Entry Of Seawater Research Articles

Dampak Banjir Rob terhadap Perekonomian Warga Desa Loireng Kecamatan Sayung Kabupaten Demak

Loireng Village is one of the villages in Sayung subdistrict that is affected by the rob disaster caused by low ground levels, rising sea levels, and loss of drainage which results in the entry of sea water into land areas, especially enter the rice field area. Rob disaster that occured in Loireng vill age very impactful to the local resident. Therefore researchers want to study the impact of rob floods on the economy of the residents of Loireng village. As for the data collection stages used comes from observation, documentation and interviews with residents whose land is affected by rob flooding. this type of research is qualitative research thats analyzing, describe a phenomenon or incedents on the object under study. The analysis results fom research is show that the impact of rob floods which resulted in the death of rice fields and converted into pond area so that it can support and improving the economy of the residents of Loireng village.

Study on diffusion and migration characteristics of impurities in secondary side of simplified u-tube steam generator

During the operation of nuclear power systems, the occurrence of leakage accidents of primary and secondary condensers are a major concern due to the potential threat to safe operation. The entry of seawater into the secondary loop from the condenser, along with impurities such as Cl-, can accumulate near the heat transfer tube, causing wear and corrosion, which can further aggravate the situation. Therefore, it is essential to accurately understand the migration and diffusion process of impurities in the secondary side of the steam generator. This study aims to investigate the three-dimensional multi-tube physical model of fluid–structure coupling heat transfer in the primary and secondary loops of the steam generator, including the heat exchange tube, to gain insights into the migration and diffusion of Cl- and other impurities. The distribution of important thermal parameters, such as volume vapor fraction, temperature, and velocity, in a U-shaped tube bundle were analyzed by numerical simulation of heat transfer and fluid flow. The diffusion and migration of Cl- in a two-phase flow were also studied. Results of this study reveal that impurities concentration is influenced by the effective diffusion coefficient, which is further influenced by the boiling intensity and flow velocity of the coolant. The combined effect of the boiling intensity and flow velocity of the coolant has a synergistic effect on the migration and diffusion of Cl-. In conclusion, this study provides valuable insights into the flow heat transfer impurity migration under a multi-tube coupled heat transfer condition of the steam generator, which can be used as a scientific basis for the design optimization and operation of steam generators.

A comparison study of crevice corrosion on typical stainless steels under biofouling and artificial configurations

In this work, the crevice corrosion behavior and biofouling coverage of 316L stainless steel (316L SS), 2205 duplex stainless steel (2205 DSS), and 2507 super duplex stainless steel (2507 SDSS) in natural seawater were investigated through long-term field exposure tests. The results revealed that both artificial crevice corrosion and biofouling-induced crevice corrosion occurred on the surface of three stainless steels. The corrosion rate was ranked as 316L SS » 2205 DSS＞2507 SDSS. The deepest area of the artificial corrosion pit was at the edge of the crevice, which was related to the IR drop and acidification of the localized solution. The highest biofouling coverage and the most severe biofouling-induced corrosion occurred on the surface of 316L SS. The attachment of large organisms to the metal surface formed a fouling barrier layer, further blocking the flow of material over the crevices, and the artificial crevice corrosion was accelerated. The initiation of barnacle-induced corrosion was due to the formation of a crevice between the barnacle and the substrate, resulting in the entry of seawater. The acidification of the solution caused by catalytic-occluded cells was responsible for the continuous development of barnacle-induced corrosion, which was similar to the propagation of the artificial crevice corrosion.

