To increase the understanding of chemical/geochemical processes influencing biological systems in aquatic mixing zones under severe dis-equilibrium conditions due to acidity vs. liming.
Liming is extensively used in the restoration of acidified lakes and rivers, not only to increase the water pH and alkalinity, but also to reduce the amount of "toxic" aluminium species to fish and other sensitive organisms. Recent field studies have documented Al-toxicity to fish in the mixing zones between limed streams and acid tributaries. The conditions of severe chemical dis-equilibrium present within such mixing zones appear to result in enhanced toxicity for fish; rates of mortality are higher than in the original acidic waters.
This project, therefore, will address the questions concerning the chemical/geochemical processes leading to enhanced toxicity towards fish in mixing zones between neutral or limed rivers and their acid tributaries. The chemical studies will include aluminium speciation, transformation processes and the kinetics involved. These investigations will be complemented by biological and physiological studies on possible toxic mechanisms responsible for the observed fish mortality.
Experiments will be carried out in the field in two catchments in Norway and Scotland during different seasons (different hydrology, temperatures, and life stages of fish) and in laboratories under controlled exposure (Norway, UK, Belgium, and in the Netherlands). The experiments will focus on:
- the characterisation of Al species by fractionation techniques, and trace element analysis;
- transformation processes and kinetics involved, especially the polymerisation of 10w molecular weight Al-species;
- interactions with other components influencing the polymerisation of Al species, in particular silicic acid, calcium fluoride and humic substances;
- identification of biological responses, especially sublethal effects and fish mortality;
- improvement of management practices for countermeasures taken in acidified water systems, e.g. liming of rivers and waters for agricultural practices.
Funding SchemeCSC - Cost-sharing contracts
1432 Aas Nlh
6525 ED Nijmegen