Massive occurrence of benthic plastic debris at the abyssal seafloor beneath the Kuroshio Extension, the North West Pacific.

The abyss (3500-6500 m) covers the bulk of the deep ocean floor yet little is known about the extent of plastic debris on the abyssal seafloor. Using video imagery we undertook a quantitative assessment of the debris present on the abyssal seafloor (5700-5800 m depth) beneath the Kuroshio Extension current system in the Northwest Pacific. This body of water is one of the major transit pathways for the massive amounts of debris that are entering the North Pacific Ocean from Asia. Shallower sites (1400-1500 m depth) were also investigated for comparison. The dominant type of debris was single-use plastics - mainly bags and food packaging. The density of the plastic debris (mean 4561 items/km2) in the abyssal zone was the highest recorded for an abyssal plain suggesting that the deep-sea basin in the Northwest Pacific is a significant reservoir of plastic debris.

Methane mitigation is associated with reduced abundance of methanogenic and methanotrophic communities in paddy soils continuously sub-irrigated with treated wastewater.

Herein, we examined emissions of CH4 and the community structures of methanogenic archaea and methanotrophic bacteria in paddy soils subjected to a novel irrigation system, namely continuous sub-irrigation with treated wastewater (TWW). This system has recently been developed by our group to effectively reuse TWW for the cultivation of protein-rich rice. The results showed that, despite not using mineral fertilisers, the wastewater reuse system produced a rice yield comparable to that of a conventional cultivation practice and reduced CH4 emissions from paddy fields by 80%. Continuous sub-irrigation with TWW significantly inhibited the growth of methanogens in the lower soil layer during the reproductive stage of rice plants, which was strongly consistent with the effective CH4 mitigation, resulting in a vast reduction in the abundance of methanotrophs in the upper soil layer. The compositions of the examined microbial communities were not particularly affected by the studied cultivation practices. Overall, this study demonstrated that continuous sub-irrigation with TWW was an effective method to produce high rice yield and simultaneously reduce CH4 emissions from paddy fields, and it also highlighted the potential underlying microbial mechanisms of the greenhouse gas mitigation.

Impact of nitrogen compound variability of sewage treated water on N2O production in riverbeds.

Nitrous oxide (N2O), a strong greenhouse and ozone depleting gas, is known to be generated in the river environment. However, the impact of sewage treated water on the production mechanism has not been clarified. In this study, N2O production in the upper reach of a river was evaluated by field survey and activity test. The results demonstrated that the N2O production activity of the river pebbles increased with the inflow of the sewage treated water, which was supported by field survey results, such as the dissolved N2O concentrations and water quality. The emission factors of N2O were determined to be 0.02-0.05% in nitrification and 0.01-0.025% in denitrification. Our study shows that combining a field survey and an activity test improves the reliability of the results and leads to the appropriate quantitative evaluation. From a perspective of controlling the N2O emissions from the sewage treatment plant, N2O generation inside the plant is critical. However, appropriate nitrogen removal in the treatment plant is connected to the reduction of N2O generation in the river environment.

Assessment of nitrous oxide production in eutrophicated rivers with inflow of treated wastewater based on investigation and statistical analysis.

Accurate estimation and control of greenhouse gas emissions have been recognized as imperative in recent years. Therefore, frequent investigations under uniform environmental conditions are required to better understand this concept. Thus, six sampling sites with characteristic concentrations of nitrogen and other water quality parameters were selected to investigate the behavior of water quality parameters throughout the year and to statistically examine the correlations among the parameters. Dissolved nitrous oxide (D-N2O) showed the highest positive correlation coefficient with NO2-N among nitrogen species. The results of the principal component analysis suggested that river water quality could be broadly classified based on photosynthesis and contamination from treated wastewater. Photosynthesis caused an increase in pH, with concomitant decrease in D-N2O concentration. Using the results of multiple regression analysis, D-N2O was accurately estimated based on nitrogen concentration, pH, and concentration of organic matter in various situations. The results of a detailed survey suggested that D-N2O was produced in the river from nitrogen sources released from the wastewater treatment plant. The main roles of the wastewater treatment plant for D-N2O behavior in the river were the supply of the nitrogen source that was the precursor of D-N2O, the supply of the nutrients that induced the photosynthesis, and the direct supply of D-N2O at a low water temperature. The models based on multiple regression analysis could efficiently predict the D-N2O concentration produced in rivers at sites downstream of the wastewater treatment plant, except for the direct supply of D-N2O as an effluent at low water temperature.

