project VI
project I

project II

project III

project IV

project V

project VI

project VII

project VIII

project IX

project X

current vacancies


project VI: the role of dissolved organic carbon (DOC) on Hg chemistry

Major contributions have been made over the first 4 years in several research areas. First, we have developed and used new methods for the characterization of DOM. Our use, for the first time, of 3-DEEM fluorescence spectroscopy coupled with HPLC-SEC provided us with new and useful information about the chemical nature of naturally-occurring DOM. We also used new 3-DEEM methods in a series of quenching titration experiments; these results have given us key information about the binding of Hg to DOM and have provided us with the binding constants needed for our modeling of Hg. We have characterized DOM and DOM-Hg binding in many compartments of the ecosystem, including streams, wetlands, soil water, lake water, etc., so that our future modeling can be done on a whole-ecosystem basis. We now have good information about the nature of DOM, e.g. its molecular size distribution, in different components of the ecosystem, and how its nature changes as it moves through the ecosystem as a result of processes such as photodegradation. Coupled with our information on the relationships between the nature of DOM and its Hg binding properties, we have the data necessary for a process-based model.
Secondly, we have produced useful information on the effects of DOM on the bioavailability of Hg to algae and to one group of aquatic insects, black flies. In particular, we have shown how DOM molecular size affects Hg accumulation. This can be linked back to our characterization of DOM in lakes and watersheds. We also found that black flies, which form a large part of the invertebrate biomass in most streams and are a major food source for some other species, have surprisingly high Hg levels.
Thirdly, we have developed 2 successful models for the prediction of DOM in lakes and catchments. One is a GIS-based regional scale mass balance model that is derived from a number of empirical and semi-empirical relationships. This DOM model is, in turn, being used as the basis for our Hg mass balance model which we have used to develop relationships between Hg flux and concentration and Hg levels in biota. The second DOM model, INCA-C, is a dynamic, process-based model that gives us the ability to predict DOM fluxes and concentrations. This model (and MAGIC, a second process-based dynamic model) will be the basis for a process-based Hg model that will be the means by which we integrate the results of the various projects.