Papers by Takehiko Fukushima
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2015
ABSTRACT Euphotic zone depth (${Z_{{rm{eu}}}}$), defined as the depth where photosynthetic availa... more ABSTRACT Euphotic zone depth (${Z_{{rm{eu}}}}$), defined as the depth where photosynthetic available radiation (PAR) is 1% of its surface value, is of great importance in studies of water biogeochemical processes. Satellite remote sensing is a powerful technique to obtain ${Z_{{rm{eu}}}}$, as it can cover large areas at very frequent intervals. Several remote-sensing algorithms for estimating ${Z_{{rm{eu}}}}$ have been developed for oceanic water bodies; however, remote estimation of ${Z_{{rm{eu}}}}$ is still a challenging task for inland waters. In this study, an existing semianalytical algorithm (named as Lee07 in this study) was modified for remotely estimating ${Z_{{rm{eu}}}}$ in turbid inland waters by replacing the original quasi-analytical algorithm (QAA) by QAA_Turbid, an algorithm specially developed for remotely estimating total absorption and backscattering coefficients in turbid waters. Performance of the modified algorithm was evaluated using in situ radiometric data collected in Japan’s Lake Kasumigaura, known to be turbid. Results showed that yielded acceptable estimation accuracy for ${Z_{{rm{eu}}}}$ (ranging from 1.15 to 2.26 m) with root-mean-square error (RMSE) of 0.12 m, normalized root-mean-square error (NRMS) of 8.01%, and mean normalized bias (MNB) of $- 1.84% $, significantly outperforming the original version as well as three other ${Z_{{rm{eu}}}}$ retrieval algorithms. These results indicate its great potential for accurately estimating ${Z_{{rm{eu}}}}$ over widespread turbid inland waters from satellite images.
Annales de Limnologie - International Journal of Limnology, 2014
ABSTRACT In the eutrophic Lake Kasumigaura in Japan, a trend of dissolved Si (DSi) concentration ... more ABSTRACT In the eutrophic Lake Kasumigaura in Japan, a trend of dissolved Si (DSi) concentration was detected over the last three decades, probably caused by the DSi release enhanced by an increase in sediment resuspension for the same period (Arai et al., Limnol., 13, 81–95, 2012). The present study described the long-term trends of the magnitude and seasonality of diatom blooms in the lake during 1981–2010 using the database and assessed the influencing factors for the trends by the numerical simulation of DSi and diatoms. The box model was developed based on the lake budgets (inflow, outflow, release and sedimentation) and the simple diatom growth model depending on DSi, temperature and light condition. As results, database analysis detected a long-term trend of increasing diatom abundance and a shift of blooming season from spring and autumn to the winter–spring period. Si could be regarded as a main nutrient factor limiting diatom growth by analyzing N:P:Si ratios. Our model simulation relatively well-reproduced the increasing trend and the shift of seasonality of DSi and diatoms, even though peaks of diatom blooms were underestimated in some years. Among input variables, the concentration of resuspended sediments radically increased. The model simulation with the input variables or parameters changed suggested as follows: (1) the recent DSi release from resuspended sediments enhanced diatom abundance and (2) the degradation of light condition caused by resuspension affected the shift of blooming season. These findings implicate the significance of the interactions between sediments and water to phytoplankton blooms.
Http Dx Doi Org 10 1080 01431160903475365, Feb 1, 2010
The spectral decomposition algorithm (SDA), which is a new approach for the simultaneous estimati... more The spectral decomposition algorithm (SDA), which is a new approach for the simultaneous estimation of chlorophyll-a (Chl-a) and non-phytoplankton suspended solid (NPSS) concentrations in Case 2 waters using satellite data, was proposed by our previous study. Here, we investigated the effect of phytoplankton composition on the SDA based on the tank experiments using cultured samples for five phytoplankton species (three cyanobacteria, one green algae and one diatom) and lake water samples collected from Lake Kasumigaura from . The results showed that the SDA-based models obtained from the cultured samples (culture-based models) showed high accuracies for Chl-a and NPSS estimations in all phytoplankton species (root mean square error [RMSE] about 16.2 mg l -1 for Chl-a and about 11.0 mg l -1 for NPSS). However, the Landsat Thematic Mapper (TM) band combinations, which gave the smallest RMSE of the Chl-a and NPSS estimations, differed among the species. In addition, the culture-based models could apply to lake water samples with similar accuracies if the optimal standard reflectance spectra (SRS) of endmembers in the water body could be determined. This implies the potential of the SDA-based model as follows: (1) it is less site-and time-specific compared with conventional empirical methods (single band, band ratio, and arithmetic band calculation); (2) it can be proposed by a tank experiment or by a simulation using bio-optical modelling.
Fundamental and Applied Limnology, 2010
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Aquatic Microbial Ecology, Oct 10, 2006
Dissolved organic matter (DOM) in lake water can have a harmful effect on algal growth through ei... more Dissolved organic matter (DOM) in lake water can have a harmful effect on algal growth through either direct toxicity or iron limitation induced by its complexation with iron. We assessed the effect of iron complexation with DOM on algal growth in the eutrophic Lake Kasumigaura, Japan, using 2 species of cyanobacteria, Microcystis aeruginosa and Planktothrix agardhii, by combining the algal growth potential (AGP) test and pretreatment of DOM decomposition by UV irradiation. We also determined which nutrient limited the growth of the 2 species in the lake water using the AGP test: iron limited the growth of the 2 species, as did nitrogen and phosphorus in Lake Kasumigaura. Moreover, the growth of the 2 species was inhibited by iron complexation with DOM. This is consistent with our results regarding iron speciation in Lake Kasumigaura by cathodic stripping voltammetry: most (> 99.9%) of the dissolved iron was present as organic species in the lake water. Furthermore, data from our AGP test suggest that iron requirement or iron availability between the 2 species are different. This difference in growth characteristics between algal species would be an important determinant of the dominance of specific algal species.
