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An increase in available nitrogen loading in intertidal ecosystems causes eutrophication and macroalgae blooms. Denitrification and anaerobic ammonium oxidation (anammox) lead to the removal of bioavailable nitrogen, but few studies have examined this in intertidal sediments. The sediment anammox and denitrification rates in September 2015 and November 2016 were measured using a 15N tracer technique at two sites, with and without macroalgae, in the hypereutrophic Yatsu tidal flat, eastern Japan. At both sites, the rate of N2 production via anammox was consistently low compared with that via denitrification, accounting for

The Fukushima Dai-ichi Nuclear Power Plant accident on 11 March 2011 released large amounts of radiocesium (134Cs and 137Cs) and contaminated the environment of Gunma Prefecture in eastern Japan. Concentrations of 640 Bq kg−1-wet radiocesium were found in wakasagi (Hypomesus nipponensis) in Lake Onuma on Mt. Akagi in Gunma Prefecture in August 2011. To elucidate the effect of body size on radiocesium levels in the Lake Onuma ecosystem, we determined age, body weight class, and radiocesium concentrations in wakasagi from 2012 to 2019. Furthermore, we estimated the effective ecological half-life of 137Cs using 137Cs concentration survey data and decay function models. A body size effect was found for the 137Cs concentration of wakasagi from 2012 to 2015, i.e., the 137Cs concentration increased with increased body weight. Conversely, no body size effect was found from 2016 to 2019. This may be due to the 137Cs concentration of the lake water stabilizing after May 2014, and wakasagi being a small plankton-feeding fish. The decay of the 137Cs concentration in wakasagi at age 0+ consisted of fast- and slow-term components, and the 137Cs concentration decay rate was greatly reduced. Although the radiocesium contamination level of wakasagi inhabiting Lake Onuma has decreased, contamination has continued and monitoring studies should be continued.

The Fukushima Daiichi Nuclear Power Plant accident on March 11, 2011 released substantial amounts of radiocesium (134Cs and 137Cs) and contaminated the environment across eastern Japan. In this study, we aimed to elucidate the temporal dynamics of 137Cs in the aquatic ecosystem of Lake Onuma, Mt. Akagi. We estimated the effective ecological half-life of 137Cs in fish and lake water, using 137Cs concentration survey data collected from 2011 to 2019, and single- and two-component decay function models (SDM and TDM, respectively). TDMs provided a good fit for 137Cs concentration decline processes in wakasagi (Hypomesus nipponensis), pale chub (Zacco platypus), and lake water. We concluded that 137Cs concentrations approached a state of dynamic equilibrium between these aquatic organisms (wakasagi and pale chub) and the lake water. However, SDMs better predicted decline processes in 137Cs concentrations in charr (Salvelinus leucomaenis), Japanese dace (Tribolodon hakonensis), and western waterweed (Elodea nuttallii). The 137Cs mass balance in Lake Onuma suggests that 137Cs may be eluted from the lake bottom sediments. In summary, 137Cs contamination levels in Lake Onuma have significantly decreased, but monitoring surveys should continue to further our understanding of the processes underlying this reduction.

Chionaster nivalis is frequently detected in thawing snowpacks and glaciers. However, the taxonomic position of this species above the genus level remains unclear. We herein conducted molecular analyses of C. nivalis using the ribosomal RNA operon sequences obtained from more than 200 cells of this species isolated from a field-collected material. Our molecular phylogenetic analyses revealed that C. nivalis is a sister to Bartheletia paradoxa, which is an orphan basal lineage of Agaricomycotina. We also showed that C. nivalis sequences were contained in several previously examined meta-amplicon sequence datasets from snowpacks and glaciers in the Northern Hemisphere and Antarctica.

Large quantities of radionuclides were released after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident on March 11, 2011. The e-book entitled Impacts of Fukushima Nuclear Accident on Freshwater Environments summarizes radionuclides accumulation and its effects on the ecosystem in the freshwater environment. This chapter introduces an overview of research with radiocesium in the freshwater environment presented in this book.

