Effects of hypoxia on benthic organisms in Tokyo Bay,Japan: A review

Bottom hypoxia (dissolved oxygen concentration ⩽2 ml l⁻¹) from anthropogenic eutrophication is a growing global concern. Here, we summarized characteristics of hypoxia and its effects on benthic organisms in Tokyo Bay. Despite recent decreases in nutrient inputs, hypoxia has been increasing in duration and spatial extent, suggesting that the substantial loss of tidal flats from reclamation is contributing to a decrease in the ability of Tokyo Bay to recycle nutrients. Hypoxia develops in the central to northern part of the bay and persists from spring to autumn, causing defaunation of benthic organisms. After the abatement of hypoxia in autumn, the defaunated area is recolonized, either through migration or larval settlement. Some megabenthic species with a spawning peak in spring and summer experience failure of larval settlement, which is probably due to hypoxia. The adverse effects of hypoxia are an impediment to recovery of benthic organisms in Tokyo Bay.     

Effects of hypoxia on benthic organisms in Tokyo Bay, Japan: a review

Bottom hypoxia (dissolved oxygen concentration ≤2 ml l(-1)) from anthropogenic eutrophication is a growing global concern. Here, we summarized characteristics of hypoxia and its effects on benthic organisms in Tokyo Bay. Despite recent decreases in nutrient inputs, hypoxia has been increasing in duration and spatial extent, suggesting that the substantial loss of tidal flats from reclamation is contributing to a decrease in the ability of Tokyo Bay to recycle nutrients. Hypoxia develops in the central to northern part of the bay and persists from spring to autumn, causing defaunation of benthic organisms. After the abatement of hypoxia in autumn, the defaunated area is recolonized, either through migration or larval settlement. Some megabenthic species with a spawning peak in spring and summer experience failure of larval settlement, which is probably due to hypoxia. The adverse effects of hypoxia are an impediment to recovery of benthic organisms in Tokyo Bay.     

Distribution and characteristics of suspended particulate matter in a heavily eutrophic estuary, Tokyo Bay, Japan

Bulk suspended particulate matter (SPM), chlorophyll a (Chl a), ignition loss, particulate organic carbon (POC), organic nitrogen, inorganic phosphorus (PIP), and organic phosphorus were investigated in the heavily eutrophic Arakawa River estuary, Japan. Chl a was high (approximately 35 microg l(-1)) in summer and low (approximately 6.7 microg l(-1)) in winter and autumn. POC from living phytoplankton accounted for approximately 34% and approximately 70% of total POC during low- and high-biomass seasons, respectively. During the low-biomass season, detrital POC distribution was conservative, and less reactive, land-derived materials mainly composed particulate organic materials (POM), but complex mixing of land-derived POM and autochthonous planktonic detritus caused nonconservative detrital POC behavior during the high-biomass season. PIP concentration in SPM decreased with increasing salinity, likely by desorption of soluble orthophosphate (ortho-P). The ortho-P released from SPM, 56% of the ortho-P input from the Arakawa River to the bay, was a significant potential source of biologically available phosphorus causing eutrophication of coastal environments.     

夏季短期调水对太湖贡湖湾湖区水质及藻类的影响

贡湖湾作为"引江济太"工程长江来水进入太湖的第一站,湖湾水体生态环境的变化是对调水工程净水效果的最好响应,因此本文针对贡湖湾一次夏季短期调水展开调查研究,分别取2013年7月24日(调水前)和2013年8月18日(短期调水后)两次监测水样的水体理化指标和浮游藻类群落数据进行了对比分析,并对浮游藻类群落与环境因子做了相关性分析.结果表明:受来水影响,短期调水后监测区水体的p H略有下降,溶解氧、浊度、硝态氮、总氮、总磷以及高锰酸盐指数等水体理化指标浓度均较调水前有所升高;其中受调水影响最为显著的区域为望虞河的入湖口区、湾心区.两次监测调水前后湖区水体优势藻种属未发生变化,仍以微囊藻为主,但蓝藻种属比例有所下降,绿藻和硅藻等种属比例则有所上升.望虞河入湖口区和贡湖湾湾心区的Shannon-Wiener多样性指数和Pielou均匀度指数受调水的影响升高.同时,浮游藻类群落结构与受水水体理化参数的冗余分析结果表明,此次监测的短期调水后,太湖贡湖湾监测湖区水体p H、溶解氧、硝态氮、总氮、总磷、高锰酸盐指数等环境因子与浮游藻类的群落分布呈显著相关,是影响受水水体中藻类群落的主要环境因子.     

