Abstract Mn oxides are one of the most significant groups of substances which control the distribution of heavy metals in river sediments. This occurs because of their favourable structures, sizes and surface areas. In the Tyne, Tees and Yorkshire Ouse river basins in northeast England, heavy metal-bearing, X-ray amorphous Mn oxides are common (forming upto 15 modal % of heavy metal-bearing grains) though not always abundant phases in river channel and floodplain sediment. Manganese oxides, however, contain significantly more Pb (upto 23 wt.%) than do Fe oxides, and also contain Zn, Cd and Cu (up to 19 wt.%, 0.5 wt.% and 0.8 wt.%, respectively). Within floodplain alluvium, Mn oxides play a major role in controlling the post-depositional redistribution of heavy metals. This is shown by authigenic, Pb-, Zn-, Cd- and Cu-bearing Mn oxides in alluvial profiles at Blagill and Prudhoe in the Tyne basin, and overbank alluvial sediments at Myton-on-Swale and York in the Yorkshire Ouse basin containing multiple horizons of X-ray amorphous Mn-Ba oxides, some of which contain up to 1.0 wt.% Zn. The overbank alluvial sediments at Myton-on-Swale contain the Ba (-Mn) silicate verplanckite [Ba 2 (Mn,Fe,Ti)Si 2 O 6 (OH) 2 . 3H 2 O], although this contains negligible (<0.1 wt.%) amounts of Zn, Pb, Cr, Ni and Co. Manganese oxides play an environmentally significant role in sequestering heavy metals, as shown by contents of upto 39—74% of total sediment-borne Pb, and 10—35% of total Zn, held by Mn oxides in north-east England fluvial sediments. Lower proportions of readily removable Pb and Zn (0.8 — 18% of total Pb, and 3—26% of total Zn) under ambient conditions suggest that the Mn oxides may be long-term sinks for heavy metals in the fluvial environment.

Abstract Geomorphological, geochemical and geochronological investigations of Holocene fluvial sedimentary sequences have been undertaken within a range of upland, piedmont and lowland valley floor reaches in the Yorkshire Ouse catchment, northern England. The aims of these studies have been to: (a) evaluate the effects of prehistoric and historic land-use change on catchment erosion and sediment delivery to river channels and floodplains; (b) establish the degree to which episodes of river erosion and sedimentation are controlled by climate-related variations in flood regime; and (c) assess the spatial heterogeneity of river response to environmental change and how this is likely to influence short- and long-term sediment storage, as well as sediment transfer to the Humber Estuary. Similar discontinuities in the Holocene alluvial record are evident at many sites in the Yorkshire Ouse catchment, though local differences in river sensitivity to externally imposed change have resulted in a complicated and often unique relationship between river behaviour and environmental change. The large proportion of particulate-borne contaminant metals (resulting predominantly from historical mining) stored in the Vale of York strongly indicates that sediment delivery from the Ouse catchment to the Humber Estuary during the Holocene may have been relatively low. This suggests that the degree of connectivity between river, estuarine and coastal transport systems, as well as spatial and temporal variations in fluvial sediment storage, are the key controls of long-term land-ocean sediment fluxes.