Radiocesium contamination of lake sediments and fish following the Fukushima nuclear accident and their partition coefficient

To evaluate the influences of the Fukushima nuclear accident in 2011 on lake sediments and fish and to understand the difference in their contamination levels, data on radiocesium concentrations (137Cs and 134Cs) were analyzed for sediments and 18 fish species (including one freshwater prawn) taken from 15 lakes in northeastern Japan. Temporal trends in radiocesium concentrations (referenced to radioactivity on 15 Mar 2011) were not clear during 2011–2013 except in a few species of fish. There was a decrease among topmouth gudgeon (Pseudorasbora parva), icefish (Salangichthys microdon), and pond smelt (Hypomesus nipponensis) but an increase among channel catfish (Ictalurus punctatus) and kokanee (Oncorhynchus nerka). Significant positive correlations between lake-averaged radiocesium concentrations of sediments and fish were observed for most fish species. The partition coefficients (PCs), defined as fish concentration divided by sediment concentration on a dry weight basis, clustered mostly in the range of 0.3–3 ([Bq/kg-dry]/[Bq/kg-dry]) and were high in large-sized types (e.g., channel catfish, and brown trout [Salmo trutta]) but low in small-sized types (e.g., topmouth gudgeon and icefish). After normalization, the PCs of the respective lakes were analyzed together with lake characteristics related to water exchange and lake dimensions, water quality, and sediments and were found to be high in the lakes with high water retention time and vice versa, suggesting prolonged contact and equilibration between the water and the sediments. Finally, the efficacy and potential problems of using the PCs between sediments and fish are discussed

An easily implemented method to estimate impervious surface area on a large scale from MODIS time-series and improved DMSP-OLS nighttime light data

It is important for researchers and policy-makers to frequently update the amount and spatial distribution of impervious surface area (ISA) on earth, because the level of imperviousness not only indicates urbanization, but is also a key indicator of ecological conditions. In this study, we developed an easily implemented method for estimating the ISA percentage (ISA%) from vegetation index data obtained from a moderate resolution imaging spectroradiometer (MODIS) and nighttime light data obtained from the Defense Meteorological Satellite Program’s Operational Line-scan System (DMSP-OLS). The proposed method consists of four major steps. First, a non-vegetation fraction map was generated from 16-day composited time-series MODIS normalized difference vegetation index data using the temporal mixture analysis method. Second, the enhanced-vegetation-index-adjusted nighttime light index (EANTLI) was used to overcome the saturation problem and blooming effects in the original DMSP-OLS data. Third, the relationship between ISA% and EANTLI was derived based on a statistical analysis of the non-vegetation fraction image and the EANTLI image to obtain a preliminary ISA% map. Finally, the final ISA% map was obtained by selecting smaller values from the preliminary ISA% map and non-vegetation fraction map for each pixel. The validation results showed that the developed method has promising accuracy for estimating the ISA% in our study area (mainly consisting of four Southeast Asian countries: Thailand, Laos, Cambodia, and Vietnam), with a root mean square error value of 0.111, a systematic error value of 0.061, and a determination coefficient of 0.87. Another important finding is that there are two relationships between ISA% and improved nighttime light (i.e., EANTLI): the natural logarithmic function is suitable for ISA% values between 0% and 50%, and the quadratic polynomial function should be used for ISA% values larger than 50%. The developed method has high potential for application to the generation of global ISA% maps with frequent updates due to its easy implementation and the ready availability of input data

A pre-screened and normalized multiple endmember spectral mixture analysis for mapping impervious surface area in Lake Kasumigaura Basin, Japan

The impervious surface area (ISA) has emerged not only as an indicator of the degree of urbanization, but also as a major indicator of environmental quality for drainage basin management. However, since almost all of the methods for estimating ISA have been developed for urban environments, it is questionable whether these methods can be successfully applied to drainage basins, such as those found in Japan, which usually have more complicated vegetation components (e.g. paddy field, plowed field and dense forest). This paper presents a pre-screened and normalized multiple endmember spectral mixture analysis (PNMESMA) method, which includes a new endmember selection strategy and an integration of the normalized spectral mixture analysis (NSMA) and multiple endmember spectral mixture analysis (MESMA), for estimating the ISA fraction in Lake Kasumigaura Basin, Japan. This new proposed method is superior to the previous methods in that the estimation error of the proposed method is much smaller than the previous SMA- or NSMA-based methods for drainage basin environments. The overall root mean square error was reduced to 5.2%, and no obvious underestimation or overestimation occurred for high or low ISA areas. Through the assessment of environmental quality in Lake Kasumigaura Basin using the ISA fraction, the results showed that the basin has been in the impacted category since 1987, and that in the two decades since, the environmental quality has continued to decline. If this decline continues, then Lake Kasumigaura Basin will fall into the degraded category by 2017

