Primary Productivity, Sulfate Reduction and Sulfer Isotope Fractionation in Algal Mats and Sediments of Hamelin pool, Shark Bay, W. A.

Abstract

A variety of benthic algal mats grow in the intertidal and subtidal environments of Hamelin Pool. Primary productivity ranged from 17 mhCm^-2 h^-1 for smooth mat, present in the high intertidal zone, to 113 mgC m^-2 h^-1 for colloform mat, found only in subtidal areas. Although pustular mat showed high photosynthetic efficiency [9.1 mgC (mg Chla)^-1h^-1] sulfate reduction was undetectable in underlying sediments. The rates of sulfate reduction in sediments close to intertidal stromatolites and in sediments beneath smooth mat were similar (5 mmol m^-2d^-1). In the intertidal zone stromatolitic debris has formed sediments in which sulfate reduction is rapid (14-46 mmol m^-2d^-1). Sulfur isotope distribution indicates a semiclosed system in the latter sediments (δ³⁴S‰,: SO₄^2-, +22.0 to +27.7; S^2-, - 11.2 to -14.5) and an open system in the smooth mat sediments (δ³⁴S‰: SO₄^2-,+20.7; S^2-, -23.2). Fractionation factors are between 1.033 and 1.044. The geobiological significance of these data is discussed.