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The availability of nutrients for primary producers has long been thought to be the main limiting factor for primary productivity in nutrient-poor lake ecosystems. However, recent studies have indicated that the availability of light energy is also important. On the other hand, the amount of phototroph was reported to decrease in summer in Antarctic lakes, furthermore, the light environment underwater was shown containing high amount of ultraviolet energy in small Antarctic lakes. Here, we hypothesized that primary productivity is limited by not only nutrients and simple light quantity but also light quality in nutrient-poor lakes. Then, we investigate factors influencing primary production by benthic phototrophic communities in shallow nutrient-poor lakes. We examine the relationships between primary production in 17 Antarctic freshwater lakes and nutrient concentrations in lake and benthic water, temperature and light energy. Primary production is decreased by ultraviolet energy reaching the lake bed, showing that production is determined by light quality. We also correlate ultraviolet energy in lake water with the catchment area of each lake. Our results show that the underwater light environment has an important influence on primary production as a key limitation factor and is sensitive to materials in runoff from the surrounding environment for pristine lakes.

Most freshwater lakes in continental Antarctica are in a paradoxical situation as they are in nutrient-poor conditions despite luxuriant vegetation growth covering the entire lakebed. Although the phytobenthos possibly take up nutrients from inside lakebeds, the amount of nutrients and their utilization by these phytobenthos are unclear. Sediment cores were collected from 17 freshwater lakes in East Antarctica, then dissolved inorganic nitrogen (DIN) and phosphate of the lake waters, and the vertical profiles of the interstitial water in the sediment cores were analyzed. Here we revealed that there are abundant nutrients inside lakebeds surface with 3–220 times the amount of DIN and 2–102 times concentration of phosphate than those in lake water, and the nutrient profile inside the sediment suggested that the phytobenthos can utilize the much nutrients from lakebeds. We also show that nitrogen stable isotope ratios of shallower phytobenthos lying on the small amount of nutrients in a lake are similar to that of terrestrial cyanobacteria possessing N2 fixation ability.

Ecological degradation of the benthic littoral zone is an emerging, urgent problem at Lake Baikal (East Siberia), the most species-rich lake on Earth. Within the last 5 years, multiple changes have occurred in the nearshore benthos where most of the lake's endemic species reside. These changes include proliferation of benthic algae, death of snails and endemic sponges, large coastal wash-ups of dead benthic algae and macrophytes, blooms of toxin-producing benthic cyanobacteria, and inputs of industrial contaminants into parts of the lake. Some changes, such as massive coastal accumulations of benthic algae, are currently shared with the Laurentian Great Lakes (LGLs); however, the drivers of these changes differ between Lake Baikal and the LGLs. Coastal eutrophication from inputs of untreated sewage is causing problems at multiple sites in Lake Baikal, whereas in the LGLs, invasive dreissenid mussels redirect pelagic nutrients to the littoral substrate. At other locations in Lake Baikal, ecological degradation may have different causes including water level fluctuations and the input of toxic industrial contaminants. Importantly, the recent deterioration of the benthic littoral zone in both Lake Baikal and the LGLs has occurred while little change has occurred offshore. This highlights the necessity of monitoring both the littoral and pelagic zones of large lakes for assessing ecosystem health, change and conservation.

Deposition of atmospheric nutrients is known to alter oligotrophic ecosystems such as the open ocean, but the role of such nutrients in the further deterioration of eutrophic aquatic ecosystems is largely unknown. The Hii River watershed in Japan encompasses lagoons that have been eutrophic since 1980s. This study examined the atmospheric deposition of nitrogen and phosphorus in the Hii River watershed and the nitrogen and phosphorus concentrations in the Hii River over an 11-yr period. Total nitrogen (TN) concentrations of both precipitation and river water were significantly higher in cold months (November–March) than in warm months (April–October). Most of the TN was nitrate, which suggests that the TN source was atmospheric nitrogen from East Asia transported by seasonal winds. In contrast, total phosphorus (TP) concentrations of both precipitation and river water were significantly higher in warm months. Over time, the TN concentration in the river water showed a decreasing trend although the trend was not significant, while the TP concentration increased significantly. This was attributed to an increase in the atmospheric deposition of TP originating from East Asia since 2000. The increase in the deposition of atmospheric phosphorus might also have increased phosphorus leakage from the soils. In this work, the TN : TP ratios for both atmospheric deposition and river water indicate that changes in atmospheric nutrient deposition affect loading rates and N : P ratios. These changes, especially the latter, could have significant ecological effects in eutrophic systems by lowering the N : P ratios, which could induce cyanobacteria blooms.

