Journal of Conference Abstracts

What Happens after Pollutant Injection into a
Freshwater Ecosystem? On-Location and
Chemico-Thermodynamical Modeling

Boris S. Smolyakov (Ecol@che.nsk.su) & Vladimir I. Belevantsev (l311@che.nsk.su)

Institute of Inorganic Chemistry of SB RAS, 630090 Novosibirsk, Russia.

Migration and bioavailability of pollutants injected into freshwater ecosystems depend, at least in part, on the distribution of their chemical forms under different conditions of pH, redox potential, ion composition, colloid and dissolved organic compound concentrations, etc. Because freshwater ecosystems are dynamic and heterogeneous, these key parameters change over space and time. To predict pollutant behaviour and pollutant effects on biotic activities in natural water bodies with spatially and temporally changing conditions, we need to combine experimental data with descriptions of the processes of pollutant transformation.

In addition to monitoring of key parameters and their dynamics, we used on-location modeling (LM) of pollutant behaviour and pollutant effect after their injection into mesocosms - spatially isolated systems situated within the natural water body. A high degree of similarity of processes in the mesocosms and in the natural water body is ensured because of correspondence of water, sediments, biotic composition, temperature, illumination, and other parameters (excluding water exchange), at least during 10-15 days. Pollutants were injected into mesocosms and the kinetics of their removal from water, as well as daily primary production were controlled in time at different depths, from surface to bottom. Background mesocosms (without added pollutants) used as controls. For assessment of pollutant effects on biotic activities, we measured daily primary production, which was calculated from changes in pH measured over a 24 hr period.

To describe physicochemical processes in the natural water body, we chemico-thermodynamical modeling, based on local and partial equilibria, concepts of "initial system", completeness of description, levels of specification and expedient decomposition.

Results of on-location modeling in combination with monitoring and chemico-thermodynamical modeling for one of typical northern freshwater ecosystem, the Novosibirskoe reservoir, are presented and discussed. In particular, we found that after injection of pollutants (NH₄⁺, NO₃^-, and PO₄^3-, alone or in combination), changes in daily primary production are variable in value and in sign depending on initial pollutant concentrations and period of observation. The rate of phosphate-P removal from water increases in the presence of NH₄⁺ and NO₃^-. The injection of Cu(II), Cd(II) and Pb(II)-salts caused different responses of biotic activities, up to an irreversible decrease in daily production. We note that chemico-thermodynamical modeling reveals a different distribution of various metal species (free ions, organic bonded, carbonate, hydroxyl, other complex forms) at different depths in the same water body, as a result of pH change. The distribution of metal species is also a function of ion composition and integral binding capacity of dissolved organic compounds. These two key parameters are variable in northern freshwater ecosystems.

In our opinion, the approach of combined monitoring, on-location modeling and chemico-thermodynamical modeling has much potential for yielding information about pollutant behaviour and pollutant effects on the functioning of freshwater ecosystems.

References

Belevantsev, V.I., Gushchina, L.V., Obolensky, A.A., Smolyakov B.S. & Sukhenko, S.A., Chem. Sustainable Dev. 3, 3-10 (1995).

Smolyakov, B.S. & Plekhanov, D.F. Zhurn. ekol. chimii 3, 201-205 (1994).

Smolyakov, B.S. & Dronyk, M.I., Chem. Sustainable Dev. 3, 217-223 (1995).