Interannual variability of subsurface temperature in summer induced by the Kuroshio over Bungo Channel,Tosa Bay,and Kii Channel,south of Japan

Using historical in situ temperature record, we investigate interannual variability of temperature in summer over Bungo Channel, Tosa Bay, and Kii Channel (hereafter “BTK”), south of Japan. This study aims to reveal the interregional relation of the subsurface temperature variability between the shelf and slope as well as between BTK, and specify the primary cause of the temperature variability in terms of the Kuroshio path. It is shown that 100-m temperature on the slope of BTK is synchronous with each other and highly correlated with coastal sea levels from Kyushu to Kii Peninsula, suggesting that subsurface temperature over the slope varies simultaneously on spatial scales of 400–500 km in the along-slope direction. The 100-m temperature on the slope is also correlated with the near-bottom temperature on the shelf, implying that the near-bottom temperature is determined mainly by the larger-scale variability over the slope. The Kuroshio state in summer of each year is classified into the large meander (LM), non-large meander (NLM), and intermittent larger meander (IM) propagating eastward along the slope. It is found that remarkable temperature increases are accompanied by the IM propagations south of BTK. Temperatures during the IM and LM period are significantly different, the means of which are the highest and lowest, respectively. Temperature during the NLM period with the second highest mean value exhibits the largest variance. Statistical analysis suggests that this variance is related to the Kuroshio axis shift over Izu Ridge between the nearshore and offshore NLM paths.     

Influence of wind upon water quality in Liverpool Bay

Comprehensive distribution patterns of physical and chemical characteristics have been obtained from a series of cruises in Liverpool Bay. The marked feature of these distributions was their temporal variability, suggesting that the surface residual circulation is also temporally variable. The influence of wind stress upon the circulation pattern and hence water quality of this sea area is illustrated.     

Response of a summertime anticyclonic eddy to wind forcing in Funka Bay,Hokkaido, Japan

Flow fluctuations inside an anticyclonic eddy in summertime Funka Bay were examined using three moorings and hydrographic data. The flow pattern above a sharp pycnocline with a concave isopycnal structure during the mooring period was characterized by high mean kinetic energy and relatively low eddy kinetic energy. The ratios of eddy to mean kinetic energy were equal to or less than one, and the mean flow field and isopycnal structure indicated the existence of a stable anticyclonic eddy above the sharp pycnocline under approximate geostrophic balance. Larger flow fluctuations with periods longer than 7 days were dominant inside the eddy. The low-frequency flow fluctuations are accompanied by north to northeastward movement of the eddy with deepening of the pycnocline and spin-up of the anticyclonic circulation. The wind field over Funka Bay is characterized by bay-scale wind fluctuations. The bay-scale winds are greatly influenced by the land topography around Funka Bay, resulting in non-uniform structure with significant wind stress curl. The bay-scale wind fluctuations are termed “locally modified wind” in the present study. The locally modified wind has a negative (positive) wind stress curl in the central–northeastern (southwestern) region of Funka Bay. The north to northeastward movement of the eddy is caused by horizontal non-uniform supply of vorticity from the locally modified wind forcing by the Ekman pumping process. Through this process, the anticyclonic circulation is enhanced (weakened) in the central–northeastern (southwestern) part of the eddy, resulting in the eddy moving north to northeastward with the pycnocline deepening and spin-up of the anticyclonic circulation. The locally modified wind forcing induces low-frequency flow fluctuations through the movement of the eddy in summertime Funka Bay.     

