TRACE-ELEMENT INTERRELATIONSHIPS FOR THE HUMBER RIVERS - INFERENCES FOR HYDROLOGICAL AND CHEMICAL CONTROLS

Data on a wide range of trace elements, determined by multi-element pr ocedures based on inductively coupled plasma emission and mass spectro metry, are presented for the major rivers entering the Humber estuary. The average trace element chemistry varies significantly across the r egion with a clear divide between the southern and northern rivers. Th is pattern is related to lead-zinc-barium mineralisation and flood pla in sediment contamination from historic mining activity, and to histor ic and current industry and urbanisation to the south. For the industr ial/urban rivers, most dissolved components dilute with flow; this pat tern is most clearly seen for those components with little acid availa ble particulate (AAP) fractions. In the rural/mineralised areas, disso lved components show more variable flow patterns. AAP fractions and di ssolved components with significant associated AAP fractions usually i ncrease with flow in all rivers. The different trace elements show mul ti-linear relationships with one another. These are much tighter than the links between dissolved and AAP components of the same element. Tw o main groups of closely associated elements emerge, but these groups are different on northern and southern rivers. The first group corresp onds to elements which dilute with flow and this group includes signif icantly more trace elements to the south where industrial and urban in puts dominate. For this group, within-river chemical processes do not seem to be operative as linear relationships with each of the trace el ements of the group and chloride are observed: chloride is chemically conserved within river systems and is predominantly found in the point source effluent discharges. The second group corresponds to those det erminands which increase with increasing flow for both dissolved and A AP fractions and they have a high AAP fraction: relationships show muc h more scatter for this group. Links between dissolved and particulate fractions for this second group are weak and are not well described b y empirical partition coefficient relationships which are commonly use d in environmental modelling studies. Rather, AAP fractions are much m ore closely linked with suspended solid concentrations than theThe res ults point to the importance of contributing sources and hydrological controls in determining dissolved and AAP concentrations in the Humber rivers. The role of within-river chemical controls is much less clear -cut and may well be of second order importance. (C) 1997 Elsevier Sci ence B.V. dissolved component. The reasons for the contrasting behavio ur between the two groups probably reflects the inability of 0.45 mu m filtration (47 mm diameter cellulose nitrate Whatman sterile filters in this case) to remove all colloidal sized materials. Thus, for this second group, at high flows, when suspended sediments are at their hig hest, there is the greatest potential for acid available enriched micr o-particulates to pass through the filters. This feature provides a fu ndamental schism for environmental research for this second and wide r anging group: process based water suspended-sediment interaction model ling requires a clear separation between truly dissolved and truly par ticulate fractions; water industry based environmental sampling and ma nagement strategies, as well as legislative water consent controls, ar e based on a 0.45 mu M separation.