Drop In Water Temperature Research Articles

Physical and ecological processes of internal waves on an isolated reef ecosystem in the South China Sea

Field measurements at Dongsha Atoll in the northern South China Sea showed frequent drops in daily water temperature up to 8°C during intrusions of large nonlinear internal waves. The internal waves had a period of about 4 hours and velocity amplitude of 0.3 m s−1. Large variations of dissolved oxygen were observed a week after cold‐water intrusion, which was followed in another 2 days by a significant increase of chlorophyll content. The 7–8‐day delay suggests that phytoplankton blooms occurred after the nutrients were released through microbial decomposition of organics brought up by the internal waves. This study highlights the effects of internal waves and the possible role of the microbial food web on nutrient regeneration in a tropical reef ecosystem.

Experimental research on a new solar pump-free lithium bromide absorption refrigeration system with a second generator

This paper is concerned with experimental research on a new solar pump-free lithium bromide absorption refrigeration system with a second generator. By using the second generator together with a lunate thermosiphon elevation tube, the required minimum driving temperature of the heat source is only 68 °C compared to above 100 °C in traditional absorption refrigeration systems. Based on the horizontal-tube falling-film method, the performance of the absorber can be enhanced by the second generator due to an increase in the differential concentration of the solution between the inlet and the outlet of the absorber and an increase in the temperature difference between the inlet and the outlet of the cooling water in the absorber. The yield of condensate with the second generator open is increased by 68% compared to that with the second generator closed. The performance of the evaporator is significantly improved due to the increase in temperature drop of the chilled water and the decrease in the outlet temperature of the chilled water. This leads to an improvement of the performance of the overall refrigeration system. The maximum coefficient of performance (COP) approaches 0.787.

Bottom temperature monitoring in Lake Baikal

We report results of bottom temperature monitoring of 2003–2004 in the deepwater South Baikal basin (Lake Baikal) near active gas-fluid methane vents at lake depths of 1020 and 1350 m. Sediments and water temperatures were measured using an autonomous temperature recorder designed at the Institute of Geophysics (Novosibirsk). Experiments implied short-duration recording and pioneering continuous 350 day-long monitoring near the Staryi vent. Measurements within a 1 m thick layer above and below the bottom showed notable variations in water (up to 0.07 °C) and sediment temperatures and in geothermal gradient. The long temperature records include a relatively steady period (mid-June 2003-early February 2004) with smooth temperature variations (especially in sediments) and two transient unsteady periods. The steady season is the best time for heat flow studies in the South Baikal basin. The 0.04–0.05 °C drop in bottom water temperature during the unsteady periods may result from intrusion of cold surface water. A positive temperature anomaly of ∼0.04 °C recorded in April 2003 may be caused, among other reasons, by active gas venting.

Coseismic effects of water temperature based on digital observation from Tayuan well, Beijing

On the basis of digital records from Tayuan well, we study coseismic effects of water temperature caused by remote earthquakes. The records show that the water temperature changes are consistently following the process of drop-rise-recovery regardless of focal mechanism or epicentral directions. The step amplitude of water temperature increases with the increase of earthquake magnitude, and decreases with the decrease of epicentral distances. They have rather well correlation. Water temperature rising after earthquake is influenced by water level variations. Finally, the mechanisms of coseismic effects of water temperature have been discussed. Preliminary study shows that accelerated convection and mixing of different temperature water in virtue of seismic wave are the main causes of water temperature drops. Seismic wave accelerates water convection, which causes warm water to move up from deeper part of the well and cold water to go down from the upper part. Temperature probe will detect water temperature drops at early stage. After the occurrence of earthquake, as the fluctuation of water level gradually quiets down, water temperature near the probe begins to rise.

Performance improvement of gas turbines of Fars (Iran) combined cycle power plant by intake air cooling using a media evaporative cooler

In this paper, a media evaporative cooling system installed in the gas turbines of the Fars (Iran) combined cycle power plant are modeled and evaluated. In this model, different design parameters such as inlet air velocity, geometric shape and sizes and depth of the media have been considered. Analysis of the results shows that at a constant Prandtl number, the cooler effectiveness decreases and pressure drop increases, as incoming air velocity increases. The water evaporation rate and temperature drop of the cooler have been calculated, and the effects of temperature, relative humidity and pressure of the ambient have been investigated as well. The practical and analytical results show that the output of a gas turbine of the Fars combined cycle power plant at 38 � C ambient temperature and 8% relative humidity is 11 MW more, and the temperature drop of the inlet air is about 19 � C with media evaporative cooling installations. Because of annual power augmentation of 5280 MWh and considering 2.5 Cents/kW h selling price for excess electricity generated, the payback period obtained is about four years. � 2006 Elsevier Ltd. All rights reserved.

