Importance of temporal and spatial scale in the analysis of mercury transport and fate: an example from the Carson River system, Nevada

It is generally accepted that the transport and fate of mercury (Hg) released to the environment from mining operations occurs over a continuum of temporal and spatial scales. Rarely, however, has Hg cycling within fluvial (river) systems been examined using data collected for the range of time and space scales over which Hg dispersal has occurred. An exception is the Carson River system of west-central Nevada, which has been intensively investigated for nearly a decade. Integration of these studies demonstrates that three fundamental aspects of the transport and fate problem vary with time and space. They are (1) the source areas from which Hg-contaminated particles are derived, (2) the factors upon which the transport, deposition, and storage of Hg are dependent, and (3) the dynamic nature of Hg transport and storage as defined by the magnitude and frequency of change in Hg concentrations through time. In general, processes that function over shorter time periods and smaller areas are more dynamic than those that function over larger scales. Moreover, the transport and fate of Hg-contaminated particles at any particular scale are dependent on the processes and controlling factors that function over larger areas and longer timeframes.