The paper presents the first paleontological data (pollen, plant macrofossil, diatom and ostracod) on the sediments of Lake Beloye, which is situated in the forest-steppe zone of Western Siberia. Our study contributes to better understanding of the Middle–Late Holocene regional to local environmental changes. Regionally, we recognized a cold stage of 3.4–2.3 calibrated ka BP and a dry stage of 2.8–1.7 ka BP. The dry stage coincides with the climate-driven lowered level of the lake at 2.6–1.5 ka BP. Later, the climate changed to warmer and wetter, which resulted in a highest stand of the lake at 1.3–0.2 ka BP and was followed by the lowering of the lake. Forest-steppe persisted in this area during the whole period under consideration, but probably shifted southward. Such a shift is reflected in the environment around Lake Beloye similar to that of modern taiga, which existed at 3.2–1.3 ka BP, however, compared to the colder and wetter climate of taiga, the conditions were colder and drier. The local plant associations and the lake ecosystem were affected by those events of climate and lake level changes. The initial eutrophic sedge-reed swamp evolved to the oligo-mesotrophic sphagnum bog, which existed around the lake at 3.2–1.3 ka BP. Later, the bogging process was interrupted by the lake transgression, after which the dried bog around the lake was occupied by the birch forest. The lake ecosystem was strongly affected by the 3.4 ka BP climate change: the low-alkaline eutrophic lake with abundant water higher plants and diatoms changed to the alkaline oligotrophic lake with calcium-fixing macrophytic algae and angiosperms. This resulted in total change of lake's bio-geochemical and sedimentation patterns.

Sediment structure, rock-magnetic and bio-geochemical records obtained from sapropel core samples in Lake Beloye, southern Western Siberia, indicate an abrupt ecosystem change at 3.4 calibrated ka BP. The lake changed from eutrophic to oligotrophic, its vegetation — from carbon-fixing macrophytic angiosperms to calcium-fixing macrophytic algae and angiosperms, and, as a result, the type of sedimentation shifted from peaty sapropel to carbonate-rich sapropel. Those changes could be induced by climate, which was warmer and wetter before 3.4 ka BP and cooler and drier after this. Nevertheless, our data show that those ecosystem changes occurred when the lake became shallower to get about 1 m depth and started to freeze to the bottom in winter time. The full freezing of the lake led to the deposition of carbonates, which resulted in: i) death of carbon-utilizing macrophytic angiosperms; and ii) winter precipitation of calcium carbonate. In summer, additional portions of Ca 2+ and HCO 3 − ions come into the lake from the surrounding CaCO 3 rich loess sediments with ground water. The Beloye Lake thus represents an example of interrelated regional climatic and local ecological factors, which combination resulted in the 3.4 cal. ka BP dramatic change of its ecosystem.

Antarctic climate changes influence environmental changes at both regional and local scales. Here we report Holocene paleolimnological changes in lake sediment core Sk4C-02 (length 378.0 cm) from Lake Skallen Oike in the Soya Kaigan region of East Antarctica inferred from analyses of sedimentary facies, a range of organic components, isotope ratios of organic carbon and nitrogen, and carbon-14 dating by Tandetron accelerator mass spectrometry. The sediment core was composed of clayish mud (378.0–152.5 cm) overlain by organic sediments (152.5 cm-surface). The age of the surface and the core bottom were 150 (AD1950-1640) and ca. 7,030 ± 73 calibrated years before present (cal BP), respectively, and the mean sedimentation rate was estimated to be 0.55 mm/year. Multi-proxy analyses revealed that the principal environmental change in the core is a transition from marine to lacustrine environments which occurred at a depth of 152.5 cm (ca. 3,590 cal BP). This was caused by relative sea level change brought about by ongoing retreat of glaciers during the mid-Holocene warming of Antarctica, and ongoing isostatic uplift which outpaced changes in global (eustatic) sea level. The mean isostatic uplift rate was calculated to be 2.8 mm/year. The coastal marine period (378.0–152.5 cm, ca. 7,030–3,590 cal BP) was characterized by low biological production with the predominance of diatoms. During the transition period from marine to freshwater conditions (152.5-approximately 135 cm, ca. 3,590–3,290 cal BP) the lake was stratified with marine water overlain by freshwater, with a chemocline and an anoxic (sulfidic) layer in the bottom of the photic zone. Green sulfur bacteria and Cryptophyta were the major photosynthetic organisms. The Cryptophyta appeared to be tolerant of the moderate salinity and stratified water conditions. The lacustrine period (approximately 135 cm-surface, ca. 3,290 cal BP-present) was characterized by high biological production by green algae (e.g. Comarium clepsydra and Oedegonium spp.) with some contributions from cyanobacteria and diatoms. Biological production during this period was 8.7 times higher than during the coastal marine period.

