Temperature and acclimation effects on salinity preferences of post-larvae of the giant Malaysian prawn, Macrobrachium rosenbergii (de Man)

The movement of individual post-larvae of Macrobrachium rosenbergii (de Man) among horizontally-juxtaposed salinity layers of 0, 7, 14, 21, and 28%. was observed during 135-min test periods. The time that post-larvae spent in each salinity was measured at 20, 27, and 34 °C with prawns acclimated to 0, 14, and 28%. salinity.

The young prawns generally moved readily into salinities lower than the acclimation salinity at 27°C, and less frequently into higher salinities. At both 27 and 34°C, post-larvae tended to spend more time in lower salinities than in the salinities to which they were acclimated. Post-larvae acclimated to fresh water rarely reentered saline waters.

Temperature effects on activity resulted in little movement of the prawns at 20°C. High temperature shortened the range of salinities post-larvae occupied for significant periods of time.     

The estuarine character of the Gulf of Nicoya,an embayment on the Pacific coast of Central America

Hydrography and exchange processes in a tropical estuary, the Gulf of Nicoya, Costa Rica, are described from data collected in 1979 and 1980. The measurements and analyses were made in both the dry season and wet season and include temperature, salinity, and density at twenty locations in the gulf and currents (over a semi-diurnal tidal cycle) at five locations. These new results enlarge on the early study by Peterson (1958). Circulation in the lower gulf shows a marked east-west asymmetry due to the predominant runoff along its eastern shore from Rio Barranca and Tarcoles. The freshened surface water from the upper gulf combines with the runoff from these rivers and flows southward along the eastern side of the lower gulf. This flow is compensated by a northward flow of more saline water on the western side at all depths and on the eastern side along the bottom. The boundary between the southward and northward surface flow is marked by a strong salinity front in the rainy season. There is a rapid increase in tidal energy density toward the shoaling northern reaches of the lower gulf, between San Lucas Island and Puntarenas Peninsula. Enhanced mixing must accompany this increase, and direct measurements in the constriction between San Lucas and Puntaneras show that tidal mixing is dominant in transporting salt into the upper gulf against the freshwater runoff.     

山东半岛南部产卵场温跃层对鳀鱼鱼卵垂直分布的作用

2000～2004年5～7月"北斗"号生物资源调查船对山东半岛南部产卵场进行多学科综合调查期间,于2003年6月17～18日和6月27～30日分别在35°01.9′N、120°32.9′E海区和35°03.3′N、120°26.4′E海区进行了25 h和64 h的水团追踪观测调查,鳀鱼鱼卵的数量、垂直分布与水温的分布为重点调查内容.调查结果表明:水温垂直分布的变化、海水混合的强弱、水体的辐聚/辐散等物理过程对水体中鳀鱼鱼卵数量和鳀鱼鱼卵在不同水层的分布有很大影响.温跃层分布深度的波动引起水体的垂直交换(混合)、水平对流(辐聚/辐散)和跨跃层的物质交换.温跃层深度变浅时,上混合层水体的厚度变薄,跨跃层的向上混合,将下混合层水体中和温跃层中的鳀鱼鱼卵输运到温跃层和上混合层中,同时表层水体发生辐散现象,使得下混合层、温跃层和上混合层水体中鳀鱼鱼卵数量减少、密度减小,导致整个水柱内鳀鱼鱼卵的数量减少;温跃层深度加深时,上混合层水体的厚度增加,跨跃层的向下混合,将上混合层水体中和温跃层中的鳀鱼鱼卵输运到温跃层和下混合层水体中,同时表层水体发生辐聚现象,使得上混合层、温跃层和下混合层水体中的鳀鱼鱼卵数量增多、密度增大,导致整个水柱内鳀鱼鱼卵的数量增多;温跃层水体中鱼卵数量和密度的变化较上混合层和下混合层水体更为显著.水体中温跃层的存在、温跃层分布深度的波动及其波动的程度对上混合层和温跃层中鳀鱼鱼卵的数量和密度的变化起着主导作用,导致鳀鱼鱼卵数量垂直分布的剧烈变化.     

