Abstract:
Trace element distributions, partitioning, and speciation were examined at 15 sites in the Patuxent River
watershed from May 1995 through October 1997 to determine possible sources of trace elements to the river and estuary,
to examine the relationship of the trace element discharges to freshwater discharges as well as to land use and geographic
region, to validate previous estimates of loadings to the river, and to provide baseline data for trace elements in the
Patuxent River watershed and estuary. Six freshwater sites were examined, representing different basins and geographic
provinces, and nine sites along the estuarine salinity gradient. Subregions within the watershed varied considerably in
concentrations and areal yields for some elements. Concentrations of As, Cd, Ni, Pb, and Zn were elevated in the Coastal
Plain sites compared to the Piedmont sites, while Cu and Hg were more evenly distributed. Cadmium, Cu, Hg, Ni, Pb,
and Zn showed overall positive correlations with river flow while As and methylHg (meHg) showed negative correlations
with river flow. Concentrations of trace elements in the estuarine portion of the river were generally low, and consistent
with mixing between Patuxent River water with elevated concentrations and the lower concentrations of the Chesapeake
Bay. Interesting features included a local Cd maximum in the low salinity region of the estuary, probably caused by
desorption from suspended sediments, and a significant input of water containing high As concentrations from the
Chesapeake Bay and from As being released from bottom sediments in summer. Comparisons between the estimated
annual flux of trace elements and the estimates of suspected source terms (atmospheric deposition, urban runoff, and
known point sources) suggest that, except for Hg, direct atmospheric deposition is small compared to fluvial loads.
Current estimates of trace element inputs from point sources or from urban runoff are inadequate for comparison with
other sources, because of inappropriate techniques and/or unacceptably high detection limits. A complete examination
of trace element dynamics in the Patuxent River (and in other coastal systems) will require better data for these potential
sources.
