New Zealand Journal of Marine and Freshwater Research abstracts

---

Underwater light and photosynthesis at three sites in Pelorus Sound, New Zealand

WARWICK F. VINCENT

CLIVE HOWARD-WILLIAMS

MALCOLM T. DOWNES

SUSAN J.DRYDEN

Taupo Research Laboratory
Division of Water Sciences
Department of Scientific and Industrial Research
P.O. Box 415, Taupo, New Zealand

Abstract Optical and photosynthctic measurements were made at 3 sites in Pelorus Sound, New Zealand, in late summer 1985. The attenuation of underwater light increased towards the landward end of the Sound, with an abrupt rise in scattering parameters (the scattering coefficient b, asymptotic reflectance/?_a, and the ratio of scalar to downwelling irradiance EJE) in the inner sound region (Mahau Sound). The effects of scattering were offset by changing water column depth and a high average irradiance was experienced by the phytoplankton community (22-34% of surface irradiance) at the 3 sites. Spectral scans of the water from Pelorus Sound showed an increasing absorbance by dissolved organic material (DOM) as well as paniculate materials towards the inner sound. Maximum photo-synthetic rates for the water column and per unit chlorophyll a were similarly high at all 3 sites, but chlorophyll a concentrations were consistently low (0.5-2.5 mg nr³). Population losses to zooplankton or other herbivores seem the most likely explanation of the low phytoplankton standing stocks despite the high productivity per unit biomass. A close adaptive coupling of the phytoplankton to nutrient supply and the underwater light field was suggested by large site-to-site differences in the photosynthesis versus irradiance parameters.

Keywords algal growth; estuary; light; optical properties; Pelorus Sound; photosynthesis; phytoplankton; primary production; tidal inlet

New Zealand Journal of Marine and Freshwater Research, 1989, Vol. 23: 79-91 0028-8330/89/2301-0079$2.50/0 © Crown copyright 1989 Received 26 January 1988; accepted 25 May 1988

PDF file of entire paper: medium quality (980K); (scanned from paper original: notes about this process)

---

This year's abstracts | Journal home page | All abstracts | Publishing home page