Save the Mekong Delta from drowning.

Policy must address drivers, not just symptoms, of subsidence.

The impact of fine sediment accumulation on the survival of incubating salmon progeny: implications for sediment management.

This paper draws on results from a recent research programme on the impact of fine sediment transport through catchments to present a case for the development of new approaches to improving the quality of salmonid spawning and incubation habitats. To aid the development of these programmes, this paper summarises the mechanisms by which fine sediment accumulation influences the availability of oxygen (O2) to incubating salmon embryos. The results of the investigation indicate that incubation success is inhibited by: (i) the impact of fine sediment accumulation on gravel permeability and, subsequently, the rate of passage of oxygenated water through the incubation environment; (ii) reduced intragravel O2 concentrations that occur when O2 consuming material infiltrates spawning and incubation gravels; and (iii) the impact of fine particles (clay) on the exchange of O2 across the egg membrane. It is concluded that current granular measures of spawning and incubation habitat quality do not satisfactorily describe the complexity of factors influencing incubation success. Furthermore, an assessment of the trends in fine sediment infiltration indicates that only a small proportion of the total suspended sediment load infiltrates spawning and incubation gravels. This casts doubt over the ability of current catchment-based land use management strategies to adequately reduce fine sediment inputs.

Reducing sediment inputs to Scottish streams: a review of the efficacy of soil conservation practices in upland forestry.

The historical process by which a soil conservation strategy has evolved within the UK forestry industry is briefly reviewed. Particular attention is given to the development of practical and effective guidelines to prevent both soil damage and sediment entering water courses. It is concluded that the 'Forest and Water Guidelines', together with other forest industry manuals, largely provide adequate protection for aquatic habitats from pre-afforestation cultivation and from harvesting activities. The problem of soil erosion owing to ploughing of open furrows has largely been obviated by improved drainage network design coupled with the use of vegetated buffer strips and sediment catchpits. Alternative site preparation techniques, such as 'moling' or 'dolloping' of afforestation sites, are now preferred. However, the effects on slope hydrology and the improved soil conservation associated with these methods require quantifying. Additional understanding of effective buffer strip function, for example, on a variety of slope angles, soil types and vegetation associations would be beneficial. The design of forest roads and the associated network of drains, culverts and sediment catchpits is addressed in forestry guidelines. Future potential in this area may involve the use of Geographical Information Systems in the effective design of road networks which minimise adverse effects on slope hydrology. Similarly computer simulation of flow routing might aid in the design of road drain networks. At the more local scale there remains scope for further research aimed at minimising soil disturbance by machinery. Consideration should also be given to the long-term sustainability of the soil structure through second and subsequent crop rotations.

Chemical and ecological effects of a pennine peat-slide.

A peat landslide which occurred in Upper Teesdale in 1983 is described. The slide followed thunderstorm rainfall of a very rare intensity (104.8 mm in 2.5 h) and a long predicted return period (2500 years). A large mass of peat (30,000 tonnes wet weight) entered the headwaters of the River Tees, resulting in chemical changes such as increases in suspended solids, iron, aluminium and lead in the river, and a consequent fish kill. The probable cause of the fish kill was the high suspended solid content (particularly peat and iron hydroxide) of the flood water. Effects on the invertebrate fauna of the River Tees are also considered.