Activation of a sensorimotor pathway in response to a water temperature drop in a teleost fish

When common carp, Cyprinus carpio L., experience a rapid temperature drop, the cerebral blood volume is strongly reduced to dampen the temperature drop in the brain. Simultaneously, the preoptic area and pituitary gland are activated to launch whole-body adaptive responses. However, the preferred reaction of fish to a temperature change is an escape reaction, which implies activation of a sensorimotor pathway. Here, we used blood oxygenation level-dependent (BOLD)- and cerebral blood volume (CBV)-weighted functional magnetic resonance imaging (fMRI) to identify a sensorimotor pathway, during a 10 degrees C temperature drop in common carp. Transient activation was observed in the region where the sensory root of the trigeminal nerve enters the brain, and in the valvula cerebelli. In both regions, metabolic activity increased (increased deoxyhemoglobin content demonstrated by a decreased BOLD signal) within 30 s after the onset of the temperature drop, peaked after 2-3 min, and then decreased, even though the temperature continued to drop for another 2 min. These brain structures appear to respond to temperature change, rather than to the absolute temperature. Thus, during a temperature drop, the sensorimotor pathway consisting of the trigeminal nerve, the primary sensory trigeminal nucleus, the valvula cerebelli and some motornuclei, is active, in line with perception of temperature change in the buccal cavity, leading to motor activity for escape. This pathway operates in parallel to an acclimation pathway, which involves the preoptic area to pituitary gland pathway.

Temperature distributions in trapezoidal built in storage solar water heaters with/without phase change materials

Built in storage solar water heaters (BSSWHs) have been recognized for their more compact constructions and faster solar gain than conventional solar water heaters, however, their water temperatures quickly go down during the cooling period. A trapezoidal BSSWH without PCM storage unit was used as the control heater (reference) to investigate the effect of two differently configured PCM storage units on the temperature distributions in water tanks. In the first design, myristic acid was filled into the PCM storage tank, which also served as an absorbing plate. In the second design, lauric acid was filled into the PCM storage tank, which also served as a baffle plate. The water temperature changes were followed by five thermocouples placed evenly and longitudinally into each of the three BSSWHs. The effects of the PCMs on the water temperature distributions depended on the configuration of the PCM storage unit and the longitudinal position in the water tanks. The use of lauric acid lowered the values of the peak temperatures by 15% compared to the control heater at the upper portion of the water tanks because of the low melting temperature of lauric acid, but it did not have any consistent effect on the retention of the water temperatures during the cooling period. The ability of the myristic acid storage unit to retain the water temperatures got more remarkable, especially at the middle portion of the water tank. The myristic acid storage increased the dip temperatures by approximately 8.8% compared to the control heater. In conclusion, lauric acid storage can be used to stabilize the water temperature during the day time, while the myristic acid storage unit can be used as a thermal barrier against heat loss during the night time because of its relatively high melting temperature and low heat conduction coefficient in its solid phase. The experimental results have also indicated that the thermal characteristics of the PCM and the configuration of the PCM storage unit can result in advantageous control of the water temperature rise and drop during both day and night time.