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in March 2011 emitted radioactive substances into the environment, contaminating the fishes in Lake Chuzenji. To evaluate the radioactive contamination in brown trout (Salmo trutta), we measured the concentration of cesium-137 (137Cs) in the muscle tissue and stomach contents in brown trout collected from Lake Chuzenji 7 years after the FDNPP accident. Throughout the period, there was considerable individual variation in 137Cs activity concentrations. The activity concentrations of 137Cs in brown trout were higher in spring and summer than in winter and autumn. Fish weight was the most significant factor affecting the activity concentrations of 137Cs in individual fish, and this size effect was significant in all seasons. Main prey items by intake of 137Cs in brown trout were invertebrates in winter and spring and fishes in summer and autumn. Further monitoring of radiocesium concentrations in brown trout (including information on intake and excretion of 137Cs) is needed to predict the long-term dynamics of radiocesium concentrations in these fish.

Lake Chūzenji in Tochigi Prefecture, Japan, was contaminated by radiocesium released during the Fukushima Dai-ichi Nuclear Power Plant accident on March 11, 2011. 137Cs activity in sediment from the center of the lake was 15,100 Bq/m2 after the accident. The sum of dissolved 137Cs in a layer of lake water at about 20 m depth and at the bottom water layer was high, accounting for about half of total dissolved 137Cs in the lake. The fluxes of 137Cs activity associated with sediment flow in and out of Lake Chūzenji from 2014 to 2016 were 161.8, 223.7, and 65.0 Bq/m2/year, respectively. In 2014, the total annual inflow and outflow of 137Cs activity in Lake Chūzenji were 1.34 and 2.0 GBq, resulting in a net outflow of 0.66 Bq which accounted for about 1% of the cumulative dose in the lake since the 2011 nuclear accident. The total 137Cs activity of suspended and dissolved matter in Lake Chūzenji in July 2015 were 28 and 36.2 GBq, respectively. About 40% of the 137Cs activity from the 2011 nuclear accident was still in lake water in 2014. 137Cs activity of sedimentation flux of Lake Chūzenji was 1.1%/year.

Remobilization of radiocesium from anoxic sediments can be an important mechanism responsible for long-term contaminations of lakes. However, it is unclear whether such remobilization occurs in shallow lakes, where concentrations of dissolved oxygen in the hypolimnion (bottom DO) change temporally in response to meteorological conditions, and whether remobilized radiocesium influences the activity in fish. We examined the seasonal dynamics of the activities of dissolved

It is important to understand the change in aquatic humic substances (AHS) induced by light due to the upward trend in ultraviolet (UV) radiation reaching the surface of the Earth. Changes in the q...

Understanding ecosystem dynamics of radionuclides is necessary to ensure effective management for food safety. The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident on March 11, 2011 released large amounts of radiocesium (134Cs and 137Cs) and contaminated the environment across eastern Japan. In this study, we aimed to elucidate the temporal dynamics of 137Cs in the aquatic ecosystem of Lake Onuma on Mt. Akagi. The effective ecological half-life (Teff) of 137Cs in fishes, western waterweed (Elodea nuttallii), seston (phytoplankton and zooplankton), and lake water was estimated using survey data of 137Cs concentration collected from 2011 to 2016, and single- and two-component decay function models (SDM and TDM, respectively). The decay processes of 137Cs concentrations in wakasagi (Hypomesus nipponensis), pale chub (Zacco platypus), phytoplankton, and total 137Cs concentrations of the water column (WC) in the lake were well suited by the TDMs. The Teff in the fast component of the TDMs in these samples ranged from 0.49 to 0.74years. The Teff in the slow component of the TDMs could converge towards the physical half-life of 137Cs. Nearly five and a half years after the FDNPP accident, we concluded that 137Cs concentrations approached a state of dynamic equilibrium between some aquatic organisms (wakasagi, pale chub, and phytoplankton) and the environment (lake water). However, the decay processes of 137Cs concentrations in Japanese dace (Tribolodon hakonensis), western waterweed, zooplankton, and particulate- and dissolved-forms in the WC were better predicted for the SDM. The total 137Cs concentrations in inflowing river and spring waters were one to two orders of magnitude lower than lake water under normal flow conditions. However, particulate 137Cs contamination level in the river water was high after heavy rains. Overall, 137Cs contamination levels have significantly decreased in Lake Onuma, but monitoring surveys should be continued for further understanding of the reduction processes.