Dead Sea water trajectories in the T–S space

The Dead Sea water column is composed, to a first approximation, of two water bodies: the deep waters, constituting most of the lake's volume, and a shallow upper layer a few meters thick. The temperature and salinity profiles can both be either stabilizing or destabilizing, depending on the regime and the season; if salinity is destabilizing, and double-diffusive processes are attained, the two water bodies mix at a much faster rate than normal turbulent diffusion can account for. The trajectories of the Dead Sea brines since 1977 belong to one of three different categories: upper layer under a meromictic regime, upper layer under a holomictic regime, and lower layer under a holomictic regime. The lower layer during the meromictic regime of 1979– 82 remained constant in its properties and its trajectory is thus represented by one single point. This revised version was published online in July 2006 with corrections to the Cover Date.     

Some generalizations based on stratification and vertical mixing in meromictic Lake Shira,Russia, in the period 2002–2009

In a brackish, temperate, 24-m-deep Lake Shira, the profiles of salinity, temperature, oxygen and sulfide concentrations were measured on a seasonal basis from 2002 to 2009. The lake was shown to be meromictic with autumnal overturn restricted to mixolimnion. The depth of mixolimnion and position of oxic–anoxic interface varied annually. The spring mixing processes contribute to the formation of mixolimnion in autumn. The exceptionally windy spring of 2007 caused the deepening of mixolimnion in the winter of 2008. The winter position of oxic–anoxic interface was affected by the position of lower boundary of mixolimnion in all winters. The salinity in the winter mixolimnion increased compared with the autumn because of freezing out of salts from the upper water layers meters during ice formation and their dissolution in water below. The profiles of salinity and temperature were simulated by the mathematical 1-D model of temperature and salinity conditions taking into account ice formation. The simulated profiles generally coincided with the measured ones. The coincidence implies that simplified one-dimensional model can be applied to roughly describe salinity and density profiles and mixing behavior of Lake Shira.     

Assessment of Salinity-Related Mortality of Freshwater Bacteria in the Saint Lawrence Estuary

The growth response of freshwater bacteria from the St. Lawrence River, exposed to brackish waters (salinity of 0 to 20(permil)) from the upper estuary, was assessed by a methodology requiring the combined use of dilution cultures and diffusion chambers. The longitudinal distribution of bacterial abundance in waters within this salinity range was also examined. Growth of the freshwater bacteria was reduced by 15 and 50% after exposure to salinities of 10 and 20(permil), respectively. At lower salinities, no growth reduction was observed, and at a salinity of 2(permil), growth was even stimulated. Longitudinal distribution data showed that bacterial abundance also peaked at this salinity. In contrast with an earlier hypothesis, this study shows that the decline of bacterial abundance in the low-salinity waters of the estuary is not caused by salinity-related mortality of freshwater bacteria, because the mixing time between fresh and marine (>20(permil)) waters is relatively long (days). However, results suggest that mortality of freshwater bacteria can be an important process in estuaries with shorter mixing times (hours). The combined use of diffusion chambers and dilution cultures proved to be a valuable methodology for assessing growth (or mortality) of bacteria exposed to environmental gradients.     

Planktonuntersuchungen in einem holländischen Meeresarm vor und nach der Abdeichung

The Veersche Gat and the Zandkreek formed a sea-arm, which since its closure has been known as the Veerse Meer. Changes in the environment and plankton before and after the closure are reviewed. For the quantitative plankton investigations the method ofLohmann (1908) was applied. As parts of the Oosterschelde system the Veersche Gat and the Zandkreek were poly-euhaline biotopes. Partial isolation of the central stations of the Zandkreek was caused by the existence of a tidal divide at Wolfaartsdijk (Fig. 2). The effect of this divide was illustrated by aberrant chlorinity values and by different qualitative and quantitative composition of the plankton communities. The Zandkreek plankton appeared to be a neritic biocoenose, consisting of a phytoplankton community of mainly pelagic diatoms together with a zooplankton community with strongly littoral characteristics. The size of the standing crops generally increased towards the sea. Phytoplankton at the tidal divide sometimes showed an autochthonous development. Sometimes phytoplankton organisms occurring throughout the whole water body were seen to bloom notably within the area of the tidal divide. In summer a strong autochthonous development of littoral zooplankton made the standing crops within the Zandkreek larger than those of the Veersche Gat. In the second and third years after the formation of the Veerse Meer, a decline in salinity transferred this water body from a polyeuhaline into a meso-polyhaline environment. This decrease in salinity was coupled with a strong eutrophication, evidenced, for example, by high phosphorous contents of the water and caused by the discharge of water from the neighbouring polders and by pollution from sewage. The elimination of many polyhaline-marine species was associated with the gradual appearance of many brackish-water species with flagellates and dinoflagellates as the most important groups. At the same time the standing crops increased greatly. The severe winter at the beginning of 1963 resulted in a marked salinity stratification. In the course of the spring when the ice cover disappeared and the temperature of the upper layers rose, the halocline was combined with a thermocline, and this double stratification was observed until August, 1963, when the wind gradually succeeded in mixing all layers of the water.     

