Why is saltmarsh vanishing in Northeast Florida?

Marine wetlands can’t keep pace with sea level rise

Mangrove trees impeding on saltmarsh along the Intracoastal waterway at the Guana Tolomato Matanzas National Estuarine Research Reserve. (wjxt)

Scenic reeds of grass appear everywhere along the backsides of our barrier islands and you can’t get to the beach without seeing salt marsh from local bridges.

But over the past 24 years we are seeing less of it. Northeast Florida has lost approximately 10,000 acres of salt marsh and scientists point to the acceleration of sea level rise as the primary driver behind the ecosystem decline.

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So much depends on this grassy buffer between the ocean and mainland that without it our seafood stock would dwindle, the coast would be exposed to more frequent storm flooding and water quality would suffer.

These are the concerns addressed during Friday’s UNF Environmental Symposium with members of the community and regulatory agencies responsible for developing and implementing environmental policy.

Tidal marshes are drowning as sea level rise sprints upwards at 10 to 20 millimeters per year.

Professor Jeremy Stalker from Jacksonville University pointed out the sea level does not rise at a steady pace but more like a stair step curve upwards. Stalker says the average rise over 50 years had been about three millimeters per year or the height of three stacked pennies; a rate plant growth could keep pace as sediments washed in to elevate the root zone.

Marshes could migrate over the decades to compensate for slow changes in sea levels. Nowadays plants are locked in place by seawalls and development.

Organic plant material left behind builds up marsh elevation but as saltwater intrudes farther into the estuary by deepening and widening rivers like the St. Johns, the marsh sinks.

Mangroves are taking over

Mangroves once confined to central and south Florida are showing up in northeast Florida due to warming climate. (wjxt)

Make room for the mangroves. While global warming is shifting salt grass habitat, black and red mangrove trees are taking advantage of the warmer climate by overtaking areas historically that were too chilly.

The most northern reported sighting of a mangrove is documented in the Timucuan preserve and experts say they may spread farther up in latitude in coming years.

Threatened wetlands could benefit from the stabilization mangroves provide to the shoreline since the species has success keeping up with the rise in sea level. However retired UNF coastal biologist Courtney Hackney, cautions they don’t behave the same way. Salt marshes harbor far more beneficial microalgae in the ecosystem.


About the Author:

After covering the weather from every corner of Florida and doing marine research in the Gulf, Mark Collins settled in Jacksonville to forecast weather for The First Coast.