THE CHANGES IN STREAM WATER TEMPERATURE AND WATER QUALITY PARAMETERS DURING RAINFALL EVENTS IN FORESTED WATERSHEDS: SCALING OF OBSERVATIONS

ABSTRACT We studied the changes in stream water temperature (Tw) and water quality (Wq) during rainfall events in forested watersheds. The parameters ofWq (88, DOC, N03--N, DTN, Na+, 8i and r) were observedinfour regionsof Japan from June 2004 to December 2005. The R values between Tw and those Wq parameters and between specific discharge (Qs) and Wq were positive, exceptfor the negativeones (Na+ and Si). Similarto the relationbetweenQs vs. Tw, hysteretic loops in the relations between Qs vs. those Wqparameters were clockwise, exceptfor Na+ and Si as counter-clockwiseloops. This indicatesthat the\u27surface and subsurface flows contain higher concentrations of SS, DOC, IC, N03--N and DTN. To the contrary,the deeperpathwayscontainhigherconcentrationsof Na+ and Si. These results suggest that the changes in Tw and Wq could be used to interpret theflow paths. KeyWords: stream water temperature, water quality, rainfall event,hysteretic loop

Temporal mixture analysis for estimating impervious surface area from multi-temporal MODIS NDVI data in Japan

As a proxy measure of the human ecological footprint, impervious surface area (ISA) has recently become a key concept in the field of urban remote sensing, with a focus on estimation of the ISA at a city-scale by using Landsat-style satellite images. However, ISA estimation is also in demand in disciplines such as the environmental assessment and policy making at a national scale. This paper proposes a new method for estimating the ISA fraction in Japan based on a temporal mixture analysis (TMA) technique. The required inputs for the proposed method are rearranged MODIS NDVI time-series datasets at the temporal stable zone (i.e., the first to the sixth largest NDVI values in a year). Three ISA distribution maps obtained from Landsat-5 TM data were used as reference maps to evaluate the performance of the proposed method. The results showed that the proposed TMA-based method achieved a large reduction in the effects of endmember variability compared with the previous methods (e.g., SMA and NSMA), and thus the new method has promising accuracy for estimating ISA in Japan. The overall root mean square error (RMSE) of the proposed method was 8.7%, with a coefficient of determination of 0.86, and there was no obvious underestimation or overestimation for the whole ISA range

PAHs concentration and toxicity in organic solvent extracts of atmospheric particulate matters and sea sediments

The concentration of polycyclic aromatic hydrocarbons (PAHs) and the toxicity to marine bacteria (Vibrio fischeri) were measured for the organic solvent extracts of sea sediments collected from an urban watershed area (Hiroshima Bay) of Japan and compared with the concentrations and toxicity of atmospheric particulate matters. Among atmospheric particulate matters, the PAHs concentration was highest in FPM collected during cold seasons. The concentrations of sea sediments were 0.01-0.001 times those of atmospheric particulate matters. 1/EC50 was 1-10 L g-1 PM for atmospheric particulate matters and 0.1-1 L g-1 dry solids for sea sediments. These results imply that toxic substances from atmospheric PM are diluted several tens or hundreds times in sea sediments. The ratio of the 1/EC50 to PAHs concentration ((1/EC50)/16PAHs) was stable for all sea sediments (0.1-1 L μg-1 16PAHs) and was the same in the order of the magnitude as that of FPM and CPM. The ratio of sediments collected from the west was more similar to that of CPM while that of the east was to FPM, possibly because of hydraulic differences among water bodies. The PAHs concentration pattern analyses (principal component analysis and isomer ratio analysis) were conducted and from the results. PAHs pattern of sea sediments was fairly different from that of FPM and CPM. Comparison to previously conducted PAHs analyses suggested that biomass burning residues comprised a major portion of these other sources.This work was supported by Kurita Water and Environmental Foundation and Grant-in-Aid for Scientific Research (C

Will hypolimnetic waters become anoxic in all deep tropical lakes?