Phosphorus uptake rates of cotton roots at different growth stages from different soil layers

A greenhouse experiment was conducted to determine P uptake at different growth stages by cotton plants from upper and lower 30 cm layers of 60 cm deep uniform soil columns. A radioisotope tracer technique was used to separate uptake from the two soil layers. Root lengths were measured in both layers at each growth stage. P fluxes were calculated for each layer. Root length increased significantly with time from square formation through peak flowering. At all growth stages, total P uptake from the upper soil layer was greater than that from the lower soil layer. P flux from either layer was greater during early growth stages than during later stages. A significant decrease in P flux occurred when plants reached the flowering stage. The flux from the upper layer was about twice that from the lower layer at square forming stage but the difference decreased as the plants matured. Both layers showed similar P fluxes at the first open boll stage. Our data indicate that roots located 30 to 60 cm below the surface are less effective per unit root length than those located at 0 to 30 cm depth when all roots are in the same soil environmental conditions. However, the effectiveness of P absorption from different soil depths under field conditions may depend on the environmental conditions that exist in each soil depth.     

Zur Dynamik exploitierter Populationen vonTisbe holothuriae (Copepoda,Harpacticoida)

In weekly exploited populations of the harpacticoid copepodTisbe holothuriae Humes, the dynamics of population development and the effect of the rate of water renewal were studied under conditions of surplus food supply, constant temperature (22° C) and salinity (30 ‰). At exploitation rates of 10, 30, 50, 70 or 90% per week, the populations maintained stable mean populations sizes. None of the populations established stationary equilibria. Reduced rates of water renewal resulted in a reduction of mean population density, in the course of which the density of adults plus copepodids was diminished to a lesser degree when low, as opposed to high, percentages of specimens were removed. The density of nauplii was distinctly reduced at all exploitation levels. The age structure shifted in favour of the adults and copepodids and was subject to higher variability at moderate exploitation rates and lowered rate of water renewal. To avoid and to remove difficulties inherent to current concepts of population dynamics, the populations were regarded as a component of a feedback control system, and an attempt has been made to describe the observed processes by analogy to technical control systems. According to not yet completed series of experiments, populations undergoing higher exploitation rates seem to compensate more succesfully for perturbations of their environment, than populations exploited at lower rates.     

Dissolved and particulate trace metal geochemistry in the scheldt estuary,S. W. Netherlands (water column and sediments)

The geochemistry of dissolved and particulate trace metals has been studied in the water column and the sediments of the Scheldt estuary between 1987 and 1990. A strong seasonal influence on the behaviour of dissolved Cd, Cu and Zn is observed, related to the redox conditions in the upper estuary and phytoplankton activity in the lower estuary (which are both seasonally dependent variables). The dissolved trace metal concentrations in the fresh water end-member are remarkably low during spring and summer, due to metal sulphide precipitation in the anoxic Scheldt river. However, the dissolved concentrations increase rapidly with increasing salinity, due to oxidation of metal sulphides that are present in the suspended matter, accompanied by (e.g. chloro-)complexation of the released metals. Readsorption of Cd and Zn occurs in the lower estuary during the spring phytoplankton bloom. During winter, when the Scheldt river is not completely anoxic, much higher dissolved trace metal concentrations are observed in the fresh water end-member since metal sulphide precipitation in the water column is precluded. Rapid trace metal removal is observed in the low salinity, high turbidity zone, due to adsorption onto suspended matter and freshly precipitated iron and manganese oxyhydroxides. Upon further mixing, desorption is apparent, due to a similar oxidation-complexation mechanism as observed during spring and summer. Pore water infusion may also contribute to the enrichment of dissolved Cd, Cu and Zn in the mid-estuarine region. The trace metal contents of the suspended matter and the sediments show a continuous decrease with increasing salinity. This behaviour is to a very large extent due to physical mixing of contaminated fluvial particulates and relatively unpolluted marine particulates. Desorption of Cd, Cu and Zn can be identified but is of minor importance compared to the conservative mixing process. The distribution of dissolved Cd, Cu and Zn in the pore waters of the mid-estuarine region reflects the impact of early diagenetic processes. Trace metal peaks are observed near the sediment-water interface, and at greater depth in the manganese and iron reduction zones. These peaks are attributed to oxidation of reduced trace metal compounds (e.g. sulphides) and reduction of the (iron and manganese) oxide carrier phases, respectively. At greater depth, the dissolved trace metal concentrations are much lower due to metal sulphide precipitation in the sulphate reduction zone. Analysis of a large sediment dataset indicates severe trace metal pollution of the Scheldt estuary at the end of the fifties. A major reduction of the pollution by As, Cr, Hg, Pb, and Zn has occurred in the seventies, and of Cd and Cu in the eighties. The Ni pollution has increased over the time period considered. In spite of this improvement, the present-day pollution status of the Scheldt estuary is still reason for concern.     