Long-term changes in Secchi disk transparency in Lake Nakaumi, Japan, from 1932 to the present, which includes the periods before and after the loss of eelgrass (Zostera marina L.) beds, were compiled from previous reports. During the first (July 1932–February 1934) and the second (January 1949–November 1950) periods, the mean transparency was greater than 3 m at all observed stations. Data during the third period (July 1954–March 1956) are only available for the station at the center of the lake. The mean transparency during the third period was significantly lower than that of the second period but higher than the mean during the fourth period. This observation suggests that the decrease of transparency occurred during the third period. Because the decline of eelgrass beds in Lake Nakaumi occurred in the mid-1950s, the decrease of transparency most likely resulted from the shift in primary producers from submerged macrophytes to phytoplankton. Although the maximum transparency sometimes exceeded 3 m, mean transparencies during the fourth period (May 1975–December 2003) were less than 2 m at all stations, significantly lower than those during the first and second periods. The shift in the chief primary producer, from benthic macrophytes to phytoplankton, caused a subsequent shift in secondary producers. The opportunistic filter-feeding bivalve Musculista senhousia, regarded as a biofouling species of local fisheries, increased in Lake Nakaumi. The long-term monitoring data of transparency suggested that restoration of submerged aquatic vegetation may be indispensable for the remediation of the lake environment in this shallow eutrophic lagoon.

Alkenone sea surface temperature (SST) records were generated from the Ocean Drilling Program's (ODP) Sites 1014 and 1016 to examine the response of the California Current System to global climate change during the last 136 ka. The temperature differences between these sites (ΔSSTNEP=SSTODP1014–SSTODP1016) reflected the intensity of the California Current and varied between 0.4 and 6.1 °C. A high ΔSSTNEP (weaker California Current) was found for late marine isotope stage (MIS) 2 and early MIS 5e, while a low ΔSSTNEP (stronger California Current) was detected for mid-MIS 5e and MIS 1. Spectral analysis indicated that this variation pattern dominated 23- (precession) and 30-ka periods. Comparison of the ΔSSTNEP and SST based on data from core MD01-2421 at the Japan margin revealed anti-phase variation; the high ΔSSTNEP (weakening of the California Current) corresponded to the low SST at the Japan margin (the southward displacement of the NW Pacific subarctic boundary), and vice versa. This variation was synchronous with a model prediction of the tropical El Nino-Southern Oscillation behavior. These findings suggest that the intensity of the North Pacific High varied in response to precessional forcing, and also that the response has been linked with the changes of tropical ocean–atmosphere interactions.

Zostera marina L. was intensively harvested until the early 1950s in Lake Nakaumi, a eutrophic estuarine lagoon. We have estimated the amount of nitrogen (N) and phosphorus (P) removed from the lagoon through Z. marina harvesting. Lake Nakaumi lies in Tottori and Shimane prefectures, and the annual harvest of Z. marina in the late 1940s in Tottori was recorded as at least 56,250 t wet weight. The nutrient content of 56,250 t of Z. marina was calculated to be 61.9 t of N and 12.9 t of P, which is equivalent to 5.3% and 11%, respectively, of present annual nutrient loads to the lake. The nutrients formerly used by Z. marina were likely used by phytoplankton after the Z. marina started to decline in the mid-1950s at Lake Nakaumi. This shift in the chief primary producer, from benthic macrophytes to phytoplankton, caused a subsequent shift in secondary producers. Benthic fish and crustacean populations decreased and the non-commercial filter-feeding bivalve, Musculus senhausia, increased in Lake Nakaumi after the decline of seagrass beds. This affected the local economy, inducing not only eutrophication but also the collapse of local fisheries. On the other hand, at adjacent Lake Shinji, loss of submerged aquatic vegetation induced an increase of the commercial filter-feeding bivalve, Corbicula japonica, which doubled the fishery yield in the lake.

