Scientists have long known that Louisiana is sinking. Its southern coast is widely regarded as being among the fastest-disappearing areas in the world and over the past 50 years the state has lost valuable wetlands equal to ten times the size of New York City. Now, research from Tulane University has confirmed that the Pelican State’s loss of landmass is happening at the rate of what was previously considered to be the worst-case scenario.
Jaap Nienhuis, postdoctoral fellow in environmental science and lead author of the research was shocked by the findings. ‘Previous studies that were based on less data had rates at somewhere between three to four millimetres per year, with worst-case scenarios of about eight to ten millimetres per year,’ he explains. ‘We found that nine millimetres per year is actually the average.’
The new total comes from readings taken by surface-elevation tables – mechanical levelling devices used to measure relative sediment elevation changes – in 274 stations around the coast.
The main reason for the loss is the natural process of sediment compaction. Over time, wetland soils become more compressed, leaving them with less air and water between sediment. This means they form thinner layers. The compaction is usually offset by the build up of more sediment from the floods of the Mississippi river. However, this process has been stopped by the construction of dams and levees. ‘We’re keeping a large part of the Mississippi River sand and mud behind all the dams further upstream,’ says Nienhuis, ‘and the rest is being flushed between the levees straight into the sea.’ The problem is being exacerbated further by oil, gas and groundwater extraction, which causes compression at deeper layers underground.
As well as sediment loss, the sea level is rising, swallowing the land by 3mm per year. Together the dual pressures mean the state is losing a yearly average of 12mm of coastal wetlands, regions that often serve as vital ecosystems, agricultural land, or buffers for storms.
This was published in the August 2017 edition of Geographical magazine.
