Invasive Phragmites Increases Blue Carbon Stock and Soil Volume in a St. Lawrence Estuary Marsh

Abstract

AbstractOur study of a St. Lawrence Estuary marsh reveals that, compared to native Spartina patens‐dominated vegetation, invasive Phragmites australis makes a greater contribution to soil volume and carbon stock (referred to as blue carbon). Phragmites' contributions to soil volume enhance marsh sustainability in face of sea level rise, and its greater contribution to soil carbon helps to reduce the atmospheric concentration of CO2. Phragmites australis (common reed) is a cosmopolitan species growing in fresh to brackish wetlands. An invasive genetic strain, introduced from Europe or Asia, has expanded extensively along the St. Lawrence River in the last few decades but has been little studied on the estuarine portion. We collected soil cores from three sites within an invasive Phragmites stand and one site within S. patens‐dominated stand in a St. Lawrence Estuary salt marsh near la Pocatiere, Quebec. We measured the bulk density, carbon content, volume, and mass of belowground organic matter in 2‐cm‐thick soil layers of three cores at each Phragmites site. Bulk density and carbon content were measured in 5‐cm‐thick soil layers of three cores at S. patens site. Results showed that soil in the Phragmites stands held 37–77% more blue carbon than in the S. patens‐dominated marsh. Based upon their diameter size, Phragmites rhizomes could be contributing 7.4–10.2 cm to the thickness in the upper 20 cm of soil. We suggest that any management of invasive Phragmites include consideration of its role in increasing blue carbon stocks and marsh resilience along with other ecosystem services.