of microbes associated with leaves by 32–52%. Cave forms of G. minus had a 15% greater stimulatory effect on microbial respiration. The stimulatory effect of G. minus on microbial respiration is evident in cave streams as well as in the laboratory. It appears that G. minus plays a particularly important role in cave systems by converting leaves to fine particles and stimulating microbial films which are important foods for many cave animals.

In situ detection of novel Acidobacteria in microbial mats from a chemolithoautotrophically based cave ecosystem (Lower Kane Cave, WY, USA)

Lower Kane Cave, Wyoming (USA), has hydrogen sulfide-bearing springs that discharge into the cave passage. The springs and cave stream harbour white filamentous microbial mats dominated by Epsilonproteobacteria. Recently, novel 16S rRNA gene sequences from the phylum Acidobacteria, subgroup 7, were found in these cave mats. Although Acidobacteria are ubiquitously distributed in many terrestrial and marine habitats, little is known about their ecophysiology. To investigate this group in Lower Kane Cave in more detail, a full-cycle rRNA approach was applied based on 16S and 23S rRNA gene clone libraries and the application of novel probes for fluorescence in situ hybridization. The 16S and 23S rRNA gene clone libraries yielded seven and six novel acidobacterial operational taxonomic units (OTUs) respectively. The majority of the OTUs were affiliated with subgroups 7 and 8. One OTU was affiliated with subgroup 6, and one OTU could not be assigned to any of the present acidobacterial subgroups. Fluorescence in situ hybridization distinguished two morphologically distinct, rod-shaped cells of the acidobacterial subgroups 7 and 8. Although the ecophysiology of Acidobacteria from Lower Kane Cave will not be fully resolved until cultures are obtained, acidobacterial cells were always associated with the potentially chemolithoautotrophic epsilon- or gammaproteobacterial filaments, suggesting perhaps a lifestyle based on heterotrophy or chemoorganotrophy.

Chemical and Bacterial Quality of Aeration‐Type Waste Water Treatment System Discharge

AbstractOn‐site waste water treatment systems are a potential source of chemical and bacterial contamination to ground water in areas with highly susceptible aquifers such as the sinkhole plain of southwestern Illinois. Ground water from wells, cave streams, and water that discharges from the numerous springs in this area is typically contaminated with nitrate and enteric bacteria and thus may pose a health hazard to those who come into contact with it. In order to determine if the most popular type of on‐site waste water treatment systems in the study area was a potential source, samples of effluents discharged at the land surface from 23 domestic aeration‐type on‐site waste water treatment systems were collected to characterize their water quality and bacterial contents. Most of the effluents contained relatively large concentrations of sodium (Na+), chloride (Cl−), nutrients (nitrogen [N], phosphate [PO43−], and potassium [K+]), and enteric bacteria. Ion concentration ranges (in mg/L) were Na+ (46 to 416), Cl− (21 to 618), N (4.7 to 67), PO4‐P (1.4 to 48), and K+ (6.0 to 257). The sources of elevated Na+ and Cl− were human waste and NaCl used in the water softening systems of the houses. Ammonium was usually the dominant inorganic N species, indicating incomplete oxidation of the waste water. Discharge of Na+, Cl−, and nutrients could also have negative impacts on ground water and surface water quality, subsurface and surface aquatic ecosystems, and vegetation. Our characterization of effluent from these waste water treatment systems revealed their generally poor quality and the likelihood that they can contaminate ground water in areas with highly vulnerable aquifers.

Conservation Strategies Supported by Non-Lethal Life History Sampling of the U.S. Federally Listed Illinois Cave Amphipod, Gammarus Acherondytes

Many cave species exhibit k-selected life history characteristics, i.e., long life span, slow growth, and low reproductive effort, which can reduce their ability to survive rapid changes in environmental conditions and their potential for recovery from events that reduce their densities. In this study, we examined aspects of the life history, growth rate, and reproductive timing of the U.S. federally listed Illinois cave amphipod, Gammarus acherondytes, to assess its potential for recovery. Sampling between October 2003 to March 2005 with non-lethal techniques in Reverse Stream Cave, Illinois, U.S.A. showed that pre-juveniles and juveniles generally constituted |$\gt 50\% $| of the population and thus strongly influenced fluctuations in population density. Except in September 2004, ovigerous females were collected every month, indicating that reproduction occurred year-round. Distinct peaks of pre-juveniles were observed from February to May and August to October. The seasonal recruitment of young appeared to be correlated with incubation time and flood events. Because it was difficult to track individual cohorts, the exact time to maturity or the life span could not be determined empirically. However, the minimum time to maturity was estimated at 14 to 16 months using a modeled growth curve. Our results suggest that G. acherondytes should recovery rapidly from perturbations if left undisturbed. A management strategy to aid recovery could be to reduce cave visitation during the major phases of recruitment. Additionally, our results indicate that establishing a laboratory population for use in future studies or to propagate individuals for reintroduction should require only one-and-a-half to two years. Our study shows how basic life history information obtained via non-lethal sampling can provide managers with vital information to develop conservation strategies for endangered species.