Hydrochemistry and stable isotopes in a coastal lagoon affected by evaporation, Cabo de Gata (Almería)

The Salinas de Cabo de Gata are a natural coastal lagoon that has been anthropically transformed to favor the entry of seawater and its evaporation until saturation in sodium chloride. For this, it is compartmentalized in a series of ponds in which the seawater is guided by a circuit along which the salinity increases. Sediment samples have been taken at the bottom of these ponds and water samples to recognize which hydrogeochemical processes occur along the route. In the first ponds (evaporators) the suspended solids are decanted and carbonate precipitation occurs, along with the formation of pyrite linked to the high concentration of organic matter. On the other hand, in the last ponds (crystallizers) gypsum precipitation occurs when 70% evaporation is reached and, finally, halite when it reaches 90%. This precipitation notably changes the chemical composition of the waters, reducing the concentration of the ions present in the minerals that precipitate. From the isotopic point of view, gypsum precipitation also has its mark, reducing the proportions of 18O/16O and 2H/1H in the pond water. The study of these processes, in a mesoscale system, has great advantages for making palaeoenvironmental inferences at the basin scale, such as knowing what percentage of seawater must be evaporated so that gypsum or halite can precipitate in a basin.

Results of land subsidence measurement using GPS method in the Jakarta groundwater basin in 2015-2019

The development of population and development activities in big cities in Indonesia, especially in the city of Jakarta and surrounding areas is very rapid. From several land subsidence studies, several factors have been identified that cause land subsidence, namely: excessive groundwater extraction, reduction due to building/infrastructure loads, subsidence due to natural consolidation of soft soil layers, and subsidence due to tectonic forces. At present the exploitation of ground water for industrial and residential needs is at a level that needs attention. Excessive pumping of groundwater will cause a decrease in the quantity of ground water, entry of seawater into the land (sea water intrusion) and land subsidence. Symptoms of the negative impact of land subsidence have been felt in several areas, especially in industrial areas located in the northern part of Jakarta. This land subsidence can be measured by GPS or satellite geodetic method, which have begun to develop in Indonesia in the past two decades. Measurements were made using the radial method at 53 GPS points in 2015 up to 100 measurement points in 2019 in Jakarta Groundwater Basin. The result of these campaign GPS surveys that is northern part of Jakarta relatively had higher subsidence rate than the southern. The largest subsidence almost reached 6.2 cm/year in Muara Baru in northern area which is southern area only suffered an average rate of 1.16 cm/year.

Spatio-Temporal Salt Ponds in Madura Island in 2009-2019 for Managing Sustainable Coastal Environments

The salt pond ecosystem has a very important ecological function, especially for the coastal region of Madura. One of the ecological functions of the salt pond is supporting the economy of the community. The purposes of this study are: (1) To determine changes in salt ponds in Madura Island in the last 10 years (2009-2019) based on remote sensing data and Geographic Information System; (2) To make a simulation of structuring the Salt Pond area on Madura Island in the management of a sustainable coastal environment. This type of research is a descriptive-analytic survey method using remote sensing data and Geographic Information System. The object of the study is the Tambak Garam (salt pond) area in Madura Island focusing on Sampang Regency, Pamekasan Regency, and Sumenep Regency. Data collection techniques carried out by observation, interviews, and documentation. Changes in Salt Ponds data analysis were carried out using remote sensing data extraction method with true-color image input and NDVI. The results show that the area of salt ponds decreased from year to year in the district of Sampang, Pamekasan, and Sumenep. Management intensification using more modern technology is done to increase production in the declining salt pond areas. Salt production runs optimally if it is carried out in coastal areas with sloping morphology and soil that is not porous in the form of clay soil, which does not absorb seawater. Sloping morphology was chosen to support the entry of seawater into salt pond plots that use tidal power.