The spatial distribution of radiation air dose was assessed on the floor of a secondary mixed forest located 35 km northwest of the Fukushima Daiichi Nuclear Power Plant. All trees with diameter at breast height ≥5 cm were measured and mapped within two plots. Radiation air doses were measured on the forest floor at each 1-m grid point and at stem bases and were analyzed in relation to bark texture, tree strata position, and leaf phenology. Radiocesium concentration measured from soils sampled in a similar manner (2-m grid point and at stem bases) in one of the two plots showed significant correlation with the air dose rate. Air dose rate showed a highly heterogeneous spatial distribution and tended to increase toward the stem bases. This trend was distinctive in some tree functional groups, with the rate being higher in some smaller deciduous trees with smooth bark (e.g. Fraxinus lanuginosa, Acer rufinerve). The trends were indistinctive in larger canopy trees with thick, coarse bark (Quercus mon...

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident has resulted in the contamination of the environment in Gunma Prefecture with radioisotope cesium (radio-Cs, 134Cs and 137Cs). Concentrations of radio-Cs >500Bqkg-1 were found in wakasagi (Hypomesus nipponensis) in Lake Onuma at the top of Mount (Mt.) Akagi in August 2011. To explain the mechanism of this contamination, monitoring studies have been conducted around Lake Onuma by measuring radio-Cs concentrations in samples of fish, aquatic plants, plankton, lake water, lake sediments, and surrounding soil. The leachability of radio-Cs was evaluated using sequential extraction by Tessier et al. The total concentration of radio-Cs in Lake Onuma ecosystems decreased gradually with time. In the brown forest soil, radio-Cs concentrations of 2000 to 6000Bqkg-1 were detected. The abundance ratio of the easy-elution form (exchangeable and carbonate forms) in the samples was

Remobilization of radiocesium from anoxic sediments can be an important mechanism responsible for long-term contaminations of lakes. However, it is unclear whether such remobilization occurs in shallow lakes, where concentrations of dissolved oxygen in the hypolimnion (bottom DO) change temporally in response to meteorological conditions, and whether remobilized radiocesium influences the activity in fish. We examined the seasonal dynamics of the activities of dissolved 137Cs and 137Cs in fish (pond smelt and crucian carp) from Lake Kasumigaura, a shallow, hypereutrophic lake, five years after the Fukushima Daiichi Nuclear Power Plant accident. The activities of both dissolved 137Cs and 137Cs in fish declined during that time, but the declines showed a clear seasonal pattern that included a summer peak of 137Cs activity. The activity of dissolved 137Cs increased when the bottom DO concentration decreased, and a nonlinear causality test revealed significant causal forcing of dissolved 137Cs activity by bottom DO. The fact that NH4-N concentrations in bottom waters were higher in the summer suggested that remobilization of 137Cs from sediments could result from highly selective ion-exchange with NH4-N. Despite the shallow depth of Lake Kasumigaura, winds had little influence bottom DO concentrations or dissolved 137Cs activities. The fact that seasonal means of 137Cs activities in pond smelt and crucian carp were positively correlated with the seasonal means of dissolved 137Cs activities suggested that remobilized 137Cs may have influenced the seasonal dynamics of radiocesium in fish through food-chain transfer, but higher feeding rates in warm water could may have also contributed to the seasonal dynamics of 137Cs activity in fish. Our findings suggest that in shallow lakes, intermittent but repeated hypoxic events may enhance remobilization of radiocesium from sediments, and remobilized radiocesium may contributed to long-term retention of radiocesium in aquatic organisms.

To provide new insights into microbial functions in the Kushiro Wetland, Japan, we measured vertical profiles of fluorescein diacetate hydrolysis (total microbial activity), β-glucosidase and xylosidase (organic matter decomposition), acid phosphatase (phosphate production) and potential denitrifying (denitrification) activities as microbial enzyme activities in soil to depths of approximately 1.5 m from two sites with different vegetation in November 2008 (winter) and August 2009 (summer). Active organic matter decomposition, phosphate production and denitrification were evident in shallow litter and peat layers, and total microbial activity was high. Almost no differences in decomposition and total microbial activity were observed between seasons, whereas phosphate production and denitrification were higher in summer. All activities were low in mid-depth volcanic-ash and clay layers because of low carbon, nitrogen and phosphorus levels. Surprisingly, the total microbial activity and decomposition in deep clay & peat and peat layers were the same as or higher than in shallow layers. However, denitrification was limited, probably because dissolved organic matter containing humic-like substances was unsuitable as a substrate. Moreover, total soil phosphorus levels, acid phosphatase activity and multiple linear regression analysis revealed that the soil in the Kushiro Wetland is likely P limited.

