John E. Brittain

Invertebrate drift — A review

This paper reviews the literature on invertebrate drift in running waters, emphasising papers published during the last 10–15 years. The terms constant drift, catastrophic drift, behavioural drift, active drift and distributional drift are defined, but their use should be limited as much confusion has arisen. Sampling methods are briefly reviewed.The composition of drift in streams and rivers is assessed, especially with respect to temporal variation, drift densities and drift distances. This body of descriptive literature is subsequently analysed in relation to both abiotic and biotic variables, such as current/discharge, photoperiod, temperature, benthic densities, predators and life cycle stage.The ecosystem significance of drift in terms of colonization and distribution, population dynamics and its importance as a food resource are then reviewed and discussed. Drift enables organisms to escape unfavourable conditions and gives them the potential to colonize new habitats. However, mortality poses a constant threat. The drift community is composed of components whose presence in the drift may be due to widely differing reasons. This renders unsuccessful most attempts to explain drift in terms of one or even a few factors, except in extreme cases, such as floods or pollution. The question whether drifting organisms are alive, dead, or “ecologically dead” is seldom addressed, as is variation at the level of the individual.The drift literature is dominated by large numbers of discriptive papers and there is a need for laboratory and field studies aimed at testing specific hypotheses.

Life History Strategies in Ephemeroptera and Plecoptera

The major part of the life of Ephemeroptera (mayflies) and Plecoptera (stoneflies) is spent in the aquatic environment, while their short terrestrial life is primarily concerned with reproduction. Such a complex cycle passing through two different phases, each having its own selection pressures, places evolutionary constraints on life cycle strategies.

Review and assessment of models used to predict the fate of radionuclides in lakes

A variety of models for predicting the behaviour of radionuclides in fresh water ecosystems have been developed and tested during recent decades within the framework of many international research projects. These models have been implemented in Computerised Decision Support Systems (CDSS) for assisting the appropriate management of fresh water bodies contaminated by radionuclides. The assessment of the state-of-the-art and the consolidation of these CDSSs has been envisaged, by the scientific community, as a primary necessity for the rationalisation of the sector. The classification of the approaches of the various models, the determination of their essential features, the identification of similarities and differences among them and the definition of their application domains are all essential for the harmonisation of the existing CDSSs and for the possible development and improvement of reference models that can be widely applied in different environmental conditions. The present paper summarises the results of the assessment and evaluation of models for predicting the behaviour of radionuclides in lacustrine ecosystems. Such models were developed and tested within major projects financed by the European Commission during its 4th Framework Programme (1994-1998). The work done during the recent decades by many modellers at an international level has produced some consolidated results that are widely accepted by most experts. Nevertheless, some new results have arisen from recent studies and certain model improvements are still necessary.

INFLUENCE OF DAM OPERATION ON MAYFLY ASSEMBLAGE STRUCTURE AND LIFE HISTORIES IN TWO SOUTH-EASTERN AUSTRALIAN STREAMS

The mayfly fauna, and in particular the life histories of two mayflies, Coloburiscoides sp. and Baetis sp. 3, was studied in two nearby streams located in the headwaters of the River Murray, SE Australia. The Mitta Mitta River is regulated by the Dartmouth Dam which releases cold water in summer for irrigation. Snowy Creek is a tributary of the Mitta Mitta River with natural flow and temperature regimes. The structure of the mayfly assemblage differs in the two streams. In the regulated Mitta Mitta there are 11 species, of which, caenids (Tasmanocaenis tonnoiri and River Murray sp. C), Coloburiscoides sp. and Baetis sp. 3 dominate. Snowy Creek, with a richer assemblage of 17 species, was dominated by Coloburiscoides sp., Baetis sp. 3 and two Austrophlebioides species. Monthly collections of mayfly nymphs and adults between September 1987 and August 1988, in both streams, allowed evaluation of possible life history changes in relation to dam operation. Coloburiscoides sp. and Baetis sp. 3 had synchronous life histories at both regulated and unregulated sites. Coloburiscoides appeared to be univoltine, and Baetis polyvoltine. At the regulated site, nymphal abundance in both Coloburiscoides and Baetis declined during the summer release, which coincided with the beginning of nymphal recruitment and appeared to delay nymphal hatching in Coloburiscoides.

Modelling of radiocesium in lakes : the VAMP model

Abstract The objective of this work is to present a new, state-of-the-art model for predicting radiocesium in lakes. The target variables to model and predict are Cs concentrations in lake water and in predatory fish. These results emanate from IAEA s VAMP project, initiated after the Chernobyl accident in 1986. The sites included in this work cover a wide range of lake and catchment characteristics. This new VAMP model has nine specific components (see below), which are meant to increase the predictive accuracy of the model and make it easy to apply for lakes in general. (1) A seasonal variability moderator for water discharge. (2) A dimensionless moderator for the water retention rate. (3) A seasonal variability moderator for epilimnetic and hypolimnetic temperatures, which influence lake stratification and redox-induced internal loading of radiocesium from sediments. (4) A transfer coefficient to calculate relationships between biomasses. (5) An outflow rate function for the transport of cesium from the catchment to the lake. (6) A dimensionless moderator for planktonic uptake of radiocesium, i.e. for the transfer of cesium in dissolved phase in the lake water to phytoplankton. (7) An algorithm for the lake partition coefficient ( K.d ). (8) A sub-model to express biological half-lives. (9) An approach to quantify internal loading. Empirical validations, and critical sensitivity tests, have shown that the VAMP model in many lakes yields just as good predictions as parallel sets of empirical data, and this is as good as any model can yield. It should be possible to improve the VAMP model further if and when more field data become available, for both the VAMP lakes and other sites.

