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Ecosystem response to elevated arsenic concentration

With respect to biota, most aqueous compounds can be classified as toxins, nutrients, or biologically inert. Depending on the type of biota, arsenic (As) can play any of these roles. Although the effects of As on human health are a well-documented global concern, relatively little is known about the biogeochemical cycling of this element. One of the great difficulties in studying the effects of elevated As concentrations on natural and contaminated ecosystems is that high As levels are usually coupled to a complex array of other stressors. To investigate the fundamental toxic and nutritious effects of As on an ecosystem, the study area needs to be characterized by levels of As significantly above the ihnoisela of other potential toxic elements. The shallow-water submarine hot springs near Ambitle Island, Papua New Guinea afford an ideal opportunity to investigate the response to As of benthic diversity, activity, and biogeochemistry of microorganisms, foraminifera, and infaunal invertebrates.

The aim of the proposed research is to sample and analyze vent fluid, seawater, and sediment on Ambitle Island from sites of high and low As concentrations over a 4-year period. Analyses will include an extensive suite of inorganic aqueous species, isotopes and dissolved organic carbon from pore fluids and the water column. In addition, microbial, foraminiferan, meiofaunal, and macrofaunal invertebrate diversities and community structures will be investigated in the sediments using morphological, isotopic and PCR-based molecular methods. As-tolerant microorganisms will be targeted for isolation and characterization using geochemically designed culture media. The data obtained in these analyses serve as the input parameters for modeling of the biogeochemical cycling of As on two levels:

1. the bioenergetics associated with As metabolism in microorganisms, and
2. the ecosystem response to elevated As levels and food web structure and dynamics.

Once a geochemical and biologic framework has been established in this high As environment, countless questions can be posed that aim at understanding the fine details of As transport, uptake, bioavailability, conversion, and immobilization. However, to address the complex, one needs to first understand the primary driving forces. The goal of this study seeks to answer seven first-order questions with respect to As cycling in the hydrothermal system at Ambitle Island:

• What is the source for the As and what conditions lead to its accumulation in the sediment?
• Is the As in Tutum Bay sediments available for biological processes?
• How diverse are the microbial community structures at the sites, and how do these correlate with variations in chemical composition, especially As levels?
• What are the growth characteristics of As-tolerant or As-metabolizing mesophiles and thermophiles in Tutum Bay, and how do geochemical energy sources constrain their activity?
• What effect do elevated As values have on taxonomic diversity of benthic fauna in Tutum Bay sediments?
• What are the major geochemical and biotic differences between the dry and wet season?
• Can we mathematically describe and predict benthic diversities relative to As concentrations in Tutum Bay?

The project will be one of the first to systematically integrate detailed aqueous geochemistry, mineralogy, the diversity of micro- and macrofauna, bioenergetic computations, and mathematical models of benthic biota in an essentially single-stressor environment. The findings and applications will reach far beyond the thermal and geochemical boundaries of this hydrothermal environment to any ecosystem, natural or contaminated, characterized by one or more stressors.