Dissertation Research: Nitrogen to phosporus ratio as a driver of arsenic retention

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Arsenic is a trace element that can be toxic to people and at lower concentrations cause neurological symptoms or have immunological and endocrine effects. Throughout history, arsenic has been used as a poison, pesticide, weapon, and it has contaminated more than a billion-people's food and water supplies. In addition, a number of groundwater springs worldwide have naturally occurring arsenic levels that exceed those safe for human drinking water. As this groundwater seeps into streams the elevated arsenic can affect the chemistry and biology of the stream. This Doctoral Dissertation Improvement Grant (DDIG) research integrates arsenic into an ongoing study of streams in Ecuador to assess what drives arsenic retention in stream plants and animals and how that affects the transport of arsenic downstream. Understanding how arsenic interacts with other elements to cycle through water supplies will inform global mitigation efforts. Furthermore, the researchers will disseminate results to Ecuadorian communities reliant on arsenic contaminated waters. Elevated stream arsenic concentrations can alter stream ecosystem function by altering the biogeochemical cycling of nitrogen and phosphorus or via altering aquatic food webs. In addition, the bioavailability and effects of arsenic on aquatic food webs are closely interlinked with both the concentrations of nitrogen and phosphorus and the ratio of nitrogen to phosphorus present in aquatic systems. Funds from this award will be used to evaluate how the nitrogen:phosphorus ratio of stream water affects the retention and transport of arsenic in geothermal streams with varying nitrogen:phosphorus ratios. The study also will test the effect of stream resource nitrogen:phosphorus ratio on arsenic cycling in the aquatic food web and biotic excreation of arsenic and consequent downstream transport.