Abstract: Pore-water chemistry, up to a depth of 80 cm, was monitored seasonally for a three-year period at a newly constructed marsh (near the Secaucus High School) and an established marsh, both along the Hackensack River. In both cases dialysis samplers were permanently installed in selected locations of the high marsh. Samplers were also placed at lower elevations that remained permanently saturated in the newly established marsh. At the established marsh samplers were placed in locations dominated by the presence of either Spartina patens or Phragmites australis. Detailed chemical analyses yielded concentrations of chemical species at 3 cm increments, including total dissolved organic carbon, iron, sulfate, trace metals (Cr, Pb, Cu, Zn), bromide, sodium, and in selected cases sulfides and dissolved gases such as methane and hydrogen.
Results of this still ongoing investigation show that there are significant differences in the dissolved iron profiles, with significant amounts of Fe(II) present in the pore water of the newly constructed high marsh, with little or no detectable Fe(II) present at the lower elevation of the constructed marsh or the established marsh. Higher concentrations of Fe(II) mean that sulfides that are formed from the reduction of sulfate will precipitate with the Fe(II) that is present, while in the absence of Fe(II), sulfides can build up in the sediment pore water. Sulfide will also precipitate and remove from the water phase many divalent metals of concern like lead and cadmium, while it will reduce toxic and water-soluble hexavalent chromium to non-toxic insoluble trivalent chromium. Hence, in the presence of higher Fe(II) values, we also observed higher trace metal concentrations in the pore waters.
Significant differences in chemical constituent profiles are being observed in sediments dominated by Phragmites vs. Spartina. It is not clear at this point if these differences are plant- or hydrology-driven. Profiles of dissolved methane show the potential impact of a Phragmites invasion on wetland methane dynamics. The use of dissolved hydrogen as an indicator for terminal electron acceptor processes in shallow sediments will also be explored. Links between different chemical species and the dynamics affecting them in tidal marshes will be discussed as well as seasonal variability.