Diversity and community structure of fishes were studied in three neighbouring tributaries of the Mekong River in Thailand, namely the Mun, Songkhram and Gam Rivers. The rivers are located in the same ecoregion but have contrasting levels of both hydrological regulations and mitigation measures; the Mun River has a hydropower dam with a fish ladder and sluice gates that are opened during the wet season each year, the Gam River has several irrigation dams with a fish ladder at each dam site, and the Songkhram River has no dams along its river course. A total of 124 freshwater fish species were sampled in these rivers from August 2009 to June 2010. Overall species richness was highest in the Songkhram River (112), followed by the Mun (97) and Gam (54) Rivers. Average per site species richness was also significantly different among rivers but not among sampling months. Abundance–biomass comparison plots revealed considerably overlapping distributions of these two metrics from the dry to early rainy seasons in the Songkhram River and, to a lesser extent, in the Mun River. Fish assemblage data were classified into six clusters with similar community structure. Fish assemblages in the Gam River constituted a single cluster, while those in the other two rivers formed multiple clusters depending on the sampling season. The results of the cluster analysis are discussed in relation to the dominance of the three migration guilds (white, black, and grey fishes) of the Mekong River fishes. The effectiveness of the mitigation measures was determined to be limited in alleviating adverse impacts of dams in these tributaries of the Mekong River. Copyright © 2014 John Wiley & Sons, Ltd.

Understanding soil chemical properties is necessary to characterize the basic properties of ecosystems. In mangrove ecosystems, soil iron, phosphorus, methane and nitrogen have been well studied under field conditions. However, it is difficult to understand fundamental relationships between mangrove root functions and soil chemical properties, because of the multiple factors present in field data. The aim of this study was to clarify what will happen to soil chemical properties after mangrove plant colonize. To examine the effect of mangrove roots on these soil properties, three representative mangrove species (Avicennia marina, Rhizophora stylosa and Bruguiera gymnorrhiza) were cultivated in a greenhouse and selected soil chemical properties were monitored in comparison with those in unplanted soil. We detected oxidative effects in all three species, including deposition of iron oxide on root surfaces, lowered methane concentrations and increased oxidized inorganic nitrogen concentrations in the soil pore-water, suggesting that radial oxygen loss from mangrove roots had affected these soil chemical properties. Besides the oxidative effects, enhanced Fe2+ concentrations in the soil pore-water were present in A. marina, and enhanced phosphorus concentrations in the soil pore-water were present in all three species, suggesting that mangrove roots provide Fe- and phosphate-solubilizing substrates. The most remarkable change was in soil nitrogen enrichment. During the experimental period, amounts of nitrogen in the mangrove soils increased four times more than in uncolonized soil. Six months from the start of cultivation, bacterial nitrogen fixation (nitrogenase activity) was significantly higher in soil colonized by mangrove plants than in uncolonized soil, suggesting that mangrove roots stimulated bacterial nitrogen fixation. Among these properties, Phosphate mobilization and soil nitrogen enrichment are likely to be particularly important for the growth of mangrove plants, because phosphate and nitrogen are generally limited in mangrove ecosystems. This self-supporting ability of mangroves observed in this study could be one key to the high productivity of mangrove ecosystems.

Nitrogen is one of the most limiting elements for plant growth. Although nitrogen dynamics in mangrove forests are well understood at the ecosystem level, the nitrogen conditions in the root-zones of plants are less clear. The aim of this study was to analyze in detail the nitrogen conditions in the root zone of mangroves. We conducted a field survey in an area inhabited by three species of mangroves (Avicennia marina (Forsk.) Vierh., Rhizophora stylosa Griff. and Bruguiera gymnorrhiza (L.) Lam.). We collected soil and soil pore-water from the mangrove root zone, in which there were abundant fine roots, and from an area 10-cm away from the root zone (no-root zone). We determined soil organic nitrogen contents and concentrations of ammonium-N, nitrite-N and nitrate-N in soil pore-water along with soil temperature, NaCl and pH. We observed several common characteristics among the three mangrove species; in the root zone, pH was lower, soil organic matter content was higher, soil C:N was lower, and soil pore-water nitrite-N and nitrate-N were higher than their respective values in the no-root zone. These trends were observed in both summer and winter while soil temperature was about 10°C higher in summer than in winter. The fact that C:N was lower in the root zone than in the no-root zone suggests that bacterial nitrogen assimilation occurred near plant roots. The contrast in nitrogen content within a small scale (10 cm) between the root zone and no-root zone suggests that mangroves retain nitrogen source in their root zone. This property clearly works efficiently in intertidal habitats where tidal nitrogen export occurs naturally.

