Estimating the in situ distribution of acid volatile sulfides from sediment profile images

Peter S. Wilson, Kay Vopel

Limnol. Oceanogr. Methods 10:1070-1077 (2012) | DOI: 10.4319/lom.2012.10.1070

ABSTRACT: Measuring the sediment content of acid volatile sulfides (AVS), an important determinant of coastal ecosystem functioning, is laborious and therefore rarely considered in routine coastal monitoring. Here, we describe a new approach to estimate the in situ distribution of AVS in subtidal soft sediment. Using amperometric H2S microelectrodes and a flatbed scanner in the laboratory, we first established a strong correlation (R2 = 0.95) between the AVS content (as extracted by cold 1 mol L-1 HCl) and the color intensity of sediment collected at 12 m water depth off the eastern coast of Waiheke Island, New Zealand. We then used this correlation to estimate the distribution of AVS in the upper 20 cm of this sediment from sediment profile images. These images were obtained in situ with a lightweight imaging device consisting of a modified flatbed scanner housed inside a watertight acrylic tube (SPI-Scan™, Benthic Science). We made two types of estimates from the acquired images: First, we obtained a vertical AVS concentration profile by averaging the color intensities of horizontally aligned pixels. Second, we created a two-dimensional distribution plot of AVS concentration by assigning individual pixel color intensities. Because our technique enables assessments of temporal and spatial variations in the AVS content of subtidal soft sediment, we suggest using it in routine coastal monitoring.