Temporal variations in metal enrichment in suspended particulate matter during rainfall events in a rural stream

Matsunaga, Takeshi; Tsuzuki, Katsunori  ; Yanase, Nobuyuki; Kritsananuwat, R.*; Ueno, Takashi ; Hanzawa, Yukiko  ; Naganawa, Hirochika  

We studied a discharge of heavy metals/metalloids in rainfall events to a rural stream in Kuji River basin of central Japan. In terms of elemental enrichment with respect to the crustal composition, we found similarity between atmospheric deposits and suspended particulate matter (SPM) at a rural stream. Both exhibited distinctive enrichment in several metals (Ni, Cu, Pb, Sb, and Cd). Elemental analysis of SPM in the stream in rainfall events at short intervals revealed that the metal enrichment factors in SPM were progressively decreased with an increase of flow rate. Judging from features of SPM, this phenomenon was probably caused by alternative change of SPM matrices from upper soil constituents to more lithologic material with increasing stream flow rate. In quantification of respective contributions of metals of different origins to fluvial discharge, change of SPM matrices during a rainfall event and involvement of dissolved fraction need to be taken into consideration.