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Phosphate (POOur method comprises (1) POPOWe demonstrated the utility of ZrME for purification of PO

Nanomolar concentrations of NH2OH in natural water sources were determined using an Fe3+ oxidation method. A pH of 2.35 - 2.50 was used, which was adjusted by adding a chloroacetate buffer. Equal amounts (1.0 mL) of the chloroacetate solution and ferric chloride solution were added to the water sample (70 mL) to oxidize NH2OH to N2O. The resulting N2O in the sample water was then quantified by headspace analysis using a gas chromatograph with an electron-capture detector (ECD), where a limit of detection of 0.2 μgN L-1 (14 nmol L-1) was achieved. This method was successfully applied to samples of freshwater, brackish water, and seawater, and despite the various salinities no interfering substances were observed. Furthermore, NH2OH was successfully detected in samples collected from the Hii River and Lakes Shinji and Nakaumi (Shimane Prefecture, Japan). In addition, the proposed method was also applicable to samples rich in organic substance derived from phytoplankton.

We developed a method for quantifying trace NH2OH in brackish- and sea-water samples. Previously reported methods applicable to fresh water cannot be applied to such samples. We determined that interference in seawater owing to the bromide ion can be removed by the addition of phenol. In our procedure, phenol and hypochlorite solutions were added to a sample solution to oxidize NH2OH to N2O. N2O in the sample was then quantified by headspace analysis. The method is not affected by the salt content or ammonia, nitrate, or nitrite at concentrations of 300 μgN L-1 or less. It has a limit of detection of 0.2 μgN L-1, and can quantify NH2OH in natural water samples with a wide range of salinity. It was applied to samples from Lake Nakaumi, a brackish lake located in the eastern part of Shimane Prefecture, Japan.

Even though the interaction between water movements and aquatic plant is crucial for the aquatic ecosystem management, the importance of water turbulence in this regard is not well documented. To add to our knowledge on the interaction between aquatic plant communities and water turbulence, this study examined turbulence, plant, sediment and water quality at the reed community (Phragmites australis) in the Lake Shinji, Japan. Observations were conducted along transects perpendicular to the shoreline. For each transect, reed communities were observed at land ward side, centre, water ward and the outside of the reed community. An elevated level of turbulence was observed outside compared to inside reed community, where the magnitude of turbulence decreased with distance into the community interior. A significant positive correlation was observed for turbulence and surface-dissolved oxygen where the latter was negatively correlated to reed density. Sediment composition was affected by water turbulence where the content of coarse particles positively correlated to turbulence. Accumulation of organic matter in anoxic sediments together with fine particles was observed under low turbulence. Our findings can offer insight into understanding the interactions between turbulence and aquatic plant communities.

Cascading effects of pesticide use It is now well known that neonicotinoids negatively affect pollinators. As research has expanded, it has become clear that these globally used insecticides directly affect other ecosystem components, including vertebrates. Yamamuro et al. now show that these compounds are indirectly affecting species through trophic cascades (see the Perspective by Jensen). Since the application of neonicotinoids to agricultural fields began in the 1990s, zooplankton biomass has plummeted in a Japanese lake surrounded by these fields. This decline has led to shifts in food web structure and a collapse of two commercially harvested freshwater fish species. The authors argue that such dynamics are likely occurring widely. Science , this issue p. 620 ; see also p. 566

