In the period from 1950 to 1994, most of the mercury discharged to the Lagoon of Aveiro was retained in the sediments of a small area of around 1.7 km2 (25.4 × 103 kg, about 77% of the total), which corresponds to the Estarreja Channel plus a basin named Laranjo Basin located downstream. In 1994, the mercury concentration in surface sediments of the area ranged from 2.3 to 343 μg g−1, with the highest values recorded near the industrial source of the metal. In places of the basin where the sedimentation rate could be considered uniform, the highest levels of Hg (35 μg g−1) were recorded at depths around 40 cm, as result of reduction of the anthropogenic mercury input to the lagoon. Assuming an uniform sedimentation rate and a continuously low industrial input of mercury for the near future, the levels of Hg in the surface sediments would be less than 1 μg g−1 in 20 years. This may be considered the expected restoration time. The feasibility and consequences of several management options for this pollution problems is briefly presented.

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Glaciers in most parts of the world are retreating, releasing water and sediments to downstream rivers. Studies have found elevated levels of fallout radionuclides (FRNs) and other contaminants in glacial sediments, especially cryoconite, in European glaciers and Greenland. However, there are no equivalent studies for glaciers in North America. We report concentrations of FRNs (i.e. 137 Cs, 210 Pb un and 241 Am) and other contaminants (i.e. metal(loids), phosphorus) in cryoconite and proglacial sediments from a glacier in British Columbia, Canada, and compare values to suspended sediments from the downstream river. The mean concentrations of 137 Cs, 210 Pb un and 241 Am in cryoconite were 2,123 ± 74, 7,535 ± 224 and 11.5 ± 3.0 Bq kg −1 , respectively, which are an order of magnitude greater than those for most soils and surficial materials. FRNs were much lower in suspended sediments and decreased with distance away from the glacier. Geochemical elements were enriched in cryoconite relative to local clastic materials and upper continental crust. Concentrations of FRNs in cryoconite were correlated with organic matter, which suggests this is important in controlling the scavenging of hydrophobic contaminants in glacial meltwater. Low concentrations of FRNs and contaminants in suspended sediments suggest that glacial meltwater and the delivery of cryoconite have limited impact on downstream aquatic ecosystems.

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Soil resources in parts of Tanzania are rapidly being depleted by increased rates of soil erosion and downstream sediment transport, threatening ecosystem health, water and livelihood security in the region. However, incomplete understanding to what effect the dynamics of soil erosion and sediment transport are responding to land-use changes and climatic variability are hindering the actions needed to futureproof Tanzanian land-use practices. Complementary environmental diagnostic tools were applied to reconstruct the rates and sources of sedimentation over time in three Tanzanian river systems that have experienced changing land use and climatic conditions. Detailed historical analysis of sediment deposits revealed drastic changes in sediment yield and source contributions. Quantitative sedimentation reconstruction using radionuclide dating showed a 20-fold increase in sediment yield over the past 120 years. The observed dramatic increase in sediment yield is most likely driven by increasing land-use pressures. Deforestation, cropland expansion and increasing grazing pressures resulted into accelerating rates of sheet erosion. A