Louisiana Coastal Protection and Restoration Authority, Baton Rouge Area Foundation, U.S. Geological Survey Ecosystems Program and Restore the Mississippi River Delta Campaign via Coalition to Restore Coastal Louisiana

Relationships between salinity and short-term soil carbon accumulation rates from marsh types across a landscape in the Mississippi River Delta

The Challenge

Many of Louisiana’s coastal wetlands depend upon the annual cycle of birth and death of plant material to help build up soil height as a way of trying to stay ahead of relative sea level rise caused by the combination of sinking land and rising waters. However, as coastal land loss continues and more fresh marsh types are impacted by saline water, the question was raised – how will this increase in salt water impact the ability of the marsh to produce enough plant material for the soils to keep up with projected sea level rise, especially in an area starved of mineral sediment

The Approach

The Institute collected field data by looking at the accumulation of organic plant material at 24 marsh sites in southeast Louisiana across four marsh types – fresh, intermediate, brackish, and saline. Soil cores were collected and used to look at bulk density, total carbon, and accretion of the site which were compared to annual surface water salinity data from 2000 to 2015.

Culminating in a 2017 paper published in “Wetlands,” the work shows that although researchers found relatively little difference in the rates of this short-term accumulation categorized via marsh types, as surface water salinity in wetlands rises, the amount of organic carbon in soil that can accumulate as a buffer against relative sea level rise decreases. That also means freshening of certain wetlands with coastal restoration project such as sediment diversions being planned for the Mississippi River or even additional rainfall, can help wetlands regain some of this organic storage ability and perhaps give these areas a buffer against succumbing as quickly to higher water levels.

Other authors of the paper include researchers from the U.S. Geological Survey, Louisiana Department of Wildlife and Fisheries, and the Department of Earth & Environmental Sciences at Tulane University.