This study aimed to evaluate the loading of nutrients of agricultural origin. We investigated monthly nutrient concentrations at 11 stations located in the Hii River, Japan. The nitrogen and oxygen stable isotope ratios in nitrate were applied to distinguish the origin of nitrogen, i.e., from fertilizers applied to paddy fields or from sewage. Although total nitrogen (TN), presumably from transboundary air pollution, was mainly loaded during the cooler season, nitrate originating from fertilizers applied to paddy fields became the main source of nitrogen in the river water during the warmer season. Phosphorus was mainly added in particulate form, and showed increased loading at the upstream stations in the warmer season, but not in the cooler season. Potassium and magnesium—components of fertilizers—showed an increasing trend in the downstream section of the paddy fields. Our results suggest that controlled application of fertilizers is necessary to decrease the nitrogen loads originating from farmlands, particularly from paddy fields. Since the nitrogen isotope of TN in fertilizer showed significantly lower values (mean value −4.6 ‰) than that in river water (mean value 1.8 ‰) or treated water (mean value 21.9 ‰), we could use these values to determine the contribution of TN from fertilizers to river water quality, and can use them to monitor fertilization levels in watersheds.

Geosmin is an earthy-muddy smelling compound produced in aquatic ecosystems by microorganisms including cyanobacteria. An increase in geosmin levels affecting the local fishery occurred in May 2007 in Lake Shinji, Japan, and geosmin-producing colonial cyanobacterium, Coelosphaerium sp. G2, was isolated from a water sample from the lake and identified. Cyanobacteria Coelosphaerium sp. is commonly found in Lake Shinji; however, prior to 2007, earthy-muddy odors were not a frequent issue. Further, there was no information regarding the geosmin biosynthetic gene in colonial cyanobacteria. Here, the geosmin biosynthetic gene (geoA) in strain G2 was identified and its nucleotide sequence was determined. It was found that geoA had 79% and 78% identity with geoA from filamentous geosmin-producing cyanobacteria Fischerella sp. PCC 9431 and geoA2 from Phormidium sp. P2r, respectively. The deduced amino acid sequence of GeoA consisted of two domains that were annotated as terpene cyclase. In 2015, geosmin non-producing Coelosphaerium sp. S3C5 was isolated from Lake Shinji and identified by morphological and genetic analyses. There was no difference in morphology or nucleotide sequences of 16S rRNA and 16S-23S internal transcribed spacer (ITS) between geosmin-producing and non-producing strains, which are therefore closely related and can exist in Lake Shinji. Distinguishing the two strains by observation under a microscope and sequencing of 16S rRNA and 16S-23S ITS have proven difficult. Inconsistency between the appearance of Coelosphaerium cells and the detection of the odor in water samples could therefore be attributed to dominance by the geosmin-producing strain or the non-producing strain. The increase in earthy smell is assumed to be caused by an increase in the geosmin-producing strain in Lake Shinji. Genetic analysis of geoA in Coelosphaerium sp. and the relative abundances of geosmin-producing and non-producing Coelosphaerium strains in Lake Shinji can be used to mitigate the economic damages caused by geosmin. Development of a molecular method to monitor the geosmin-producing strain in water ecosystems is equally important to alleviate the earthy smell caused by this particular strain.

Deposition of atmospheric nutrients is known to alter oligotrophic ecosystems such as the open ocean, but the role of such nutrients in the further deterioration of eutrophic aquatic ecosystems is largely unknown. The Hii River watershed in Japan encompasses lagoons that have been eutrophic since 1980s. This study examined the atmospheric deposition of nitrogen and phosphorus in the Hii River watershed and the nitrogen and phosphorus concentrations in the Hii River over an 11-yr period. Total nitrogen (TN) concentrations of both precipitation and river water were significantly higher in cold months (November–March) than in warm months (April–October). Most of the TN was nitrate, which suggests that the TN source was atmospheric nitrogen from East Asia transported by seasonal winds. In contrast, total phosphorus (TP) concentrations of both precipitation and river water were significantly higher in warm months. Over time, the TN concentration in the river water showed a decreasing trend although the trend was not significant, while the TP concentration increased significantly. This was attributed to an increase in the atmospheric deposition of TP originating from East Asia since 2000. The increase in the deposition of atmospheric phosphorus might also have increased phosphorus leakage from the soils. In this work, the TN : TP ratios for both atmospheric deposition and river water indicate that changes in atmospheric nutrient deposition affect loading rates and N : P ratios. These changes, especially the latter, could have significant ecological effects in eutrophic systems by lowering the N : P ratios, which could induce cyanobacteria blooms.