Kushiro Mire is the largest mire in Japan and in 1980 was the first wetland in Japan registered under the Ramsar Convention. Recent reports indicate an increase in nutrient loading into Kushiro Mire from changes in land use. We measured vertical profiles of dissolved inorganic nitrogen (DIN; NO3 –, NO2 –, NH4 +), dissolved organic carbon (DOC), and various types of microbial activity in soil samples collected to approximately 1.5 m deep at two sites in Kushiro Mire. We found an accumulation of NO3 – and DOC in the deeper soil. Denitrifying activity was highest in the shallower soils and decreased drastically with depth, whereas higher levels of fluoresceindiacetate hydrolysis, β-glucosidase, acid phosphatase, and xylosidase enzyme activity were found in the deeper layers. We also detected humic-like substances as components of the DOC. These results suggest that the DOC in the wetland soil cannot be used as a substrate for denitrification, causing denitrification to be suppressed in the deeper soil. In addition, denitrifying activity would be very low in the deeper layers due to low soil temperature. As a result, nitrogen input to the mire has resulted in a large accumulation of NO3 – in the deeper soil. This will eventually change the mire ecosystem through effects such as increased eutrophication and acidification.

(2009). Impacts of anthropogenic structural changes to the Mekong River watershed on seasonal hydrologic dynamics in the watershed and floodplain. SIL Proceedings, 1922-2010: Vol. 30, No. 5, pp. 794-800.

We measured fluxes of carbon dioxide (CO(2)), methane (CH(4)), and nitrous oxide (N(2)O) simultaneously in two typical fringing zones, sandy shore and salt marsh, of coastal lagoon, Lake Nakaumi, Japan, in mid-summer 2003. Our aim was to quantify net the greenhouse gases (GHGs) fluxes and examine key factors, which control variation of the GHGs fluxes in the two sites. Net CO(2) and CH(4) fluxes were markedly different between the two sites; magnitudes and variations of the both fluxes in sandy shore were lower than those of salt marsh. Meanwhile, magnitude and variation of net N(2)O flux in the two sites were similar. In sandy shore, temporal and spatial variation of the three GHGs fluxes were highly controlled by water level fluctuation derived from astronomic tide. In salt marsh, spatial variation of the three GHGs fluxes were correlated with aboveground biomass, and temporal variation of CO(2) and CH(4) fluxes were correlated with soil temperature. The sum of global warming potential, which was roughly estimated using the observed GHGs fluxes, was ca. 174-fold higher in salt marsh than in sandy shore.

Speciation of Al, including inorganic monomeric Al (Ali, the sum of aquo, hydroxy and inorganically complexed forms), organic monomeric Al (Alo, the organically complexed form), and colloidal mineral Al (Alc, the fine particulate form that passes through a 0.4-μm pore size membrane filter), was investigated in stream waters (pH 6–8) of 4 watersheds in Japan. Total dissolved Al (Alt, the sum of Alc, Ali and Alo) ranged from 0.03 to 3.31 μM, and Alc was a minor component ( 1 μM). In spite of the variation in the range of reactive Al (Alr, the sum of Ali and Alo) in the 4 watersheds (Miomote, 0.03–3.27 μM; Tsukuba, 0.06–0.71 μM; Dorokawa, 0.05–0.71 μM; Tama, 0.03–0.38 μM), the entire data set for Alr could be expressed as a function of the ratio of dissolved organic C (DOC) and Ca: [Alr (μM)] = 0.13 [DOC/Ca (mol/mol)] + 0.11 (r = 0.86, P NO 3 - + SO 4 2 - in stream waters, a high level of Ca (instead of Al) is serving as a major counterion for NO 3 - + SO 4 2 - . However, an additional loading of acidic deposition may result in shortage of Ca and mobilization of Al as a counterion for NO 3 - + SO 4 2 - , and continuous observation of the speciation of Al in Japanese stream waters may reveal future change in the conditions for mobilization of Al from “low Ca and high DOC” to “low Ca and high NO 3 - + SO 4 2 - ”.