Mesosphere summer echoes,temperature, and meridional wind variations at mid- and polar latitudes

VHF Radar echoes in the summer mesosphere at mid- and polar latitudes ([P]MSE—[polar] mesosphere summer echoes) are connected with very cold temperatures where ice particles can exist. Temperature variations can cause conditions for the generation and evaporation of ice particles and affect the [P]MSE occurrence. The impact of temperature and meridional wind oscillations on [P]MSE is described. Generally at mid-latitudes, strong mesosphere summer echoes are strongly affected by meridional wind variations if the mean temperature is near the frost point of water vapor. In contrast, at polar latitudes there is mostly no significant impact of the meridional wind on radar echoes. A mean temperature well below the frost point and a weaker meridional temperature gradient than at mid-latitudes are reasons for this reduced influence. Due to higher temperatures in 2002, long period temperature and meridional wind variations impact the PMSE more than during the other years.     

Liquefaction of soil in the Tokyo Bay area from the 2011 Tohoku (Japan) earthquake

Immediately following the 11th March 2011 M_w 9.0 Tohoku (Japan) earthquake, a field investigation was carried out around the Tokyo Bay area. This paper provides first-hand observations (before or just at the onset of repair) of widespread liquefaction and the associated effects. Observations related to uplift of manholes, settlement of ground, performance of buildings and bridges and the effects of ground improvements are also presented. Recorded ground motions near the Tokyo Bay area were analysed to understand their key characteristics (large amplitude and long duration). Lessons learnt are also presented.     

Indications for a long-term temperature change in the polar summer middle atmosphere

Middle atmosphere temperatures have been measured by in situ and by remote sensing instruments for several decades. Extensive temperature measurements by rocket-borne falling spheres (FS) were performed from Andøya Rocket Range in northern Norway from the late 1980s onwards. About 90 rockets were successfully launched within eight measurement campaigns and compiled to an empirical temperature statistic. About half of these measurements were in July and August. Since 1997 the Bonn University Rayleigh/Mie/Raman lidar has been operated at Esrange in northern Sweden during winter as well as during summer. One hundred and eight night mean temperature profiles were obtained for July and August from this data set and have been compared to the FS-statistics. A systematic difference could be observed, i.e. the weekly average temperatures taken from the FS-based empirical temperature statistics are up to 10 K warmer than the temperatures measured by lidar, depending on altitude. In particular comparisons during August show larger differences than comparisons with July data. Temperatures were additionally derived from the Rayleigh-scattered light of the Bonn University Na-resonance lidar which was operated during the 1980s at Andøya. No systematic differences between these measurements and the FS-data were found. Gravity waves, tides, volcanic aerosol, and the solar cycle are not likely to cause the observed differences, since their influence is minimised either by data selection (gravity waves and tides) or by measurement times (volcanic aerosol, solar cycle). Additionally to the temperature difference a change in the gravity wave activity was observed, in particular during summer 2002 and 2006. During these years also noctilucent clouds occurred rather late in the season. The latest unambiguous observation of a noctilucent cloud by the U. Bonn lidar at Esrange was on 24 August 2006. All these observations are indications of a long-term temperature change in the polar summer middle atmosphere as predicted by model calculations. While similar changes have already been observed at middle and low latitudes, temperature trend analyses for the polar atmosphere did not reveal any variation up to now.     