Dominant Microbial Populations in Limestone-Corroding Stream Biofilms, Frasassi Cave System, Italy

Waters from an extensive sulfide-rich aquifer emerge in the Frasassi cave system, where they mix with oxygen-rich percolating water and cave air over a large surface area. The actively forming cave complex hosts a microbial community, including conspicuous white biofilms coating surfaces in cave streams, that is isolated from surface sources of C and N. Two distinct biofilm morphologies were observed in the streams over a 4-year period. Bacterial 16S rDNA libraries were constructed from samples of each biofilm type collected from Grotta Sulfurea in 2002. beta-, gamma-, delta-, and epsilon-proteobacteria in sulfur-cycling clades accounted for > or = 75% of clones in both biofilms. Sulfate-reducing and sulfur-disproportionating delta-proteobacterial sequences in the clone libraries were abundant and diverse (34% of phylotypes). Biofilm samples of both types were later collected at the same location and at an additional sample site in Ramo Sulfureo and examined, using fluorescence in situ hybridization (FISH). The biomass of all six stream biofilms was dominated by filamentous gamma-proteobacteria with Beggiatoa-like and/or Thiothrix-like cells containing abundant sulfur inclusions. The biomass of epsilon-proteobacteria detected using FISH was consistently small, ranging from 0 to less than 15% of the total biomass. Our results suggest that S cycling within the stream biofilms is an important feature of the cave biogeochemistry. Such cycling represents positive biological feedback to sulfuric acid speleogenesis and related processes that create subsurface porosity in carbonate rocks.

Persistence of 17 -Estradiol in Water and Sediment-Pore Water from Cave Streams in Central Missouri

Concentrations less than 10 ng/L of 17 β-estradiol (E2), a natural estrogen, have been linked to adverse health effects in fish, including skewed sex distributions, reproductive failure, and organ impairment. The persistence of E2 in carbonate aquifer systems is not well documented. Water and sediment from cave streams within the Ozark Plateau of Missouri, USA, were collected and analyzed for E2. The persistence of E2 in the water was examined in two separate experiments, in which the holding temperatures (20°C vs. 4°C), bottle type, exposure to light, and filtration were varied. During two trials, no statistical difference was observed in the concentration of E2, suggesting that E2 is stable within the water. The fate of E2 was also examined in sediment-pore water collected from the cave streams in two independent trials. In trial 1, a significant decrease in E2 was noted over the 29 days of the experiment. However, in trial 2, no change in E2 concentration was observed. The results indicate that E2 is relatively stable in cave stream water and may persist in the sediment.

Metals in sediments of springs and cave streams as environmental indicators in karst areas

The content of heavy metals and arsenic in sediments of karst streams in southern Missouri was investigated for its potential use as an indicator of pollution. A three-step sequential extraction procedure was utilized for this purpose. The amount of trace elements bound to each extraction phase gives insight of its availability and geochemical dependence. These results were complemented with analyses of correlation and spatial variability. Although sediments collected in this study remained below EPA’s critical value guidelines, concentration in the mobile phases and higher normalized Mn values successfully identified sites with concentrations higher than background levels. Correlation among elements was poor in most cases; among the trace metals only Cu and Zn correlated while Pb correlated with Ca, Al, Mn and Fe. Spatial variability analysis confirmed that natural variation among adjacent sediment samples is a common occurrence. The urban spring Ward Branch showed the highest levels of Cr, Zn, Pb and As.

