Mark G. Macklin

Mineralogy and geochemistry of alluvium contaminated by metal mining in the Rio Tinto area, southwest Spain

The Rio Tinto in SW Spain drains Cu and pyrite mines which have been in operation since at least the Bronze Age. Extensive metal mining, especially from 1873 to 1954, has resulted in contamination of the Rio Tinto alluvium with As, Cu, Pb, Ag and Zn. X-ray diffraction (XRD), wavelength-dispersive X-ray mapping, scanning electron microscope petrography and X-ray energy-dispersive (EDX) analysis has revealed that 4 major groups of contaminant metal and As-bearing minerals, including sulphides, Fe-As oxides, Fe oxides/hydroxides/oxyhydroxides, and Fe oxyhydroxysulphates, occur in the alluvium. Sulphide minerals, including pyrite, chalcopyrite, arsenopyrite and sphalerite, occur in alluvium near the mining areas. Iron hydroxides and oxyhydroxides such as goethite and possibly ferrihydrite occur in cements in both the mining areas and alluvium downstream, and carry minor amounts of As, Cu and Zn. Iron oxyhydroxysulphates, including jarosite, plumbojarosite and possibly schwertmannite, are the most common minerals in alluvium downstream of the mining areas, and are major hosts of Cu, Pb, Zn and of As, next to the Fe-As minerals. This work, and other field observations, suggest that (1) the extreme acidity and elevated metal concentrations of the river water will probably be maintained for some time due to oxidation of pyrite and other sulphides in the alluvium and mine-waste tips, and from formation of secondary oxide and oxyhydroxysulphates; (2) soluble Fe oxyhydroxysulphates such as copiapite, which form on the alluvium, are a temporary store of contaminant metals, but are dissolved during periods of high rainfall or flooding, releasing contaminants to the aqueous system; (3) relatively insoluble Fe oxyhydroxysulphates and hydroxides such as jarosite and goethite may be the major long-term store of alluvial contaminant metals; and (4) raising river pH will probably cause precipitation of Fe oxyhydroxides and oxides/hydroxides/oxyhydroxides and thus have a positive effect on water quality, but this action may destabilise some of these contaminant metal-bearing minerals, releasing metals back to the aqueous system.

River Basin Sediment Systems: Archives of Environmental Change

The context: fluvial archives of environmental change alluvial systematics. Tectonic forcing: crustal instability and the fluvial record the mass terrace sequence at Maastricht, SE Netherlands - evidence for 200m of late Neogene and Quaternary surface uplift flow in the lower continental crust as a mechanism for the Quaternary uplift of the Rhenish Massif, northwest Europe. Climate forcing: records of Pleistocene and Holocene river behaviour. Geoarchaeological perspectives and the human impact. Modelling and monitoring of sediment fluxes and river channel dynamics.

Sediment slugs: large-scale fluctuations in fluvial sediment transport rates and storage volumes

Variations in fluvial sediment transport rates and storage volumes have been described previously as sediment waves or pulses. These features have been identified over a wide range of temporal and spatial scales and have been categorized using existing bedform classifications. Here we describe the factors controlling the generation and propagation of what we term sediment slugs. These can be defined as bodies of clastic material associated with disequilibrium conditions in fluvial systems over time periods above the event scale. Slugs range in magnitude from unit bars (Smith, 1974) up to sedimentary features generated by basin-scale sediment supply disturbances (Trimble, 1981). At lower slug magnitudes, perturbations in sediment transport are generated by local riverbank and/or bed erosion. Larger-scale features result from the occurrence of rare high- magnitude geomorphic events, and the impacts on water and sediment production of tectonics, glaciation, climate change and anthropogenic influences. Simple sediment routing functions are presented which may be used to describe the propagation of sediment slugs in fluvial systems. Attention is drawn to components of the fluvial system where future research is urgently required to improve our quantitative understanding of drainage-basin sediment dynamics.

The long term fate and environmental significance of contaminant metals released by the January and March 2000 mining tailings dam failures in Maramureş County, upper Tisa Basin, Romania

In January and March 2000 two tailings dam failures in Maramures County, northwest Romania, resulted in the release of 200,000 m3 of contaminated water and 40,000 tonnes of tailings into tributaries of the Tisa River, a major tributary of the Danube. The high concentrations of cyanide and contaminant metals released by these dam failures resulted in pollution and fish deaths not only in Romania, but also downstream in the Tisa and Danube rivers within Hungary, Serbia and Bulgaria. Following these accidents, a research programme was initiated in northwest Romania to establish metal levels in rivers affected by the tailings dam failures and to compare these to metal values in river systems contaminated by historic mining and industrial activity. In July 2000, 65 surface water, 65 river sediment and 45 floodplain sediment samples were collected from trunk streams and principal tributaries of the Lapus/Somes rivers (affected by the January 2000 spill) and the Viseu/Tisa rivers (affected by the March 2000 Novat spill) down to the Hungarian and Ukrainian borders, respectively. Sample analyses for Pb, Zn Cu and Cd show that metal contamination in surface water and river sediment decreases rapidly downstream away from presently active mines and tailings ponds. Concentrations of heavy metals in water and sediment leaving Romania, and entering Hungary and the Ukraine, generally fall below EC imperative and Dutch intervention values, respectively. However, Zn, Cu and Cd concentrations in river sediments approach or exceed intervention values at the Romanian border. The results of this survey are compared with earlier surveys to ascertain the long-term fate and environmental significance of contaminant metals released by mine tailings dam failures in Maramures County.

