Changes in Wetland Soil Processes and Ecosystem Functions Six Years After Marsh Creation in Barataria Bay, Louisiana

Abstract

Louisiana contains about 40% of the conterminous United States coastal and estuarine wetlands but also has the highest rates of wetland loss at around 80% of the total. Approximately 4,900 km2 of coastal land in Louisiana has been lost since 1930. Our study location, Barataria Bay, has one of the highest coastal wetland erosion rates in the nation, at ∼41 km2 per year; and therefore, is a high priority for wetland restoration activities. In 2014, sandy sediment dredged from the bed of the Mississippi River was placed in Barataria Bay as part of a restoration effort. Samples were taken from each of two marsh creation areas and one natural, adjacent control marsh. The moisture content and bulk density of the marsh creation areas were 48% and 596% of the control marsh, respectively. The total C and total N values were 17.9% and 14.2% of the control marsh, while microbial biomass C and N were 16.6% and 25.4% of the control marsh, respectively. The N mineralization rates in the created marsh soil were 15.6% of the control marsh, indicating significantly less soil microbial activity in the created marsh areas. When comparing the surface soil changes over time, the MC has increased in 4 years from 34.9% to 62.8% of the control marsh, while bulk density decreased from 583% to 405% of the control. The total C increased from 15.4% to 28% and TN increased from 7.4% to 23.7% in the surface soil compared to the control; while total P decreased from 42.5% to 39.7% in the surface soil. MBC increased from 13.1% to 24% and MBN increased from 4.7% to 47% in the surface soil compared to the control marsh. The N mineralization rate increased from 3.6% to 26.1% of the control in the surface soil, indicating an increase in nutrient availability to plants. Using data from two time points, the estimated trajectory of select marsh soil physiochemical and microbial measures to reach 95% of the control marsh is 18.4 ± 6.7 years. More time points are needed to better estimate the time lag until full wetland function.