巢湖微囊藻和浮游甲壳动物昼夜垂直迁移的初步研究

2002年10月进行了巢湖微囊藻和几种优势浮游甲壳动物的昼夜垂直变化的研究,结果表明:微囊藻具有明显的昼夜垂直变化现象。白天上层水中的微囊藻密度显著高于下层水中,夜晚逐渐下沉使得下层水中的密度相对高于上层水。微囊藻与叶绿素a、水温、溶解氧和pH等均呈显著的正相关(p<0.01)。几种优势浮游甲壳动物的昼夜垂直迁移存在较大的差异。短尾秀体溞和角突网纹溞白天在下层水(1.5m和2.5m)中的密度较高,夜晚则倾向于在上层水(0m和0.5m)中活动。相反,卵形盘肠溞白天在上层水中密度较高,象鼻溞则在11:00和15:00时各水层中的密度显著高于夜晚。汤匙华哲水蚤和广布中剑水蚤白天倾向于在下层水中活动,夜晚则逐渐迁移到上层水中。许水蚤在夜晚和凌晨3:00时各水层中的密度显著高于白天。中华窄腹剑水蚤昼夜垂直变化不明显。微囊藻与短尾秀体溞密度呈显著的负相关,而与象鼻溞和卵形盘肠溞呈显著的正相关(p<0.01)。     

Effects of shallow and deep sediment disturbance on whole-stream metabolism in experimental sand-bed flumes

Water flow causes complex patterns of sediment disturbance in sand-bed streams, but effects on stream metabolism resulting from different depths of sediment scour and fill are poorly known. We assessed such effects by manually disturbing sandy sediments of 16 experimental outdoor flumes to two different depths (1 and 4 cm) during an early and a more advanced stage of stream community succession. To separate effects on heterotrophic and autotrophic metabolism, half of the flumes were permanently covered. At the early successional stage, sediment disturbance did not affect net community production (NCP), while sediment mixing reduced production independent of disturbance depth in the later stage. Microbial respiration, in contrast, was significantly stimulated when sediment was mixed to greater depth. These results suggest that disturbing sediments during early successional stages has no effect on whole-stream metabolism, whereas at later stages, deep sediment disturbance can lead to a transitory shift toward heterotrophy. The recovery time of NCP from perturbation was independent of disturbance depth. Similar trajectories observed after deep and shallow sediment disturbance indicate that delayed recovery was not simply due to mixing algae into deeper sediment layers but primarily a result of disrupting the fine structure of the surface sediment.     

Soil water regime of agricultural field and forest ecosystems

The unsaturated zone of soil is one of the most important and complicated parts considering the water movement in the hydrologic cycle. Water transfer through its upper and lower boundary directly influences the amount of water in this zone. The depth of groundwater table usually delimits the lower boundary. The soil surface with or without plant canopy is the upper boundary. The soil surface reacts directly on meteorological conditions primary through evapotranspiration. It is determining the inflow of precipitation into deeper layers of a soil profile. Both physical and hydrophysical properties of the upper soil layer are changed under the extreme meteorological conditions. In case of such conditions the water can flow along preferential pathways down to the groundwater without filling up the soil matrix. Changes of physical and hydrophysical characteristics of the soil surface layer or of the root zone depend on the vegetation type, too. The water storage of 0–30 cm and 30–60 cm soil layers was calculated from monitored data of soil water contents in two different ecosystems, and the calculated water storages were compared with the integral water contents that are related to hydrolimits (field capacity, point of decreased availability and wilting point) in 1999 and 2000. It should be noted that it was considerably dryer in 2000 than in 1999, and during the vegetation period, it was also warmer in 2000 than in 1999. The higher air temperatures during the vegetation season and the lower cumulative rainfall in 2000 comparing to 1999 resulted in a decrease in the integral water contents in the root zone.     