Analysis of the dynamics of coastal landform change based on the integration of remote sensing and gis techniques: Implications for tidal flooding impact in pekalongan, central java, Indonesia

Abstract Coastal landforms are located in the interface zone between atmosphere, ocean and land surface systems formed by the geomorphic process of erosion, depositional, and subsidence. Studying the dynamics of coastal landform change is important for tracing the relationship between coastal landform changes and tidal flooding in the coastal areas of Pekalongan, Indonesia. The method of integrating remote sensing data with geographic information system (GIS) techniques has been widely used to monitor and analyze the dynamics of morphology change in coastal landform areas. The purpose of this study is to map the dynamics of landform change in the study area from 1978 to 2017 and to analyze its implications for the impact of tidal flooding. The results of the mapping and change analysis associated with coastal landforms can be classified into four landform types: beach, beach ridge, backswamp and alluvial plain. Changes in coastal morphology and landform topography affected by land subsidence and changes in land use/ land cover have contributed to the occurrence of tidal flooding in the study area. Beach ridges perform an important role as natural levees which hold back and prevent the entry of seawater at high tide in coastal areas. A limitation of this study is that, as it focuses only on the physical aspects of coastal landform characteristics for one of the factors causing tidal flooding.

Simulation of the effect of floodway on Batang Kandis River flood control

Floods often occur in Padang City, mainly in the areas of Pasia Nan Tigo Village and Lubuk Buaya Village, caused by the overflow of Batang Kandis when heavy rains occur (intensity of rainfall >15mm/hours). To decrease the river overflow an artificial canal with 300 m long and 50 m wide (floodway) was constructed to bypassing the river flow from the Batang Kandis River to the ocean. In order to find out the effects of the floodway, four scenarios are performed the scenario 1 and 2 were the simulation condition of Batang Kandis River before and after the construction of floodway. While to increase the effectiveness of floodway, simulations 3 and 4 were carried out. Scenario 3 was the combination of floodway with normalization and embankment. To prevent the entry of seawater into the Batang Kandis River, because the floodway is affected by the tide of the sea, then 3-door motion weir was simulated namely scenario 4. Scenario 4 was the combination of floodway normalization, embankment, and a 3 door motion weir. From the simulations, we found that the floodway was effective to decrease the water surface level up to 15 m and 20 m during 10 years and 25 year return period of discharge respectively. From the scenario 3, we found that the embankment with 1.5 m and 2 m was effective to prevent overflow by 10-year and 25-year return period of discharge respectively. While for scenario 4 the water level rises 0.5 m due to motion weir So, that it is needed to extend the embankment with 0,5m high.

Change of hydrological and morphometric characteristics of Kuyalnik Liman after inflow of seawater

The water level of the liman, volume and area of surface reduced to record low values as a result of intensification of evaporation process in 2014. By the autumn of 2014 the liman was on the verge of extinction. Entry of seawater in the liman through the pipeline began in December of 2014 to prevent environmental degradation of the liman.
 Purpose of this publication consists in analyzing the changes of hydrological and morphometric characteristics of Kuyalnik liman in 2014-2016 associated inflow of sea water.
 Methods of study. Hydrological and morphometric characteristics of the liman were calculated on the basis of: field studies, bathygraphic curves, data of satellite images «Landsat».
 Results. There was dynamics of change of water surface area, volume, level and salinity of liman’s water during the driest periods, at the time and after the inflow of seawater into the liman. The results of measurements of discharge of seawater and coastal watercourses. The effect of evaporative processes taking into account temperature conditions (Odessa, Lyubashevka) on liman’s hydraulicity after the cessation of seawater supply was analyzed.
 Conclusion. Inflow of seawater into the liman after the first entry of seawater allowed to temporarily stabilize water-salt regime of the liman, however, hydrological and morphometric characteristics of the liman in autumn of 2015 almost returned to the values of early autumn of 2014. During subsequent inflows of seawater into the liman it is desirable to maintain the regime observed during the inflow of water in 2014-2016.