尾瀬ヶ原では例年5月～6月の融雪時期にアカシボと呼ばれる彩雪現象がみられる。この着色の原因は, 雪中の赤褐色粒子に起因し, 融雪時期に積雪下の湿原表面から雪原表層にむけての水の動きに従い着色が進み, 融雪の後期には雪原表面全体に赤褐色化が拡大する。赤褐色粒子は緑藻類, Phacotaceae科Hemitoma sp. の休眠胞子で, 被殻には多量の酸化鉄が存在した。この赤褐色粒子数は雪の中の全鉄量と高い相関関係があった。尾瀬ヶ原のアカシボ現象はHemitoma 属の休眠胞子に由来すると推測した。

春の融雪期に, 尾瀬ケ原の一部で, 例年「アカシボ」と呼ばれる彩雪現象がみられる。このアカシボ雪の中や表面に, 線虫類, ソコミジンコ類, ケンミジンコ類, ミズダニ類, クマムシ類, 貧毛類, ガガンボ科幼虫, ヌカカ科幼虫, ユスリカ科幼虫などが出現した。この中でも特に, ソコミジンコ類, 貧毛類, ガガンボ科幼虫, ヌカカ科幼虫, ユスリカ科幼虫の密度が高かった。見本園アカシボの総密度は雪中で2.4～3.6×104個体m-2, 雪表面で0.3～2.2×103個体m-2であった。見本園の根雪前, 融雪後のアカシボ残存物中にはアカシボ雪と共通の分類群が出現することより, アカシボ雪の無脊椎動物は湿原の土壌動物に由来するものと推定された。土壌動物がアカシボ雪中に移動する原因として, 融雪期に積雪下の地表面が湛水すること, 溶存酸素濃度が低下すること, さらにアカシボ雪の形成時にFe2+の酸化のために, 酸素が消費され, 雪中の酸素濃度が低下することが推定された。雪原食物網研究の重要性について考察した。

Estimation of the isotopic turnover rate in the tissues of organisms allows us to estimate the temporal relationship between the isotope ratio of an organism and its prey, and to analyze seasonal variations of food webs and migratory patterns of animals. We analyzed the isotopic turnover rate in the tissue of lacustrine sockeye salmon, Oncorhynchus nerka, of three age classes in a laboratory food alteration experiment to clarify the isotopic turnover rate. The contribution of growth to isotopic turnover was higher in young and fast-growing lacustrine sockeye salmon than in older and slow-growing fish. Maturation masks the relationship between the contributions of growth and metabolism to isotopic change. Our estimate of the isotopic time lag of lacustrine sockeye salmon can be used to research trophic relationships of anadromous sockeye salmon.

This reseach aims at investigating about vegetation changes and topographic feature in the delta of Obitsu estuary, while comparing this time (2001) and the past vegetation maps (1974, 1995, 1984). The change of geographical feature using the vegetation maps in 1974, 1984, 1995 and 2001 was found that in north sandbar, the creek connected with seaside in 1974, but it was closed a part by deposition of sand in 2001. In south sandbar, the distribution of Pinus thunbergii community was confirmedon the south in 1974, but a part of Pinus thunbergii community was eroded in 2001. The sandbank was expanded from 1974 to 2001. Compared with vegetation maps in 1974, 1984, 1995 and 2001, the area of the back marsh vegetation was expanded from 1974 to 2001. In regard to the area of each vegetation type in 1974, 1984, 1995 and 2001, the salt swamp plant community of covered water type at high tide, such as Phragmites australis community, Carex pumila corrununity, Calystegia soldanella community were reduced, and that of uncovered water type at high tide, such as Phacelurus latifolus community was expanded. Sand dune community, grassland plant community and woody plant community were reduced. Ruderal plant community such as Pueraria lobata community, Solidago altissima community was expanded.

