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

Abstract

Nitrogen (N) and light availability limit phytoplankton growth and hence regulate food supply for mussel farming in Pelorus Sound, New Zealand. In Beatrix Bay, a large 35-m deep embayment off Pelorus Sound, the supply of N is heavily influenced by physical factors. Bottom intrusions of N-rich or depleted oceanic water occur in the main channel of Pelorus Sound and Ndepleted, phytoplankton-enriched Pelorus River water characterises the near-surface low salinity field. Inside Beatrix Bay, nutrient cycling via phytoplankton uptake, sedimentation, and subsequent regeneration from the sediments by mineralisation, also has an important influence on the availability of N in the water column. However, almost continuous salinity or thermally induced density stratification, or both, within Beatrix Bay meant that the upper and lower water columns were often decoupled so that N regenerated from the sediments was not readily available in the upper water column, and phytoplankton settling from the upper water column may not reach the sediments directly below because of large horizontal transport. The N supply in the upper water column of Beatrix Bay, where the mussels are farmed, is most likely regulated by advection in and out of the bay from external sources. Conversely, the N concentrations below the pycnocline could be almost entirely supplied via mineralisation from the sediments. The rates of sediment N regeneration were seasonally dependent. During winter, when sedimentation exceeds mineralisation, N accumulates in the sediments at a rate of up to 10 mg m -2 day -1 , whereas in summer, when mineralisation exceeds sedimenation, N is lost from the sediments at rates of up to 9 mg m -2 day -1 .

Physico-chemical characterization of the benthic environment of the Golfo San Jorge, Argentina

“…The lack of synchronicity would suggest that the labile carbon compounds were degraded by heterotrophic organisms in the surface layer limited by the thermocline and that only a small proportion of larger particles (particularly faecal pellets) and macroaggregates were deposited in sediments. These results coincide with those observed by di¡erent authors in the neritic zone of the north-west Mediterranean (Cahet et al, 1972), in Norway ¢ords (Sargent et al, 1983) and in Beatrix Bay, New Zealand (Gibbs et al, 2002). In similar environments, breakage of the pycnocline by wind and hydrodynamic conditions favour the export of autochthonous material towards the bottom (Olesen & Lundsgaard, 1995;Pesant et al, 2002).…”

River inputs, re‐mineralisation and the spatial and temporal distribution of inorganic nutrients in Tasman Bay, New Zealand

“…10, 11), where near bottom DIN concentrations were often significantly elevated. Gibbs et al (2002) have calculated that up to 80% of the annual DIN supply for Beatrix Bay (a large embayment within the Marlborough Sounds, New Zealand) may come from sediment recycling. However, as they point out, during strongly stratified periods much of this DIN may not be accessible to phytoplankton within the upper water column.…”

Benthic nutrient fluxes in a eutrophic, polymictic lake

“…On three sampling occasions (August andNovember 2003, andJanuary 2004), in situ DO sensors (Van Essen Instruments) were also used to record changes in DO concentration at 15 min intervals in a light and a dark chamber (sites 1 and 2) or in all chambers (site 3). Sediment NH 4 and SRP fluxes were calculated from the slope of linear regressions of chamber nutrient concentrations with time (Gibbs et al, 2002). After correcting for the effect of dilution associated with sample removal, rates of change of nutrient concentrations in the chamber were divided by the sediment surface area in the chambers, to give an aerial release rate.…”