Methane and nitrous oxide emissions from paddy fields with no fertilizer use under continuous irrigation with treated municipal wastewater.

Treated wastewater (TWW) irrigation has been recommended as an environmentally friendly agricultural practice and has been applied in many countries for decades. The effects of wastewater irrigation on rice yield and quality, as well as on the environment, with particular focus on greenhouse gas emissions from paddy fields with municipal wastewater irrigation, have gained substantial attention. In this study, bench-scale experiments were conducted in two cultivation seasons where seedlings of Bekoaoba, a large-grain high-yield rice variety, were transplanted and irrigated with TWW without fertilization. A control experiment was performed to simulate the cultivation conditions of normal paddy fields. The study aimed to quantify the effects of TWW irrigation on rice yield and quality, in addition to CH4 and N2O emissions. The highest rice yield (10.4 t ha-1) and protein content in brown rice (13.8%) was achieved when the soil was repeatedly subjected to bottom-to-top TWW irrigation without any synthetic fertilizer. Bottom-to-top TWW irrigation decreased CH4 emissions by up to 95.6% when compared with tap water irrigation, whereas bottom-to-top and top-to-top TWW irrigation increased N2O emissions by 5 and 15 times, respectively. Bottom-to-top irrigation of TWW could be considered a promising solution for reducing greenhouse gas emissions as TWW irrigation resulted in a lower combined global warming potential than tap water irrigation. Further, bottom-to-top irrigation of TWW produced less CH4 and N2O than top-to-top irrigation.

Estimating the population mean for a vertical profile of energy dissipation rate.

Energy dissipation rates are an important characteristic of turbulence; however, their magnitude in observational profiles can be incorrectly determined owing to their irregular appearance during vertical evolution. By analysing the data obtained from oceanic turbulence measurements, we demonstrate that the vertical sequences of energy dissipation rates exhibit a scaling property. Utilising this property, we propose a method to estimate the population mean for a profile. For scaling in the observed profiles, we demonstrate that our data exhibit a statistical property consistent with that exhibited by the universal multifractal model. Meanwhile, the population mean and its uncertainty can be estimated by inverting the probability distribution obtained by Monte Carlo simulations of a cascade model; to this end, observational constraints from several moments are imposed over each vertical sequence. This approach enables us to determine, to some extent, whether a profile shows an occasionally large mean or whether the population mean itself is large. Thus, it will contribute to the refinement of the regional estimation of the ocean energy budget, where only a small amount of turbulence observation data is available.

Identification of skipjack tuna (Katsuwonus pelamis) pelagic hotspots applying a satellite remote sensing-driven analysis of ecological niche factors: A short-term run.

Skipjack tuna (SJT) pelagic hotspots in the western North Pacific (WNP) were modelled using fishery and satellite remotely sensed data with Ecological Niche Factor Analysis (ENFA) models. Our objectives were to model and predict habitat hotspots for SJT and assess the monthly changes in sub-surface temperatures and mixed layer depths at fishing locations. SJT presence-only monthly resolved data, sea surface temperature, chlorophyll-a, diffuse attenuation coefficient, sea surface heights and surface wind speed were used to construct ENFA models and generate habitat suitability indices using a short-term dataset from March-November 2004. The suitability indices were then predicted for July-October (2007 and 2008). Monthly aggregated polygons of areas fished by skipjack tuna pole and line vessels were also overlaid on the predicted habitat suitability maps. Distributions of sub-surface temperatures and mixed layer depths (MLD) at fishing locations were also examined. Our results showed good fit for ENFA models, as indicated by the absolute validation index, the contrast validation index and the continuous Boyce index. The predicted hotspots showed varying concurrences when compared with 25-degree polygons derived from fished areas. Northward shifts in SJT hotspots corresponded with declining MLDs from March to September. The MLDs were shallower in summer and deeper in autumn and winter months. The habitat hotspots modeled using ENFA were consistent with the known ecology and seasonal migration pattern of SJT. The findings of this work, derived from a short-term dataset, enable identification of SJT hotspots in the WNP, thus contributing valuable information for future research on SJT habitat prediction models.

Continuous Sub-Irrigation with Treated Municipal Wastewater for Protein-Rich Rice Production with Reduced Emissions of CH4 and N2O.

