Hypoxia and Hydrogen Sulfide (H2S) in Padilla Bay, WA from 2014-07-09 to 2014-09-30 (NCEI Accession 0156596)

Hypoxia has the potential to be a stressor to eelgrass as it can lead to tissue anoxia at night. These tissues then must undergo anaerobic metabolism, which is less energetically efficient and can produce toxic byproducts. Hypoxia may also work in synergy with other stressors, such as sediment pore-water sulfide. Hypoxia can facilitate the intrusion of sulfide, a known phytotoxin, into eelgrass tissues. This study examined the interaction between sulfide and hypoxia on the growth and photosynthetic efficiency of Zostera marina. Eelgrass shoots were collected from Padilla Bay, Washington and placed into seawater tanks in 18 oz. cups of sediment with a disk of agar at the bottom to simulate organic enrichment and to stimulate sulfide production. The growth rate and photosynthetic efficiency of the eelgrass shoots were monitored weekly for six weeks. After week three, the water columns of six of the tanks were reduced to hypoxic conditions (<2mg L-1). During week 6, the oxygen concentration was dropped further to near anoxic conditions. After week 6, eelgrass tissue samples were collected for measurement of total sulfur, carbon, and nitrogen. The results indicated that hypoxia had a significant negative effect on Z. marina shoots, which was evidenced by strong reductions in growth rates and photosynthetic efficiencies. These findings indicate that hypoxia in conjunction with sediment organic enrichment harms eelgrass health and enhances the intrusion of sulfide into plant tissues, over a wide range of pore-water sulfide concentrations.