Ecological Research, Jul 1, 2008
We examined the effects of dams on freshwater fish species based on data collected during 1990-20... more We examined the effects of dams on freshwater fish species based on data collected during 1990-2004 from 200 drainage systems in Japan. Of the 76 fish species examined, the occurrence of 20 species within Petromyzontidae, Cyprinidae, Cobitididae, Salmonidae, Cottidae, and Gobiidae was negatively affected by the presence of dams located in the downstream reaches of fish survey sites, whereas the occurrence of 12 species within Cyprinidae, Adrianichthyidae, Centrarchidae, and Gobiidae was positively associated with the presence of dams. A significantly higher proportion of the fishes with a negative damming effect were diadromous species as compared to the fishes with a positive damming effect. Conversely, the latter group had a significantly higher proportion of nonnative species than the former. A significant interaction existed between the effects of damming and the effects of elevation on family-specific species richness. Families dominated by native migratory species showed a greater reduction in the number of species above dams at lower elevations, whereas families represented primarily by nonnative species had higher species richness above dams at higher elevations, except for Centrarchidae, which was always higher in species richness above dams regardless of elevation. Based on our findings, dams in Japan have adversely affected native freshwater fishes by blocking their migration routes, favoring nonnative fishes, or altering existing habitats.
Environmental Monitoring and Assessment, 2011
A geochemical study of the bottom sediments of Lake Shinji and the River Ohashi in southwestern J... more A geochemical study of the bottom sediments of Lake Shinji and the River Ohashi in southwestern Japan was carried out to determine their elemental compositions and to evaluate the pollution status of lake sediments by employing enrichment factor (EF), pollution load index (PLI), and geoaccumulation index (I geo ). Present-day water quality was also assessed. Results showed that the water quality of Lake Shinji contrasts slightly between the upper and lower parts. The chemical composition of the sediments, as measured by X-ray fluorescence, included major and trace elements and total sulfur (TS). Average abundances of As, in the Shinji sediments were 10, 29, 143, 27, 19, and 54 ppm, respectively, compared to 6, 18, 57, 16, 10, and 37 ppm in the river sediments. Based on the EF, PLI, and I geo , the lake sediments are moderately to strongly polluted with respect to As, moderately polluted with Pb, Zn, and Cr, and unpolluted with Cu and Ni. The high EF and I geo for As, Pb, and Zn in the lake sediments indicate that metal concentration has occurred in Shinji. Increases in the abundances of these metals are likely related to the fine-grained nature of the sediments, reducing conditions of the bottom sediments, enrichment in organic matter, and possibly a minor contribution from non-point anthropogenic sources. Trace metal contents are strongly correlated with Fe 2 O 3 and TS, suggesting that Fe oxides and sulfides play a role in controlling abundances in the investigated areas.
Aquatic Sciences, May 31, 1996
The seasonal and spatial changes in dissolved organic carbon (DOC) in Lake Kasumigaura, a shallow... more The seasonal and spatial changes in dissolved organic carbon (DOC) in Lake Kasumigaura, a shallow, eutrophic lake, were analyzed and the lability of DOC was tested by long-term incubations. There was a nearly 1 mgC 1 i downstream increase in refractory DOC in the lake; at the center it fluctuated little seasonally. The characteristic UV-absorbanee: DOC ratios were determined for samples from the influent rivers (pedogenic: used interchangeably with "allochthonous') and outdoor experimental ponds (autochthonous) during incubations. These ratios were then used to calculate the proportion of total measured lake water DOC in each of four components: pedogenic-refractory (PR), pedogenic-labile (PL), autochthonous-refractory (AR) and autochthonous-labile (AL). PR was uniform (around 1.5 mgC 1-0 or diminished very slightly over time. AR increased from nearly zero at the station closest to an influent river to i mgC 1 -~ at the lake center, PL declined downstream from 0.3 mgC 1 -~ to zero. AL was virtually constant at 0.8 mgC 1 -~ except at the station closest to the influent river. The constancy of the UV-absorbance: DOC ratio during the biodegradation process was confirmed for Lake Kasumigaura; hence a two-component model (pedogenic-autochthonous) could be applied here without consideration of DOC lability. However, this assumption is not always met for other water bodies, and therefore it should be checked before applying a two-component model elsewhere.
Soils and Foundations -Tokyo-
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2012 Second International Workshop on Earth Observation and Remote Sensing Applications, 2012
ABSTRACT With the rapid increase of the population, the quantification of the impact from the hum... more ABSTRACT With the rapid increase of the population, the quantification of the impact from the human activities becomes critical not only for the environmental science but also the urban engineering under the global urbanization and climate change. This paper focused on the estimation of two human activity-related indexes, fractions of impervious surfaces and crop fields with remote sensing technology. Temporal mixture analysis (TMA) was applied to the sorted NDVI profile from MODIS to calculate the fractions of impervious surfaces and crop (plowed and paddy) fields in Japan. The optimal length of the sorted NDVI profile for accurate estimation was also investigated. The accuracy of fractional impervious surfaces was assessed by impervious surface map made by Landsat images; fractional plowed and paddy fields were assessed by local geographic database. The smallest RMSEs of the TMA were 0.096 for impervious surface, 0.177 for plowed field and 0.141 for paddy field, respectively. In summary, TMA has the potential to map impervious surfaces and crop fields over large areas.
Journal of Japan Society on Water Environment
Journal of Japan Society on Water Environment
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Papers by Takehiko Fukushima