Herein, we introduce continuous sub-irrigation with treated municipal wastewater (TWW) as a novel cultivation system to promote resource recycling and cost-effective forage rice production in Japan. However, both TWW irrigation and forage rice cultivation were previously considered to intensify CH4 and N2O emissions. In the present study, therefore, we evaluate the emissions of greenhouse gases (GHGs) and yielding capacity of forage rice between conventional cultivation and continuous sub-irrigation systems employing different water supply rates. Results indicated that continuous sub-irrigation with TWW resulted in high rice yields (10.4-11 t ha-1) with superior protein content (11.3-12.8%) compared with conventional cultivation (8.6 t ha-1 and 9.2%, respectively). All TWW irrigation systems considerably reduced CH4 emissions, while higher continuous supply rates significantly increased N2O emissions compared with the conventional cultivation. Only the continuous irrigation regime employing suitable supply rates at appropriate timings to meet the N demand of rice plants decreased both CH4 and N2O emissions by 84% and 28%, respectively. Overall, continuous sub-irrigation with TWW provides high yields of protein-rich forage rice without the need for synthetic fertilisers and effectively mitigated GHG emissions from paddy fields.

Contribution of dissolved N2O in total N2O emission from sewage treatment plant.

The characteristics of nitrous oxide, N2O, from a sewage treatment plant, which conducts nitrogen removal, and the river that receives its effluent water, were investigated by intensive daily surveys in summer and winter. N2O production in the sewage treatment plant was promoted in winter when nitrite accumulated in the reaction tank. The dissolved N2O concentration in the effluent water was also high in winter, which caused the dissolved N2O concentration to increase in the river downstream. In contrast, the N2O production inside the plant and the dissolved N2O emission through the effluent water, the dissolved N2O discharge, was controlled in summer when the nitrogen removal was more complete and there was no-nitrite accumulation. The dissolved N2O in the effluent water was rapidly lost after leaving the plant by as much as 26% in summer and 59% in winter. Additionally, the amount of the dissolved N2O discharge in winter was almost equal to that of the indirect N2O emission. When the nitrogen removal proceeded successfully, the amount of dissolved N2O discharge was small. In contrast, when the nitrogen removal was insufficient, the dissolved N2O discharge became an important N2O source.

The comparison of greenhouse gas emissions in sewage treatment plants with different treatment processes.

Greenhouse gas emissions from different sewage treatment plants: oxidation ditch process, double-circulated anoxic-oxic process and anoxic-oxic process were evaluated based on the survey. The methane and nitrous oxide characteristics were discussed based on the gaseous and dissolved gas profiles. As a result, it was found that methane was produced in the sewer pipes and the primary sedimentation tank. Additionally, a ventilation system would promote the gasification of dissolved methane in the first treatment units. Nitrous oxide was produced and emitted in oxic tanks with nitrite accumulation inside the sewage treatment plant. A certain amount of nitrous oxide was also discharged as dissolved gas through the effluent water. If the amount of dissolved nitrous oxide discharge is not included, 7-14% of total nitrous oxide emission would be overlooked. Based on the greenhouse gas calculation, electrical consumption and the N2O emission from incineration process were major sources in all the plants. For greenhouse gas reduction, oxidation ditch process has an advantage over the other advanced systems due to lower energy consumption, sludge production, and nitrogen removal without gas stripping.

A new Approach to El Niño Prediction beyond the Spring Season.

The enormous societal importance of accurate El Niño forecasts has long been recognized. Nonetheless, our predictive capabilities were once more shown to be inadequate in 2014 when an El Nino event was widely predicted by international climate centers but failed to materialize. This result highlighted the problem of the opaque spring persistence barrier, which severely restricts longer-term, accurate forecasting beyond boreal spring. Here we show that the role played by tropical seasonality in the evolution of the El Niño is changing on pentadal (five-year) to decadal timescales and thus that El Niño predictions beyond boreal spring will inevitably be uncertain if this change is neglected. To address this problem, our new coupled climate simulation incorporates these long-term influences directly and generates accurate hindcasts for the 7 major historical El Niños. The error value between predicted and observed sea surface temperature (SST) in a specific tropical region (5°N-5°S and 170°-120°W) can consequently be reduced by 0.6 Kelvin for one-year predictions. This correction is substantial since an "El Niño" is confirmed when the SST anomaly becomes greater than +0.5 Kelvin. Our 2014 forecast is in line with the observed development of the tropical climate.

The seasonal variation of emission of greenhouse gases from a full-scale sewage treatment plant.

