The Application Of Radioisotopes In The Study Of Estuarine Sedimentary Processes

The spatial and temporal distributions of some radionuclides in effluents originating from the British Nuclear Fuels Ltd (BNFL) reprocessing plant at Windscale, which are released into the Irish Sea, have been studied in sediments at 16 sites in the salt marsh region near Newbiggin on the Esk estuary Cumbria, England. The concentration of non-conservative radionuclides in surface sediments of the area cannot be described by a single parameter, but there is a high correlation with organic C, Cu, Al and the Si : Al ratio with particle size. The preservation of the historical record of the BNFL effluents in the Esk sediments is dependent on the hydrology of the area, as it effects such processes as accretion, erosion and remixing. From the 106Ru and 210Po concentrations and the 137Cs : 134Cs ratio in the sediment profiles with depth, we have identified these processes. Sedimentation rates at sites of accretion vary between 0·5 and 3 cm year−1. However, at some sites they appear to be much higher, approximately 6 cm year−1 in the top 10 cm, but they are not consistent throughout the depth profiles. This may be a true reflection of variable accretion related to sediment type, or one which is influenced by surficial mixing. Some cores showed evidence of continuous accretion but no significant radioactivity was detected at depths below 35–40 cm, indicating an overall sedimentation rate of approximately 1·5 cm year−1 for the 25–30-year period since BNFL effluents first entered the Irish Sea.

Parameterisation of bivalve functional traits for mechanistic eco-physiological dynamic energy budget (DEB) models

Mechanistic models such as those based on dynamic energy budget (DEB) theory are emergent ecomechanics tools to investigate the extent of fitness in organisms through changes in life history traits as explained by bioenergetic principles. The rapid growth in interest around this approach originates from the mechanistic characteristics of DEB, which are based on a number of rules dictating the use of mass and energy flow through organisms. One apparent bottleneck in DEB applications comes from the estimations of DEB parameters which are based on mathematical and statistical methods (covariation method). The parameterisation process begins with the knowledge of some functional traits of a target organism (e. g. embryo, sexual maturity and ultimate body size, feeding and assimilation rates, maintenance costs), identified from the literature or laboratory experiments. However, considering the prominent role of the mechanistic approach in ecology, the reduction of possible uncertainties is an important objective. We propose a revaluation of the laboratory procedures commonly used in ecological studies to estimate DEB parameters in marine bivalves. Our experimental organism was Brachidontes pharaonis. We supported our proposal with a validation exercise which compared life history traits as obtained by DEBs (implemented with parameters obtained using classical laboratory methods) with the actual set of species traits obtained in the field. Correspondence between the 2 approaches was very high (>95%) with respect to estimating both size and fitness. Our results demonstrate a good agreement between field data and model output for the effect of temperature and food density on age-size curve, maximum body size and total gamete production per life span. The mechanistic approach is a promising method of providing accurate predictions in a world that is under in creasing anthropogenic pressure.