Making the Cave Less Green

This article was originally published in The Midden – Great Basin National Park: Vol. 20, No. 1, Summer 2020.

Growth near cave lights may not only consist of algae, but also moss and bacteria.

NPS Photo by Gretchen Baker

by Gretchen Baker, Ecologist

While we’re striving to make the park a greener park (more energy efficient and conservation-minded), we are also trying to make the cave less green, literally. You can see green in the cave next to the artificial cave lights, and that green is made up of algae, moss, and bacteria, sometimes referred to as lampenflora. The lampenflora provides an unnatural food source to the cave’s wildlife. It also can become part of the speleothems and damage their growth and beauty.

Spraying algae with a 10% bleach solution helps kill it, but also introduces a chemical to the delicate cave environment.

NPS Photo by Gretchen Baker

Over the years we’ve experimented with different light wavelengths and changed out most of the lightbulbs to LEDs to make the cave less green. Nevertheless, last year was a very wet winter and spring, which meant that we had water dripping into the cave for months, refilling pools and making many speleothems grow. The extra moisture encourages algae growth. BYU Researcher Steve Leavitt and his students sampled the algae in May and November 2019, finding very different assemblages both times. After his sampling, selected algae was sprayed with a 10% bleach solution in November and December 2019 (Table 1).

Table 1. Date and amount of algae sprayed near lights in Lehman Caves.

During the two lint camps in January, nearly all the algae was sprayed (except areas that were too difficult to access). Still, algae found a way to grow. In March, the algae was sprayed once more. Each time, the amount of algae that needed to be sprayed decreased, starting with over 1,000 square feet on January 17th, and dropping to 445 square feet on March 20th (Table 1). The average amount of algae per light dropped from 5.9 square feet to 2.6 square feet. That’s still a lot of algae, though.

Cave algae discolors cave speleothems and may also hasten the demise of historic cave signatures.

NPS Photo by Gretchen Baker

With the lights in Lehman Caves will be off for weeks/months, that may be the final death throe for much of the algae. Caves that are closed for the winter, like Timpanogos Cave and Crystal Cave in Sequoia National Park, have much less of an algae problem than caves that are open year-round, like Mammoth Cave, Carlsbad Caverns, and Lehman Caves. One solution we may be able to use in the future is to have lantern or flashlight Explorer Tours in the winter to reduce the amount of light in the cave, avoid spraying bleach in the cave (which is not good for the native cave life), and give visitors a cool opportunity to feel like an explorer and help conserve the cave.