| Popis: |
Modified assemblages corresponding with the zone of dispersion of acid-iron effluents from the manufacture of titanium oxide pigments in a range of marine and freshwater receiving waters have been identified in tropical and temperate climates. The findings of these studies over several years are reviewed using a wide range of examples. The methodology used for the collection and extraction of the macrofauna, small invertebrates and meiofauna is described. Multivariate analytical techniques used to identify and delineate impact zones are illustrated and the high resolution attributed to the detailed examination of the meiofauna. The shape of such impact zones is dependent, among other factors, on the strength and direction of current flow. Although the sediments in the impact zones which we have studied are not abiotic, their assemblages tend to be characterized by a reduced species richness and a corresponding increase in abundance of resistant species. Results from one of these detailed surveys (Calais), over a 5 year period, indicate that the impact zone is remarkably stable and occupies a similar area in successive years. Disposal of these anthropogenic wastes thus appears to modify assemblage structure in a way which is essentially similar to that imposed by natural stress factors. |