Survey of dioxins in Tokyo Bay bottom sediment

This paper examines dioxin profiles in bottom sediments from Tokyo Bay, Japan using sedimentation dating based on 210Pb measurements and dioxin measurements based on particle size distributions. Dioxin concentrations in surface sediment ranged from 3.2 to 52 pg-TEQ g(-1), with the concentrations in the bay back and central region being higher than those at the front of the bay. The vertical dioxin concentration in sediment core samples showed peak levels from years 1962 to 1980, with the maximum being 110 pg-TEQ g(-1). Principal component analysis indicates that the main source of dioxins in bottom sediment from the back of bay are herbicides such as CNP, while in the front of bay atmospheric deposition due to incineration activities are responsible. Dioxins in bottom sediment were mainly found in the particles <75 microm in size.     

水体浊度对风速、风向及其时间累积效应的响应——以太湖贡湖湾为例

水体浊度是影响水下光场及营养盐循环的关键要素之一,其变化过程与水生生态环境演变关系密切.基于2015-2016年7个时段于太湖贡湖湾内外的金墅和上山村两站点的水体浊度及东山气象站的逐时风场数据,利用分位统计等方法,探讨了风速、风向及时间累积效应对水体浊度的影响.结果表明：在以风场驱动为主要动力来源的大型浅水湖泊中,春、秋两季水体浊度的变化频率高于夏、冬两季,且春季变率更为突出;冬季风场和水体浊度的变率均较夏季明显.风场（包括风速、风向及其累积时间）是影响水体浊度变化的关键因素.其中风速是主要决定性因子;风向对水体浊度有较明显的影响,其通过对风速效应的修正进而影响水体浊度,该修正作用可用三角函数表征;水体浊度变化同时还受前期风场累积的影响,其前期时间累积效应的有效时段为2~10 h.该研究给出了风速、风向及风场累积效应的耦合对水体浊度的影响模型,有助于弄清风场对水体浊度变化的影响机制.     

Stable isotope fractionations in the evaporation of water: The wind effect

We performed pan evaporation experiments with the objective of exploring the behaviour of the long-standing Craig–Gordon (C–G) stable isotope model for evaporation under different conditions of air turbulence. The water lost through evaporation was automatically replenished so that a steady isotopic composition was reached, the value of which depended on the isotopic composition of the replenishment water and environmental parameters like temperature, relative humidity and isotopic composition of the atmospheric vapour, and the air turbulence index. The pans were exposed to artificial winds ranging from 0 to 2.5 m/s to change the air turbulence index, which governs the repartition between vapour transported by molecular diffusion and turbulent diffusion. Our data revealed that for wind speeds >0.5 m/s the isotopic composition of the evaporating water deviated from that predicted by the C–G model. This deviation was hypothetically attributed to microdroplets of liquid water removed by the wind without any isotopic fractionation. Isotope mass balance equations allowed us to quantify this water loss, which at wind speeds of ~2 m/s reached 10% of the total evaporation losses. An alternative kinetic evaporation model was proposed whereby the equilibrium layer and the atmospheric laminar layer above the evaporating water of the C–G model were destroyed by the wind and evaporated water molecules were directly injected into the atmosphere. In this model, the isotopic fractionations were due to the slower kinetics of hydrogen bond breakage between molecules in liquid water when heavy isotopes are involved. Accordingly, our data suggested that for isotope water balance studies where winds are frequently above 2 m/s, the C–G model may be inadequate without appropriate corrections for spray vaporization, or the introduction of appropriate kinetic isotope fractionation factors.     

The conditional probability of earthquake occurrence and the next large earthquake in Tokyo, Japan

