Dynamics of nutrient cycling and related benthic nutrient and oxygen fluxes during a spring phytoplankton bloom in South San Francisco Bay (USA)

Abstract

Benthic oxygen uptake and nutrient releases of N, P and Si were measured weekly at 2 sites in South San Francisco Bay around the 1996 spring bloom. Exchanges across the sediment-water interface were estimated from whole core incubations performed in the laboratory at in situ temperature and in dark. Fluxes changed significantly on a weekly time scale. Over a period of 15 wk the fluxes of dissolved inorganic N, P and Si ranged from -40 to +200, 0 to 13 and from 30 to 400 pm01 m-' h-' respectively. Sediment oxygen demand increased from 10 before to 64 mg O2 m-2 h-' just after the bloom period. During the bloom, nutrient fluxes represented about 20, 16 and 9 % of the Si. P and N requirements for primary production. Before and after the bloom period, Si fluxes contributed up to 30 and >loo% of this requirement and P and N fluxes up to 15 and 50% respectively. Simple empirical models explain most of the spatial-temporal variability of benthic f l u e s of Si, P and NH, (but not NO3) from 3 predictor variables: sediment porosity, nutrient concentration in bottom waters and chlorophyll content of surficial sediments. These models show that algal blooms influence benthic-pelagc nutrient exchange through 2 processes: (1) depletion of nutrients from the water column (which enhances gradient-driven transports across the sediment-water interface) and (2) sedimentation of labile phytodetritus (which promotes remineralization in or on the surficial sediments]. Rates and patterns of nutrient cycling were very different at the shallow and deep study sites, illustrating the challenge of extrapolating measurements of coupled algae-nutrient dynamics to whole ecosystems.

Nutrient cycling and fluxes in Beatrix Bay, Pelorus Sound, New Zealand

“…This is consistent with reoxygenation of the sediments during winter mixing and lower biological process rates in the colder water. This range of levels is comparable with SOD rates of -0.19 to -0.7 g m -2 day -1 reported in the outer Thames estuary (Trimmer et al 2000), -0.17 to -0.67 g m -2 day -1 in the coastal waters of Denmark (Forster et al 1999), and up to -0.56 g m-2 day -1 before the spring bloom in South San Francisco Bay (Grenz et al 2000).…”

Role of phytoplankton in mercury cycling in the San Francisco Bay estuary

“…Previous research has demonstrated that MeHg is produced in San Francisco Bay sediments (Olson and Cooper 1974; Marvin-DiPasquale and Agee 2003), presumably as a result of methylation of inorganic Hg by bacteria that reduce sulfate and/or Fe (Benoit et al 2003;Kerin et al 2006). As the bloom decayed, conditions would have been favorable for mercury methylation because the decomposing algae likely depleted dissolved oxygen in sediments, as was seen following the South Bay bloom in 1996 (Grenz et al 2000).…”

Concentration–discharge relationships reflect chemostatic characteristics of US catchments

“…At a species to community level, site-to-site comparisons reveal that benthic macroinvertebrate and diatom species diversity is a function of total dissolved solid concentration, conductivity or salinity in some streams, lakes and fjords (Metzeling, 1993, Ryves et al, 2004. Solute fluxes, especially the amount of Si relative to other potentially limiting nutrients, can be a predictor of phytoplankton blooms and diatom growth (LePape et al, 1996;Grenz et al, 2000). Si concentrations relative to concentrations of Fe, N and P strongly control diatom nutrient uptake and growth rates.…”