Impact of hydrotalcite deposition on biogeochemical processes in a shallow tropical bay

• Published in: Marine environmental research 2011-03, Vol.71 (2), p.111-121
• Main Authors: Alongi, Daniel M., McKinnon, A. David
• Format: Article
• Language: English
• Subjects: Aluminum Hydroxide - pharmacology; Animal and plant ecology; Animal, plant and microbial ecology; Anoxia; Australia; Bacteria - drug effects; Bacterial Load; Benthic; Biological and medical sciences; Carbon; Carbon cycling; Cell Respiration - drug effects; Cycles; Deposition; Fundamental and applied biological sciences. Psychology; Geologic Sediments - chemistry; Geologic Sediments - microbiology; Geological Phenomena; Hydrotalcite; Magnesium Hydroxide - pharmacology; Marine; Mats; Microorganisms; Northern Territory; Oxygen - metabolism; Pelagic; Plankton - drug effects; Plankton - microbiology; Sea water ecosystems; Seawater - chemistry; Seawater - microbiology; Sediments; Sulfates; Sulfates - metabolism; Sulfides; Synecology; Tropical Climate
• ISSN: 0141-1136; 1879-0291
• DOI: 10.1016/j.marenvres.2010.11.006

The biogeochemistry of a tropical shoal bay (Melville Bay, Australia) impacted by the effluent release, precipitation, and deposition of hydrotalcite from an alumina refinery was studied in both wet and dry seasons. Within the deposition zone, sulfate reduction dominated benthic carbon cycling accounting for ≈100% of total microbial activity, with rates greater than those measured in most other marine sediments. These rapid rates of anoxic metabolism resulted in high rates of sulfide and ammonium production and low C:S ratios, implying significant preservation of S in stable sulfide minerals. Rates of total microbial activity were significantly less in control sediments of equivalent grain size, where sulfate reduction accounted for ≈50% of total benthic metabolism. Rates of planktonic carbon cycling overlying the deposition zone were also greater than those measured in the control areas of southern Melville Bay. At the sediment surface, productive algal and cyanobacterial mats helped stabilize the sediment surface and oxidize sulfide to sulfate to maintain a fully oxygenated water-column overlying the impacted zone. The mats utilized a significant fraction of dissolved inorganic N and P released from the seabed; some nutrients escaped to the water-column such that benthic regeneration of NH 4 + and PO 4 3− accounted for 100% and 42% of phytoplankton requirements for N and P, respectively. These percentages are high compared to other tropical coastal environments and indicate that benthic nutrient recycling may be a significant factor driving water-column production overlying the deposition zone. With regard to remediation, it is recommended that the seabed not be disturbed as attempts at removal may result in further environmental problems and would require specific assessment of the proposed removal process. ► Within a shoal bay impacted by hydrotalcite deposition, sulfate reduction dominated benthic carbon cycling. ► Rates of total microbial activity were significantly less in control sediments of equivalent grain size. ► Rates of planktonic carbon cycling overlying the deposition zone were also greater than those measured in the control areas productive algal and cyanobacterial mats helped stabilize the sediment surface and oxidize sulfide to sulfate to maintain a fully oxygenated water-column.