The use of probability distribution ofrecurrence times as described by theexponential, Weibull and Rayleihgprobability densities form the core of theprobabilistic seismic prediction analysispresented in this paper. Using these threeprobabilistic models we derive threeformulas to calculate the conditionalprobability P(t|t) than an earthquakeevent will occur in the time interval (t, t+ t), provide that it has not occurredin the elapsed time t since the last largeearthquake (M 6.4) in the Tokyo area.This paper proposes a new method toestimate the time interval t foroccurrence of a new large earthquake inTokyo area. This time interval is measuredafter the elapsed time (t) since the lastlarge earthquake. To do this we use thethree formulas for the conditionalprobability P(t|t) and the criterionof the maximum conditional probability ofearthquake occurrence.Using a list of historical earthquakeswhich have occurred in the Tokyo area asgiven by Usami (1976, pp. 235–243), wefound that: (1) Using the exponentialmodel, it is estimated that a highlydamaging earthquake magnitude M 6.4, mayoccur before the year 2009.50, orequivalently before June 2009; (2) Usingthe Weibull model, it is estimated that thedamaging earthquake (M 6.4) may occurbefore the year 2129.80, or equivalentlybefore October 2129.     

The effect of wind averaging time on wind erosivity estimation

The Wind Erosion Prediction System (WEPS) and Revised Wind Erosion Equation (RWEQ) are widely used for estimating wind‐induced soil erosion at a field scale. Wind is the principal erosion driver in the two models. Wind erosivity, which describes the capacity of wind to cause soil erosion, is defined as erosive wind power density (WPD) in WEPS, and wind value (W) in RWEQ. In this study, the daily average WPD (AWPD) and the daily average W (Wf) were chosen to investigate the effect of averaging time on wind erosivity estimation based on observed wind data. We compare the daily AWPD and Wf calculated from 1, 5, 10, 15, 30, and 60 minute average wind speed data. The results of comparisons indicate that averaging wind speed can significantly influence estimates of wind erosivity. Compared with the daily AWPD and Wf calculated from one minute average wind speed data, all daily AWPD and Wf values calculated from 5, 10, 15, 30, and 60 minute averaged wind speeds tend to be significantly lower than values calculated from one minute values. In general, longer averaging times tend to produce smaller values of daily AWPD or Wf, which may lead to an under‐estimation of wind erosion. Further studies are needed to extend and apply the findings obtained in this study to actual wind erosion predictions. Copyright © 2012 John Wiley & Sons, Ltd.     

Distribution and origin of biologically available phosphorus in the water of the Meiliang Bay in summer

The investigation and continuous monitoring with an innovative iron oxide embedded cellulose acetate membrane (FeO/CAM) on the concentrations of biologically available phosphorus (BAP) were conducted in the Meiliang Bay of the Taihu Lake during summer in 2004. The results showed that the concentrations of dissolved (FeO-DP), particulate (FeO-PP) and total bioavailable phosphorus (FeO-P) had similar horizontal distribution. The BAP concentrations were the highest in those estuaries in the northern bay. With the decrease of the distance to the estuary or long shore, there was little difference between BAP concentrations in an open lake area. During the observation period, algal blooms occurred in most waters of the northern bay, which was reflected from the high concentrations of chlorophyll a (Chl-a). While they were not highest in the estuarine waters of those major rivers, this is the case for the BAP concentrations. The concentrations of Chl-a had a significantly positive correlation with those of bioavailable phosphorus in the open area of the Meiliang Bay. With the sediment resuspension induced by wind and wave, BAP concentrations increased in a short-term, indicating that the riverine P inputs mainly contribute to the concentrations of BAP in the estuarine water while internal P release was the major source of BAP in the open lake area. In the eutrophic shallow lake, the blooms of alga may cause pH increase and further result in internal P release. The above results showed that the new membrane of FeO/CAM can be used to monitor the concentrations of BAP and provide the scientific justifications for the control strategy of the lake eutrophication.     