The seasonal variety of greenhouse gas (GHGs) emissions and the main emission source in a sewage treatment plant were investigated. The emission coefficient to treated wastewater was 291gCO2m(-3). The main source of GHGs was CO2 from the consumption of electricity, nitrous oxide from the sludge incineration process, and methane from the water treatment process. They accounted for 43.4%, 41.7% and 8.3% of the total amount of GHGs emissions, respectively. The amount of methane was plotted as a function of water temperature ranging between 13.3 and 27.3°C. An aeration tank was the main source of methane emission from all the units. Almost all the methane was emitted from the aeration tank, which accounted for 86.4% of the total gaseous methane emission. However, 18.4% of the methane was produced in sewage lines, 15.4% in the primary sedimentation tank, and 60.0% in the aeration tank.

An observing system simulation experiment for the Western North Pacific region.

This study investigated the effectiveness of concentrated observations for ocean state estimation in a region remote from the observation site. I executed a twin observing system simulation experiment (OSSE) for the North Pacific region, using an ocean data synthesis system, to examine how the potential effectiveness is for a well-defined criterion, the representativeness of the subsurface salinity minimum corresponding to North Pacific Intermediate Water (NPIW). The results of the OSSE show that data synthesis confined to the region corresponding to the recent origin of the NPIW (35 °N-53 °N, 130 °E-170 °E) can affect the modeled extent of the NPIW in the central Pacific at 35 °N, 180°. The interannual variability of the NPIW is not well reproduced in terms of the standard deviation value (std), only by the data input in the origin region. The root mean square difference between the "true" and the synthesized field is twice larger than the std although there the representativeness of the scale of salinity minimum is improved by about one-third of the difference between the "true" and "first-guess" fields in a snapshot. These results imply that combinations of concentrated and other in situ observations should be required for the dynamic state estimation of the NPIW.

Improvement of ocean state estimation by assimilating mapped Argo drift data.

We investigated the impact of assimilating a mapped dataset of subsurface ocean currents into an ocean state estimation. We carried out two global ocean state estimations from 2000 to 2007 using the K7 four-dimensional variational data synthesis system, one of which included an additional map of climatological geostrophic currents estimated from the global set of Argo floats. We assessed the representativeness of the volume transport in the two exercises. The assimilation of Argo ocean current data at only one level, 1000 dbar depth, had subtle impacts on the estimated volume transports, which were strongest in the subtropical North Pacific. The corrections at 10(°)N, where the impact was most notable, arose through the nearly complete offset of wind stress curl by the data synthesis system in conjunction with the first mode baroclinic Rossby wave adjustment. Our results imply that subsurface current data can be effective for improving the estimation of global oceanic circulation by a data synthesis.

Effective design of profiling float network for oceanic heat-content monitoring.

Schemes for optimizing ocean observation programs are presently the subject of increased interest since in principle they should lead to the improved understanding of the dynamical state of the ocean that is required within the present regime of climate change. Here we use an adjoint sensitivity analysis together with a four-dimensional fluctuating oceanic current system to identify key regions for intensive monitoring by drifting profiling float. In this way we aim to maximize observational efficiency. As a scientific benchmark for the validity of our approach, we have attempted to define the ambient sensitivity of the oceanic heat content to a subtle change in water temperature within the Pacific Basin. We focus on the interannual to multidecadal variations in particular. As a result, sensitivity signals reflecting changes in heat content exhibit a characteristic pattern in the three-dimensional continuum and have drastic temporal changes. This implies that the key regions will depend greatly on the operational timeframe of the observing system. We demonstrate a more effective geographic deployment strategy for the profiling floats monitoring changes in the oceanic heat content on a decadal timescale.

Simulated rapid warming of abyssal North Pacific waters.

Recent observational surveys have shown significant oceanic bottom-water warming. However, the mechanisms causing such warming remain poorly understood, and their time scales are uncertain. Here, we report computer simulations that reveal a fast teleconnection between changes in the surface air-sea heat flux off the Adélie Coast of Antarctica and the bottom-water warming in the North Pacific. In contrast to conventional estimates of a multicentennial time scale, this link is established over only four decades through the action of internal waves. Changes in the heat content of the deep ocean are thus far more sensitive to the air-sea thermal interchanges than previously considered. Our findings require a reassessment of the role of the Southern Ocean in determining the impact of atmospheric warming on deep oceanic waters.