Tetsunori Inoue

Respiration and ingestion rates of the filter-feeding bivalve Musculista senhousia : implications for water-quality control

Abstract To evaluate the effect of filter-feeding bivalves on water quality, batch and flow type measurements were recorded to estimate the respiration and ingestion rates of Musculista senhousia, which predominates the macrobenthos of Lake Nakaumi, Japan. The results for the respiration rate experiments had a low stable rate at about 15 mg O2 day−1 DFW g−1 (where DFW means dry flesh weight) at low temperatures (between 5°C and 10°C) that increased at middle and high temperatures (from 10°C to 30°C), reaching a maximum rate of about 200 mg O2 day−1 DFW g−1 at 30°C. The dependence of respiration rate on temperature is significant, especially between 10°C and 15°C (Q10=6.9). The vertical 2-BOX numerical model showed that continuous stratification of the water column must be averted if M. senhousia are to survive. Ingestion rate of particulate matter also increased with temperature between 10°C and 20°C. Ingestion rates at 30°C, after being incubated for more than 1 day, were almost the same as ingestion rates at 20°C. Filtration rates were calculated from concentrations of chlorophyll a (Chl.a), particulate total phosphorus (PTP) and particulate total nitrogen (PTN). Obvious differences were observed between the filtration rate calculated from the Chl.a concentration compared to those from PTP and PTN. This may imply that M. senhousia selectively ingested a particular species of phytoplankton. The horizontal 2-BOX model showed a relationship between the Chl.a concentration in L. Nakaumi and the water exchange rate. The ingestion potential of organic matter by M. senhousia is greater than those of the nutrient loads in the field and has less risk of depleting dissolved oxygen (DO) in the bottom layer. If, therefore, the phosphorus and nitrogen supply to M. senhousia increased, and adult M. senhousia are collected and removed efficiently, water quality in L. Nakaumi would improve.

A re-evaluation of the taxonomic status of Halophila euphlebia Makino (Hydrocharitaceae) based on morphological features and ITS sequence data

Abstract Identification of Halophila ovalis samples from various parts of the world has long been accompanied by taxonomic uncertainties because of morphological variability. This led to the hypothesis that H. ovalis represents a “collective species” which may include cryptic species. Recent studies applying molecular techniques to the assessment of phylogenetic relationships in the genus Halophila also came to a similar conclusion. In this study, one Halophila species from Japan, previously described as H. euphlebia and later treated as a synonym of H. ovalis, was critically re-examined using molecular phylogenetic analyses of the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA. Morphological examinations of vegetative and reproductive structures were also undertaken. Results obtained from both morphological and molecular data, combined with a critical review of the relevant literature provide support for recognition of the plant in question as being distinct from H. ovalis. The entity conforms to Makinos description of H. euphlebia. This raises the current number of Halophila species in Japan to three: H. ovalis, H. decipiens and H. euphlebia.

Effects of Hydrodynamic Conditions on DO Transfer at a Rough Sediment Surface

A numerical model was developed to calculate the rate of dissolved-oxygen (DO) diffusion across a sediment surface taking into account the surface roughness and biochemical reactions of the sediment. Estimates of DO transfer rate from the model were compared with results from laboratory experiments conducted in a rectangular flume using roughness elements. In experiments, there was maximum value for the nondimensionalized DO transfer rate (Stanton number, St) in the transitional region of surface roughness, in which the mass flux was two to five times larger than that of the smooth surface. The reproducibility of the experimental results by numerical analysis was significantly improved by including terms for flushing frequency of water in cavities between the roughness elements and for nonsteady variations in the diffusion rate due to step changes in DO concentration in the flushed region. A simple method to estimate enhancement effect for St caused by nonsteady variations was also presented.

A New Method for Measuring Flow Structure in the Benthic Boundary Layer Using an Acoustic Doppler Velocimeter

Abstract A new system for precise measurement of vertical profiles of mean and turbulent flow structure immediately above the sediment–water interface is introduced. This system has an acoustic Doppler velocimeter (ADV) attached to an elevation system to allow for the precise measurement of the vertical profiles of three-component velocities in the range of 0.1–27 cm above the sediment surface in the field. This system enables an onboard operator to accurately measure height and move the ADV vertically to any point. The system was applied to in situ measurements of velocity profiles immediately above the sediment. The shear velocity, Reynolds stress value, roughness height, turbulent kinetic energy, and dissipation rate of turbulent energy were calculated and compared with often-cited values. The results showed the same flow properties as those from laboratory experiments and literature values. The advantages and disadvantages of the system are discussed.

