Predicting the distribution of acid volatile sulfide in marine sediment from colour analysis of sediment-profile images
Organic enrichment of coastal sediments is a major concern worldwide. It is caused by an increase in the deposition of organic matter via terrestrial runoff (Gray et al. 2002) and aquaculture (Holmer & Kristensen 1994), or as a result of eutrophication driven by anthropogenic loading of coastal waters with phosphorus and nitrogen (Nixon 1995, Cloern 2001, Rosenberg et al. 2009). In coastal waters the majority of deposited organic carbon is mineralised by bacterial sulfate reduction because of the abundance of sulfate in the marine environement (Thode-Andersen & Jørgensen 1989, Bagarinao 1992). Hydrogen sulfide (H2S), produced during sulfate reduction, reacts with dissolved iron or reactive iron minerals to form acid-extractable iron sulfides (termed acid volatile sulfide, AVS) that contribute to the distinct black colouration of organic-rich sediment. Although there is a strong relationship between sedimentary sulfide content and organic matter input, its measurement has not been used in routine monitoring because of its laborious nature. Bull and Williamson (2001) tested a new approach to predict the sediment AVS concentration from sediment images. The authors used film photography in a laboratory and found a weak linear correlation (R2 = 0.67) between sediment colour and AVS concentration.