Benthic trophic status and nutrient fluxes in shallow-water sediments |
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| Authors: | Anna Engelsen Stefan Hulth Leif Pihl Kristina Sundbck |
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| Institution: | aDepartment of Marine Ecology, The Sven Lovén Centre for Marine Sciences, University of Gothenburg, Kristineberg Marine Research Station, SE-450 34 Fiskebäckskil, Sweden;bDepartment of Chemistry, University of Gothenburg, SE-412 96 Göteborg, Sweden;cDepartment of Marine Ecology, University of Gothenburg, Box 461, SE-405 30 Göteborg, Sweden |
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| Abstract: | Proliferation of fast-growing ephemeral macroalgae in shallow-water embayments constitutes a large-scale environmental change of coastal marine ecosystems. Since inorganic nutrients essential for the initiation and maintenance of macroalgal growth may be supplied from the underlying sediment, we investigated the coupling between benthic inorganic nutrient (mainly N and P) fluxes and sediment properties in 6 bays representing a wide gradient of sediment characteristics (grain size, organic matter content, solid phase C and N). The initial characterization of bays was made in June and also included measurements of oxygen flux and microphytobenthic and macrofaunal biomass. In September, still within the growth season of the macroalgae, complementary experiments with sediment-water incubations for benthic flux measurements of oxygen and nutrients focused on trophic status (balance between auto- and heterotrophy) as a controlling factor for rates of measured benthic nutrient fluxes. Generally, sediments rendered autotrophic by microphytobenthic photosynthesis removed nutrients from the overlying water, while heterotrophic sediments supplied nutrients to the overlying bottom water. Estimations of the green-algal nutrient demand suggested that late in the growth season, net heterotrophic sediments could cover 20% of the N-demand and 70% of the P demand. As the benthic trophic status is a functional variable more closely coupled to nutrient fluxes than the comparably conservative structural parameter organic matter content, we suggest that the trophic status is a more viable parameter to classify sediments and predict benthic nutrient fluxes in shallow-water environments. |
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| Keywords: | sediment characteristics benthic fluxes autotrophy– heterotrophy macroalgal growth benthic microalgae |
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