Dissolved iron (dFe) transported by the Amur River greatly contributes to phytoplankton growth in the Sea of Okhotsk. Nevertheless, there has been little research on the source of dFe to rivers, ...especially in the Amur‐Mid Basin, which is situated in a sporadic permafrost area. In the Amur‐Mid Basin, permafrost generally exists in wetlands in flat valleys, and these permafrost wetlands could be a source of dFe to rivers. To assess the importance of permafrost wetlands for dFe export, we conducted a local survey on land and soil characteristics of wetlands, and moreover analyzed the chemical composition (dFe, dissolved organic carbon DOC, pH, and electrical conductivity EC) of 24 rivers with different watershed sizes in summer. As a result of local survey, the thickly accumulated peat soils in the permafrost wetland were almost saturated and rich in organic matter from the surface to a greater depth near the permafrost table. In addition, the coverage of such permafrost wetlands in watersheds showed significant positive correlations with dFe (r2 = 0.67, p = 1.7e−6) and DOC (r2 = 0.48, p = 1.8e−4) and a negative correlation with EC (r2 = 0.52, p = 7.7e−5). The dFe concentration was also correlated well with DOC concentration (r2 = 0.68, p = 7.3e−7) but not correlated with pH and watershed area. These findings are the first to indicate that permafrost wetlands in the Amur‐Mid Basin considerably contribute to dFe and DOC export to rivers, and their coverage primarily determines riverine dFe and DOC concentrations in summer.
Plain Language Summary
Dissolved iron (dFe) is a key factor that limits phytoplankton growth in the ocean. In the Amur‐Okhotsk ecosystems, dFe transported by the Amur River greatly contributes to phytoplankton growth in the Sea of Okhotsk; however, there has been little research on the dFe source to rivers, especially in the Amur‐Mid Basin, which is situated in a sporadic permafrost area. In this study, we focused on permafrost wetlands in the Amur‐Mid Basin and investigated the soil characteristics and the relationship between wetland coverage and dFe concentrations in 24 watersheds. Permafrost wetlands contain waterlogged and organic‐rich peat soils, and more importantly, their coverage clearly shows strong positive relationships with riverine dFe and dissolved organic carbon (DOC) concentrations. This is the first study to show that permafrost wetlands impact water chemistry in the Amur‐Mid Basin, primarily as sources of dFe and DOC.
Key Points
We provide water chemistry data from 24 rivers with different watershed sizes in the Amur‐Mid Basin during summer
dFe and dissolved organic carbon concentrations showed a significant positive correlation with the coverage of the permafrost wetland in the watersheds
Permafrost was confirmed underneath wetlands, and thickly accumulated peat soils were rich in organic matter
CsI calorimeter for the J-PARC KOTO experiment Sato, K.; Lee, J.W.; Banno, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2020, Letnik:
982, Številka:
C
Journal Article
Recenzirano
Odprti dostop
An electromagnetic calorimeter made of undoped CsI crystals is used in the J-PARC KOTO experiment to search for new physics beyond the standard model with the KL→π0νν̄ decay. The calorimeter is ...designed to operate in vacuum of 0.1 Pa and in a high-rate environment where the counting rate due to KL decays is O(100) kHz. A special method to calibrate the calorimeter during the data taking without using a tracking system for charged particles is reported. The energy, position, and timing resolutions of the calorimeter were evaluated in several beam tests, and the resolutions satisfy the required performance. The energy resolution with the total energy E is 0.66⊕1.81∕EGeV% in the inner region of the calorimeter.
In the main ring (MR) of the Japan Proton Accelerator Research Complex (J-PARC), the power supplies of magnets induce large ripples in the betatron tunes. The tune ripples degrade the quality of the ...beam spill on the slowly extracted beam. To improve the spill quality, the J-PARC MR employed a feedback system using a beam spill monitor; however, the existing system could not correct the beam spills suitably, since the tune ripples were too large. We developed a new correction system using the information of magnet currents as an input of the correction. The new system consists of current monitors and a corrector quadrupole, and it allows us to correct the ripples in real time. Using this system, we successfully corrected the tune ripples for the first time in the J-PARC MR. The correction system improved the spill quality from 3% (without any correction) to 30% (with the new correction), whereas the quality using the present feedback system is 17.4%.
We have developed a low-mass and high-efficiency charged-particle detector for an experimental study of the rare decay
$K_L \rightarrow \pi ^0 \nu \bar {\nu }$
. The detector is important for ...suppressing the background with charged particles to the level below the signal branching ratio predicted by the Standard Model
$\left (O\left (10^{-11}\right )\right )$
. The detector consists of two layers of 3 mm thick plastic scintillators with embedded wavelength-shifting fibers and multi-pixel photon counters for the readout. We manufactured the counter and evaluated the performance in terms of light yield, timing resolution, and efficiency. With this design, we achieved an inefficiency per layer against penetrating charged particles of less than
$1.5 \times 10^{-5}$
, which satisfies the requirement of the KOTO experiment determined from simulation studies.
We developed a high voltage system for the electromagnetic calorimeter of the KOTO detector. The system is designed around a low noise, low power Cockcroft–Walton (CW) photomultiplier tube base with ...a high gain preamplifier. The low power makes it suitable for operations in vacuum. The low noise and high gain allow detecting signals in the 1MeV range. We achieved a final noise level below 180μVrms for a preamplifier gain of more than 40. A vacuum tolerant control system for the CW bases power distribution was also designed. This system is able to control and monitor the high voltage of each individual base.
We describe a novel multi-GeV photon detector which operates under an intense flux of neutrons. It is composed of lead–aerogel sandwich counter modules. Its salient features are high photon detection ...efficiency and blindness to neutrons. Monte Carlo (MC) simulations show that the efficiency for photons with energy larger than 1 GeV is expected to be higher than 99.5% and that for 2 GeV/
$c$
neutrons is less than 1%. Performance of photon detection with an underlying large flux of neutrons was measured by a partial detector with 12 modules. We confirm the efficiency for photons with energy
$>1$
GeV is consistent with the MC expectation within an uncertainty of 8.2%.
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