A TWO-YEAR SOURCE TO SINK MONITORING STUDY TO INTERPRET ELEMENTAL AND ISOTOPIC VARIABILITY IN A KARST SYSTEM IN SOUTH-EASTERN NEW-MEXICO

Speleothem records hold great potential for reconstructing changes in surface vegetation, floods, and rainfall amount through time within the carbonate Critical Zone. Investigation of speleothem data simultaneously with cave monitoring data allows for an empirically-based interpretation of speleothem stable isotope (seasonal preference of infiltration) and trace element (transition metals - labile solutes transmitted through infiltration) variability. We monitor (July 2017 – Nov. 2019) Sitting Bull Falls (SBF) Cave (32°14’N, 104°41’W) in south-eastern New Mexico. Cave dripwater sourced from a spring-fed perennial stream permits a spring-stream-cave dripwater source to sink study of stable isotope and trace element variations.We present stable isotopic compositions of water collected every 2 months from SBF Cave (4 sites), SBF Spring (1 site ), and Stream (4 sites along stream). Cave dripwater dD values range from -59 to -46 ‰, d¹⁸O values range from -8.8 to -6.8 (μ = -7.4) ‰. Spring and stream dD values range from -60 to -52 ‰, d¹⁸O values range from -9.0 to -7.0 (μ = -8.5)‰. Spring, stream, and cave dripwater d¹⁸O and dD data do not seasonally vary over period of monitoring. However, cave dripwater have higher d¹⁸O values than stream and spring water. dD does not capture this bias between spring-stream and cave dripwater. By eliminating seasonal preference of infiltration, we infer that evaporation of stream water causes dripwater to have higher d¹⁸O values. The results suggest that evaporation between surface and subsurface water is an important process that affects d¹⁸O of cave dripwater in SBF Cave. We present trace elemental concentrations collected at the same location as stable isotope data. Preliminary transition metal (Fe, Cu, Zn) concentrations of cave dripwater do not increase in concentration following known infiltration events. A possible reason could be that the surface runoff water in the recharge zone above the cave did not have enough labile solute material. Transition metal data collected from the stream during the duration of infiltration events are will be analyzed. The results will illustrate the evolution of transition metal concentrations during infiltration events for this karst system. Transition metal analyses to be conducted on samples of the stream collected during infiltration events will inform the dynamics of transition metal behavior during infiltration in this karst system. This in turn will constrain interpretation of stalagmite transition metal time series as recharge records in this setting