Restoration of hurricane-damaged mangroves at Punta
Yoav Bashan, Patricia Gonzalez-Zamorano, and Bernardo Salazar
Environmental Microbiology Group,
Dedication: This website is dedicated to the memory of the
In autumn 2001, a hurricane passed through the Bay of La Paz in Baja California Sur, Mexico, moving a large sand dune and blocking the outlet channel of a small mangrove forest consisting of two depressions with an area of about 10 hectares. This barrier sand bar, known as El Mogote, lies across the lagoon called Ensenada de La Paz from the city of La Paz. The authorities were not alerted, and in the absence of daily tidal flow, the mangrove forest deteriorated. Many trees died and the rest suffered from osmotic shock that led to defoliation. The two depressions lost all of their secondary mud channels, and had a thick salt crust on the dried depression bed and a hypersaline depression. Only halophytes of the genus Salicornia thrived in the degraded forest. In 2003, a land developer proposed to turn a large portion of the head of El Mogote into a suburban residential community and golf facility. This initiated an environmental evaluation of the area. The damaged mangrove was to be part of a future shopping mall. The survey for the environmental impact evaluation in early 2003 detected and recorded the deteriorated mangrove. A formal request for restoration was submitted to the Mexican environmental authority (SEMARNAT) and approved (Permit 1 and 2. During the administrative approval process, in late 2003 another hurricane passed through the area. It removed most, but not all of the sand blocking the main outlet channel.
Mangroves after hurrican, prior to restoration (2003).
In the absence of substantial funding for transporting heavy earth-moving equipment by water to this roadless area, only manual labor could be used to excavate the mouth of the outlet channel. Funding was limited to excavating only the mouth of the outlet channel, leaving the secondary channels untouched.
A natural and simple approach to restoration
Our goal was to use the power of the tides to clear the outlet and secondary channels in the mangrove. To enhance the excavating power of the water current, we only used shovels to deepen the mouth of the outlet channel during a very low tide to 1 m below mean sea level. This created a temporary set of low rapids at the entrance of the mangrove channel. Like any steep gradient drop, the rapids retreated upstream into the mud of the degraded mangrove forest, first reopening the outlet channel and then carving out new secondary channels. During this process, which lasted about two weeks, the excavated outlet was filled to mean sea level with mud transported by the receding current from the mangrove. We repeated the excavation two weeks later and a third time about a month later. The three excavations of the outlet channel were sufficient to effectively improve the entire mangrove, and, in the process, create two deep secondary channels, allowing adequate flooding of the lagoons. The bed of the mouth of the outlet channel eventually rose to mean sea level and functions as a natural channel. For more than a year, the tidal flow has kept the channels open to the daily and natural ebb and flow needed by mangrove forests; the salt crust has disappeared, the trees are recovering and showing new foliage; and the wildlife have returned. We consider the mangrove restored. In a few years, it should resemble the adjacent, nearly pristine mangroves of El Mogote.
Mangroves one year after restoration (2005)
This website contains photos (all the above photos in a photo gallery), three Power Point presentations of the restoration process [before, (2003) (544 kb), during (2004) (1.16 MB) and after restoration (2005) (1.27 MB)], and a PDF text describing mangrove conditions in the restoration area.
Key words: Arid zone mangroves, Baja California, coastal restoration, Costal lagoon, tidal effects, wetlands.
Dr. Yoav Bashan