Uncertainty analysis and validation of environmental models: the empirically based uncertainty analysis

Abstract In the present paper, the principles of Empirically Based Uncertainty Analysis (EBUA) are described. EBUA is based on the evaluation of ‘performance indices’ that express the level of agreement between the model and sets of empirical independent data collected in different experimental circumstances. Some of these indices may be used to evaluate the confidence limits of the model output. The method is based on the statistical analysis of the distribution of the index values and on the quantitative relationship of these values with the ratio ‘experimental data/model output’. Some performance indices are described in the present paper. Among these, the so called ‘functional distance’ (d) between the logarithm of model output and the logarithm of the experimental data, defined as d 2 = Σ n 1 ( ln M i − ln O i ) 2 n where Mi is the ith experimental value, Oi the corresponding model evaluation and n the number of the couplets ‘experimental value, predicted value’, is an important tool for the EBUA method. From the statistical distribution of this performance index, it is possible to infer the characteristics of the distribution of the ratio ‘experimental data/model output’ and, consequently to evaluate the confidence limits for the model predictions. This method was applied to calculate the uncertainty level of a model developed to predict the migration of radiocaesium in lacustrine systems. Unfortunately performance indices are affected by the uncertainty of the experimental data used in validation. Indeed, measurement results of environmental levels of contamination are generally associated with large uncertainty due to the measurement and sampling techniques and to the large variability in space and time of the measured quantities. It is demonstrated that this non-desired effect, in some circumstances, may be corrected by means of simple formulae.

Fractionation of cesium isotopes and90Sr in snowmelt run-off and lake waters from a contaminated Norwegian mountain catchment

Cesium isotopes and90Sr have been determined in the inflow and outflow rivers of a Norwegian subalpine lake. The lake is situated in an area contaminated by Chernobyl fallout. Sampling was carried out during the spring peak discharge period associated with snowmelt. Transported coatse particulate plant material was collected by traps. Particles and colloids were removed from water samples by hollow fibre ultrafiltration. The results illustrate that run-off during the spring snowmelt is an important pathway for these radionuclides. The cesium isotopes are predominantly transported as colloids, while90Sr is present in the form of low molecular weight mobile species. Based on lake budget calculations, more than 50% of the cesium input is retained in the lake, while more than 90% of the90Sr is transported through the lake and into lower parts of the drainage system.

Radiocesium in brown trout (Salmo trutta) from a subalpine Lake ecosystem after the chernobyl reactor accident

Abstract After Chernobyl in April 1986, radioactive cesium has been measured in Ovre Heidalsvatn, a Norwegian subalpine lake, situated in an area of high fallout. The lake is an important reference site and has been the subject of extensive ecosystem studies since the 1950s. Emphasis has been given to measuring long-term trends in the activity content of radioactive cesium in the Brown trout ( Salmo trutta ) population. After ice-break in June 1986, the average total cesium activity content rose to 7000 Bq/kg wet weight. The activity content fell during 1987 and at ice-break in 1988 was 4000 Bq/kg. However, there was no further reduction during the summers of 1988 and 1989, possibly due to increased inputs from the catchment. There is considerable variation in the radiocesium activity content measured in individual fish. On the basis of the changes in cesium activity content in trout since 1986, an observed half-life for 137 Cs and 134 Cs in trout of 3·0 and 1·3 years, respectively, has been estimated.

MOIRA-PLUS: A decision support system for the management of complex fresh water ecosystems contaminated by radionuclides and heavy metals

The accidental release of radioactive substances into the environment leads to the necessity of applying suitable countermeasures for the restoration of the polluted environment. However, despite their obvious benefits, such interventions may result in detrimental effects of an economic, ecological and social nature that must be carefully evaluated. MOIRA-PLUS is a PC-based user-friendly, computerised decision support system (DSS) that helps decision makers to choose optimal countermeasure strategies for different kinds of aquatic ecosystems and contamination scenarios. The DSS MOIRA-PLUS is based on:(a)Validated models to evaluate the behaviour of radionuclides in contaminated water bodies and biota and to assess the effect of countermeasures on contamination levels; (b)Models to assess the radiation dose to people and biota (fish) by relevant exposure pathways, the effect of countermeasures, and the associated economic impact; (c)A multi-attribute analysis (MAA) module to evaluate the effectiveness of different countermeasure strategies by accounting for the social, ecological and economic detriments and costs in relation to their benefits; (d)A software system consisting of: (1) software realisation of the mathematical models; (2) a Geographic Information System (GIS) and associated databases to select the aquatic system of interest and, if necessary, the default environmental data required to run the models; (3) a graphical user interface (GUI); (4) an operating system connecting all the above parts. The flexible structures of the environmental models implemented in MOIRA-PLUS DSS give the potential for the application of these models to several other types of pollutants, such as heavy metals. The DSS can be applied to complex water systems comprising lakes, reservoirs and rivers. In this paper, the main principles underpinning the functioning of the DSS MOIRA-PLUS are described and discussed.

The role of physical processes controlling the behaviour of radionuclide contaminants in the aquatic environment: a review of state-of-the-art modelling approaches.

This paper is aimed at presenting and discussing the methodologies implemented in state-of-the-art models for predicting the physical processes of radionuclide migration through the aquatic environment, including transport due to water currents, diffusion, settling and re-suspension. Models are briefly described, model parameter values reviewed and values recommended. The different modelling approaches are briefly classified and the advantages and disadvantages of the various model approaches and methodologies are assessed.