Recently a gigantic swath of dead mangroves, east of the Indian River Lagoon on Hutchinson Island in Jensen Beach was brought to my attention. About a year ago, I had noticed the dead forest of trees; however, with my full attention on toxic-algae, water-quality, or lack thereof, I had put this graveyard of walking trees out of my mind. Until I got a phone call a couple of days ago…
My contact, as many others, proposes fundamental changes, such as culverts or another small inlet between the barrier island and the IRL to allow more flushing and increase salinity, pointed out that the primary reason the mangrove forest died, post Hurricane Irma, was too much fresh water. He also noted that the toxic-algae, as bad as it is, is not the worst killer for our St Lucie River. The worst killer is an old enemy: too much fresh water from Lake Okeechobee and area canals. The fluorescent toxic algae has just “put a face” on the carrier, the real enemy, too much fresh water.
The St Lucie is an estuary (https://oceanservice.noaa.gov/facts/estuary.html) and needs salt water to exist, also the microcystin toxin cannot survive in a brackish system. The constant discharges, from Lake Okeechobee especially, continually push fresh water through a once brackish system, poisoning it, and toxic algae is along for the ride…
I found this message a powerful tool in visualizing what has happened to our St Lucie River. The dead mangroves are indeed a metaphor for the entire St Lucie River/Indian River Lagoon system: our lush seagrass beds have died and the water quality is terrible, leaving little or no wildlife.
We must remember, below our waters, too much fresh water has caused a dead forest too.
#Stop the Discharges
Algae and Cyanobacteria in Fresh Water, World Health Organization: http://www.who.int/water_sanitation_health/bathing/srwe1-chap8.pdf
Below, I am including Martin County’s response to my inquiry about the dead mangrove forest as a matter of public interest and education.
Jacqui,
This loss of mangroves at the JBI site prompted a serious investigation by the Mosquito Control and Environmental Resources Divisions. Given the large-scale mortality event, testing was conducted to rule out site contamination. Water quality testing was also conducted to determine dissolved oxygen, pH, salinity, and hydrogen sulfide levels. The Florida Department of Environmental Protection, St. Johns Water Management District, Smithsonian, a local mangrove arborist and Ecological Associates Inc. were all consulted regarding concerns over the mangroves. The majority opinion was that heavy late season rain and high water levels were the primary cause of the mangrove mortality with hurricane stress and suspended solids associated with storm surge as secondary causes. Additionally, lack of species and age structure diversity contributed to the loss, more diverse communities are associated with greater resiliency. Areas in close proximity to the JBI show evidence of mortality caused by ‘ponding’ in which high freshwater levels result in the loss of vegetation.
Recommendations going forward are to improve hydrological connectivity through the installation of additional culverts, clear out channel sedimentation, and install spillways. These actions will improve water quality by allowing for more exchange with the IRL and also increase the discharge capacity of the south cell to prevent high water levels associated with heavy rain and storm surge. In order to accomplish these actions, a capital improvement plan for the site was tentatively approved by the board on April 10th, 2018. Additional funding opportunities will be sought for site improvements and the board granted permission on July 24th, 2018 for staff to pursue State Wildlife Grant funding from the Florida Fish and Wildlife Commission.
While funding opportunities are being sought, in-house activities have been pursued. Specifically, staff gauges have been installed to monitor natural tide conditions to allow for careful water level monitoring. The Project Engineer from Field Operations has put together a conceptual plan. A failed culvert is in the process of being replaced. Blockages along the perimeter have been identified and several have been cleared. Transects are being put in for vegetative monitoring. New growth can be seen within the JBI site, however, this is primarily restricted to the areas in closest proximity to the IRL. Culverts are currently opened to allow for natural recruitment and mosquito control is being accomplished through alternative means to allow the area to reseed.
Let me know if you would like to meet to discuss this.
Terry B. Rauth, P.E., Public Works Director, Martin County Board of County Commissioners