Lake Shinji from 1635 up to the time of the widening of the Ohashi River, which was carried out from 1924 to 1933 (from the late Taisyo era to the early Syowa era) has been believed as a fresh water lake. This belief is based on previous reports on the damage from salt after the widening, or a diatom analysis of the core sediments of Lake Shinji. To confirm the validity of this belief, the salinity of Lake Shinji before the widening was investigated from various viewpoints from reports on fishery operation, fishery statistics, sediment analysis and a hydraulic study. From this investigation, we propose that Lake Shinji before the widening was an oligohaline lake, with intermittent saline water intrusion from the adjacent Lake Nakaumi depending on meteorological conditions. The intrusion of saline water was considered to increase in summer with a decrease in fresh water inflow, and made brackish water fishes migrate and inhabit Lake Shinji. In the case of a dry year, marine dinophyceae predominated, which was recorded in the core sediments of the lake. Our results strongly suggest that a single approach to reconstructing past environments can be easily misinterpreted, and that an interdisciplinary approach is indispensable for such purpose.

To determine whether dugongs along the Thai coast prefer relatively faster-growing Halophila ovalis due to its nutritional value, we analyzed the contents of carbon (C), nitrogen (N), phosphorus (P), ash, fiber, and lipids in several species of seagrass collected near dugong feeding trails. CNP concentrations in the faster-growing H. ovalis were distinctly lower than those in the slower-growing species. Lipid concentrations were comparatively not as low; they were equivalent to the values of the slower-growing Enhalus acoroides in the leaves and to Thalassia hemprichii and Cymodocea rotundata in the rhizomes and roots. The ash content of H. ovalis was the highest of all species in both the above and below ground parts. The reason that dugong feeds exclusively on H. ovalis at this site may be the potentially large supply due to its high growth rate, rather than its nutritive qualities.

In a coral reef environment, a slight increase in dissolved inorganic nitrogen (DIN;⩾1.0 μM) can alter the ecosystem via macroalgal blooms. We collected seagrass leaves from the tropical and subtropical Pacific Ocean in five countries and examined the interactions between nutrient concentrations (C, N, P), molar ratios of nutrients, and δ 15 N to find a possible indicator of the DIN conditions. Within most sites, the concentrations of nutrients and their molar ratios showed large variations owing to species-specific values. On the other hand, almost identical δ 15 N values were found in seagrass leaves of several species at each site. The correlations between δ 15 N and nutrient concentrations and between δ 15 N and molar ratios of nutrients suggested that nutrient availability did not affect the δ 15 N value of seagrass leaves by altering the physiological condition of the plants. Increases in δ 15 N of seagrass leaves mostly matched increases in DIN concentrations in the bottom water. We suggest that δ 15 N in seagrass leaves can be a good tool to monitor time-integrated decrease/increase of DIN concentrations at a site, both in the water column and the interstitial water.

We measured the C/N ratio and d 15 N values of two brown macroalgae— Padina spp. and Dictyota sp., which are distributed over all the subtropical fringing reefs of the Ryukyu Islands, Japan—to evaluate the feasibility of these algae as indicators of the terrestrial nitrogen load to the reef. The correlations between the distance from the shoreline and algal C/N ratio and surrounding NO concentrations were not clear, although their average values among the 2 3 reefs seemed to indicate differences in nitrogen loadings from the land. The d 15 N values of these algae, on the other hand, linearly or curvilinearly decreased from 18‰ to 12‰ with increasing distance from the shoreline, indicating the difference in nitrogen sources available to macroalgae. The slope of the decline among eight study areas had different characters, which seemed to depend on the residence time of reef seawater and the fluxes of terrestrial nitrogen. Using d 15 N values of brown algae as an indicator, we confirmed that primary producers, such as macroalgae on the reefs, assimilated land-derived nitrogen and successfully evaluated time-integrated effects of terrestrial nitrogen on coral reef algae, which had been missed by conventional monitoring of the water column nutrients.

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.

Variation in fish assemblages was investigated to clarify the migration patterns and growth rates of marine, brackish and freshwater species in three adjacent areas with different salinities. In the polyhaline Lake Nakaumi, Japan, benthic fishes and crustaceans were negatively affected by oxygen depletion in the lower water under stratification during the warm seasons. On the other hand, marine and brackish species that once migrated into the Honjo Area, which is isolated from L. Nakaumi and has a homogeneous salinity structure, remained and grew there until winter. In the mesohaline Lake Shinji, two types of fishes were distinguished: one that migrated into the lake during the warmer seasons; and the other which stayed in the lake during winter. Fauna and production in L. Shinji were compared with those of a comprehensive study carried out approximately 35 years ago. For 35 years, Konosirus punctatus and Sardinella zunasi have increased in abundance, while Carassius sp. and Hypomesus nipponensis have decreased. Even with the recent acceleration in eutrophication of the lake, fish production during the warmer seasons has not declined for 35 years, but the fish fauna have drastically changed.

