River mining: ecological effects of river mining. (CR/03/162N).
This report is one of a series of Technical Reports on alluvial mining of sand and gravel aggregate in developing countries, most of which relate to Jamaica (see Preface for details). They are the output from the 'Effective Development of River Mining' project which aims to provide effective mechanisms for the control of sand and gravel mining operations in order to protect local communities, to reduce environmental degradation and to facilitate long-term rational and sustainable use of the natural resource base. The work was carried out under the Department for International Development Knowledge and Research programme, as part of the British Government's programme of aid to developing countries. The project was undertaken in collaboration with key organisations in Jamaica and Costa Rica, who provided field guidance and local support.
The key objective of this part of the River Mining project was to investigate the effects of sand and gravel mining activities at the rivers Yallahs and the Rio Minho in Jamaica using indices of biological diversity. This study examined the ecological impacts of aggregate abstraction and sediment redistribution in the two rivers. In each river there are a series of depositional and removal processes operating in close proximity. The extraction of river sediments and the associated redistribution of sediment and the ecological disturbance resulting from such activities in rivers is generally considered injurious to the overall aquatic (riverine) habitat and the biota therein.
The research results show major disturbances (both an increase and decrease) to the overall biodiversity of the benthic macroinvertebrate fauna at both rivers as one moves downstream. The greatest change in faunal assemblage occurs in the immediate vicinity and immediately downstream of gravel mining localities. Biological (in terms of species completeness) recovery from these activities is slow following the catastrophic removal of the stream bed, which results in massive habitat loss for the benthic fauna. Recolonisation of these disturbed habitats is also slow, resulting in areas of very low diversity. A serious stressor to these rivers would appear to be the removal of benthic sediments (gravel/ sand) from the watercourse.
Further longer-term studies, more data collection (or possibly a re-analysis of the data already held by various departments or by members of staff at the University of the West Indies) from a larger number of impacted rivers, and enhanced dialogue with both stakeholders and decision makers are needed to demonstrate the extent and longer-term impacts of river mining activities.
This report is available for downloading in full colour (5250 kb) and black and white (5250 kb).