Magnetostratigraphy and luminescence dating on a sedimentary sequence from northern East China Sea: Constraints on evolutionary history of eastern marginal seas of China since the Early Pleistocene

Owing to the large and increasing population density in low-lying coastal regions, even small changes in sea level can have substantial societal and economic impacts. Alternations of terrestrial and marine sediments deposited in coastal areas or continental shelves are important and effective indicators of sea-level changes, and thus, have been widely studied in the marginal seas of China over the past 30 years. However, sea-level change results from not only eustatic factors but also tectonic activity. The Zhe-Min (or Zhejiang–Fujian) Uplift (ZMU) was such an important factor in geomorphology, and formed a barrier preventing entry of sea water into the northern marginal seas of China, but its Quaternary history is poorly known.In this study, a new borehole (ECS-DZ1) was drilled in the Zhoushan Islands, northern East China Sea to obtain information on the evolution of the ZMU during the Quaternary. Information from paleomagnetic and luminescence dating was combined with data on sedimentary changes. The main results are: (1) constrained by luminescence ages, the upper sedimentary units were extrapolated to have been deposited since ∼0.2 Ma; (2) paleomagnetic results suggest that the ECS-DZ1 borehole sequence spans from the pre-Olduvai Matuyama reverse chron to the Brunhes normal chron, approximately constraining the age of the basal sedimentary unit to ∼2.0 Ma; (3) a significant hiatus or erosion between two major sedimentary units possibly occurred between the late Early Pleistocene and Middle Pleistocene.As the Zhoushan Islands are within the ZMU and considering previous transgression studies around this region, it is inferred that the ZMU subsided at ∼2.0 Ma, allowing sea water to invade northward in the Yellow Sea basin. The ZMU might have been uplifted again no later than 1.0 Ma, causing a sedimentary hiatus or lacustrine development. After ∼0.2 Ma, the ZMU subsided completely, allowing large transgressions to develop across the northern marginal seas of China in the context of global sea-level changes.

Cover Picture: Materials and Corrosion. 1/2014

Cover: The use of preservation treatments for hydrostatic test waters is a crucial practice to provide protection of subsea pipelines against corrosion. The potential effects of seawater ingress into 316L lined pipes filled with treated seawater during subsea tie‐in operations on corrosion performance were investigated. Fluorescence imaging shows microorganisms attached to 316L coupons exposed to treated seawater in the event of oxygen ingress into the system. 3D optical surface images show typical pits found on 316L exposed to treated seawater in the presence of high concentrations of oxygen. Pit profiles were determined from optical microscopy to measure pit depths. The entry of seawater into the system can introduce aggressive species such as oxygen which is shown to have a negative impact on the biocidal and oxygen scavenging efficiency of the chemical treatments and a detrimental effect on pitting corrosion.More detailed information can be found in: L. L. Machuca, L. Murray, R. Gubner, S. I. Bailey, Evaluation of the effects of seawater ingress into 316L lined pipes on corrosion performance, Materials and Corrosion 2014, 65, 8.

Picophytoplankton community in a tropical estuary: Detection of Prochlorococcus-like populations

The influence of hydrography on the picophytoplankton (PP) abundance in estuaries was studied by sampling along a salinity gradient for the first time in an Indian estuary. Prochlorococcus-like cells were detected at salinities ranging from 0.06 to 35, which otherwise is reported from offshore regions, thereby showing that this group is capable of surviving in estuarine waters. PP also comprised picoeukaryotes and two groups of Synechococcus, one rich in phycoerythrin (SYN-PE) and other in phycocyanin (SYN-PC). Salinity played an important role in the picophytoplankton distribution. SYN-PE was represented by two sub-groups, one which was found only in saline waters (SYN-PEII) and the other throughout the salinity gradient (SYN-PEI). SYN-PEI and SYN-PC dominated downstream and upstream, respectively but were present throughout the salinity gradient unlike in other estuarine regions. Picoeukaryotes abundance showed an increasing trend from saline to brackish water and decreased in freshwater. The entry of seawater into the estuary regulated SYN-PE and Prochlorococcus-like cells downstream whereas their higher abundance in freshwater could be due to different strains of freshwater origin. The average contribution of PP to the total photosynthetic biomass during spring and neap tides was 43% and 29% respectively, which highlights the importance of PP in estuaries.

