Karst and Cave Water Chemistry: a Source of Alkalinity to the Coastal Ocean?

In Bocas Del Toro, Panama there are approximately 30 known limestone caves that continue to grow as water weathers away the limestone. The location for our study is the La Gruta cave, which is one of the most visited bat caves on Colon Island in Panama. There is a diverse ecosystem in the cave consisting of several species of bats, cave crickets, and whip scorpion. In La Gruta cave, there is a stream channel that developed during cave formation that consists of cave water, rainwater, and conduit water. The main goal of this project was to determine trends in water chemistry from upstream to downstream, and if these cave systems are producing alkalinity that could help buffer the coastal ocean. Six sites were sampled along the course of the cave stream, three being from the mainstream and three from side conduits feeding into the mainstream. At these sites pCO2, alkalinity, DO, pH, alkalinity and other parameters were analyzed. From these sites, it was found that there weren't distinct trends from upstream to downstream in regard to main channel chemistry, but differences were seen within the conduit chemistry. One conduit showed differing chemistry from the other two, with higher pCO2 and much lower dissolved oxygen. This was determined to be a true conduit, which is a conduit where the water has not been previously exposed to the cave air, whereas the other two conduits had more similar chemistry to the main channel samples. Surprisingly, aside from the one conduit, these waters did not have high alkalinity as expected. Karst stream water from the main channel had lower alkalinity than seawater (1.9 mmol/L; seawater ~2.2 mmol/L). One conduit had high alkalinity (4.4 mmol/L), but these are not enough to leverage the main channel. In summary, these tropical cave systems do not seem to be a large source of alkalinity to the coastal ocean.

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Union College (Schenectady, N.Y.). Department of Geology