Hydrogen Sulfide Toxicity Study

Impact of hydrogen sulfide toxicity on nearshore community structure in the Pacific Northwest region

Funded by the National Science Foundation

Co-PI’s: S. Wyllie-Echeverria and P. D. Ward

Statement of problem

Anthropogenic changes are clearly affecting global environments and in so doing creating biological change across a wide spectrum of ecosystems. While a great deal of attention is currently being paid to the potential effects of global warming, here we address a subtle shift in community structure in shallow marine environments in the Pacific Northwest (and perhaps deeper water as well) that has not received a great deal of attention. Our preliminary evidence suggests that H2S poisoning may be threatening community structure in the lower intertidal, shallow subtidal region in small embayments of the Pacific Northwest.

We suspect that this condition may be fueled by carbon accumulation patterns related to an increase in detrital accumulation associated with land clearing practices that have been enacted over the past two centuries. Over time, large stands of ancient, primarily coniferous, forests were removed and replaced by cleared land and a second and third growth blend of broadleaf trees, conifers and shrubs (e.g., Suzuki and Grady 2004, Swanson 2005). This deforestation and the continued rain of leaf litter from broadleaf tree species and shrubs introduced (and continues to introduce) enormous quantities of litter and woody debris into coastal waters. A significant amount of this material becomes entrained in sediments that rapidly become anoxic, with resultant formation of hydrogen sulfide through anoxic decomposition.

We propose to (1) determine levels of hydrogen sulfide present in areas where we have observed seagrass decline and then (2) test the effects of varying concentrations of hydrogen sulfide in sediment and water column environments on various taxa native to shallow marine and estuarine environments in the Pacific Northwest. To do this we plan to link field measurements and observations with laboratory experiments within controlled environmental chambers.

Our driving questions are:

  • 1. Is trapped H2S transforming the lower intertidal and shallow subtidal regions of coastal waters in the Pacific Northwest into hostile environments for flora and fauna common to this region?
  • 2. Can H2S/O2 profiles leading to lethal conditions for the seagrass, Zostera marina, and invertebrate infauna and epifauna, in the seagrass zone, be discovered using environmental chambers with controlled treatments of light, temperature and H2S?