Earth and Planetary Sciences ETDs

Publication Date

7-2-2012

Abstract

This study provides a hydrochemical baseline survey of water-filled sinkholes at Bitter Lake Nation Wildlife Refuge (Roswell, NM). Water samples from 10 representative sinkholes taken at 1.0m increments were analyzed for major ions, stable isotopes [δ18O, δD], and dissolved gases. Sinkholes are surface features at a constant head boundary found at the discharge region for the Roswell Artesian Basin, recharged by upwardly flowing artesian springs. Constant head is confirmed by a lack of measured change in depth during two sampling sessions (October 2008, May 2009), low relief (<10m change across study area), and deployment of autonomous sensors (sondes). Sinkhole waters – regardless of depth or season – fall along a common isotopic evaporation trajectory (δD = 3.387*δ18O – 19.38), and adopt a Na-Cl chemical endmember facies. Driven primarily by physical sinkhole geometry (e.g., depth and surface area), sinkhole water follows a predictable evolutionary progression from a spring-like well-mixed ("young"), to moderately saline well-mixed ("transitional"), to saline and stratified ("old" or "evolved"), based on the relative volume of water that has entered and subsequently been evaporated from the system. The modality of water column structure may be predicted by measuring the density, TDS or conductivity at sinkhole surface, as these parameters can be used as a proxy for evolutionary "age." Simple geochemical models reveal calcium- and sulfate-bearing minerals (calcite, gypsum) precipitate early in the reaction while halite and magnesium-containing minerals precipitate late, yielding increased Cl- and Mg+ concentrations in fluids subjected to prolonged evaporation. More complicated models are needed to fully consider precipitation of additional mineral species and water budget. Both PO4 and NH4 were present in biologically-significant concentrations in sinkholes with chemically controlled water columns, and photosynthetic bacteria were found to organize at the bottom of the photic zone. High NH4 and CO2 accompanying low O2 dissolved gas values confirm the increased biological control in stratified sinkholes. Resident fish populations are affected by water chemistry which reduces reproductive success or exceed the survivable range of habitable conditions. Results of this study may be used to aid with biological resource management and to predict stratified conditions using measurable proxies.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Dahm, Clifford

Second Committee Member

Fischer, Tobias

Language

English

Keywords

Bitter Lake, Sinkhole, hydrochemistry

Document Type

Thesis

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