| Abstract |
The determination of the age of a sediment layer is invaluable for understanding geochemical processes and their time-scales. The application of Pb-210 as a radiometric chronometer has been extensively researched in recent years, being applied to a variety of freshwater, estuarine and marine environments worldwide. The estimation of sedimentation rate changes using Pb-210 dating can also provide valuable information on possible causes for variation in a water body's physiochemical and biological characteristics; making the technique relevant to environmental remediation. However, to reliably draw conclusions based on Pb-210 dating; a comprehensive understanding of the influence that other natural and anthropogenic variables have on Pb-210 is essential._x000D_
This literature review summarises the key factors which may influence both unsupported Pb-210 deposition from the atmosphere and the unsupported Pb-210 activity found in sediments. The deposition of unsupported Pb-210 is shown to be predominantly via the rain-out mechanism (within-cloud scavenging) as opposed to wash-out (below cloud), and the suppression or release of Rn-222 exhalation from sediments may also be controlled by surface air temperatures and pressures, which consequently will result in seasonal variations in atmospheric Pb-210 concentrations and Pb-210 deposition. Organic matter (OM), silt and clay content also have an influence on the sediment unsupported Pb-210 activity; thus leading to a general consensus of positive correlation between unsupported Pb-210 activity and the OM, silt or clay content as a result of greater adsorption affinity for Pb-210 and an enhanced specific surface area relative to sand and larger particles. Bioturbation will also impact the unsupported Pb-210 activity in sediments, however mathematical models used to estimate this influence still require further refinement to accurately represent activity variation associated with different species' burrowing techniques and different soil porosities. Anthropogenic influences on sediment unsupported Pb-210 activity may also have been observed i.e. additional Pb-210 from the anthropogenic source, though research on these are limited and further research is advised in assessing the impact of anthropogenic activities such as farming, mining and fossil fuel combustion. |