대청호 상류 하천에서 강우시 하천 수온 변동 특성 및 예측 모형 개발

강우시 저수지로 유입하는 탁수의 시공간분포를 실시간으로 예측하기 위해서는 하천 유입수 수온의 정확한 예측이 필요하다. 본 연구에서는 강우시 하천 수온의 변동특성을 조사하기 위해 2004년 홍수기 동안 대청호 상류 하천에서 한 시간 단위의 연속측정을 실시하였다. 강우사상 동안 하천수온은 강우 전 보다 최대 <TEX>$5\sim10^{\circ}C$</TEX> 정도 하강하는 것으로 나타났으며, 이것은 저수지로 유입하는 하천수의 밀도를 <TEX>$1.2\sim2.6$</TEX> tcg/<TEX>$m^3$</TEX> (<TEX>$0.12\sim0.26\%$</TEX>) 상승시켜 중층 밀도류를 형성하는 원인으로 작용했다. 실측자료를 이용하여 두 가지 종류의 통계형 수온 예측모형인 로지스적모형(DLG)과 다중회귀모형(DMR-1, DMR-2, DMR-3)을 개발하였다. 모든 모형들이 강우-유출 사상에 따른 하천 수온의 급격한 강하 현상을 비교적 잘 묘사하는 것으로 나타났으나, 일 평균기온, 이슬점 온도 그리고 하천 유량을 모형의 독립변수로 사용한 회귀형모형이 대기 기온과 하천 수온의 로지스틱 함수관계를 가정한 DLG모형보다 수온예측 성능이 보다 우수한 것으로 평가되었다. An accurate prediction of inflow water temperature is essentially required for real-time simulation and analysis of rainfall-induced turbidity 烈os in a reservoir. In this study, water temperature data were collected at every hour during the flood season of 2004 at the upstream of Daecheong Reservoir to justify its characteristics during rainfall event and model development. A significant drop of river water temperature by 5 to <TEX>$10^{\circ}C$</TEX> was observed during rainfall events, and resulted in the development of density flow regimes in the reservoir by elevating the inflow density by 1.2 to 2.6 kg/<TEX>$m^3$</TEX> Two types of statistical river water temperature models, a logistic model(DLG) and regression models(DMR-1, DMR-2, DMR-3) were developed using the field data. All models are shown to reasonably replicate the effect of rainfall events on the water temperature drop, but the regression models that include average daily air temperature, dew point temperature, and river flow as independent variables showed better predictive performance than DLG model that uses a logistic function to determine the air to water relation.

CE-QUAL-W2 모형을 이용한 저수지 탁수의 시공간분포 모의

저수지를 통한 수자윈의 지속적 확보와 이용에 걸림돌이 되고 있는 탁수의 장기발생문제를 기술적으로 해결하고자 실시간 탁수 감시와 예측시스템(RTMMS)을 구축 중이며, 2004년 홍수기 동안 대청호를 대상으로 유입하는 탁수의 수리 및 수질특성을 조사하고 2차원 횡방향 평균 수리 및 수질모형인 CE-QUAL-W2(W2)를 적용하여 탁수의 밀도류 거동과 시<TEX>${\cdot}$</TEX>공간적 분포를 예측하고 실측값과 비교하여 모형의 적용가능성을 평가하였다. 강우사상 동안 하천 수온은 <TEX>$5{\sim}10^{\circ}C$</TEX> 정도 하강하였으며 탁수가 저수지내에서 밀도류를 형성하는 원인으로 작용했다. 적용된 W2모형은 수온의 성층구조 변화와 탁수의 침강점, 도달시간, 중층밀도류 두께 등 탁수의 거동특성을 비교적 잘 모의하였다. 그러나 국부적으로 탁수가 위치한 중층과 탁수 유입 전에 형성되었던 전이층에서 수온과 탁도의 모의값과 실측값이 유의할 만한 오차를 보였다. 펜티엄급 PC(CPU 2.0GHz)로 홍수기 전체기간 모의에 소요된 시간은 약 4분으로써 모형은 계산의 효율성 측면에서 실시간 모의에 적합한 것으로 평가된다. A real-time monitoring and modeling system (RTMMS) for rainfall-induced turbidity flow, which is one of the major obstacles for sustainable use of reservoir water resources, is under development. As a prediction model for the RTMMS, a laterally integrated two-dimensional hydrodynamic and water quality model, CE-QUAL-W2 was tested by simulating the temperature stratification, density flow regimes, and temporal and spatial distributions of turbidity in a reservoir. The inflow water temperature and turbidity measured every hour during the flood season of 2004 were used as the boundary conditions. The monitoring data showed that inflow water temperature drop by 5 to <TEX>$10^{\circ}C$</TEX> during rainfall events in summer, and consequently resulted in the development of density flow regimes such as plunge flow and interflow in the reservoir. The model showed relatively satisfactory performance in replicating the water temperature profiles and turbidity distributions, although considerable discrepancies were partially detected between observed and simulated results. The model was either very efficient in computation as the CPU run time to simulate the whole flood season took only 4 minutes with a Pentium 4(CPU 2.0GHz) desktop computer, which is essentially requited for real-time modeling of turbidity plume.

