Some effects of river discharges and currents on phytoplankton in the sea off Otago, New Zealand

Abstract

Major rivers on the south-eastern coast, South Island, New Zealand create plumes that are deflected north between the Southland Current and the coast. Surveys of the continental shelf water mass off the Otago coast over a 2-year period, May 1996-April 1998, confirmed that when the Southland Current surfaced it contained less chlorophyll a than mixed water subject to terrestrial influence, implying that river-borne nutrients stimulated primary production in the mixed water. The greatest boost occurred in winter when diatom abundance increased. The band of chlorophyll-rich water extended through the photic zone and was several kilometres wide suggesting that riverine influence on marine biomass is substantial. In summer, the Southland Current often lay beneath oceanic water, with no increase in chlorophyll a concentration in the overlying water, due possibly to heavy grazing by zooplankton. In summer 1997-98, seawater temperatures were higher and phytoplankton biomass lower than in summer 1996-97, consistent with a strong El Niño event in the Pacific Ocean.

Reducing the arbitrary: fuzzy detection of microbial ecotones and ecosystems – focus on the pelagic environment

“…3 ), thus revealing more conserved communities over time. The strong influence of the Clutha River in the region, with its consistent inputs of freshwater and sediments, is responsible for the existence of a well differentiated NW, and is already known to support higher levels of primary productivity [ 94 ]. These terrestrial inputs may have had an additional stabilizing effect on the particle degrading bacterioplankton communities in the surface layers sampled in this study.…”

Bryozoan-dominated benthos of Otago shelf, New Zealand: its associated fauna, environmental setting and anthropogenic threats

“…The blooms are associated with river-borne nutrients (Haywood 2004), particularly silica, which stimulates phytoplankton growth on the innerand mid-shelf (Hawke 1992;Boyd et al 1999). Silica limitation may occur during a bloom when river flow is low (Hawke 1995), thereby affecting the biological community of the whole shelf.…”

“…On Otago shelf, advection from SAW to STW (reactive phosphorus (Hawke 1989;Croot & Hunter 1998)), riverine supply (reactive silica from the Clutha River/Mata-Au (Hawke 1989(Hawke , 1992) and resuspension of bottom sediments (releasing iron (Croot & Hunter 1998)) provide nutrients for a spring plankton bloom, which is most productive on the mid-shelf (Pfannkuche Figure 3 The continental shelf seaward of Otago Peninsula, including (shaded) the known distribution of habitat-forming bryozoans ascertained from the work of Probert et al (1979), Batson (2000) and Jones (2006Jones ( ). 1998Haywood 2004). SAW has a low concentration of chlorophyll (0.3 mg L…”