Trace element concentrations in the major rivers entering the Humber estuary, NE England

Abstract

Measurements of trace element concentrations in the major rivers discharging into the Humber estuary, NE England, show a broad separation between the southern rivers draining urban and industrial areas and northern rivers draining predominantly rural, mineralised catchments. An evaluation of the dissolved and acid available particulate phases has been made. The results show that the trace elements can be classified into two groups: (1) elements with a significant acid available particulate component (Al, As, Ba, Cr, Co, Cu, Fe, Pb, Mn, Ni and Zn) and (2) elements predominantly in dissolved form (B, Li, Mo, Rb, Sc and Sr). The relationships between concentrations and flow are used to evaluate sources of trace elements. In the rural, mineralised northern catchments, concentrations of dissolved Al and most transition metals show a positive relationship with flow, indicating diffuse sources derived from near-surface runoff. Concentrations of dissolved B, Ba, Li, Sc and Sr show a negative relationship with flow and appear to be derived from groundwater sources. Within the southern rivers draining urban and industrial catchments, most elements in the dissolved phase exhibit negative relationships with flow, indicating that point-source discharges provide the major source of trace elements to the rivers. The exceptions to this relationship are Al and Ba, which exhibit a positive relationship with flow, indicating predominantly diffuse near-surface sources of these elements. For the acid available particulate fraction, concentrations increase with increasing flow as would be anticipated owing to the increase in suspended load at high flow. The trace element concentrations in the rivers draining the southern industrial urban catchments, although significantly higher than background levels, are low compared with other major industrial rivers of Europe (e.g. the Rhine), with the exception of iron and manganese, and meet UK Environmental Quality Standards for dissolved trace elements set for sensitive fish species, such as sahnonids.