Experimental Phragmites control through enhanced sediment sulfur cycling

Additions of sulfate or sulfur (So), with and without carbon amendments, were made to large cores vegetated with Phragmites collected from a brackish N.J. marsh. Impairment of Phragmites growth from various carbon and sulfur additions was monitored over 1 yr. Initial increase in porewater sulfide was inhibited by sediment sulfide sequestration capacity concentrated in more inorganic surface layers which required millimolar sulfide inputs before concentrations rose to biologically significant levels. Even with sulfate concentrations sufficient to support sulfate reduction, sorption and reoxidation kept sulfide levels <250 μM in surface layers. Either dextrose or sulfate additions resulted in small increases in porewater sulfide levels (<120 μM), primarily at depth (22.5 cm). Carbon plus sulfate additions resulted in large, sustained enhancement of dissolved sulfide (∼1500 μM) throughout the sediment column. Elevated sulfide levels alone or in concert with porewater salinities greater than 20 ppt, did not kill emergent Phragmites although evapotranspiration and regrowth, indicated 'stress'. Sulfide levels were limited by sulfate and/or biologically available carbon. Determination of adequate sulfate dose also requires an initial measurement of the sulfide sequestration capacity of the sediments to allow adequate sulfate availability to support porewater sulfide levels sufficient to cause plant stress.