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Microphytobenthos activity and fluxes at the sediment-water interface: interactions and spatial variability
Bartoli, M.; Nizzoli, D.; Viaroli, P. (2003). Microphytobenthos activity and fluxes at the sediment-water interface: interactions and spatial variability. Aquat. Ecol. 37(4): 341-349
In: Aquatic Ecology. Springer: Dordrecht; London; Boston. ISSN 1386-2588, more
Peer reviewed article  

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Keywords
    Ammonium compounds; Denitrification; Diatoms; Nutrient cycles; Oxygen; Phytobenthos; Sediment-water exchanges; Sediment-water interface; Silicate minerals; Spatial variations; ANE, Sweden, Gotland, Tjarno [Marine Regions]; Brackish water

Authors  Top 
  • Bartoli, M.
  • Nizzoli, D.
  • Viaroli, P.

Abstract
    In this study oxygen and nutrient fluxes and denitrification rates across the sediment-water interface were measured via intact core incubations with a twofold aim: show whether microphytobenthos activity affects these processes and analyse the dispersion of replicate measurements. Eighteen intact sediment cores (i.d. 8 cm) were randomly sampled from a shallow microtidal brackish pond at Tjarno, on the west coast of Sweden, and were incubated in light and in darkness simulating in situ conditions. During incubation O2, inorganic N and SiO2 fluxes and denitrification rates (isotope pairing) were measured. Assuming mean values of 18 cores as best estimate of true average (BEA), the accuracy of O2, NH4+, NO3- and SiO2 fluxes calculated for an increasing number of subsamples was tested. At the investigated site, microalgae strongly influenced benthic O2, inorganic N and SiO2 fluxes and coupled (Dn) and uncoupled (Dw) denitrification through their photosynthetic activity. In the shift between dark and light conditions NH4+ and SiO2 effluxes (60 and 110 µmol m-2 h-1) and Dn (5 µmol m-2 h-1) dropped to zero, NO3- uptake (70 µmol m-2 h-1) showed a 30% increase, while Dw (20 µmol m-2 h-1) showed an 80% decrease. For O2 and NO3- dark fluxes, 4 core replicates were sufficient to obtain averages within 5-10% of the best estimated mean, while 10-20% accuracy was obtained with 4-12 replicates for SiO2 and >10 replicates for NH4+ dark fluxes. Mean accuracy was considerably lower for all light incubations, probably due to the patchy distribution of the benthic microalgal community.

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