Phytoplankton sinking rate dynamics in the southern Benguela upwelling system

Abstract

Sinking rates of phytoplankton assemblages with &verse and variable taxonomic composition, growing under a variety of environmental conditions, were measured In St. Helena Bay (S. Africa) using the homogenous sample method SETCOL. These measurements and flux estimates from sediment trap recovenes enabled the role of sinking phytoplankton in the flux of organic material from the euphotic zone to b e determined. Sinking rates were found to b e influenced by the duration of the settling experiments. Chlorophyll a sinking rates ranged from 0 to 0.91 m d-' but were poorly correlated to phytoplankton carbon sinking rates which ranged from 0 to 0.78 m d-' Sinking rates of phytoplankton populations were significantly correlated not to any of the environmental parameters measured but to taxonomic properties of the assemblages, which were in turn governed by prevailing environmental conditions. Phytoplankton carbon flux estimates, made from both the SETCOL measurements and the sediment trap recovenes, were in general agreement and did not exceed 6.1 % of primary production. Losses from the euphohc zone during the study period resulting from the sinking of intact phytoplankton were therefore of limited importance to the time-dependent changes of phytoplankton biomass. Phytoplankton sinking was, however, considered to have an impact on phytoplankton composition due to the variable sinking rates of the different assemblage components.

Size-fractionated measurements of nitrogen uptake in aged upwelled waters: Implications for pelagic food webs

“…Accepting a virtual absence of mesozooplankton grazing during the day results in the accumulation of >20-pm microzooplankton and net phytoplankton production over and above the small loss through sinking. Losses through sinking of viable net phytoplankton cells is shown here as 5% of their N productivity (Pitcher et al 1989) although considerably greater losses may occur during late blooms.…”

Dynamics of bacterioplankton, phytoplankton and mesozooplankton communities during the development of an upwelling plume in the southern Benguela

“…Maximum vertical flux from the euphotic zone amounted to 13.8 n/o of daily primary production altho'ugh in general carbon flux did not exceed 6.1 % of primary production. Netphytoplankton (< 200 pm) diatoms typically dominate developing blooms and exhibit the fastest sinking rates (Pitcher et al 1989). They have a strong requirement for NO3 assimilation, as indicated by their high (ca 0.7) f-ratio values (Probyn 1985).…”

Sinking rates of phytoplankton in the Changjiang (Yangtze River) estuary: A comparative study between Prorocentrum dentatum and Skeletonema dorhnii bloom

“…Laboratory and in situ studies have shown that phytoplankton sinking rate can be determined by the characteristics of the phytoplankton cells, including physiological state, various forms of motility, cellular morphology and density (van Ierland and Peperzak, 1984;Waite et al, 1997). In addition, some environmental parameters, such as nutrient concentration, irradiance, viscosity of the medium and even water turbulence, may also determine the sinking rate (Pitcher et al, 1989;Waite et al, 1992a).…”

“…Therefore, study of phytoplankton sinking rates is important for the comprehensive understanding of carbon sedimentation mechanisms of various phytoplankton communities, including different type of algal blooms (Johnson and Smith, 1986;Pitcher et al, 1989). Particle sinking rate can be calculated using the Stokes' law: ψ = 2 gr 2 (ρ P − ρ SW )/9η, where ψ is the sinking rate, g is gravitational acceleration, r is the spherical particle radius (m), ρ P is particle density, ρ SW is seawater density and η is dynamic viscosity (Happel and Brenner, 1991).…”