MEPS 330:13-30 (2007)  -  doi:10.3354/meps330013

Combined nutrient–toxicant effects on a shallow-water marine sediment system: sensitivity and resilience of ecosystem functions

Kristina Sundbäck1,*, Dorthe Groth Petersen1,2, Ingela Dahllöf2, Fredrik Larson1

1Department of Marine Ecology, Marine Botany, Göteborg University, PO Box 461, 405 30 Göteborg, Sweden
2Department of Marine Ecology, National Environmental Research Institute, Frederiksborgvej 399, 4000 Roskilde, Denmark

ABSTRACT: Effects of nutrient status and short-term, low-level exposure to the antifouling biocide copper pyrithione (CPT) on intact shallow-water sediment were studied in an outdoor experiment, focusing on basic ecosystem functions driven by microorganisms. These functions were trophic status (autotrophy/heterotrophy), direction of dissolved inorganic nitrogen (DIN) flux, and the ratio of algal N assimilation:denitrification, and were based on measurements of daily sediment–water oxygen and nitrogen fluxes and denitrification. Bacterial production and biomass of microphytobenthos, meiofauna, and bacteria were also measured. The recovery of the functions was studied for 38 d. CPT exposure did not change basic ecosystem functions; the sediment remained autotrophic and a net sink of DIN, where microalgal N incorporation far exceeded denitrification. However, CPT affected individual N-cycling variables (ammonium flux, denitrification), as well as community respiration and bacterial production, with the direction of the response depending on sediment nutrient status. Significant CPT effects were more frequent in the nutrient-enriched sediment. Direct toxic effects were followed by indirect food-web-mediated (top-down) effects, leading to different timing and direction of effects with different sediment nutrient status. Permutational multivariate analysis of variance showed that initial CPT effects on system functions in both nutrient regimes were followed by an oscillating recovery process, where effects remained longer in the nutrient-enriched sediment. While single CPT exposure events may not affect general metabolic functions (oxygen flux)—at least not in net autotrophic sediments—repeated CPT exposure of sediment microbiota may impact nitrogen cycling in shallow, eutrophied waters.

KEY WORDS: Sediment · Multiple stressors · Copper pyrithione · Nutrients · Oxygen · Nitrogen · Denitrification · Trophic state

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