Hydrography of four Mediterranean marine cage sites

Measurements of current speed and direction were made at three marine cage farms in Greece and one in Mediterranean Spain. At two sites where contemporaneous wind measurements were made, current velocity was correlated with wind velocity. It appears that for each of the sites in Greece, at the time of measurement, the wind was the most important driver of water movements. However, at the Spanish site, current speeds were around 10% of the wind speed in the residual flow direction, indicating that the wind was not the only driver of water movements. Mean current speed ranged from 1.2 to 9.1 cm/s, therefore being within the typical range of mean current speeds experienced at tidal North Atlantic fish culture sites. Mediterranean sites differ from Atlantic sites in terms of temperature and salinity but may possess broadly similar surface flow regimens despite lacking macro-tidal forcing.     

The influence of water velocity on the downstream movement of alevins and fry of brown trout, Salmo trutta L.

Trout eggs were planted in four experimental stream channels, each channel being run at a different but constant discharge. Survival of the eggs to hatching was low and apparently unrelated to surface water velocity. However, movement of young trout out of channels was affected by water velocity, the higher the velocity the greater the proportion of trout that were lost. Virtually all fry moved out of a channel with a mean surface water velocity of 0.73 m s⁻¹. The rate of loss was not constant over the experiment but increased as the young trout entered the free-feeding stage. At the end of the experiment loss of fry, after abrupt increases in discharge, was demonstrated in the lower velocity channels.     

Contribution to the hydrographical structure of the eastern German Bight

Temperature, salinity, micronutrients, seston components and mesozooplankton were measured on a cruise in the eastern German Bight during November 1976. Three different water bodies and a mixing area which is divided into two subareas could be identified. The water masses differed significantly in regard to temperature, salinity, micronutrients and seston components. In some cases differences in the amounts of mesozooplankton could be found. Temperature and salinity of the water of the Elbe estuary and of the Wadden Sea were relatively low, but amounts of micronutrients and seston were high, whereas the water of the North Sea water body was of higher temperature and salinity with lower amounts of micronutrients and seston. The North Frisian coastal water and a southern mixing area can be regarded as mixing areas between these water bodies.     

Relations between water content, potential and permeability in stems of conifers

Abstract. The influence of sapwood water content on the conductivity of sapwood to water was measured on stem sections of Pinus contorta. A reduction in relative water content from 100 to 90% caused permeability to fall to about 10% of the saturated value.
Pressure–volume curves of branchwood and stem sapwood of Pinus contorta and Picea sitchensis have been analysed to definè the tissue capacitance and the time constant and resistance for water movement between stored water and the functional xylem as functions of tissue water potential. Three phases in water loss were discernible. In the initial phase at high water potentials (> –0.5 MPa), the capacitance was large, the time constant long and the resistance to flow large in comparison with intermediate water potentials (−0.5 to −1.5 MPa). At still lower water potentials (−1.5 to −3.0 MPa), the time constant and resistance declined still further but the capacitance had a tendency to increase again, especially in the stemwood of Sitka spruce. Typical values in the second phase were for the time constant 5 s, for the resistance 4 × 10⁻¹³ N s m⁻⁵ and for the capacitance (change in relative water content per unit change in potential) 1×10⁻¹¹ m³ Pa⁻¹. These parameters define the availability of stored water and are being used in a dynamic model of water transport in trees.     