A simple and rapid in situ method for the determination of hydrazine based on the concentration of aldazine compound formed by the reaction of hydrazine with p-dimethylaminobenzaldehyde was developed. This method was based on solid-phase extraction using a Sep-Pak C18 cartridge, followed by the quantification of hydrazine using a spectrophotometric method. To a sample solution of environmental water, p-dimethylaminobenzaldehyde solution was added to form aldazine by the reaction with hydrazine. The solution was passed through a Sep-Pak C18 cartridge for the adsorption of aldazine. In the laboratory, the aldazine adsorbed on the Sep-Pak C18 cartridge was eluted by passing a hydrochloric acid-ethanol (1:10) solution through the cartridge, and the color intensity of the solution was measured at 457 nm. The limit of detection for the new method was 0.2 mgN L-1 of hydrazine. The determination of hydrazine in solution was not influenced even by hydrogen sulfide and organic matter. This method was then applied to the brackish water of Lake Nakaumi in the eastern area of Shimane Prefecture, Japan. This method was used to determine hydrazine in freshwater, seawater and wastwater.

Estuarine ecosystems are easily deteriorated by organic pollution because of its high primary productivity. To identify chemical proxies for the possible sources of autochthonous organic matter [phytoplankton-derived particulate organic material (POM), macroalgae and seagrass], we measured C:N:P and the ratios of carbon and nitrogen stable isotopes (δ13C and δ15N values) in two estuarine environments, the polyhaline lagoon, Lake Nakaumi, and the oligohaline lagoon, Lake Shinji, in Japan. Due to vigorous photosynthesis, the δ13C of phytoplankton-derived POM in Lake Nakaumi was larger than what would normally be expected from estuarine salinity gradients. Concentrations of nitrogen and phosphorus did not affect the δ13C of phytoplankton-derived POM. The δ15N of all plants was uniform and was higher than the δ15N of sediments. The seagrass showed a higher C:N ratio than POM and macroalgae, while the macroalgae showed a higher N:P ratio. Thus, simultaneous evaluation of C:N and N:P ratios would distinguish these three plant groups, and it would be possible to identify the source plants from the elemental ratios of the sediments.

In Lake Shinji, Japan, periodic outbreaks of musty odour have occurred since mid-May 2007. Although the substance responsible for the odour was identified as geosmin, the odour-producing organism was unknown. We cultivated an axenic unialgal strain and determined that a species of Coelosphaerium (Synechococcales) was responsible for the production of geosmin in Lake Shinji. Our analysis was conducted using gas chromatography/mass spectrometry to determine the odorous compound. To determine the algae species, it was observed by optical microscopy to describe its morphological characteristics and the polymerase chain reaction was used to characterise the nucleotide sequence of the 16S rRNA gene and the 16S-23S rRNA internal transcribed spacer region. In addition, we explored the relationship between the number of cells of the Coelosphaerium sp. and the concentration of geosmin. In conclusion, geosmin, the cause of the musty odour in Lake Shinji in autumn 2009, was produced by Coelosphaerium sp., and to our knowledge, this is the first report of a geosmin-producing species in the family Coelosphaeriaceae.

A method for determination of hydrogen sulfide in microsamples (200 μL) was developed by modifying the methylene blue method. Samples were collected using a micropipette and were combined with sulfide coloring reagent and 5 mL of 0.1 M HCl in test tubes. Absorbance of the solution was measured spectrophotometrically at 667 nm. This modified method did not require any special labware or technique, and can be used in a variety of research fields.