1998年3月から2003年5月の融雪期に東北地方に発生した47地点の赤雪についての原因調査を行った。赤雪中には赤褐色の粒子が多数存在し,高濃度のFeが含まれていた。この赤褐色の粒子の多くは緑藻Hemitoma sp.の休眠胞子であり,粒子数と全Fe含有量とのあいだには高い相関関係があった。赤雪の発生地域は融雪時期に積雪下層部と湿原もしくは土壌との境界面に流れた水が留まる窪地であった。休眠胞子形成の時期や胞子形成の機構は不明であるが,融雪期に融雪水の動きに伴って積雪中を移動し,雪の表層にあらわれ出てくるため,雪が赤褐色に着色するものと推定した。

底泥中の酵素活性は空間的,時間的に変動するため,干潟底泥の酵素活性から干潟生態系の機能を評価するには適切に試料採取する必要がある。本報告では,適切な試料採取法を検討するために,小櫃川河口の盤洲干潟において2001年6,9月に調査を行い,7個所の調査地点で5層位(0-75mm)から底泥試料を採取し,3種類の酵素活性(エステラーゼ,EST;β-グルコシダーゼ,GLU;β-アセチルグルコサミニダーゼ,AGA)を測定し,酵素活性の分布と変動および変動要因を調べた。計70点の試料についての平均値と標準偏差はそれぞれ0.022±0.012 unit g-1h -1 (EST),10.4±8.5μmol g-1h-1 (GLU),6.8±5,0μmol g-1h-1 (AGA)であった。調査時期,地点,層位の酵素活性への影響を3元分散分析法で解析した結果,調査地点,層位および両者の交互作用は有意に寄与していた。一方,表層(0-15mm)の14試料を除いた56試料について分散分析を行った結果,地点間差は酵素活性の変動に有意に寄与していたが,層位はGLUとAGAの変動に対しては有意でなかった。以上の結果から,干潟底泥の酵素活性を評価するには表層を除いたある層位から試料を採取することにより採取誤差が軽減できる事が示された。

干潟生態系の有機物分解機能を底泥の酵素活性から評価する事を目的として,日本国内5地域(北海道東部,東京湾,伊勢湾,有明海,八重山諸島),13箇所の干潟において夏季干潮時に底泥を採取し,セルロース分解酵素(セルラーゼ,CEL)及びキチン分解酵素(β-アセチルグルコサミニダーゼ,AGA)活性を,それぞれカルボキシルメチルセルロースとp-ニトロフェニル-b-D-グルコサミドを基質として測定した。その結果,CEL活性は2-30nmolg-1h-1,AGA活性は10-140nmolg-1h-1の範囲で干潟問で大きな差が認められた。これらの酵素活性の間には高い相関が見られた。また、これらの酵素活性と底泥の有機物量,シルト粘土含量の間には概ね正の相関が認められ,泥質で有機物含量の高い干潟で酵素活性は高く,分解機能も高いことが示唆された。また,甲殻類の多い干潟ではAGA活性が相対的に高い傾向が見られた。これらの結果から,干潟底泥の酵素活性は干潟の理化学性,生物特性によって大きく変動し,分解機能の指標の一つになると考えられた。

We studied the role of adventitious roots in supplying water to Ipomoea pes-caprae growing on sand dunes at Yagaji, Okinawa, Japan. For this purpose, all of the adventitious roots were dug up and the diurnal changes in stomatal conductance (at 7:00, 12:00 and 17:00) and leaf water potential (at predawn and 12:00) were measured at various distances from the taproot in January and June. Digging up roots had significant influences on stomatal conductance (at 7:00 in January and at 17:00 in June) and water potential (except for predawn water potential in January), though no significant differences could be detected in stomatal conductance and water potential between the control and treated plants in other measurements. Moreover, a close linear relationship between water potential and distance from the taproot could not be detected. These results suggest that the adventitious roots are not so useful for supplying water to the mother plant and the demand of water in leaves attached at every position on the vine was supplied from the taproot.

The restoration of the wetland ecosystems is an essential problem in the world, however, the evaluation technique for the functions of ecosystems, especially in the intertidal wetlands, has not been established still in spite of the ecosystems adjoining with the human life. The Functions of a wetland tend to roughly correspond with characteristics of both the water and sediments of the wetland. In this study, the 13 intertidal sandy and muddy flat wetlands were selected from Hokkaido to Okinawa, and the indicators for water and sediments were investigated as a first step of the functional ecosystem assessment in Japan. The classification for traditional landform subclass, i. e. fore-beach, estuary and lagoon, was unclearly changeable, and it often did not agree with the functional classification. In the intertidal sandy and muddy flat wetlands in Japan, the subclass fo HGM Approach should be set corresponding to the characteristics of influent water and sediments, and it was considered that the ecosystem evaluation should be carried out in each Hydrogeomorphic Unit classified at smaller-scale than the original HGM Approach in U.S.

