Nutrient Exchange Kinetics in Water-Sediment Interface by C.P.C. Poon, pp. 881–895

Deep-sea sediments with high contents of rare-earth elements and yttrium (REY) are expected to serve as a potential resource for REY, which have recently been proved to be mainly contributed by phosphate component. Studies have shown that the carriers of REY in deep-sea sediments include aluminosilicate, Fe-Mn oxyhydroxides, and phosphate components. The ∑REY of the phosphate component is 1–2 orders of magnitude higher than those of the other two carriers, expressed as ∑REY = 0.001 × [Al2O3] − 0.002 × [MnO] + 0.056 × [P2O5] − 32. The sediment P2O5 content of 1.5% explains 89.1% of the total variance of the sediment ∑REY content. According to global data, P has a stronger positive correlation with ∑REY compared with Mn, Fe, Al, etc.; 45.5% of samples have a P2O5 content of less than 0.25%, and ∑REY of not higher than 400 ppm. The ∑REY of the phosphate component reaches n × 104 ppm, much higher than that of marine phosphorites and lower than that of REY-phosphate minerals, which are called REY-rich phosphates in this study. The results of microscopic observation and separation by grain size indicate that the REY-rich phosphate component is mainly composed of bioapatite. When ∑REY > 2000 ppm, the average CaO/P2O5 ratio of the samples is 1.55, indicating that the phosphate composition is between carbonate fluoroapatite and hydroxyfluorapatite. According to a knowledge map of sediment elements, the phosphate component is mainly composed of P, Ca, Sr, REY, Sc, U, and Th, and its chemical composition is relatively stable. The phosphate component has a negative Ce anomaly and positive Y anomaly, and a REY pattern similar to that of marine phosphorites and seawater. After the early diagenesis process (biogeochemistry, adsorption, desorption, transformation, and migration), the REY enrichment in the phosphate component is completed near the seawater/sediment interface. In the process of REY enrichment, the precipitation and enrichment of P is critical. According to current research progress, the REY enrichment is the result of comprehensive factors, including low sedimentation rate, high ∑REY of the bottom seawater, a non-carbonate depositional environment, oxidation conditions, and certain bottom current conditions.

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Fast oxygen exchange kinetics of pore-free Bi1−xSrxFeO3−δ thin films

Physical Chemistry Chemical Physics ◽

10.1039/c1cp21684h ◽

2011 ◽

Vol 13 (37) ◽

pp. 16530 ◽

Cited By ~ 42

Author(s):

Anja Wedig ◽

Rotraut Merkle ◽

Benjamin Stuhlhofer ◽

Hanns-Ulrich Habermeier ◽

Joachim Maier ◽

...

Keyword(s):

Thin Films ◽

Oxygen Exchange ◽

Exchange Kinetics ◽

Kinetics Of

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Hydrogen exchange kinetics of human hemoglobins. The pH dependence of solvent accessibility in cyanomet-, oxy-, and deoxyhemoglobin.

Journal of Biological Chemistry ◽

10.1016/s0021-9258(17)34858-5 ◽

1978 ◽

Vol 253 (10) ◽

pp. 3702-3707

Author(s):

B.E. Hedlund ◽

P.E. Hallaway ◽

B.E. Hallaway ◽

E.S. Benson ◽

A. Rosenberg

Keyword(s):

Hydrogen Exchange ◽

Solvent Accessibility ◽

Ph Dependence ◽

Exchange Kinetics ◽

Kinetics Of

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Nitrogen removal processes in lakes of different trophic states from on-site measurements and historic data

Aquatic Sciences ◽

10.1007/s00027-021-00795-7 ◽

2021 ◽

Vol 83 (2) ◽

Author(s):

Beat Müller ◽

Raoul Thoma ◽

Kathrin B. L. Baumann ◽

Cameron M. Callbeck ◽

Carsten J. Schubert

Keyword(s):

Eutrophic Lake ◽

Oligotrophic Lake ◽

Removal Rates ◽

N Removal ◽

Central Switzerland ◽

Denitrification Activity ◽

Historic Data ◽

Anthropogenic Nitrogen ◽

Removal Processes ◽

Sediment Interface

AbstractFreshwater lakes are essential hotspots for the removal of excessive anthropogenic nitrogen (N) loads transported from the land to coastal oceans. The biogeochemical processes responsible for N removal, the corresponding transformation rates and overall removal efficiencies differ between lakes, however, it is unclear what the main controlling factors are. Here, we investigated the factors that moderate the rates of N removal under contrasting trophic states in two lakes located in central Switzerland. In the eutrophic Lake Baldegg and the oligotrophic Lake Sarnen, we specifically examined seasonal sediment porewater chemistry, organic matter sedimentation rates, as well as 33-year of historic water column data. We find that the eutrophic Lake Baldegg, which contributed to the removal of 20 ± 6.6 gN m−2 year−1, effectively removed two-thirds of the total areal N load. In stark contrast, the more oligotrophic Lake Sarnen contributed to 3.2 ± 4.2 gN m−2 year−1, and had removed only one-third of the areal N load. The historic dataset of the eutrophic lake revealed a close linkage between annual loads of dissolved N (DN) and removal rates (NRR = 0.63 × DN load) and a significant correlation of the concentration of bottom water nitrate and removal rates. We further show that the seasonal increase in N removal rates of the eutrophic lake correlated significantly with seasonal oxygen fluxes measured across the water–sediment interface (R2 = 0.75). We suggest that increasing oxygen enhances sediment mineralization and stimulates nitrification, indirectly enhancing denitrification activity.

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