Doctoral Dissertations

Ying Feng

Date of Award

8-1995

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Nuclear Engineering

Major Professor

L. F. Miller

Committee Members

S. M. Bartell, P. G. Groer, J. S. Iannelli

Abstract

A comprehensive study of the radioecological exposure assessment for a contaminated aquatic ecosystem has been performed in this dissertation. The primary objectives of this research were to advance the understanding of radiation exposure in nature and to increase current capabilities for estimating aquatic radiation exposure with the consideration of spatial and temporal effects in nature. This was accomplished through the development of a two-dimensional aquatic exposure assessment framework and by applying the framework to the contaminated Chernobyl cooling lake (pond). This framework integrated spatial and temporal heterogeneity effects of contaminant concentration, abundance and distribution of ecosystem populations, spatial- and temporal-dependent (or density-dependent) radionuclide ingestion, and alternative food web structures. The exposure model was built on the population level to allow for the integration of density dependent population regulation into the exposure assessment. Plankton population dynamics have been integrated into the hydrodynamic-transport model to determine plankton biomass density changes and distributions. The distribution of contaminant in water was also calculated using a hydrodynamic-transport model. The significance of adding spatial and temporal effects, spatial and temporal related ecological functions, and hydrodynamics in the exposure assessment was illustrated through a series of case studies. The results suggested that the spatial and temporal heterogeneity effects of radioactive environments were substantial. The conventional bioaccumulation factors with the assumption of homogeneous and steady-state conditions significantly over estimated the radionuclide accumulation in predator-fish by a factor of four to six, while they under estimated the exposure in planktons at some locations. Among the ecological functions considered, the food web structure was the most important contributor to the variations of fish exposure. The results obtained using a multiple prey food web structure differed by a factor of 10 from the equilibrium concentration, and by a factor of 2.5 from the concentration obtained using a single-prey food web. Impacts of changes in abundance and distribution of biomass on contaminant bioaccumulation varied among different populations, spatially and temporally. It is necessary to consider the biomass effects for fish during periods of accelerated growth, or when the radionuclides or ecological species have low radiobiological turn-over rates. Influences of adding spatial- and temporal-dependent ingestion rates into the exposure model structure were not significant for this study when there were excess prey relative to the predators. The influence of hydrodynamics on radioactive material transport and distribution was significant in the study of the contaminated Chernobyl cooling lake. The framework is cast in a generalized form such that extension to other aquatic exposure assessment problems is direct.

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