In situ phosphorus release rates in three contiguous shallow brackish lakes were calculated by considering the amount of water inflow, changes in salinity and phosphorus stock, and loading from phosphorus inflow based on monthly data. The annual amount of sedimental phosphorus relative to that of phosphorus inflow was different for each of the three water bodies: 16% for Lake Shinji, 3% for the Honjo area, and −8% for Lake Nakaumi, as estimated in a 10-year period from January 1993 to December 2002. During the warm season, the quantity of phosphorus released surpassed sedimentation in these three water bodies. The low annual sedimentation ratio in Lake Nakaumi is related to a large seawater backflow resulting in phosphorus removal, in addition to a stable stratified structure promoting phosphorus release from sediment due to oxygen depletion in the lower layer. In Lake Nakaumi, field data shows that if dissolved oxygen at the sediment surface falls below 2.54 mg L−1, phosphorus release from the sediment begins to be accelerated.

We collected rainwater samples from every rainfall in Matsue, Japan in order to study variations of nitrogen and phosphorus concentrations over time. The seasonal average concentration by magnitude order of Total Nitrogen (here after T-N) was highest in winter, then in spring, fall, and summer and that of Total Phosphorus (here after T-P) was highest in spring, then in winter, fall, and summer. These seasonal variations were examined in relation to the transportation paths of arrived air masses by using a backward trajectory and rainfall patterns from a surface synoptic weather chart. In winter, continental air masses frequently flow from China or Siberia and the resultant winter rainfall is on many occasions of a continental type. In summer, maritime air masses frequently arrive from the Pacific Ocean and this resultant rainfall therefore was often of maritime type. Looking at average concentrations of T-N and T-P for each rainfall type, continental types were high range and maritime types were low. It was therefore concluded that the monthly average concentration of T-N was affected by continental air masses from northern China in winter and by maritime ones from the Pacific Ocean in summer. The maximum deposition of T-N was caused by this concentration in winter and rainfall depth in summer. Seasonal variation of T-P showed a different fluctuation tendency from T-N, with a maximum concentration in spring, and minimum in summer and fall. T-P was susceptible to the yellow sand phenomenon which maximised T-P deposition in spring.

To study the long-term change in nutrient loads from the Hii River to Lake Shinji, water samples were taken repeatedly over a year in 1983/1984 and again in 2001/2002. Annual total nitrogen (TN) loads, estimated from observations of water quality and river flow, increased from 860 to 920 t with a corresponding increase in NO3–N concentration during the cool season. In contrast, total phosphorus (TP) loads decreased from 96 to 62 t. Annual TN and TP loads, calculated using emission factors and annual statistics for the catchments, showed a tendency to decline from 1986 to 2002. No source could be identified which would result in the increase in TN in the catchments, therefore, the increase in observed TN loads was considered to originate in other areas. Atmospheric nitrogen deposition transported from long distances has elevated the sum of NH4–N and NO3–N concentration in rainwater in the cool season. Therefore, it was considered that this resulted in the increase in TN loads in the Hii River.

Submerged aquatic vegetation (SAV) aids in maintaining a clear stable state in shallow lakes. However, charophytes are more effective in increasing transparency compared to angiosperms. Lake Shinji was more transparent prior to the beginning of herbicide use for rice weed control in the mid-1950s, because its bottom was covered by SAV up to 3 m depth. Although Chara braunii C.C. Gmelin and Nitella hyaline (De Candolle) C. Agardh were recorded in the 1960s, there are no reports on SAV in the 1950s. Therefore, in the present study, we aimed to show that the SAV of Lake Shinji was mostly composed of charophytes prior to the 1950s, by conducting a seed analysis. We obtained charophyte oospores from the sediment, but seeds of angiosperms were not identified. In addition to C. braunii that was previously recorded in Lake Shinji, we also found two newly identified species, Chara corallina Willdenow and Chara fibrosa C. Agardh ex Bruzelius. Overall, this study indicates that seed analysis is helpful in reconstructing the former flora of Lake Shinji.

