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.

Laboratory Simulation Of Chemical Processes Induced By Estuarine Mixing - The Behavior Of Iron And Phosphate In Estuaries

A series of well stirred tank reactors has been shown to provide an adaptable laboratory analogue of a one-dimensional estuarine mixing profile which can be applied dynamically to the study of the chemistry of estuarine mixing. Simulations of the behaviour of iron and phosphate in the low salinity region of an estuary have been achieved with this system. The well documented general features of iron removal, involving rapid aggregation of river-borne colloids, were reproduced. Phosphate removal is attributable in part to the coagulation process, although specific adsorption of phosphate by colloids also appears to be significant.

Nutrient Distributions In An Estuary - Evidence Of Chemical Precipitation Of Dissolved Silicate And Phosphate

Continuous autoanalytical recordings of the axial distributions of dissolved nitrate, silicate and phosphate in the influent freshwater and saline waters of the Tamar Estuary, south-west England have been obtained. Short-term variability in the distributions was assessed by repetitive profiling at approximately 3-h intervals on a single day and seasonal comparisons were obtained from ten surveys carried out between June 1977 and August 1978. Whereas nitrate is always essentially conserved throughout the upper estuary, the silicate- and phosphate-salinity relationships consistently indicate a non-biological removal of these nutrients within the low (0–10%) salinity range. Attempts to quantify precisely the degree of removal and to correlate this with changes in environmental properties (pH, turbidity, chlorophyll fluorescence, salinity, freshwater composition) were mainly inconclusive due to short-term fluctuations in the riverine concentrations of silicate and phosphate advected into the reactive region and to the rapid changes in turbidity brought about by tidally-induced resuspension and deposition of bottom sediment.