Internal tidal bore warm fronts and settlement of invertebrates in central Chile

We studied the occurrence of large high frequency temperature fluctuations and their potential association with settlement of intertidal invertebrates during the spring/summer period 1999/2000 at Las Cruces, on the coast of central Chile. Our results showed the existence of internal tidal bores, characterized by sharp drops in water temperature at the surface and near the bottom, and subsequent temperature increases, which occurred with a semidiurnal periodicity. Measured currents support the hypothesis of alternating onshore and offshore movement of warm-water fronts. The frequency of the events varied through the summer and their amplitude seems to be modulated by onshore winds. The strongest events were observed when strong onshore winds occurred in late afternoon hours and the entire water column showed a semidiurnal temperature signal. Highest values of chlorophyll concentration in the intertidal zone and daily settlement of bivalves, gastropods and crustaceans were observed at times when conditions were favorable for occurrence of internal tidal bores. Results suggest that internal tidal bore warm fronts could play an important role in the transport of neustonic larval invertebrates and the delivery of phytoplankton to at least some intertidal sites along the coast of Chile.

Multiple acute temperature stress affects leucocyte populations and antibody responses in common carp, Cyprinus carpio L.

Stress is a potential factor causing increased susceptibility of fish to pathogens. In this study, stress-induced immunological changes that may contribute to a decreased immune status were investigated. A 3 h drop in ambient water temperature of 9 °C was used as a relative mild and acute stress model for carp. Effects of this stressor on the dynamics of leucocyte populations were determined with specific monoclonal antibodies. The relative number of circulating B-lymphocytes in the total leucocyte population decreased significantly within 4 h after the onset of single or multiple cold shocks. This decrease was reversible, as B-lymphocyte numbers were restored within 24 h. Most probably, a redistribution of B-lymphocytes contributed to this phenomenon. In head kidney, an increase was measured in the relative number of B-lymphocytes. Granulocyte numbers showed opposite reactions: the percentage of granulocytes in the total leucocyte population nearly doubled in circulation and decreased significantly in the head kidney. This demonstrates that in vivo, a mild stressor differentially alters the distribution of leucocytes. In stressed carp, the percentage of apoptotic lymphocytes in blood is significantly higher compared with the unstressed animals. B-lymphocytes as well as Ig −lymphoid cells contributed to this increased apoptosis. Labelling of blood lymphocytes with a polyclonal antiserum against the glucocorticoid receptor also showed, besides B-lymphocytes, part of the Ig −lymphoid cell population to be glucocorticoid receptor positive. As the distribution of B-lymphocytes was substantially affected, the effect of temperature stress on T-lymphocyte-independent (trinitrophenyl–lipopolysaccharide) and T-lymphocyte-dependent (dinitrophenyl–keyhole limpet hemocyanin) humoral antibody responses was determined. Kinetics of the primary antibody response to the T-lymphocyte-independent antigen showed lower antibody titres in stressed carp during the onset of the immune response, implying a slower development of the antibody response against the T-lymphocyte-independent antigen.

Growth and diet of anadromous Arctic charr after their return to freshwater

Abstract –The post smolt of anadromous Arctic charr (Salvelinus alpinus) from Lake Storvatn, northern Norway (70°39′48″), continued to feed and grow after their return to freshwater in late summer, but in late autumn (October) both their growth rate and feeding intensity ceased along with the drop in water temperature. In contrast, adult, sexually mature anadromous charr did not appear to feed during their freshwater residency. The stomach fullness of post smolts were similar to that of resident Arctic charr during early autumn, and their diets were similar, being dominated by pelagic prey such as surface insects,Holopediumsp.,Bosminasp. and chironomid pupae. Later in the autumn, the resident charr also included some more benthic prey, in particular gastropods, whereas the post smolts continued to feed predominantly on zooplankton and surface insects, but with a lower stomach fullness than the resident fish. This suggests that after arrival in freshwater, the post smolts continue their pelagic feeding behaviour displayed during the sea‐migration.

Change in color of the hot spring deposits at the Chinoike-Jigoku hot pool, Beppu geothermal field

