Effects of Bioirrigation and Salinity on Arsenic Distributions in Ferruginous Concretions from Salt Marsh Sediment Cores (Southern Brazil)

• Published in: Aquatic geochemistry 2021-06, Vol.27 (2), p.79-103
• Main Authors: Costa, Larissa, Mirlean, Nicolai, Quintana, Guilherme, Adebayo, Segun, Johannesson, Karen
• Format: Article
• Language: English
• Subjects: Analytical Chemistry; Aquatic plants; Arsenic; Biogeochemical cycles; Biogeochemistry; Biogeosciences; Bioturbation; Brackish water; Concretions; Cores; Crustaceans; Decapoda; Earth and Environmental Science; Earth Sciences; Earth System Sciences; Estuaries; Estuarine dynamics; Geochemistry; Granulation; Growth; Iron; Manganese; Marine crustaceans; Mineralogy; Mud flats; Nodules; Oceanography; Original Article; Oxides; pH effects; Pore water; Redox potential; Salinity; Salt marshes; Saltmarshes; Sediment; Sedimentary structures; Sediments; Spartina alterniflora; Sulfate reduction; Sulphate reduction
• ISSN: 1380-6165; 1573-1421
• DOI: 10.1007/s10498-020-09387-7

Arsenic (As), iron (Fe), and manganese (Mn) contents were measured in sediment nodules and associated pore waters obtained from sediment cores collected from a salt marsh on Pólvora Island (southern Brazil). Sediment cores were obtained when brackish water dominated the estuary, at two different environments: an unvegetated mudflat colonized by crabs ( Neohelice granulata ), and a low intertidal stand vegetated by Spartina alterniflora . We determined the percentage of nodules in each depth interval of the cores, along with redox potential, and As, Fe, and Mn contents of the nodules. The mineralogy of the nodules was investigated, and results showed they are mainly composed by quartz, phyllosilicates, and amorphous Fe–Mn oxides/oxyhydroxides. Pore water results showed that bioturbation by local crabs supports oxygen penetration to depths of ca. 25 cm below the salt marsh surface, with lower Fe contents in pore water associated with the brackish period. However, S. alterniflora growth appears to have a greater impact on sediment geochemistry of Fe, Mn, and possibly As due to sulfate reduction and the associated decrease in pore water pH. Higher Fe concentrations were observed in the pore waters during the period of brackish water dominance, which also corresponded to the S. alterniflora growth season. The study demonstrates that differences in geochemical conditions (e.g., Fe content) that can develop in salt marsh sediments owing to different types of bioirrigation processes (i.e., bioirrigation driven by crabs versus that related to the growth of S. alterniflora ) play important roles in the biogeochemical cycling of As.