Epigean and subterranean ichthyofauna from the São Domingos karst area, Upper Tocantins River basin, Central Brazil

In a survey of epigean and cave streams in the São Domingos karst area, 38 species were present in the stream reaches, including 10 characiforms, 19 siluriforms, seven gymnotiforms and two perciforms. One species of Astyanax and the new armoured catfish species Parotocinclus were the most common epigean fishes in São Domingos. The most conspicuous non‐troglomorphic cave fishes were Hoplerythrinus unitaeniatus, Astyanax sp., Brycon sp. and two species of Imparfinis, with I. hollandi being the most common fish in most caves. São Domingos karst area has the most diverse and abundant Brazilian cavefish fauna, not only in terms of troglobitic species but also in general fish richness, with 22 non‐troglomorphic species recorded in caves in addition to five troglobitic ones. Most fishes examined for stomach contents had at least partially full stomachs. The studied fishes were carnivorous, feeding primarily on aquatic insects. Fishes with developed gonads recorded in caves were I. hollandi, Rhamdia quelen, Pseudocetopsis plumbeus, Hoplerythrinus unitaeniatus and Cichlasoma araguaiensis, indicating a potential for reproduction in the subterranean habitat.

Influences of agricultural practices on water quality of Tumbling Creek cave stream in Taney County, Missouri

Influences of agricultural practices on water quality of the Tumbling Creek cave stream are of particular interest because of the karst nature of the area and the recent implementation of a Better Management Practice (BMP). Water quality parameters, measured bi-weekly during one year, consisted of pH, turbidity, water temperature, specific conductivity, total dissolved solids, alkalinity, and chloride. Heavy metals, nutrient and bacteria levels were also monitored during the study. Effects of land use were most obvious in turbidity, nitrate, chloride, and bacteria levels. Sites within the recharge area that pose a major threat to its water quality were identified. Results provide a baseline for these water quality parameters and their seasonal variability that can be used in future studies to address the effects of water quality and stream sediment contamination on the cave’s ecosystem and to determine the effectiveness of the BMP implemented in this karst area.

FOOD WEB STRUCTURE AND THE ROLE OF EPILITHIC BIOFILMS IN CAVE STREAMS

Cave stream food webs rely exclusively on detritus from the surface for energy and represent a heterotrophic end point in the continuum of stream types. Both dissolved organic matter (DOM) and particulate organic matter, and associated microbes, are available in caves, but the relative importance of these foods is unclear. We examined trophic structure and the roles of particulate organic matter and DOM retained in epilithic biofilms in three cave streams using natural abundance isotopes (13C and 15N) and 13C tracer additions. Natural abundance 15N ratios showed that cave animals occupied two trophic levels: primary consumers and predators. Epilithic biofilms and animals were highly enriched in 15N, suggesting that dissolved organic matter from surface soils was incorporated into epilithon and supported stream food webs, even when coarse particulate organic matter (CPOM) from the surface was abundant. We conducted 28-day 13C-acetate tracer additions to trace the use of epilithon carbon in the food webs. T...

Imperilled subsurface waters in Australia: Biodiversity, threatening processes and conservation

Subsurface waters in Australia span massive aquifers to small cave streams and fluctuating hyporheic zones where stream water exchanges with groundwater. Groundwater resources have been exploited heavily, especially in the arid zone, and usage is predicted to increase. Ironically, preliminary surveys of some groundwater habitats in arid northwestern Australia indicate an extraordinarily diverse subsurface fauna with apparently highly localised distributions. Elsewhere in Australia, changes to river flows, gravel extraction, and poorly managed catchment land uses have altered the extent and ecological integrity of the hyporheic zone in most gravel and sand bed rivers. In many cave streams and karst aquifers, sedimentation, pollution and changes to the water table have caused extinction or reduction of the dependent biodiversity. Most of these subsurface habitats harbour ancient groups absent from surface waters (relictual stygofauna) and are ‘hotspots’ of unexpected aquatic biodiversity. Unfortunately, our knowledge of the regional extent of this biodiversity and its functional significance is fragmentary. Current threats vary according to the subsurface habitat. For example, lowering of the water table in calcrete aquifers by water abstraction may jeopardise isolated, endemic relictual faunas in Australia's arid zone whereas in many gravel bed rivers, siltation threatens the biodiversity and filtration capacity of the hyporheic zone. Groundwaters in karst, especially cave streams and their dependent fauna, are vulnerable to impacts in their surface catchments but these linkages are seldom obvious. Recognition of the intimate linkages between groundwater and many surface ecosystems has led recently to policies aimed at protecting ‘Groundwater Dependent Ecosystems’ in Australia. However, such protection is hampered by our scant taxonomic and ecological knowledge of these ecosystems. Successful conservation and management of groundwaters and their dependent ecosystems rely on better public understanding of their unique fauna and ‘ecosystem services,’ further research on subsurface processes and taxonomy, and legislative protection of rare and threatened subterranean communities and species.

