Sulfate Fertilization and Changes in Stable Sulfur Isotopic Compositions of Lake Sediments

Abstract

A combination of stable isotopic measurements was used to study food web structure of Georges Bank, northwestern Atlantic. Particulate, invertebrate, and fish samples were analyzed to test d13C, d15N, and d34S measurements as trophic-level indicators in offshore systems. Neither S nor C measurements proved valuable. Isotopic compns. showed little change with trophic level, and an apparent diversity of phytoplankton C isotopic inputs at the base of the food web complicated use of d13C to estimate trophic position. N isotopic distributions were, however, robust measures of trophic position and showed 4 broad trophic levels; unsampled large top carnivores may represent a fifth trophic level.