The fate of particle-reactive radionuclides on the Amazon and Yangtze continental shelves

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1986

OSTI ID:5014219

McKee, B A

Water column and seabed samples collected from the continental shelves adjacent to the Yangtze and Amazon Rivers were analyzed for particle-reactive radionuclides ({sup 234}Th, {sup 228}Th, {sup 210}Pb), and their respective parent nuclides ({sup 238}U, {sup 228}Ra, {sup 226}Ra). On the Amazon shelf, dissolved {sup 238}U activities increase with increasing salinity to a shelf maximum (4.6 dpm 1{sup {minus}1}) that is much higher than the open-ocean value (2.5 dpm 1{sup {minus}1}) because uranium is desorbed from the ferric-oxyhydroxide coatings of bottom sediments and advected into the overlying water column during periodic resuspension events. As a result, measurement of only the riverine flux of dissolved {sup 238}U underestimates (by a factor of 5) the flux of dissolved uranium from the Amazon shelf to the open ocean. K{sub e} values decrease with increased SSC and range from 10{sup 5}{center dot}10{sup 6} ml g{sup {minus}1} for Th and from 10{sup 4}{center dot}10{sup 6} ml g{sup {minus}1} for Po and Pb. The approach to equilibrium can best be described as a two-step process that is initially rapid (rate constants: 10-100 d{sup {minus}1}, during the first 30 minutes), but becomes less rapid (rate constants: 1-4 d{sup {minus}1}) as equilibrium is attained. Distribution coefficients for {sup 234}Th, {sup 228}Th and {sup 210}Pb exhibit large spatial variability on the Amazon shelf (range: 10{sup 3} - 10{sup 6} ml g{sup {minus}1}) and on the Yangtze shelf (range: 10{sup 4} - 10{sup 6} ml g{sup {minus}1}). On the Amazon shelf, particle residence time is short (2-3 hours) relative to scavenging residence time (15-20 hours) therefore, only 1-31% of equilibrium between dissolved and particulate thorium is attained. On the Yangtze shelf, particle residence time is long (12-89 hours) relative to scavenging time (2-23 hours) resulting in K{sub d} values near (97-100%) equilibrium.

• Research Organization: North Carolina State Univ., Raleigh, NC (USA)
• OSTI ID: 5014219
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ACTINIDE ISOTOPES
ALKALINE EARTH ISOTOPES
AMAZON RIVER
CONTINENTAL MARGIN
CONTINENTAL SHELF
DATA
DATA ANALYSIS
ENVIRONMENTAL TRANSPORT
EXPERIMENTAL DATA
INFORMATION
ISOTOPES
LEAD ISOTOPES
MASS TRANSFER
MEASURING INSTRUMENTS
MEASURING METHODS
NUMERICAL DATA
RADIONUCLIDE MIGRATION
RADIUM ISOTOPES
RIVERS
STREAMS
SURFACE WATERS
THORIUM ISOTOPES
URANIUM ISOTOPES
YANGTZE RIVER