Physical, chemical, and biological characteristics of weathering pits, Moab, Utah.

摘要

Potholes is a vernacular term for weathering pits in rock with miniature endorheic basins found typically in clusters on exposed sandstone mesa edges, fins, and tors, and measure at the meter to decameter scale. The potholes retain water after rains, and large, deep potholes contain pools that can persist nearly all year, even in years of drought. In this study, an investigation spanning 6 years is presented on the physical, chemical, and biological characteristics of pothole pools in the Moab area including an annual time-series on pool water chemistry, identification of pothole pool diatoms from five locations, and a historical reconstruction of a pothole sediment core.;A 13-month water chemistry study was completed on four pools, every month from April 2003 to April 2004 that included oxygen measurement through 24-hour periods. Pools are always dilute, freshwater systems, yet have large daily and seasonal fluctuations in temperature, oxygen, and pH. Multivariate analysis shows a spring reduction of oxygen causing increases in iron and manganese, and increasing ionic concentrations due to drying phases and freezing events. The pools are clearly influenced by geology, as is evidenced from high levels of copper and barium in pools adjacent to the Moab fault.;Diatoms were countable in sediments from all 29 pools sampled. Twenty-four genera of diatom were tallied. Counts showed that pools typically have one or two diatom species dominating a pool. Samples obtained years apart from the same pool indicate diatom species of a pool can change from year to year, from one clearly dominant species to a different species. A 29.5 cm sediment core was obtained from one pothole and sectioned for diatom analysis. A carbon date on organic material suggests more than a century and a half of sediment deposition in the pothole. Diatoms were countable throughout the core. The core produced 28 genera of diatoms, four more than all samples of modern diatom species from five locations. Multivariate statistical analysis shows five discrete zones of diatom species assemblage. A surface sediment sample taken from the pool years after the core was extracted exhibits a complete turnover of diatoms.