Pseudocodium okinawense (Bryopsidales, Chlorophyta), a new species from Okinawa and the first report of the genus from eastern Asia

A new species of the green algal genus Pseudocodium is described on the basis of specimens collected from Okinawa, southern Japan. It differs from the generitype species P. de-vriesii Weber-van Bosse from South Africa, P. australasicum Womersley from Australia and P. floridanum C. J. Dawes & A. C. Mathieson from Florida in its smaller size (1–2 cm in height, axes 0.5–1.0 mm in width) and infrequent branching. Unlike P. de-vriesii and P. australasicum also is its total lack of constricted or articulated axes. Molecular-phylogenetic analyses based on plastid encoded rbcL gene sequences show the Okinawan plants to group with Atlantic P. floridanum but to be specifically distinct owing to substantial base pair differences (88 bp, 11.876%). Remarkable differences in morphometric data, ecological preferences and geographic distribution were also found between them. We thus describe the Okinawan entity as Pseudocodium okinawense E. J. Faye, M. Uchimura et S. Shimada sp. nov. In addition, on the basis of laboratory culture experiments, a diminutive, entirely tubular growth form showing great morphological dissimilarity with field materials is newly observed in the genus, thus adding further details to our understanding of the plants vegetative phenology at early developmental stages.

Potential technique for improving the survival of victims of tsunamis

We investigated a method for surviving tsunamis that involved the use of personal flotation devices (PFDs). In our work, we succeeded in numerically demonstrating that the heads of all the dummies wearing PFDs remained on the surface and were not dragged underwater after the artificial tsunami wave hit them. In contrast, the heads of all the dummies not wearing PFDs were drawn underwater immediately; these dummies were subsequently entrapped in a vortex. The results of our series of experiments are important as a first step to preventing the tragedies caused by tsunamis.

DIEL VARIATION OF RESUSPENSION AND EFFECT OF RESUSPENSION ON PHOSPHATE RELEASE RATE FROM THE SEDIMENT

Continuous field observations of water temperature, conductivity, turbidity and flow velocity were performed at a central point of Lake Shinji, a shallow lagoon in Japan, in summer for a month. Observational results revealed that turbidity in the overlying water showed a distinct diel variation, independent on the existence of the stratification. As wind-induced wave diurnally developed when the atmosphere became unstable in the afternoon, and as wind-induced wave propagated to the bottom layer even under the stratified condition in the water column, diurnal fluctuation of resuspension was possible under stratified conditions. Furthermore, experimental results showed that sediment resuspension enhanced phosphate release rate from the sediment under anoxic condition. As anoxic water often develops under stratified conditions, these results strongly indicate that the anoxic resuspension caused by the wind-induced wave enhances phosphate release from the sediment.

RELATIONS BETWEEN FLOW PATTERNS AND WATER QUALITY IN THE BANJO ESTUARY

3工 修 国 土 環 境 株 式 会 社 名 古 屋 支 店(〒455-0032愛 知県 名 古 屋 市 港 区入 船1 -7-15) 4正 会 員 工 博(独 法)港 湾 空 港 技 術研 究 所 海 洋 ・水 工 部(〒239-0826横 須 賀 市 長 瀬3 -1-1) 5フ ェ ロー 工 博 九州 大 学 大 学 院 教 授 工 学 研 究 院 環 境 都 市 部 門(〒812 -8581福 岡 市 東 区 箱 崎6-10-1) 6正 会 員 農 修 西 日本 技 術 開 発 株 式 会 社 環 境 部(〒810 -0004福 岡 市 中央 区渡 辺 通1-1-1) 7正 会 員 工 博 大 分 工 業 高 等 専 門学 校 助 教 授 土 木 工 学 科(〒870 -0152大 分 市 大 字 牧1666) 8国 土 交 通 省 九 州 地 方 整 備 局佐 伯 河 川 国 道 事 務 所(〒876-0813大 分 県 佐 伯 市 長 島町4-14 -14)