Fluvial metal loadings

The average annual fluvial trace metal loadings to the Inland Bays were computed as the sum of the annual measured loadings from each stream, pro-rated to account for input from the streams not sampled. The scaling factors utilized were 1.27 for 1991 (12 streams sampled) and 1.34 for 1992 and 1993 (7 streams sampled). Thus, the calculation inherently assumes that the metal concentrations in the streams not sampled are equal to the mean of the sampled streams. In the absence of major point sources, this is probably a reasonable approximation, given the similar land use patterns within the watershed. 

A comparison of atmospheric versus fluvial loading of selected dissolved trace elements to Delaware s Inland Bays indicates that on an annual basis, aeolian input provides as much as a third of the total input for Zn and at least 5% for the other metals. On shorter time scales, the relative atmospheric and fluvial loadings can vary significantly. Approximately half of the atmospheric input is directly to the surface waters of the bays, a majority of which is derived from wet deposition. The transmission of atmospheric inputs through the watershed varies among elements and for each sub-basin. Overall, atmospheric flux appears to provide quantitatively and qualitatively important inputs for a number of trace metals of ecological concern. 

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