Geodynamic responses to a two-step model of the Messinian salinity crisis

Abstract There is a growing consensus that the sulfates and halite within the massive evaporite deposits on the shallow margin and deep floor of the Mediterranean sea formed in two steps. Both phases had geodynamic consequences. The current evidence indicates that during the first step when the first cycle “Lower Evaporites” were deposited primarily in marginal settings, the surface of the Mediterranean remained at or very close to the level of the external Atlantic. The geodynamic response resulted from the increasing weight of the brine layer as it concentrated from normal marine salinity to the threshold for sulfate precipitation and then to the threshold for halite precipitation. This weight alone significantly deepened the Mediterranean basins by isostatic loading. Flexure of the lithosphere caused a peripheral bulge to appear that may have been the agent to close off the further entry of Atlantic seawater. Step two began with the subsequent evaporative drawdown and the deposition of the second cycle “Upper Evaporites”. As the basins dried out the loss of weight of the water led to regional isostatic uplift that permanently closed the prior inlets. Sediments removed from the margins by early subaqueous mass-wasting and later subaerial erosion and delivered to the basin floors further accentuated uplift of the margins and subsidence of the depocenters. The principal result has been to progressively tilt the Mediterranean substrate downwards from the margin towards the basin centers. This tilting was enhanced with the flooding of the desiccated sea at the climax of the salinity crisis. Consequently the salt layer rests today out of equilibrium on a surface that is more inclined after precipitation than before. The current mobility and flowage of the salt away from its margins and towards the basin centers is therefore not so much a response to the differential thickness and weight of overlying sediments, but to the combination of geodynamic processes that have produced the seaward tilting. Other giant salt deposits seem to have experienced a similar two-step evolution.

Stratigraphic development during the Late Pleistocene and Holocene offshore of the Yellow River delta, Bohai Sea

A 61-m-long sediment core (HB-1) and 690 km of high-resolution seismic profiles from offshore of the Yellow River delta, Bohai Sea, were analyzed to document the stratigraphy and sea-level changes during the Late Pleistocene and Holocene. Accelerator mass spectrometry 14C dating and analyses of benthic foraminifera, ostracods, the mineral composition, and sedimentary characteristics were performed for core HB-1, and seven depositional units (DU 1–DU 7 in descending order) were identified. The seismic reflection data were interpreted in light of the sedimentological data of the core and correlated with other well-studied cores obtained previously in the Bohai Sea area. Seven seismic units (SU 1 to SU 7 in descending order) were distinguished and interpreted as follows: SU 7 corresponds to marine facies in Marine Isotopic Stage (MIS) 5; SU 6, to terrestrial facies in MIS 4; SU 5 and SU 4, to alternating terrestrial and marine facies (DU 7–DU 5) in MIS 3; SU 3, to terrestrial facies (DU 4) in MIS 2; SU 2, to Holocene marine facies (DU 3 and DU 2); and SU 1, to modern Yellow River delta sediments deposited since 1855 (DU 1). The sedimentary facies from DU 7 to DU 5 reflect sea-level fluctuations during MIS 3, and the boundary between DU 5 and DU 6, which coincides with that between SU 4 and SU 5, is a distinctive, laterally continuous, undulating erosion surface, with up to ∼20 m of relief. This surface reflects subaerial exposure between transgressions during MIS 3. Estimated sea levels during MIS 3 ranged from −35 ± 5 to −60 ± 5 m or lower, with short-term fluctuations of ∼20 m. Sedimentary environments in the Bohai Sea area were governed mainly by eustatic sea-level changes and the Bohai Strait topography, which controls the entry of sea water into the Bohai Sea area. The mineral composition of the sediment core suggests that the Yellow River did not discharge into the Bohai Sea, or at least did not influence the study area significantly, during parts of MIS 3 and MIS 2 to the early Holocene (∼11–8.5 cal kyr BP).

