Yuan-Hui Li

A kinetic approach to describe trace-element distribution between particles and solution in natural aquatic systems

The partitioning of radioactive trace elements between seawater and particulate matter from surface sediments and sediment traps was investigated in laboratory experiments. For the elements Na, Zn, Se, Sr, Cd, Sn, Sb, Cs, Ba, Hg, Th and Pa (group I) constant distribution coefficients (Kd) were found after a few days of equilibration, whereas the elements Be, Mn, Co and Fe (group II) showed an increasing Kd over the whole time of observation of 108 days. The time dependence of Kd is described by an adsorption-desorption equilibrium (group I elements), followed by a lattice transport reaction step (group II elements). The reaction rate constants are compared to Mn oxidation rates and to adsorption rate constants derived from in situ measurements of the UTh disequilibrium as available from literature.

Denudation of Taiwan Island since the Pliocene Epoch

The average denudation rate of the Central Range of Taiwan Island has been increasing since the Pliocene Epoch. Today it is at least 1,365 mg/cm 2 yr, which is probably the highest known value in the world.

Partition of radiotracers between suspended particles and seawater

Abstract Distinctive uptake mechanisms of different radiotracers by red clays in seawater are elucidated from the magnitude and change of distribution coefficients (Kd) for up to 17 γ-emitting radiotracers as functions of equilibration time, suspended particle concentration and compositions of solids and seawaters. The adsorption of ionic metals onto colloids and subsequent coagulation of colloids onto larger particles are the dominant removal processes of metals in the aquatic environments of low suspended particle concentration.

Natural radionuclides in the water of Narragansett Bay

Abstract The concentrations of radionuclides of the U-Th series ( 238 U, 234 Th, 234 U, 230 Th, 226 Ra, 210 Pb, 210 Po, and 232 Th, 228 Ra, 228 Th) in the water of Narragansett Bay are reported. Analysis of the total, particulate, dissolved and colloidal forms of Th isotopes reveal a consistent removal behavior which is controlled mainly by the particulate matter concentration and the sediment resuspension rate. Half-removal times of Th from solution onto particles range from 1.5 to 15 days, and settling velocities of Th containing particles range generally between 1 and 11 m/day. 210 Pb and 210 Po concentrations are seasonally dependent, with higher concentrations and slower removal during the early summer (half-removal times from solution onto particles of 1–5 days in winter and up to 2 months in early summer).

Desorption and coagulation of trace elements during estuarine mixing

Abstract Mixing experiments of seawater and the Hudson and Mississippi riverwaters with radiotracer spikes show that Co, Mn, Cs, Cd, Zn and Ba will be desorbed from river suspended particles, while significant fractions of “dissolved” Fe, Sn, Bi, Ce and Hg will be coagulated during estuarine mixing.

Pu in coastal marine environments

Abstract Analysis of water samples from the New York Bight area and Narragansett Bay reveals that a small fraction of the total Pu (probably Pu (III + IV) species) is continuously removed to the sediments at a rate similar to that of the particle-reactive isotope 228 Th. A more “soluble” Pu species appears to be released at times from the sediments to the water column in these nearshore regions. Sediments in shallow areas of the New York Bight south of Rhode Island and Narragansett Bay have high Pu inventories and relatively deep penetration of this element, although the net sediment accumulation rate is generally low ( 2 yr). The high Pu inventories can be explained if both sediment resuspension and sediment mixing are assumed to be the major controlling factors for the effective transfer of Pu from the water column to the sediments. By simultaneous modelling of the depth distribution of three tracers which operate on vastly different time scales: 234 Th (half-life 24 days), 210 Pb (half-life 22 years) and 239,240 Pu (introduced into the environment during the past 30 years), bioturbation rates ranging from 4 to 32 cm 2 /yr in the surface mixed layer (5–10 cm thick) and from 0.3 to 2.5 cm 2 /yr in the layer below (up to 40 cm thick) and net sediment accumulation rates of approximately zero to 0.14 g/cm 2 yr were calculated for these areas.

The flux of 226Ra from estuarine and continental shelf sediments

A pronounced desorption phenomenon of 226 Ra from sediment was observed in the Hudson River estuary. Mass balance calculations indicate that the desorption of 226 Ra from the river-borne sediment in estuarine environment is an important source of 226 Ra to the oceans.

A brief discussion on the mean oceanic residence time of elements

Abstract The mean oceanic residence times of elements obtained from deposition rates in deep-sea sediments are more representative than those obtained from river-input rates. The average concentration data of dissolved S, Au, Ag, Se, As, Hg, Sb, Zn, Sn, Cu and Pb in rivers contain large pollution and/or contamination components.

Rising surface ocean dissolved inorganic carbon at the Hawaii Ocean Time-series site

Abstract Surface ocean dissolved inorganic carbon (DIC) and titration alkalinity have been measured for 7 years as a part of the Hawaii Ocean Time-series (HOT) program. The time-series data set displays an interannual increase in the inventory of surface ocean DIC which we interpret as a response to increasing atmospheric carbon dioxide concentrations. The rate of increase in surface ocean DIC at the open ocean HOT site is approximately 1 μ mol kg −1 yr −1 with a 95% confidence interval of 0.72 to 1.37 μ mol kg −1 yr −1 . This accumulation rate is consistent with the rate of increase predicted from the rise in boundary layer p CO 2 .

The relative mobility of natural (Th, Pb and Po) and fallout (Pu, Am, Cs) radionuclides in the coastal marine environment: results from model ecosystems (MERL) and Narragansett Bay

The relative mobility of nuclides of Pb, Th, Pu, and Cs, which are widely used as geochemical tracers for sedimentation and bioturbation. was investigated in artificial microcosm tanks (MERL) and in Narragansett Bay. Their mobility was characterized by their removal rates from the water column, their affinity toward particles and their degree of penetration into the surface sediments. Pb, Th, and Pu transport was controlled predominantly by the affinity of these elements to particles, and the transport parameters of the particles themselves (i.e. sediment resuspension and mixing rates). Because of its low distribution coefficient, transport of Cs was controlled by molecular diffusion through pore water in the winter, while in summer, Cs transport was enhanced due to bioturbation. The increase with depth of the CsPu ratio in core profiles of MERL and Narragansett Bay sediments is thus caused primarily by the higher mobility of Cs.