Sweetwater Regulars Tackle Water Lettuce

By Tom Brown
Photos by Jeanne Walker

Last week, Luke Safford and Tucson Audubon recruited a group of regulars from the long-running Wednesday morning Sweetwater Wetlands walks to remove water lettuce, a highly invasive plant. While the origin of the plant isn’t known, its incredible growth rate and potential effect on the habitat at Sweetwater is not in doubt. Here is a recent posting from the Center for Aquatic and Invasive Plants at the University of Florida:

“Pistia stratiotes (water lettuce) mats clog waterways, making boating, fishing and almost all other water activities, impossible. The mats degrade water quality by blocking the air-water interface and greatly reducing oxygen levels in the water, eliminating underwater animals such as fish. Water lettuce mats greatly reduce biological diversity: mats eliminate native submersed plants by blocking sunlight, alter emersed plant communities by pushing away and crushing them, and also alter animal communities by blocking access to the water and/or eliminating plants the animals depend on for shelter and nesting.”

 
My personal investigations have led me to believe that this plant has been introduced to the wetlands via an illegal dumping, probably with a fish or group of fish that were in a privately owned aquarium. The plant is readily available for purchase at pet stores and aquarium suppliers as a decorative vegetation.

We found the removal job incredibly tough. The reduced water levels, the depth of the organic matter/mud, and the density of the plants were all factors working against us. Being a water-based vegetation, it’s very heavy as the leaves are full of water, and it grows in wide mats that break into small, hard to control pieces. In the end, we removed hundreds of pounds of water lettuce but found that there was no way to make a noticeable effect on the plant without a more large-scale plan.

I want to send a heartfelt thank you to everyone who showed up to help, to Tucson Water for their support and equipment, to Andrea who was not able to make it but donated coffee and doughnuts, and to Luke Safford for his never-ending energy and love of Sweetwater Wetlands.

Tom is a life long bird photographer and has had his images published in newspapers, magazines, on-line sites, and calendars internationally. After several years acting as a full-time guide, he is retired and volunteers leading field trips for Tucson Audubon.