Microphytobenthos activity and fluxes at the sediment-water interface: interactions and spatial variability

• Published in: Aquatic ecology 2003-10, Vol.37 (4), p.341-349
• Main Authors: Bartoli, Marco, Nizzoli, Daniele, Viaroli, Pierluigi
• Format: Article
• Language: English
• Subjects: Accuracy; Brackish; Cores; Denitrification; Microalgae; Sediment-water interface; Sediments
• ISSN: 1386-2588; 1573-5125
• DOI: 10.1023/B:AECO.0000007040.43077.5f

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 O^sub 2^, inorganic N and SiO^sub 2^ fluxes and denitrification rates (isotope pairing) were measured. Assuming mean values of 18 cores as best estimate of true average (BEA), the accuracy of O^sub 2^, NH^sub 4^^sup +^, NO^sub 3^^sup -^ and SiO^sub 2^ fluxes calculated for an increasing number of subsamples was tested. At the investigated site, microalgae strongly influenced benthic O^sub 2^, inorganic N and SiO^sub 2^ fluxes and coupled (D^sub n^) and uncoupled (D^sub w^) denitrification through their photosynthetic activity. In the shift between dark and light conditions NH^sub 4^^sup +^ and SiO^sub 2^ effluxes (60 and 110 µmol m^sup -2^h^sup -1^) and D^sub n^ (5 µmol m^sup -2^ h^sup -1^) dropped to zero, NO^sub 3^^sup -^ uptake (70 µmol m^sup -2^ h^sup -1^) showed a 30% increase, while D^sub w^ (20 µmol m^sup -2^ h^sup -1^) showed an 80% decrease. For O^sub 2^ and NO^sub 3^^sup -^ 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 SiO^sub 2^ and >10 replicates for NH^sub 4^^sup +^ dark fluxes. Mean accuracy was considerably lower for all light incubations, probably due to the patchy distribution of the benthic microalgal community.[PUBLICATION ABSTRACT]