Accumulation and Output of Heavy Metals by the Invasive Plant Spartina alterniflora in a Coastal Salt Marsh

Spartina alterniflora is a foreign introduced species and has far-reaching effects on salt marsh ecosystems, particularly on the biogeochemical cycle of heavy metals. To ascertain whether the invasive plant Spartina alterniflora Loisel is a source of metals in the environment, we determined the bimonthly concentrations of heavy metals, chromium（Cr）, lead（Pb）, copper（Cu）, zinc（Zn）,and manganese（Mn）, in the roots, stems, and leaves of S. alterniflora from a typical semidiurnal tidal zone in the coastal area of northern Jiangsu Province, China. Based on the measurements, we calculated annual metal primary accumulation and output. To calculate the annual output of heavy metals from S. alterniflora, a new method that calculates the annual rate of biomass loss and decomposition was developed. The annual primary accumulation of Cr, Pb, Cu, Zn, and Mn was 19.08, 84.19, 63.74, 442.58, and774.66 mg m-2, respectively, and the annual output from S. alterniflora to the surrounding environment was 4.01, 18.09, 14.00, 97.11,and 164.28 mg m-2, respectively. Spartina alterniflora only provides temporary storage, and its absorption of heavy metals could be used to remediate contaminated soil and for phytomining. The heavy metals released by S. alterniflora to the environment cannot be ignored; thus, S. alterniflora should be considered a source of metal contamination. Therefore, when we evaluate the remarkable ability of certain plant species to concentrate metals in their tissues, the balance between heavy metal accumulation and output should be considered.