The Chinoike-Jigoku hot pool in Beppu geothermal field, Central Kyushu, Japan, displays a blood-red color due to the hematite (Fe 2O 3) deposited at the bottom of the pool. The colors of the deposits collected on 1 October 1990, on 27 March 1995, and on 6 March 1996 were measured with a colorimeter. The results show that the red deposits became yellower in 1995 and 1996 than they were in 1990. X-ray diffraction (XRD) patterns and chemical compositions of the deposits indicate that the discoloration of the Chinoike-Jigoku pool water is caused by an increase in the content of jarosite [KFe 3(SO 4) 2(OH) 6]. The temperature of the subsurface thermal water beneath the Chinoike-Jigoku hot pool, as estimated by the anhydrite chemical geothermometer, has declined from 200 to 150 °C over the past 25 years. The Na and Cl concentrations of the hot spring water discharging from Chinoike-Jigoku have decreased, while the SO 4 concentration has increased. The temporal variations in subsurface temperature and dissolved ion concentrations suggest that the mixing ratio between the high–temperature, neutral Na–Cl type water and the relatively low-temperature, acid H–SO 4 type water that form the thermal water of Chinoike–Jigoku has changed over the last 25 years. Hydrothermal studies of jarosite stability have confirmed that the increase in jarosite content in the deposits was caused by a temperature drop of the mixed thermal water beneath Chinoike-Jigoku pool, due to an increase in the contribution of the cooler H–SO 4 water type to the thermal mixture.

Confirmation of catfish, Ictalurus punctatus (Rafinesque), mortality from Microcystis toxins

Unexplained deaths of pond‐grown catfish have occurred for many years. At least some of these mortalities could be from cyanobacteria toxins ingested during feeding on floating diets or passively assimilated through gills during breathing. Recently we were able to document algal production and subsequent ingestion of these toxicants by catfish during a mortality event. The causative organism, Microcystis aeruginosa, was the dominant species within the phytoplankton community during the cooler autumn‐winter season. Pond conditions included a drop in water temperature by c. 5 °C during the 10 days preceding the fish mortalities. Microcystin‐LR, a hepatotoxin produced by Microcystis, was detected in water samples and in catfish liver tissue. Fish exposed to pond water containing this toxic bloom were killed within 24 h. Necropsy of fish revealed congested liver and spleen tissues. The combination of clinical signs, detection of microcystin LR in water and in liver, and death of fish exposed to pond water supports the diagnosis of microcystin toxicosis. More research is needed to identify specific environmental conditions initiating toxin production to model and predict occurrence of these toxic algal blooms.

Spawning of the sea ravenHemitripterus villosus in Peter the Great Bay, Sea of Japan

The spawning habits of the sea ravenHemitripterus villosus were investigated by scuba diving at shallow rocky bottom sites around Bolshoi Pelis Island (Peter the Great Bay, Sea of Japan). Spawning occurs in September, when the surface water temperature drops. The optimum spawning temperature is 17–18°C. The fish density in nest sites reaches 120/300 m2. The mean individual fecundity is about 10000 eggs. Over 35% of the egg masses ofH. villosus are eaten by echinoderms, primarilyPatiria pectinifera andStrongylocentrotus nudus. Since fecundity is relatively low and parents do not take care of the egg masses, predation can strongly affect the abundance of this species.

A drop in ambient temperature results in a transient reduction of interrenal ACTH responsiveness in the gilthead sea bream (Sparus aurata, L.)

This study investigated the effects of a drop in water temperature (18 °C to 9 °C in 24 h) on the pituitary and interrenal hormones of the gilthead sea bream Sparus aurata. The in vitro sensitivity of the interrenal tissue to ACTH, plasma levels of cortisol, ACTH, α-MSH, GH, glucose, lactate and ions were determined. In vitro ACTH, stimulated the release of cortisol from isolated interrenal glands from control gilthead sea bream in a concentration dependent fashion. However, the interrenal cells were less sensitive to ACTH as soon as 24 h following the onset of the temperature drop. At this time, plasma cortisol and ACTH levels were raised, and plasma GH concentrations were decreased, whereas no significant changes were found in plasma α-MSH. After 96 h plasma ACTH levels had recovered whereas plasma cortisol levels were still higher than controls after 8 days of the beginning of the experiment. Interrenal sensitivity had recovered after 8 days. The results may help to clarify the relationship between the stress response and the aetiology of the winter syndrome in sea bream.

Cold Tolerance and Fatty Acid Composition of Striped Bass, White Bass, and Their Hybrids

Abstract Cold tolerance of striped bass Morone saxatilis, white bass M. chrysops, palmetto bass (female striped bass × male white bass), and sunshine bass (female white bass × male striped bass) were compared under controlled laboratory conditions. Two groups of each taxon were acclimated at 20°C in a recirculating-water system housed in an environmental chamber and were fed either a natural or prepared diet for 84 d. The fatty acid composition of the natural diet was 13% more unsaturated than that of the prepared diet. Fish fed the natural diet subsequently had unsaturated: Saturated fatty acid ratios 10-25% higher than fish fed the prepared diet. After being subjected to identical simulated cold fronts (10°C drop in surface water temperature, as if the fish were confined in cages or pens), all groups of fish fed the prepared diet suffered high mortality (50-90%) whereas there was zero mortality among the groups receiving the natural diet. White bass and sunshine bass fed the prepared diet had higher sur...