The migration of Siamese mud carp (Henicorhynchus siamensis and H. lobatus), two of the most economically important fish species in the Mekong River, was studied using an otolith microchemistry technique. Fish and river water samples were collected in seven regions throughout the whole basin in Thailand, Laos and Cambodia over a 4 year study period. There was coherence between the elements in the ambient water and on the surface of the otoliths, with strontium (Sr) and barium (Ba) showing the strongest correlation. The partition coefficients were 0.409-0.496 for Sr and 0.055 for Ba. Otolith Sr-Ba profiles indicated extensive synchronized migrations with similar natal origins among individuals within the same region. H. siamensis movement has been severely suppressed in a tributary system where a series of irrigation dams has blocked their migration. H. lobatus collected both below and above the Khone Falls in the mainstream Mekong exhibited statistically different otolith surface elemental signatures but similar core elemental signatures. This result suggests a population originating from a single natal origin but bypassing the waterfalls through a passable side channel where a major hydroelectric dam is planned. The potential effects of damming in the Mekong River are discussed.

(2000). Significance of dissolved organic matter in a mire pool ecosystem. SIL Proceedings, 1922-2010: Vol. 27, No. 3, pp. 1649-1652.

Pesticide residues in rainwater were investigated for the estimation of pesticide flux into a lake in Ibaraki Prefecture during the 1990 rainy season. The maximum concentration of oxiadiazon in the rainwater was 4.2μg l-1. The maximum concentrations of fenobucarb, fenitrothion and edifenphos in the rainwater were 0.58, 0.53 and 0.36μg l-1, respectively. The annual ratio of fenitrothion redeposition by rainfall was estimated at 1.5% of the total shipping amount in Ibaraki Prefecture. There was no significant difference between redepositions of pesticides by rainfall and shipping amounts in the prefecture (α= 0.05). Pesticide residues in lake water were investigated in Lake Nakanuma, Ibaraki Prefecture, from March to December 1990. The concentrations of molinate, simetryn, iprobenfos, and thiobencarb in irrigation canal water were in the high range (>1.2μg l-1). The concentrations of diazinon, malathion, and fenthion in the water were at a lower level (

Pesticide residues in water and an aquatic plant, Nelumbo nucifera , were investigated near a river mouth in Edosakiiri Bay, Lake Kasumigaura, from April to December, 1986. The maximum concentrations of fenobucarb, diazinon, iprobenfos and simetryn in the water were 1.6, 1.1, 24, and 2.4 μg 1 −1 , respectively. We detected simetryn with peak width at half height for one month, and diazinon with that for two months. The seasonal changes in simetryn concentration in N. nucifera were similar to those in the water. The simetryn residue concentration was highest in the lamina (300 μg kg −1 ) among the various plant organs. The residue and bioconcentration factor 6.0 in June for simetryn were lower than the reported values for aquatic plants.

The growth of Nelumbo nucifera GAERTN. was investigated at an artificial stand in outdoor concrete ponds. The ratio of above- to below-ground biomass (T/R ratio) ranged from 0.3 to 3. Although N. nucifera is a perennial, the reproductive organ (tuber) begins to form later in the growing period than in annual plants; in addition, the life span of the tuber is less than one year. Maximum relative growth rate was 0.037 g⋅g-1⋅day-1 in July.The leaf area index of floating leaves did not exceed 1 m2⋅m-2.The influence of initial tuber density on the foliage structure and below-ground biomass of N. nucifera were investigated. The initial death rate at the time of lamina rolling increased with leaf density. Control of the density of floating leaves was done twice ; once at the early stage of lamina rolling, and again at the late stage of the fully expanded leaf. The below-ground biomass in the following spring did not correlate with initial tuber size. When the tuber biomass was under about 400 g dry weight⋅m-2, net production of below-ground biomass of the N. nucifera stand seems to have attained a plus value. N. nucifera exhibited typical pioneer characteristics in an environment of frequent disturbances such as flooding, i.e., a high T/R ratio, high vegetative propagation by stolons and a short life span of the tuber.