Nitrogen Dynamics in Sandy Freshwater Sediments (Saginaw Bay,Lake Huron) |
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| Affiliation: | 1. Cardiovascular Center and Department of Anesthesiology, Taichung Veterans General Hospital, Taichung, Taiwan;2. Departments of Medicine and Surgery, National Yang-Ming University School of Medicine, Taipei;3. School of Public Health and Tri-Service General Hospital Department of Medical Research, National Defense Medical Center, Taipei;4. Taiwanese Injury Prevention and Safety Promotion Association, Taipei;5. Department of Medicine, Chung Shan Medical University School of Medicine, Taichung, Taiwan;6. China Medical University, Taichung, Taiwan;1. MTA Centre for Ecological Research, Balaton Limnological Institute, Klebelsberg Kuno u. 3, H-8237 Tihany, Hungary;2. Department of Microbiology, Institute of Biology, Eötvös Loránd University, Pázmány Péter stny. 1/c, H-1117 Budapest, Hungary;1. Department of Biology, John Carroll University, 1 John Carroll Boulevard, University Heights, OH 44118, USA;2. Department of Botany, University of South Bohemia, Na Zlaté stoce 1, České Budějovice 370 05, Czech Republic;1. Laboratories of Biochemistry, Faculty of Science, Kochi University, Kochi 780-8520, Japan;2. Cellular and Molecular Biotechnology, Faculty of Science, Kochi University, Kochi 780-8520, Japan |
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| Abstract: | Sediment-water nitrogen fluxes and transformations were examined at two sites in Saginaw Bay, Lake Huron, as a model for sandy freshwater sediments. Substantial ammonium release rates (74 to 350 μmole NH4+/m2/h1) were observed in flow-through cores and in situ benthic chamber experiments. Sediment-water ammonium fluxes were similar at the inner and outer bay stations even though inner bay waters are enriched with nutrients from the Saginaw River. The high net flux of remineralized ammonium into the overlying water from these sandy sediments resembles typical data for marine systems (11 to 470 μmole NH4+/m2/h1) but were higher than those reported for depositional freshwater sediments (0 to 15 μmole NH4+/m2/h1; Seitzinger 1988). Addition of montmorillonite clay (ca. 1 kg dry weight/m2) to the top of the sandy cores reduced ammonium flux. Mean “steady-state” ammonium flux following clay addition was 46 ± 2 (SE) % of the initial rates as compared to 81 ± 8% of the initial rates without clay addition. Zebra mussel excretion dominanted ammonium regeneration in the inner bay where the bivalve was abundant, but addition of zebra mussel feces/psuedofeces (3.0 g dw/m2) to sediments did not increase ammonium or nitrate flux. Partial nitrification of ammonium at the sediment-water interface was suggested by removal of added 15NH4+ from lake water passing over dark sediment cores. Sediment-water fluxes of nitrogen obtained from flow-through sediment cores resembled those from in situ benthic chambers. However, extended static incubations in gas-tight denitrification chambers caused more of the regenerated nitrogen to be nitrified and denitrified than occurred with the other two measurement systems. |
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