We analysed nutrients and basic ions (Na, Cl, K, Mg, Si, Ca, and SO4) for a period of 1 year, including every precipitation event, and sampled stream water every 2 weeks from a forest catchment in Shimane Prefecture, Japan. Backward-trajectory analysis revealed that some air masses originated within Japan, but did not affect the precipitation chemistry. Air masses originating from northern China were positively correlated with nutrients and all basic ions. Concentrations of ammonium and dissolved organic nitrogen were much lower in stream water than in precipitation, while those of nitrate and particulate nitrogen were similar in stream water and precipitation. Unlike nitrogen, the dissolved phosphorus concentration was much higher in stream water than in precipitation. Both phosphate and dissolved organic phosphorus (DOP) levels were higher in stream water than in precipitation. Particulate phosphorus (PP) concentrations were very similar in precipitation and stream water. PP showed stronger correlations than potassium with suspended solids (SS) and flow rate, while phosphate and DOP were more strongly correlated with potassium than with SS or flow rate. Stream silica concentrations were not correlated with phosphate but did exhibit a significant negative correlation with DOP. Neither phosphate nor DOP was correlated with calcium. These results suggest that phosphorus is not leaching with silica or calcium as a paired cation, but rather with potassium in this area. Lower nitrogen concentrations in stream water than in precipitation can be attributed to an enhanced uptake of nitrogen by forest soils owing to the increased atmospheric deposition of phosphorus.

A response in movement of a two-layered water body in Lake Nakaumi to a strong wind, which suddenly rose and continued for 15 h with nearly constant speed and direction, was observed using the current and salinity meters situated at two points in the lake. At the initial stage of water movement, large fluctuations in current velocity in reverse directions were observed in the upper and lower layers, accompanied by mixing between the two layers. At the stationary stage following the initial stage, current velocities in the upper and lower layers were kept constant, as was salinity. It was considered that a slab-type flow, which enhanced mixing between the two layers, occurred at the initial stage in water movement, then changed into a steady circulation flow at the stationary stage with completion of the set up in the two-layered structure.

We measured the abundance and biomass of the major taxonomic groups of mesozooplankton at six stations in Lake Shinji–Ohashi River–Lake Nakaumi brackish-water system, Japan, monthly for three full years (1995–1997), except for one station (for 1 year and 9 months). Over the entire area, copepods overwhelmingly dominated the zooplankton community both in terms of abundance (mean: 87.9%) and biomass (83.4%). The remaining taxa were cladocerans (i.e. Diphanosoma brachyurum, Evadone tergestina, Penilia avirostris, Podon leuckarti and Podon polyphemoides), appendicularians (Oikopleura dioica and Oikopleura longicauda), chaetognaths (Sagitta crassa) and the larvae of benthos (e.g. polychaetes, bivalves, gastropods and malacostracans). The geographical and seasonal variations of the mesozooplankton community were therefore principally explained by the variations of the copepod community. The geographical difference in copepod species composition was associated with salinity preference or tolerance of respective species. In Lake Shinji, where the salinity was lowest (mean: 4.0), Sinocalanus tenellus was monospecifically abundant with sporadic occurrence of Pseudodiaptomus inopinus. In Ohashi River (mean salinity: 9.9), Acartia hudsonica, Acartia sinjiensis, Eurytemora pacifica and Oithona davisae added to the community. At central and southeast Lake Nakaumi and in Honjo District, where mean salinity ranged from 16.4 to 21.7, these four species became more important than S. tenellus and P. inopinus. At the entrance of Sakai Strait, where the salinity was highest (mean: 24.0), Paracalanus spp. constituted a significant component. Due to large temperature fluctuation with season, the copepods showed remarkable seasonal variations in abundance and biomass, with enormous annual peaks in winter–spring. These annual peaks might be attributed to scarce occurrence of predators.

