Benjamin F. Schwartz

Spatial and temporal changes in invertebrate assemblage structure from the entrance to deep-cave zone of a temperate marble cave

Seasonality in surface weather results in seasonal temperature and humidity changes in caves. Ecological and physiological differences among trogloxenes, troglophiles, and troglobionts result in species-dependent responses to this variability. To investigate these responses, we conducted five biological inventories in a marble cave in the Sierra Nevada Range, California, USA between May and December 2010. The cave was divided into six quadrats and temperature was continuously logged in each (humidity was logged at the entrance and in the deep cave). With increasing distance from the entrance, temperature changes were increasingly attenuated and lagged relative to surface temperature. Linear regressions were created to determine the relationship between measured environmental variables and diversity for cavernicoles (troglobionts and troglophiles) and trogloxenes cave– wide and in the transition zone. Diversity for cavernicoles and trogloxenes peaked in the entrance and deep cave zones, respectively. Quadrat, date, 2-week antecedent temperature average, 2-week antecedent temperature range, and trogloxene abundance explained 76% of cavernicole diversity variability. Quadrat explained 55% of trogloxene diversity variability. In the transition zone, trogloxene abundance explained 26% of cavernicole variability and 2-week antecedent temperature and 2-week antecedent temperature range explained 40% of trogloxene variability. In the transition zone, trogloxene diversity was inversely related to 2-week antecedent temperature average and 2-week antecedent temperature range, suggesting that species were moving into the transition zone when temperature was most stable. In a CCA of cavernicoles distribution data and environmental variables, 35% of variation in species-specific distributions was attributable to quadrat, and non-significant percentages were explained by date and environmental variables. Differences in assemblage structure among quadrats were largely due to differences between distributions of trogloxenes and cavernicoles, but responses varied among species. Differences are likely due to ecological niche width, physiological constraints, and competition.

Chemolithoautotrophy supports macroinvertebrate food webs and affects diversity and stability in groundwater communities.

The prevailing paradigm in subterranean ecology is that below-ground food webs are simple, limited to one or two trophic levels, and composed of generalist species because of spatio-temporally patchy food resources and pervasive energy limitation. This paradigm is based on relatively few studies of easily accessible, air-filled caves. However, in some subterranean ecosystems, chemolithoautotrophy can subsidize or replace surface-based allochthonous inputs of photosynthetically derived organic matter (OM) as a basal food resource and promote niche specialization and evolution of higher trophic levels. Consequently, the current subterranean trophic paradigm fails to account for variation in resources, trophic specialization, and food chain length in some subterranean ecosystems. We reevaluated the subterranean food web paradigm by examining spatial variation in the isotopic composition of basal food resources and consumers, food web structure, stygobiont species diversity, and chromophoric organic matter (CDOM), across a geochemical gradient in a large and complex groundwater system, the Edwards Aquifer in Central Texas (USA). Mean δ13C values of stygobiont communities become increasingly more negative along the gradient of photosynthetic OM sources near the aquifer recharge zone to chemolithoautotrophic OM sources closer to the freshwater-saline water interface (FWSWI) between oxygenated freshwater and anoxic, sulfide-rich saline water. Stygobiont community species richness declined with increasing distance from the FWSWI. Bayesian mixing models were used to estimate the relative importance of photosynthetic OM and chemolithoautorophic OM for stygobiont communities at three biogeochemically distinct sites. The contribution of chemolithoautotrophic OM to consumers at these sites ranged between 25% and 69% of total OM utilized and comprised as much as 88% of the diet for one species. In addition, the food web adjacent to the FWSWI had greater trophic diversity when compared to the other two sites. Our results suggest that diverse OM sources and in situ, chemolithoautotrophic OM production can support complex groundwater food webs and increase species richness. Chemolithoautotrophy has been fundamental for the long-term maintenance of species diversity, trophic complexity, and community stability in this subterranean ecosystem, especially during periods of decreased photosynthetic production and groundwater recharge that have occurred over geologic time scales.

QUANTIFYING CONCENTRATED AND DIFFUSE RECHARGE IN TWO MARBLE KARST AQUIFERS: BIG SPRING AND TUFA SPRING, SEQUOIA AND KINGS CANYON NATIONAL PARKS, CALIFORNIA, USA

To improve water management in mountain systems, it is essential that we understand how water moves through them. Researchers have documented the importance of porous-media aquifers in mountain river systems, but no previous research has explicitly included mountain karst as part of conceptual models. To do so, we used discharge and geochemical parameters measured along upstream- to-downstream transects under high- and low-flow conditions in 2010 to assess storage characteristics and geochemical properties of two mountain marble-karst systems, the Big Spring and Tufa Spring systems in Sequoia and Kings Canyon National Parks, California. During both high- and low-flow conditions, we quantified the relative contributions of concentrated and diffuse recharge in both karst systems, and we used a simple linear mixing model to calculate specific conductance in unsampled diffuse sources that ranged from 34 m Sc m 21 to 257 m Sc m 21 . Data show that the Big Spring system has a much higher seasonal storage capacity than the Tufa Spring system, and that diffuse sources dominate discharge and geochemistry under baseflow conditions in both aquifer systems. Baseflow in Big Spring was 0.114 m 3 s 21 and in Tufa Spring it was 0.022 m 3 s 21 . Snowmelt-derived allogenic recharge dominates both systems during high discharge periods, measured at Big Spring as 0.182 m 3 s 21 and Tufa Spring as 0.220 m 3 s 21 . A conceptual model is proposed that explicitly includes the effects of karst aquifers on mountain hydrology when karst is present in the basin.

Instrumenting Caves to Collect Hydrologic and Geochemical Data: Case Study from James Cave, Virginia

Karst aquifers are productive groundwater systems, supplying approximately 25 % of the world’s drinking water. Sustainable use of this critical water supply requires information about rates of recharge to karst aquifers. The overall goal of this project is to collect long-term, high-resolution hydrologic and geochemical datasets at James Cave, Virginia, to evaluate the quantity and quality of recharge to the karst system. To achieve this goal, the cave has been instrumented for continuous (10-min interval) measurement of the (1) temperature and rate of precipitation; (2) temperature, specific conductance, and rate of epikarst dripwater; (3) temperature of the cave air; and (4) temperature, conductivity, and discharge of the cave stream. Instrumentation has also been installed to collect both composite and grab samples of precipitation, soil water, the cave stream, and dripwater for geochemical analysis. This chapter provides detailed information about the instrumentation, data processing, and data management; shows examples of collected datasets; and discusses recommendations for other researchers interested in hydrologic and geochemical monitoring of cave systems. Results from the research, briefly described here and discussed in more detail in other publications, document a strong seasonality of the start of the recharge season, the extent of the recharge season, and the geochemistry of recharge.

Exploration of Barberry Cave and the Construction of Big Bucks Pit

Barberry Cave, with a length of 3.4 miles, was discovered by a dig in a sinkhole. The entrance series was tight and time-consuming so a second entrance was excavated. The main part of the cave, with large well-decorated passages, was discovered through a low, easily flooded crawlway. Following an incident of explorers trapped by rising water, a third entrance was achieved by excavating a shaft from the surface into the large passage of the cave. Barberry Cave has some of the largest and best decorated passages in the Burnsville Cove. The Cave is located between the Chestnut Ridge caves and the Butler Cave-Sinking Creek System although no physical connections have been discovered.