Mercury In Aquatic Ecosystems
Project Number: 2491-AK710
Project Chief: David Krabbenhoft
Project Topics: All aspects of environmental mercury sources, cycling and fate
Project Support: USGS Toxics Substances Hydrology Program
Period of Project: 1998 to present
The Mercury in Aquatic Ecosystems project is funded by the Toxic Substances Hydrology program (http://toxics.usgs.gov/). This project has several overarching programmatic goals: (A) to provide a national-scale, scientific perspective of the mercury contamination problem; (B) fill identified science gaps through the conduct process-level research; (C) to provide scientific information to resource managers and decision makers; and (D) to continue to provide scientific leadership (within the USGS, nationally, and internationally) for the planning and execution of investigations of mercury biogeochemistry, transformations, transport, and fate in the environment. To achieve these goals, the MRT conducts long-term research on a few strategic topics that are presented below.
Current Research Activities:
- National Scale Assessments
- The METAALICUS study
- Atmospheric Mercury Research
- Coastal and Marine Research
Research Priorities for the next five years: (2010-2014)
Future science priorities and plans for the project all into three broad categories: (A) large-scale science integrations and studies; (B) process-level research; and (C) model formulations. A brief summary of planned research in each of these areas is as follows:
Large-Scale Studies: As a follow up to our 2009 study on methylmercury sources to the Pacific Ocean (the world’s largest ocean), we have recently concluded analysis of samples collected on the Indian Ocean – the third largest ocean – and will be publishing a paper in 2011 integrating these results an formulating a new mercury-carbon linked model of the world’s oceans. Second, we have recently completed total and methylmercury analysis of about 1,200 sediment samples collected from lakes from across the contiguous US. Currently, we are integrating these results with the other water chemistry and sediment quality data available from the USEPA and will be writing up a journal paper describing the results. Last, we intend to extend the National Methylmercury Prediction Model to include new advances in our understanding of methylation controls (e.g., abundance of selenium and nitrate).
Process-Level Studies: First, we are synthesizing the major conclusions of our work on the Mecury Experiment to Assess Atmospheric Loadings in Canada and the US (METAALICUS) project into a summary journal paper. In 2008 this unique project transitioned from a whole-ecosystem mercury loading study, to a mercury reduction study. Our focus in the future on this project is to continue to publish our results in journals and monitor the recover of the ecosystem until about 2014. Second, we are continuing to explore the unique processes that affect mercury cycling in the coastal zone. Our work focuses on the unique air chemistry of the marine boundary layer and its effect on mercury deposition to sensitive landscapes near the coasts. Third, we are currently concluding a two year evaluation of the direct effects dissolved organic matter (DOM) has on the availability of inorganic mercury for biomethylation. These lab-scale studies were conducted in pure culture and are some of the first evidence that DOM has direct effects on methylmercury production, as opposed to previously held notions it simply co-occurred in the environment. Last, we have initiated a new line of research to evaluate the effect of selenium abundance on methylation. Largely only existing at meaningful concentrations west of the Mississippi, in those locations it likely has a primary controlling influence on methylmercury production. We have located a “naturally enriched” watershed located in the Upper Peninsula of Michigan for evaluating how selenium retards methylation and/or bioaccumulation of mercury.
Model Formulation: At the present time, we are at various stages of development on three new mercury models that will greatly improve our understanding of mercury cycling in aquatic ecosystems an also should be very useful for decision making support. First, we are new conclusion on the production and publication of an atmospheric mercury deposition model for both dry and wet phase mercury. Second, we are working with METAALICUS collaborators to develop a watershed mercury model. In the absence of the unique “tracer data” from that project we are able to calibrate such a model to the many process rates we have measured as part of that project. Last, we are just beginning to formulate an “Ocean Methylmercury Production” model that will integrate our open ocean research with that from the coastal zones. The intention of this model is to help focus future research an to assist decision makers in understanding the links between reduced emissions and responses of the oceans.