In a coastal lagoon, Lake Shinji, saline water intrusion frequently occurs from the lower Ohashi River. Continuous observation of current velocity, salinity and water level in the Ohashi River revealed that intermittent intrusions takes place when diurnal periods of astronomical tide coincide with the rising stage of meteorological tides during a low discharge from the influent Hii River.The dynamics of tidal currents and saline transport in the Ohashi River were examined by numerical simulation with a simplified one-dimensional model using water level and salinity data from both river-channel ends. The calculated results reproduced well the observed time series of current velocity and salinity, though some disparity appeared under the two-layered structure. Related phenomena following the intrusion were described with respect to the formation of the stratified structure in Lake Shinji.

Continuous observation of density (water temperature and salinity), horizontal velocity and turbidity was performed in a brackish lake, Lake Shinji. Response of velocity field and mixing events in the bottom layer of the lake were observed during a severe storm passage. In the former period just after the strong wind started to blow, active entrainment was observed, while in the latter period, weaker entrainment was found accompanied with circulations separately developed in the upper and lower layers due to the wind set-up of the density interface. Turbidity maximum during the latter period suggests that a large amount of resuspension occurred due to wave motion even under stratified conditions.

We have conducted a continuous measurement of temperature and water quality in a littoral zone of a brackish lake, Lake Shinji, where filter-feeding bivalves (Corbicula japonica) are densely populated. Daytime heating and nighttime cooling created density gradients that drove strong horizontal mass exchange. Simultaneous measurement of Chlorophyl a. concentration suggests that this circuration, especially during cooling period, mainly supports feeding of phytoplankton by bivalves which are habited at the lake bottom, and thus controls natural purification process through benthic-pelagic coupling.

Three kinds of experimental methods are proposed to investigate nutrient release rate fbom the sediment and sediment oxygen demand (SOD). The first method is a continuous-flow incubation method with non-disturbed core sample of the sediment, and is suitable for conventionai use. The second is perfomed with a rectangular, closed nume, which should be used for fundamental research to investigate, i. e., hydrodynamic control of mass transfbr. The third one consists of a rectangular flume and a non-disturbed core sample, which addresses an accurate, standard method and is coupled to measurements widl microelectrodes. Advantages and disadvantages of these methods are discussed.

It is well known that the local topographic configuration has a great effect on the wind properties. In the study, to clarify the effects of local terrain on wind properties, the microscale scale topographic factors for thirty eight AMeDAS observatories located in Shikoku Island are introduced into the independent variables in the regression analysis. The factors for micro-scale topographic configurations are obtained from the scenery pictures in each direction . The new factors explain the local roughness, sheltering effect and convergence effect . Wind properties, such as mean wind speed, extreme mean wind speed for each wind direction and wind rose are investigated using ten year's data (1983-1992). All sites have the prevailing wind directions due to the local terrain, such as valley, river, hill etc . Due to the addition of new micro-scale terrain factors, the correlation coefficients increase in all analyses . It is clear that the micro-scale terrain factors for convergence effect play the important role in the all regression analyses.

Although rice production provides stable environments for aquatic plants, the wide use of herbicides is a concern for wild plants inhabiting the surroundings of rice paddies. Because commercial herbicides are typically a cocktail of chemicals, they may pose a threat to wild plants even when the constituent chemicals do not individually have detrimental effects. We sampled water from a rice paddy and a river receiving the paddy drainage immediately after the transplanting period to identify and compare the concentrations of herbicides. We also examined the effect of the sampled water on the germination of two plants: Ammannia multiflora (hygrophyte) and Vallisneria asiatica (submerged). We found that the concentrations of glufosinate in the paddy and river waters were 0.0015 and 0.0013 mg L-1, respectively, and those of pyraclonil were 0.0010 and 0.0009 mg L-1 in the same waters, indicating that these chemicals persist outside the rice paddy. The germination rate of A. multiflora was significantly diminished with exposure to river and paddy water under fluctuating temperature conditions, whereas no difference was observed for V. asiatica. For a comprehensive understanding of the influences of residual herbicides on wetland biodiversity, it is necessary to analyse the effects of herbicides on a wide range of aquatic plants and at various stages of growth.