In vivo investigation of oocyte transit and maturation in a broadcast‐spawning holothurian

Abstract. A sequential in vivo approach was used to examine the transformations undergone by oocytes during transit in the gonoduct of the sea cucumber Holothuria leucospilota, from ovulation until fertilization competency. Spasms of the ovarian muscle bands, during the pre‐spawning locomotor activity of the females, coincided with the extrusion of oocytes from the follicle cells (ovulation). No germinal vesicle breakdown (GVBD) was visible and the oocytes were not fertilizable. As the animal began to display the anterior sweeping movements characteristic of spawning, the oocytes streamed out of the gonad and were stored in the gonad basis. The oocytes, which were still non‐fertilizable, were then pressed forward through the first (proximal) section of the gonoduct. GVBD was completed during this rapid transit, but oocytes could not be fertilized unless they had soaked ≥20 min in seawater. In the second (distal) section of the gonoduct, most oocytes were readily fertilizable; fertilization rates increased noticeably after the formation of a bulge beneath the gonopore, which favored the entry of seawater. Hydration of the jelly coat was apparent (i.e., a 60% increase in oocyte surface area). Gamete release occurred in one powerful spurt ∼85 min after the onset of ovulation. This oocyte maturation sequence is expected to occur in holothurian species with similar anatomy and spawning behavior.

Ice in the 1994 Rabaul eruption cloud: implications for volcano hazard and atmospheric effects

VOLCANIC clouds are an important natural hazard to aircraft1, and host chemical reactions that interest both volcanologists2,3 and atmospheric scientists4-6. Ice has been suggested as a possible component of eruption clouds7, but there has been no direct evidence for its presence. Here we report the detection, using a satellite-borne infrared sensor, of ≳ 2 million tonnes of ice in the cloud produced by the September 1994 eruption of Rabaul volcano, in Papua New Guinea. The cloud also contained relatively low levels of sulphur dioxide (80 ± 50 kilotonnes), compared with other stratospheric eruption clouds. The unusual aspects of this cloud may be related to the entry of sea water into the volcanic vent, and its participation in the eruption column. Past eruptions that occurred in similar (coastal) settings, such as those of Krakatau and Santorini, might have had less effect on the atmosphere than their volume alone would suggest, because the presence of ice may decrease the residence time of ash and sulphur in the atmosphere. In addition, the ability of ice to mask the characteristic spectral signature of volcanic ash will increase the difficulty of designing airborne ash detection systems for aviation safety.

Rate of Water Admission Through the Madreporite of a Starfish

ABSTRACT Time course studies employing the fluorescent, high molecular weight tracer, fluorescein isothiocyanate dextran, confirm that there is a steady entry of sea water through the madreporite of the starfish, Echinaster graminicola, even under constant environmental conditions. This entry serves to supply replacement fluid to both the water vascular system and the perivisceral coelom, with more going to the latter than the former (10·67 vs 6·35 μl h−1 for a 7·25 g animal). Since nearly 2·4 days may be required for an animal to take up 1 ml of sea water through the madreporite, the rate of entry is too low to be easily seen in direct observation, or to have immediate physiological consequences if prevented. Nevertheless, the rate is probably sufficient to make a substantial contribution to fluid volume regulation, functioning along with osmolyte transport and other processes that have been emphasized in recent literature.

Evolution saisonniere du zooplancton dans trois sites peu profonds de Thau, une lagune Nord-Mediterraneenne

A monthly zooplankton survey has been conducted from March 1982 to March 1983 at three shallow stations of Thau, a northern-mediterranean lagoon. These stations differ by their distance from the entry of sea-water in the lagoon. Parameters such as pH, temperature, dissolved oxygen, conductivity and turbidity have been measured simultaneously with the sampling in the same water layer. The zooplankton collected corresponds to species usually found in marine neritic communities. In the spring, species richness is maximum. During the summer, meroplankton forms dominant populations in the communities. Autumn is marked by a reduction of the number of species and of the abundance in both components, holoplankton and meroplankton. Few species are present in the winter holoplankton while meroplankton disappears practically from the samples. The sites under observation are subjected to unpredictable changes, in water movement as well as in the organization of the zooplankton communities. These modifications are strongly influenced by weather conditions.

