{sup 234}Th and {sup 7}Be as tracers for the transport and dynamics of suspended particles in a partially mixed estuary
The sources of the natural radionuclides {sup 234}Th (half-life = 24 d) and {sup 7}Be (half-life = 53 d) to the partially mixed Hudson River estuary are distinctly different: {sup 234}Th is produced from decay of dissolved {sup 238}U that varies conservatively as a function of salinity, and {sup 7}Be is added directly from the atmosphere. {sup 234}Th and {sup 7}Be activities were measured in suspended and bottom sediments under varying conditions of river flow to evaluate the relative importance of local sediment resuspension and advection of suspended sediments through the estuary. Both radionuclides are removed from the estuarine water column on time scales of from <1 to 13 d. The {sup 234}Th{sub xs}/{sup 7}Be activity ratio is used to eliminate variations in the specific activities caused by grain size or sediment compositional changes. A simple steady-state model is used to set limits on the activity ratios expected if local processes (in situ production of {sup 234}Th, atmospheric supply of {sup 7}Be, scavenging, particle settling, and resuspension) dominate the activity ratio. During low river discharge, observed {sup 234}Th{sub xs}/{sup 7}Be ratios exceed the model upper limits in the higher salinity portions of the estuary, suggesting that particles labeled with Th and Be in higher salinities are transported to lower salinities with the estuarine circulation. Distance scales of particle transport are estimated to be from 10 to 20 km, comparable to the tidal excursion. Sampling during a high-flow event of short duration shows that the activity ratios tend toward the lower limit. Such a pattern could be produced by down-river transport of particles or by enhanced suspension. Similarities between the {sup 234}Th{sub xs}/{sup 7}Be activity ratios of suspended and bottom sediments suggest that increases in resuspension during high flow events dominate the activity ratio in the suspended sediment reservoir.
- Research Organization:
- State Univ. of New York, Stony Brook, NY (US)
- OSTI ID:
- 20000930
- Journal Information:
- Geochimica et Cosmochimica Acta, Vol. 63, Issue 17; Other Information: PBD: Sep 1999; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
Similar Records
The fate of particle-reactive radionuclides on the Amazon and Yangtze continental shelves
The chemistry of trace elements in estuaries