Polyhydric alcohol production and intracellular amino acid pool in relation to halotolerance of the yeast Debaryomyces hansenii

Changes in polyol production and the intracellular amino acid pool were followed during the growth cycle of Debaryomyces hansenii in 4 mM and 2.7 M NaCl media. The intracellular levels of polyols were markedly enhanced by high salinity, the dominant solutes being glycerol in log phase cells and arabinitol in stationary phase cells. At low salinity arabinitol was the most prominent intracellular solute throughout the growth cycle. There were no major changes in the composition of the total amino acid pool with changes in cultural salinity. The amount of total free amino acids related to cell dry weight was 15–50% lower in cells cultured in 2.7 M NaCl as compared to 4 mM NaCl media.After subtraction of contributions from intracellular polyols the calculated cellular C/N ratio was found to be unaffected by cultural age and salinity during the late log and early stationary phase. On prolonged incubation of stationary phase cells, this ratio decreased, particularly at high salinity. The sensitivity of cells towards exposure to high salinity was measured in terms of the length of the lag phase after transference to 2.7 M NaCl media. This lag phase decreased with increasing intracellular polyol concentrations. At a given polyol content, stationary phase cells were considerably less sensitive than were log phase cells.When cultured at high salinity the mutant strain, 26-2b, grew more slowly and retained less of the total polyol produced during the early growth stages than did the wildtype. Exogenously supplied mannitol, arabinitol, and glycerol stimulated the growth of the mutant in saline media. Erythritol was without effect.Abbreviations GLC gas-liquid chromatography - TCA trichloroacetic acid     

The Antarctic coastal current in the southeastern Weddell Sea

Summary Between January and March 1989 during EPOS leg 3, a hydrographic survey was carried out in the southeastern Weddell Sea on transects across the continental shelf and slope off Kapp Norvegia and Halley Bay. This data set represents oceanographic conditions during Antarctic summer. Winter observations were obtained during the Winter Weddell Gyre Study in September and October 1989. During summer the water in the surface layer is relatively warm and of low salinity. In the area of Halley Bay exceptionally warm conditions were encountered with sea surface temperatures of nearly +1°C. Over the upper continental slope a frontal zone separates Eastern Shelf Water from Antarctic Surface Water in the near surface layer and from Warm Deep Water in the deeper layers. The horizontal pressure gradient associated with the front produces the high velocity core of the Antarctic Coastal Current. In winter Antarctic Surface Water is replaced by colder Winter Water of higher salinity. Measurements from current meters moored off Kapp Norvegia and Vestkapp are used to describe the mean features of the current field and its fluctuations. At Kapp Norvegia annual mean current speeds range from 10 to 20 cm/s. The geostrophic current shear indicates that the speed of the current core decreases towards Halley Bay. The currents show significant seasonal variations with strong interannual differences. These compare well with the variations of the wind field observed at the Georg von Neumayer Station. Superimposed are higher frequency fluctuations with an energetic range between 5 and 15 days which is found in the wind measurements as well. A considerable part of the current velocity variance is due to the tides. The oceanographic conditions are strongly influenced by the local bottom topography. A topographic rise at the shelf edge off Kapp Norvegia reduces horizontal advection and allows a patch of cold Winter Water to be preserved into the summer. In contrast, a patch of Warm Deep Water was found on the shelf of Halley Bay. This illustrates rather heterogeneous conditions in the near bottom layers due to differences in the exchange rate with the open ocean as well as with the near surface layers.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Heterogeneous distribution of a floating-leaved plant,Trapa japonica,in Lake Mikata,Japan, is determined by limitations on seed dispersal and harmful salinity levels

Factors affecting the within-lake distribution of Trapa japonica were analysed in Lake Mikata, Japan, by integrating remote sensing analyses, field surveys, and laboratory experiments. The T. japonica bed has been expanding since 2006 and covered more than 60 % of the lake’s area from 2008 to 2010. However, two parts of the lake, the upper and lower areas, retained open water, even during recent years. A survey of lake-bottom sediments revealed a heterogeneous seed distribution. Although seed density exceeded 13 seeds/m² in the lake’s central area, no seeds were observed in the upper and lower areas. A seed-bag retrieval experiment showed that 75.6 % of seeds at the upper site germinated when seeds were artificially introduced, whereas 6.7 % of seeds germinated at the lower site. These results suggest that seed dispersal opportunities are the primary limitation on the distribution of T. japonica in the upper area. Brackish water was found in springs in the lower area, reflecting an adverse inflow of water from a downstream brackish lake. Laboratory experiments revealed significant adverse effects of water salinity on germination and early growth of T. japonica. Based on these results, we concluded that the heterogeneous distribution of T. japonica within the lake was determined by a combination of two factors: limitations on seed dispersal determined by the inflowing river and harmful salinity levels caused by inflows of seawater from the Sea of Japan via a downstream brackish lake.