Environmental characteristics of the Mandovi-Zuari estuarine system in Goa

Two rivers, the Mandovi and the Zuari, with their interconnecting canal, form an estuarine system in Goa on the west coast of India. Physical, chemical and biological features of this estuary are adapted to a seasonal rhythm induced by the annual cycle of the monsoon. Heavy precipitation and land runoff from June to September bring about large changes in temperature, salinity, flow pattern, dissolved oxygen and nutrients when the estuary becomes freshwater dominated. The monsoon season (July–September) is followed by a recovery period during the post-monsoon season (October–January) and thereafter a stable period of the pre-monsoon season (February–May) when the estuary becomes marine dominated. During the pre-monsoon (dry) season, the water in the estuarine system remains well mixed and the intrusion of salt water is felt as far as 65 km upstream in both the rivers; but during the monsoon season the rivers become stratified and a salt wedge is formed in each river which extends up to about 10 km upstream in the Mandovi and 12 km in the Zuari. The flow of the estuarine system is regulated by the entry of seawater with the incoming tide through Zuari which reaches Mandovi through the canal. The flow is reversed during the outgoing tide when the estuarine system is flushed. Dilution factors in both the estuaries are similar and vary from 1·2 to 8; highest values occur during the pre-monsoon season. Two shoals/sand bars occur permanently in Mandovi (Aguada Bay) close to a ramp-like inlet to the sea. This inlet poses no navigational problems for about 9 months during the dry season; but for a 3-month period during the monsoon, the waterway becomes hazardous and is closed to boat traffic. Heavy swell and intense wave activity lead to the transfer of sediments into the navigational inlet and the calm season brings the materials back to their original position with practically no overall change in the bathymetry of the bay. The oxygen cycle in the estuarine system is closely related to seasonal changes in temperature and bears an inverse relationship with salinity. In both the estuaries, the sulphate/chlorinity relationship remains uniform and similar to that of the sea except during the monsoon months when the relationship gets disturbed. Changes in phosphorus, nitrogen and silicon are largely regulated by rainfall and land runoff. There is no significant difference in the phytoplankton counts between Mandovi and Zuari which follow a rhythm similar to that of nitrate. Zooplankton biomass is higher in Zuari because of its greater marine influence. No seasonal variation was observed in the density of microflora in the two rivers. Bacterial counts were higher in the lower reaches of the estuarine system and decreased upstream. From its environmental features, the estuarine system can be classified as a tide-dominated coastal plain estuary.

海底トンネル施工時の異常出水の予知についての一例

The construction of an undersea tunnel below the Tsugaru Strait between Honshu and HokkaidoIslands in Japan through incipiently metamorphosed Miocene andesitic rocks have provided a remarkableopportunity to study the geochemical method to predict the gushing out of seawater into undersea tunnel, through fissures in zeolite facies metamorphosed rock mass from boundless overlying sea.Close relathioship between discharge rate and K (and Ca) content of the seepage waters was found.K and Ca contents of the seepage waters generally increase and decrease respectively with the increase ofdischarging rate. The K content of seawaters, after extensively interacted with rocks, became extremelylow when the discharge rate is lower than hundred liter per minite. The Cl content of the seepage water canbe used to indicate the mixing ratio of seawater/meteoric water. Therefore, K×Cl value is proposed to bethe most important chemical parameter which clearly reflects physical properties of waters such as migrationvelocity of waters within the Miocene rock mass, water/rock ratio, water pressure and discharge rate.The variation of K and Cl contents of seepage waters from pilot bore holes and faces of tunnels providedcritical informations on how rapidly fluids are penetrating the rocks between the undersea tunnel and seafloor, permitting necessary precautionary measures to be taken to avoid disastrous entry of seawater.