`Syndrome 93' in New Caledonian outdoor rearing ponds of Penaeus stylirostris: history and description of three major outbreaks

Farming of Penaeus stylirostris (Mexican strain) in New Caledonia is a developing industry conducted in flow-through semi-intensive system, at 20 to 40 animals/m 2 with a theoretical extrapolated yield of 4.2 t/ha/yr. In 1995, approximately 878 t of shrimps were produced from 352 ha of ponds. From the 1980s to 1992, production increased progressively (538 t in 1990, 648 t in 1991 and 734 t in 1992). The increase was the result of improved techniques and greater production surface area. In 1993, production decreased (621 t in 1993), then increased again in 1994 and 1995 due to increased grow out surface only. Low yields and survival rates in 1993, 1994 and 1995 were associated with abnormal mortalities. This pathology, given the name `Syndrome 93', appeared during a period of drought and was more pronounced in winter (mid-May to mid-August). The mortalities were chronic or acute. High pond biomass and sudden water temperature drop seemed to have an impact on the development of the disease. Moribund shrimps were weak, sensitive to stress and swam near the water surface. Shrimps were soft with dark and dull exoskeleton and whitish muscles. Their hemolymph clotted slowly. The hemolymph of diseased shrimps was generally infected with one predominant strain of bacteria, Vibrio sp. The hemolymph of presumed healthy shrimp was sometimes sterile or contained variable but generally limited numbers of different bacteria of the genera Vibrio, Pseudomonas, Flavobacterium and Cytophaga. Moribund shrimps exhibited classical anatomopathologic septicemic vibriosis lesions. However, numerous pycnotic hemocytes and atypical basophilic granulations were also observed in most tissues, especially the lymphoid organ, heart, connective tissue of the stomach and cuticular epithelium. These basophilic granulations seemed to correspond partly to nuclear debris and partly to intracytoplasmic inclusions which are similar to those described in penaeid viral infections (`yellow head disease', `Taura syndrome') indicating that pathogens other than Vibrio sp. could be involved.

Effects of water temperature on mucous cell distribution in channel catfish epidermis: a factor in winter saprolegniasis

The influence of an acute drop in water temperature on channel catfish (Ictalurus punctatus) mucous cell distribution in the epidermis was examined. Channel catfish were subjected to a water temperature drop from 22 to 10°C in 24h and sampled for histological examination of the epidermis at regular intervals. Three days after the drop in water temperature, there was a marked decrease in the number of mucous cells in the outermost (superficial) portion of the epidermis. The number of mucous cells returned to normal levels after fish were maintained at 10°C for 6 days. If catfish were subjected to the temperature drop and also challenged withSaprolegnia, mucous cells in the superficial epidermis did not recover to normal levels but continued to decline from day 3 until the fish subsequently died from saprolegniasis. These results may explain the dry skin appearance characteristic of catfish exhibiting winter saprolegniasis. Furthermore, sinceSaprolegniacysts are normally shed in sloughed mucus, low temperature-induced mucus loss may explain howSaprolegniacysts attach and infect catfish skin to result in disease. These results also reinforce the notion that an intact external mucus layer is the first line of defence against infectious disease in fish.

大村湾におけるリン濃度の変動

Omura Bay is located in the central part of Nagasaki Prefecture and is connected with the open sea through Sasebo Bay by two narrow straits. Therefore movement of the bay water is very stagnant and oxygen-deficient water masses are formed at the bottom layer in the central part of the bay every summer.We have been measuring the concentrations of phosphorus in this bay for twelve years.The concentrations of total phosphorus in the surface layer began to increase gradually after 1992.The concentrations in the whole bay become about 10 μg·l-1 higher after September than those in the earlier months every year. It is thought that orthophosphate in the bottom layer at the central part of the bay, which was released from the bottom sediment in summer, causes the increase of total phosphorus in the surface layer after September. This water mass which has been enriched by ortophosphate (as total phosphorus : 70-100 μg·l-1) is diffused by circulation owing to the drop in water temperature of the surface layer and mixing by wind, and the concentration of total phosphorus in the surface layer will rise.