355 research outputs found
Evaluation of nitrogen loading in the last 80 years in an urbanized Asian coastal catchment through the reconstruction of severe contamination period
Most semi-enclosed seas have experienced severe eutrophication owing to high nutrient loading from rivers during rapid population growth periods. In Japan, the coastal areas of some megacities (e.g. Tokyo and Osaka) experienced considerable economic growth during the 1960s-1970s. Therefore, determining the amount of nutrient loading during this period is essential to undertake measures for the conservation of coastal environments. However, determining the nutrient loading that occurred several decades ago is generally difficult owing to lacking water quality records. In this study, the nitrogen loading in the Yamato River catchment, an urbanized coastal catchment in Asia, for 80 years from the 1940s to the 2010s is reconstructed using the Soil and Water Assessment Tool. We considered factors such as population growth, wastewater treatment plant (WWTP) construction, and changes in land and fertilizer usage in different urbanization stages. Results show that the total nitrogen loading in the catchment peaked in the 1970s at 6616 tons yr(-1) owing to untreated wastewater discharge and rapid increase in population growth. By reducing 57% of the nitrogen loading in the 2010s from the catchment, WWTPs have been instrumental in improving the water environment. The decrease in and integration of agricultural land has reduced nitrogen loading attributed to nonpoint sources; however, this reduction was not obvious because of the high fertilizer usage before the 2000s. Overall, the findings of this study provide a comprehensive understanding of the impact of rapid urbanization in an Asian coastal catchment on nitrogen loading during the high economic growth period in the past. This study will be useful for the long-term assessment of nutrient loading in other
NO_3^--N Flux of Streams in the Setouchi Region : Effects of Fruit-Farmland Area, Water Reservoir, and Alluvial Fan
To confirm the effects of fruit-farmland area, water reservoir, and alluvial fan on nitrate load in short streams, we measured runoff and collected water samples at five or eight sites in each of four streams, Seto Inland Sea catchment. Nitrate load of the streams increased with increasing ratio of fruit-farmland area. At a downstream site of water reservoir, nitrate concentration showed a slight decrease. On the area widely domi- nated by alluvial fan, it assumed that groundwater pollution by nitrate-nitrogen is accelerated with groundwater recharge of stream water. It is necessary for conservation of water resources to consider function of these effects as well as river-groundwater mixing
X-ray magnetic circular dichroism and photoemission study of the diluted ferromagnetic semiconductor ZnCrTe
We have performed x-ray magnetic circular dichroism (XMCD) and valence-band
photoemission studies of the diluted ferromagnetic semiconductor
ZnCrTe. XMCD signals due to ferromagnetism were observed at the Cr
2p absorption edge. Comparison with atomic multiplet calculations suggests that
the magnetically active component of the Cr ion was divalent under the
tetrahedral crystal field with tetragonal distortion along the crystalline a-,
b-, and c-axes. In the valence-band spectra, spectral weight near the Fermi
level was strongly suppressed, suggesting the importance of Jahn-Teller effect
and the strong Coulomb interaction between the Cr 3d electrons
Seismic Wavefield Reconstruction based on Compressed Sensing using Data-Driven Reduced-Order Model
A seismic wavefield reconstruction framework based on compressed sensing
using the data-driven reduced-order model (ROM) is proposed and its
characteristics are investigated through numerical experiments. The data-driven
ROM is generated from the dataset of the wavefield using the singular value
decomposition. The spatially continuous seismic wavefield is reconstructed from
the sparse and discrete observation and the data-driven ROM. The observation
sites used for reconstruction are effectively selected by the sensor
optimization method for linear inverse problems based on a greedy algorithm.
The proposed framework was applied to simulation data of theoretical waveform
with the subsurface structure of the horizontally-stratified three layers. The
validity of the proposed method was confirmed by the reconstruction based on
the noise-free observation. Since the ROM of the wavefield is used as prior
information, the reconstruction error is reduced to an approximately lower
error bound of the present framework, even though the number of sensors used
for reconstruction is limited and randomly selected. In addition, the
reconstruction error obtained by the proposed framework is much smaller than
that obtained by the Gaussian process regression. For the numerical experiment
with noise-contaminated observation, the reconstructed wavefield is degraded
due to the observation noise, but the reconstruction error obtained by the
present framework with all available observation sites is close to a lower
error bound, even though the reconstructed wavefield using the Gaussian process
regression is fully collapsed. Although the reconstruction error is larger than
that obtained using all observation sites, the number of observation sites used
for reconstruction can be reduced while minimizing the deterioration and
scatter of the reconstructed data by combining it with the sensor optimization
method
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