Guidelines for sampling and determination of hydrogen sulphide (H2S) in Seawater.

Abstract

Hydrogen sulphide is a poisonous gas that readily dissolves in water. The sulphide is formed in stagnant waters, where the oxygen has been consumed by bacteria oxidizing organic matter to carbon dioxide, water, and inorganic ions. Sulphate-reducing bacteria then use the oxygen bound in sulphate ions as an electron acceptor while reducing the sulphate ions to sulphide. No higher life forms can exist in water containing hydrogen sulphide, and these areas are thus turned into oceanic deserts. Hydrogen sulphide in a water sample is easily detected by its characteristic smell, even at concentrations lower than those measurable with the method below. 1.2 Purpose and aims Monitoring of dissolved oxygen and hydrogen sulphide provide information of an indirect effect of eutrophication. The purpose of the monitoring is to map the spatial distribution of concentrations of dissolved oxygen and hydrogen sulphide, with the aim to be able to assess the status of the seafloor and the waters above and to ensure that the data is comparable for the HELCOM pre-core indicator ‘Shallow-water oxygen’ and core indicator ‘Oxygen debt’. The indicator descriptions, including their monitoring requirements, are given in the HELCOM core indicator web site: http://helcom.fi/baltic-sea-trends/indicators/oxygen.