Distribution and origin of biologically available phosphorus in the water of the Meiliang Bay in summer

The investigation and continuous monitoring with an innovative iron oxide embedded cellulose acetate membrane (FeO/CAM) on the concentrations of biologically available phosphorus (BAP) were conducted in the Meiliang Bay of the Taihu Lake during summer in 2004. The results showed that the concentrations of dissolved (FeO-DP), particulate (FeO-PP) and total bioavailable phosphorus (FeO-P) had similar horizontal distribution. The BAP concentrations were the highest in those estuaries in the northern bay. With the decrease of the distance to the estuary or long shore, there was little difference between BAP concentrations in an open lake area. During the observation period, algal blooms occurred in most waters of the northern bay, which was reflected from the high concentrations of chlorophyll a (Chl-a). While they were not highest in the estuarine waters of those major rivers, this is the case for the BAP concentrations. The concentrations of Chl-a had a significantly positive correlation with those of bioavailable phosphorus in the open area of the Meiliang Bay. With the sediment resuspension induced by wind and wave, BAP concentrations increased in a short-term, indicating that the riverine P inputs mainly contribute to the concentrations of BAP in the estuarine water while internal P release was the major source of BAP in the open lake area. In the eutrophic shallow lake, the blooms of alga may cause pH increase and further result in internal P release. The above results showed that the new membrane of FeO/CAM can be used to monitor the concentrations of BAP and provide the scientific justifications for the control strategy of the lake eu-trophication.     

The long-term salinity field in San Francisco Bay

Data are presented on long-term salinity behaviour in San Francisco Bay, California. A two-level, width averaged model of the tidally averaged salinity and circulation has been written in order to interpret the long-term (days to decades) salinity variability. The model has been used to simulate daily averaged salinity in the upper and lower levels of a 51 segment discretization of the Bay over the 22-yr period 1967–1988. Monthly averaged surface salinity from observations and monthly-averaged simulated salinity are in reasonable agreement. Good agreement is obtained from comparison with daily averaged salinity measured in the upper reaches of North Bay.The salinity variability is driven primarily by freshwater inflow with relatively minor oceanic influence. All stations exhibit a marked seasonal cycle in accordance with the Mediterranean climate, as well as a rich spectrum of variability due to extreme inflow events and extended periods of drought. Monthly averaged salinity intrusion positions have a pronounced seasonal variability and show an approximately linear response to the logarithm of monthly averaged Delta inflow. Although few observed data are available for studies of long-term salinity stratification, modelled stratification is found to be strongly dependent on freshwater inflow; the nature of that dependence varies throughout the Bay. Near the Golden Gate, stratification tends to increase up to very high inflows. In the central reaches of North Bay, modelled stratification maximizes as a function of inflow and further inflow reduces stratification. Near the head of North Bay, lowest summer inflows are associated with the greatest modelled stratification. Observations from the central reaches of North Bay show marked spring-neap variations in stratification and gravitational circulation, both being stronger at neap tides. This spring-neap variation is simulated by the model. A feature of the modelled stratification is a hysteresis in which, for a given spring-neap tidal range and fairly steady inflows, the stratification is higher progressing from neaps to springs than from springs to neaps.The simulated responses of the Bay to perturbations in coastal sea salinity and Delta inflow have been used to further delineate the time-scales of salinity variability. Simulations have been performed about low inflow, steady-state conditions for both salinity and Delta inflow perturbations. For salinity perturbations a small, sinusoidal salinity signal with a period of 1 yr has been applied at the coastal boundary as well as a pulse of salinity with a duration of one day. For Delta inflow perturbations a small, sinusoidally varying inflow signal with a period of 1 yr has been superimposed on an otherwise constant Delta inflow, as well as a pulse of inflow with a duration of one day. Perturbations in coastal salinity dissipate as they move through the Bay. Seasonal perturbations require about 40–45 days to propagate from the coastal ocean to the Delta and to the head of South Bay. The response times of the model to perturbations in freshwater inflow are faster than this in North Bay and comparable in South Bay. In North Bay, time-scales are consistent with advection due to lower level, up-estuary transport of coastal salinity perturbations; for inflow perturbations, faster response times arise from both upper level, down-estuary advection and much faster, down-estuary migration of isohalines in response to inflow volume continuity. In South Bay, the dominant time-scales are governed by tidal dispersion.