Seasonal Influence of the Needle Rush Juncus roemarianus on Saltmarsh Pore Water Geochemistry

Abstract

Previous studies have shown that saltmarsh macrophytes have a significant influence on sediment biogeochemistry, both through radial release of oxygen from roots and also via primary production and release of labile organic exudates from roots. To assess the seasonal influence of the needle rush, Juncus roemarianus, on saltmarsh sediment geochemistry, pore waters and sediments were collected from the upper 50 cm of two adjacent sites, one unvegetated and the other vegetated by Juncus roemarianus, in a Georgia saltmarsh during winter and summer. Pore waters collected at 1-to 2-cm intervals were analyzed for pH, alkalinity, dissolved phosphate, ammonium, Fe(II), Fe(III), Mn(II), sulfide, sulfate, and organic carbon. Sediments were collected at 5-cm intervals and analyzed for iron distribution in the solid phase using a two-step sequential extraction. The upper 50 cm of the sediment pore waters are mostly sulfidic during both winter and summer. The pore water and sediment geochemistry suggest organic matter degradation is coupled mostly to Fe (III) and sulfate reduction. In summer, there is greater accumulation of alkalinity, sulfide, ammonium, and phosphate in the pore waters and lower levels of ascorbate extractable Fe, which is presumed to be comprised primarily of readily reducible Fe(III) oxides, in the sediments, consistent with higher organic matter degradation rates in summer compared to winter. Lower pH, alkalinity, ammonium, and sulfide concentrations in sediments with Juncus, compared to nearby unvegetated sediments, is consistent with release of oxygen into the Juncus rhizosphere, especially during summer.

Evaluation of algal bloom mitigation and nutrient removal in floating constructed wetlands with different macrophyte species

“…The processes included are solubilisation of chemically bound carbon and the decomposition of structurally bound carbon. Here there is no reference to the component of the carbon pool produced or removed by the plants, however, Koretsky & Miller (2008) report that total organic carbon is typically higher in un-vegetated sites. Jones et al (2017) also reported a release of DOC from FCWs, which they attributed to leaching from root exudates and soil organic matter.…”

Biological Flora of Coastal Mid- and High Marshes: Juncus roemerianus Scheele

“…Decomposition of black needlerush occurs in standing senescent plants (Walker and Campbell, 2010) and decomposes more slowly than S. alterniflorus (Haines and Hanson, 1979). Koretsky and Miller (2008) reported that degradation of organic matter is coupled mostly with Fe 31 and sulfate reduction. Decomposition in the first month after plant death is attributed to leaching of water-soluble compounds followed by a weight loss of 60% to 70% in the next 7 months (McKee and Seneca, 1982).…”