To elucidate trends of hypolimnetic oxygen concentrations, vertical distributions of dissolved oxygen were measured in eight deep tropical bodies of water (one natural lake with two basins, five natural lakes, and one reservoir) in Indonesia. A comparison of those concentrations with previously reported data revealed that shoaling of hypolimnetic oxygen-deficient (around a few decimeters to a few meter per year) water had occurred in all of the lakes. Calculated areal hypolimnetic oxygen depletion rates were 0.046–5.9 g m−2 y−1. The oligomictic or meromictic characteristics of the bodies of water suppressed circulation and mixing in the hypolimnions and thus resulted in continuous shoaling of the uppermost oxygen-deficient layers. In some lakes, millions of fish sometimes died suddenly, probably owing to upward movement of oxygen-deficient water to near the surface during periods of strong winds. In the future, the rate of shoaling will be accelerated by human impacts in the basins and by climate warming, the influence of which has already been manifested by rising water temperatures in these lakes. Appropriate monitoring and discussions of future restoration challenges are urgently needed to prevent the hypolimnions of the lakes from becoming completely anoxic

Factors explaining the yearly changes in minimum bottom dissolved oxygen concentrations in Lake Biwa, a warm monomictic lake

Vertical profiles of dissolved oxygen (DO) and water temperature (WT) measured bi-monthly for 36 years (1980–2015) near the deepest part of a warm monomictic lake were analyzed with special reference to yearly minimum DO at bottom (DOmin). DOmin changed yearly (3.0 ± 1.2 mg l−1) and significant differences in DOmin were not observed between Period I (1980–1993; cooler and worse in water quality) and Period II (1994–2015; warmer and better in water quality). This unclear trend in DOmin was probably due to the offsetting influences between warming induced by global warming and oligotrophication attempted by local governments etc. for the study period. DOmin was positively correlated with disturbance time (timing of last cold water intrusion observed from Mar to Aug), which could be related to the start of DO depletion at bottom. Thus, the linear model using this parameter could predict yearly DOmin fairly well for the entire study period (r2 = 0.60). In addition, DOmin and time of disturbance were correlated negatively with water density at bottom in Jan and positively with water density equilibrated to air temperature (AT) in Mar. Higher lake water density after full depth mixing advances the disturbance time. In contrast, lower AT in Mar and/or higher density of influent water after Mar delays the time likely due to the larger amount of snowfall in the watershed. Further, DOmin was positively correlated with maximum wind velocity in Sep which probably induced the recovery of DO. Multiple-regression models to predict DOmin using these meteorological and water quality parameters were developed (r2 ≥ 0.38, worse performances than the model using disturbance time) to forecast future trends of DOmin through global warming and/or climate change. Significant influences of water or sediment oxygen demands on DOmin were not detected. We also discuss the applicability of the proposed models

The Japanese space gravitational wave antenna; DECIGO

DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) is the future Japanese space gravitational wave antenna. DECIGO is expected to open a new window of observation for gravitational wave astronomy especially between 0.1 Hz and 10 Hz, revealing various mysteries of the universe such as dark energy, formation mechanism of supermassive black holes, and inflation of the universe. The pre-conceptual design of DECIGO consists of three drag-free spacecraft, whose relative displacements are measured by a differential Fabry– Perot Michelson interferometer. We plan to launch two missions, DECIGO pathfinder and pre- DECIGO first and finally DECIGO in 2024

DECIGO pathfinder

DECIGO pathfinder (DPF) is a milestone satellite mission for DECIGO (DECi-hertz Interferometer Gravitational wave Observatory) which is a future space gravitational wave antenna. DECIGO is expected to provide us fruitful insights into the universe, in particular about dark energy, a formation mechanism of supermassive black holes, and the inflation of the universe. Since DECIGO will be an extremely large mission which will formed by three drag-free spacecraft with 1000m separation, it is significant to gain the technical feasibility of DECIGO before its planned launch in 2024. Thus, we are planning to launch two milestone missions: DPF and pre-DECIGO. The conceptual design and current status of the first milestone mission, DPF, are reviewed in this article