EXECUTIVE SUMMARY
The Aquatic Effects Technology Evaluation Program, AETE, has been established to assist the Canadian mining industry in meeting its environmental effects monitoring and related requirements, in a cost-effective a manner as possible. The program is coordinated by the Canadian Center for Mineral and Energy Technology (CANMET). The present report is a technical evaluation of monitoring methods using macrophytes, phytoplankton and periphyton to assess the impacts of mine effluents on the aquatic environment.
A wide literature review was undertaken, and for each of macrophytes, phytoplankton and periphyton, case studies reporting their use as biomonitors of contaminated environments, including areas near mining activities, are described. Then, a critical evaluation of the biomonitoring methods used was done. Other biomonitoring methods, having high potential but not yet investigated in the field, are also identified.
Macrophytes appear to have an interesting potential as biomonitoring organisms to assess the impacts of mine effluents on the aquatic environment. Their usefulness until now has been under-estimated. Many macrophyte species conform very well to many of the criteria listed for an «ideal» biomonitor organism: they are sedentary, visible to the naked eye, easy to collect and to handle, easy to identify in the field, they concentrate metals in their tissues and reflect the environmental contamination. Metals taken up by rooted submerged macrophyte species represent the bioavailable, free-metal ion concentrations in the sediment interstitial water, as well as metal contamination in the water column, if present. Plant parts to be analysed, cleaning methods and methods to deal with the variability of the results are discussed. Although biochemical indicators, such as phytochelatins and enzyme induction (peroxidase activity), have not yet been used in the field with macrophytes to assess metal contamination, their possible use as biomonitoring tools is briefly discussed. Further work needs to be done, outside of AETE, before the routine use of macrophytes as biomonitor organisms can be effectively applied in the field. It would be interesting to collect and analyse for metals submerged rooted species, along with other more routinely sampled benthic organisms used to monitor the environment, such as aquatic insects and mollusks, and to determine for all sampling sites the free-metal ion concentration at the sediment/water interface, which is the best current indicator of bioavailable metal for these organisms; and then to compare the usefulness of using macrophytes with the other more «standard» biomonitor organisms. Eriocaulon septangulare, Eleocharis acicularis and Potamogeton richardsonii appear to be particularly promising candidates for biomonitoring in the Canadian mining environment.
Because phytoplankton are very responsive to changes in water quality and are at the base of lake trophic chain, phytoplankton could be an effective and meaningful biomonitoring tool. Only methods based on biomass changes and species shifts have so far been applied to monitoring of mine sites. This review has identified several approaches that promise to be more powerful than these traditional ones: 1) community canonical analysis, 2) size distribution, 3) pigment analysis, 4) phytochelatin analysis, 5) diatom deformities, 6) tests based on community induced tolerance. All these approaches need field testing to verify their applicability and generality. The potentials and the limitations of these techniques in view of their integration into a cost effective monitoring program are discussed.
ln aquatic ecosystems, the importance of the periphytic communities is widely recognized. Periphyton is a functional system where autotrophic and heterotrophic processes take place. It plays a role at the interface between substrata and the surrounding water. This community may, consequently, influence biogeochemical pathways and the dynamics of the ecosystem. For studying environmental perturbations from mine effluents, periphyton represents many advantages. Since it is non mobile, it is easy to sample and integrate effects of environmental variables. In addition, periphyton has a rapid response to disturbance, which may create modifications of community structure and functioning. Even under very harsh disturbances, periphyton doesn’t disappear completely. On the other hand, periphytic communities are strongly influenced by the variability of physical conditions in the field. In addition, the complex and heterogeneity of this community, and the lack of methodological standardization, restrict its use in impact studies of mine effluents and explain why periphyton is less studied than phytoplankton. A literature review notes the interest for studies on changes in the kind of species or their relative abundance and distribution. lndeed, the structure of the periphytic community reflects the competitive capacity of the species forming it and can, consequently, serve as a source of integrated information which can serve as a sensitive indicator of metal or acid stress.