Modelling geomorphic response to environmental change in an upland catchment

In the UKs upland catchments river terraces and alluvial features indicate a history of periodic aggradation and degradation linked to Holocene changes in land use (primarily deforestation) and climate change (altering flood frequency and magnitude). Although both factors are important, calculating their individual effects is complicated by the likelihood of their concurrent alteration. To investigate the relative impacts of land use and climate change, a cellular model is applied to the upland catchments of Cam Gill Beck, above Starbotton, North Yorkshire. This is divided into 1 million 2 m by 2 m grid cells, to which a range of process laws are applied. These include approximate expressions for mass movement rates, soil creep, the influence of vegetation and hillslope hydrology, as well as fluvial erosion and deposition in ten grain-size fractions. This provides a good representation of valley floor geometry while retaining a fully dynamic interaction with the surrounding valley sides. Previous applications of this model have shown the detailed formation of bars and berms as well as examples of braiding, avulsion and channel range. Running on a Silicon Graphics Origin 2000 computer, an ensemble of simulations were completed, bracketing a wide range of environmental scenarios involving changes in flood frequency, magnitude and vegetation cover. Over time-scales ranging from 10 to 100 years, these showed that decreasing tree cover and increasing rainfall magnitude individually produced similar 25% to 100% increases in sediment discharge, whereas in combination they generated a 1300% rise. Furthermore, channels formed by the model in response to increased rainfall magnitudes are located where relic channels are found in Cam Gill Beck, implying that these are the products of previous periods of high rainfall magnitudes. Copyright

The use of overbank sediment for geochemical mapping and contamination assessment: results from selected English and Welsh floodplains

Abstract Overbank sediment profiles from floodplains in England and Wales contain a record of both natural geochemical patterns and those showing the influence of mans activities. It has been suggested that this characteristic can be used to allow maps to be compiled which show human impact on the fluvial geochemical environment. Studies reviewed in this paper, however, show that a single overbank profile very rarely spans the period from before anthropogenic disturbance through to the Industrial Revolution and later. Significant lateral variations in metal concentrations occur also over a relatively small area in overbank sediments of the same general age. These, and the nature of vertical changes in chemistry, make the choice of sample sites, and sampling interval within a profile, difficult. Even sediments which appear uncontaminated may record anthropogenic influences from activities such as deforestation and agriculture. A means of dating the sediment and an appreciation of river erosion and sedimentation histories are shown to be essential in order to ensure that maps intended to depict natural geochemical variations are based on material deposited before disturbance of the catchment by human activity. These considerations and associated costs may render overbank sediment non-viable as a regional geochemical mapping medium.

River response to high-frequency climate oscillations in southern Europe over the past 200 k.y.

A 200 k.y. chronology of river response to climate-related environmental change has been established for northeast Spain using newly developed luminescence dating techniques. This constitutes the best-documented record of late Quaternary river behavior currently available for the North Atlantic region and enables fluvial stratigraphies to be compared with high-resolution ice core and marine oxygen isotope climate series. Pleistocene and Holocene river aggradational episodes coincide with stadial or neoglacial events, while phases of river incision occur during interstadial or interglacial periods. Alluviation and erosion cycles would appear to track variations in sediment supply controlled by vegetation cover and winter storm frequency.

The significance of pollution from historic metal mining in the Pennine orefields on river sediment contaminant fluxes to the North Sea

Abstract Historic lead and zinc mining in the Northern Pennines, Yorkshire Dales and Peak District significantly affects water and sediment quality in river basins in the LOIS study area. Sediment-associated contaminant metals are transported, often in pulses or slugs, as suspended load under flood conditions. Although downstream decreases in metal concentrations are observed in the river systems, a substantial proportion of the metals have been incorporated into alluvial deposits. These in turn are, and will continueu to act, as a major secondary source of metal contaminants over many hundreds of years. These processes need to be taken into consideration when modelling riverine metal fluxes to the North Sea, to avoid overestimation of metal contaminants from industrial and urban sources, and underestimation of contaminants from these mining-related sources.

Sources, distribution and storage of heavy metals in the Rio Pilcomayo, Bolivia

Hudson-Edwards, K. A., Macklin, M. G., Miller, J. R., Lechler, P. J. (2001). Sources, distribution and storage of heavy metals in the Rio Pilcomayo, Bolivia. Journal of Geochemical Exploration, 72(3), 229-250.

Fluvial landscapes of the Harappan civilization

The collapse of the Bronze Age Harappan, one of the earliest urban civilizations, remains an enigma. Urbanism flourished in the western region of the Indo-Gangetic Plain for approximately 600 y, but since approximately 3,900 y ago, the total settled area and settlement sizes declined, many sites were abandoned, and a significant shift in site numbers and density towards the east is recorded. We report morphologic and chronologic evidence indicating that fluvial landscapes in Harappan territory became remarkably stable during the late Holocene as aridification intensified in the region after approximately 5,000 BP. Upstream on the alluvial plain, the large Himalayan rivers in Punjab stopped incising, while downstream, sedimentation slowed on the distinctive mega-fluvial ridge, which the Indus built in Sindh. This fluvial quiescence suggests a gradual decrease in flood intensity that probably stimulated intensive agriculture initially and encouraged urbanization around 4,500 BP. However, further decline in monsoon precipitation led to conditions adverse to both inundation- and rain-based farming. Contrary to earlier assumptions that a large glacier-fed Himalayan river, identified by some with the mythical Sarasvati, watered the Harappan heartland on the interfluve between the Indus and Ganges basins, we show that only monsoonal-fed rivers were active there during the Holocene. As the monsoon weakened, monsoonal rivers gradually dried or became seasonal, affecting habitability along their courses. Hydroclimatic stress increased the vulnerability of agricultural production supporting Harappan urbanism, leading to settlement downsizing, diversification of crops, and a drastic increase in settlements in the moister monsoon regions of the upper Punjab, Haryana, and Uttar Pradesh.