Eogenetic karst from the perspective of an equivalent porous medium

The porosity of young limestones experiencing meteoric diagenesis in the vicinity of their deposition (eogenetic karst) is mainly a double porosity consisting of touching-vug channels and preferred passageways lacing through a matrix of interparticle porosity. In contrast, the porosity of limestones experiencing subaerial erosion following burial diagenesis and uplift (telogenetic karst) is mainly a double porosity consisting of conduits within a network of fractures. The stark contrast between these two kinds of karst is illustrated by their position on a graph showing the hydraulic characteristics of an equivalent porous medium consisting of straight, cylindrical tubes (n-D space, where n is porosity,D is the diameter of the tubes, and logn is plotted against logD). Studies of the hydrology of small carbonate islands show that large-scale, horizontal hydraulic conductivity (K) increases by orders of magnitude during the evolution of eogenetic karst. Earlier petrologic studies have shown there is little if any change in the total porosity of the limestone during eogenetic diagenesis. The limestone of eogenetic karst, therefore, tracks horizontally inn-D space. In contrast, the path from initial sedimentary material to telogenetic karst comprises a descent on the graph with reduction ofn during burial diagenesis, then a sideways shift with increasingD due to opening of fractures during uplift and exposure, and finally an increase inD andn during development of the conduits along the fractures. Eogenetic caves are mainly limited to boundaries between geologic units and hydrologic zones: stream caves at the contact between carbonates and underlying impermeable rocks (and collapse-origin caves derived therefrom); vertical caves along platform-margin fractures; epikarst; phreatic pockets (banana holes) along the water table; and flank margin caves that form as mixing chambers at the coastal freshwater-saltwater “interface”. In contrast, the caverns of telogenetic karst are part of a system of interconnected conduits that drain an entire region. The eogenetic caves of small carbonate islands are, for the most part, not significantly involved in the drainage of the island.

Ammonium retention and whole-stream metabolism in cave streams

We used 4 short-term ammonium releases and 1 whole-stream metabolism estimate to examine nutrient and carbon dynamics in cave streams. Ammonium uptake lengths (34–157 m) in the cave streams fell within the range reported for surface streams. However, uptake lengths in the cave streams were longer than would be expected in surface streams of similar size. Ammonium mass transfer coefficients and uptake rates were much lower in the cave streams than have been measured in surface streams. Differences in ammonium uptake parameters among cave streams were due to both abiotic and biotic factors. Metabolism in the cave stream was relatively low (32.9 g C m−2 y−1), but fell within the range of values reported for surface streams. Benthic organic carbon (BOC) standing stock was low and turned over faster in the cave stream than in most surface streams. Our results suggest cave streams are carbon, but not nutrient, limited and that standard methods and models for nutrient and carbon cycling in surface streams are applicable to cave streams.

Leaf and wood breakdown in cave streams

Cave streams lying near the surface are important ecotones connecting energy sources from the terrestrial environment to deep groundwater. We examined leaf and wood breakdown and transport in 5 cave streams with, and 2 without, large openings that allow litter input from the surface. White oak (Quercus alba) leaf breakdown rates in cave streams spanned the range of values reported for white oak leaves in surface streams. Leaf breakdown was faster in streams with leaf-shredding invertebrates, and leaf breakdown rates were positively correlated with shredder density in leaf packs. Wood breakdown rates were fast, partly a result of the wood veneer we used, and did not differ among streams. Microbial colonization of leaves and wood followed a pattern typical of surface streams: fungal biomass and microbial respiration peaked within 62 d and then declined on leaves, but biomass and respiration on wood gradually increased to a plateau. Coarse particulate organic matter (CPOM) breakdown and microbial colonization in cave streams were not accelerated by the absence of litter, unlike surface streams, apparently because nutrients were not limiting in cave streams. Nutrient levels were high in all streams, so nutrient enrichment had little effect on microbial biomass and respiration on wood in cave streams. Leaf and stick transport distances were short and, when combined with breakdown rates, suggest that CPOM is efficiently retained near its entry point.