We measured the abundance and biomass of the major taxonomic groups of mesozooplankton at six stations in Lake Shinji–Ohashi River–Lake Nakaumi brackish-water system, Japan, monthly for three full years (1995–1997), except for one station (for 1 year and 9 months). Over the entire area, copepods overwhelmingly dominated the zooplankton community both in terms of abundance (mean: 87.9%) and biomass (83.4%). The remaining taxa were cladocerans (i.e. Diphanosoma brachyurum, Evadone tergestina, Penilia avirostris, Podon leuckarti and Podon polyphemoides), appendicularians (Oikopleura dioica and Oikopleura longicauda), chaetognaths (Sagitta crassa) and the larvae of benthos (e.g. polychaetes, bivalves, gastropods and malacostracans). The geographical and seasonal variations of the mesozooplankton community were therefore principally explained by the variations of the copepod community. The geographical difference in copepod species composition was associated with salinity preference or tolerance of respective species. In Lake Shinji, where the salinity was lowest (mean: 4.0), Sinocalanus tenellus was monospecifically abundant with sporadic occurrence of Pseudodiaptomus inopinus. In Ohashi River (mean salinity: 9.9), Acartia hudsonica, Acartia sinjiensis, Eurytemora pacifica and Oithona davisae added to the community. At central and southeast Lake Nakaumi and in Honjo District, where mean salinity ranged from 16.4 to 21.7, these four species became more important than S. tenellus and P. inopinus. At the entrance of Sakai Strait, where the salinity was highest (mean: 24.0), Paracalanus spp. constituted a significant component. Due to large temperature fluctuation with season, the copepods showed remarkable seasonal variations in abundance and biomass, with enormous annual peaks in winter–spring. These annual peaks might be attributed to scarce occurrence of predators.

Abundance and size distribution of the sublittoral meiobenthos in the upper 3 cm of the sediment were surveyed in the eutrophic, estuarine lagoons, Lakes Nakaumi and Shinji, Japan. Samples were taken in late spring from 10 stations located along salinity gradients. The density of meiobenthos was at a minimum in the intermediate salinity zone. Nematodes in L. Shinji were significantly larger in size than in L. Nakaumi, due to the size reduction of marine species in the latter. The biomass of co-existing bivalves, which would contribute more food supply to the meiobenthic fauna, did not affect the abundance and size of meiobenthos. It was suggested that the salinity gradient was the most influential factor on the abundance and size structure of meiobenthos in estuarine lagoons where salinity is fairly constant.

Diet selectivity and shift of common pochards ( Aythya ferina ) and tufted ducks ( A. fuligula ) were investigated in the eutrophic coastal lagoon, Lake Nakaumi, during three winters (1994–1997). These two diving ducks fed mainly on mussels Musculista senhousia , but used food resources differently. Common pochards foraged larger mussels that were depleted earlier than the smaller ones eaten by tufted ducks. After the mussel biomass decreased in late winter, tufted ducks shifted their diet to clams Ruditapes philippinarum and Crustacea, while common pochards shifted only to the clam. Thus, depletion of mussel biomass in the lagoon affected common pochards earlier and stronger than tufted ducks. We suggest that different use of food resources of each species influenced their wintering patterns. Tufted ducks used the wintering area for a long period, while common pochards moved to the other area when animal foods became less abundant.

To understand the physical and biological processes that occur in Lakes Shinji and Nakaumi, a coastal lagoon system, a hydrodynamic–ecological coupled model was applied. The model was run to hindcast these processes from March 1, 1995 to the end of September 1995. The simulation of physical processes suggests that the meteorologically induced sea level variation and a large episodic amount of freshwater discharge effectively caused the water exchange between the open sea and this lagoon system. The simulated results of the biological processes using the ecological model show good agreement with field data except for the phosphate concentration in the bottom water. It was also found that the microbiological processes in the water column, as well as in the sediment, contribute largely to the formation of oxygen-depleted water in the bottom layer. It was also clarified from the simulation that the two species of benthic bivalve, which have dense populations in this lagoon system, play important roles on removing organic particulate matter and nutrients from the system.

The distribution of chemical tracers in two coastal lagoons was surveyed to assess changes in the contribution of autochthonous and allochthonous (terrestrial and marine) organic matter sources to sediments along a salinity gradient. C:N:P ratios of sediments from both lagoons were closer to the ratios of phytoplankton than to those of terrestrial plants, suggesting that the contribution of terrestrial organic matter was minor. A strong correlation between δ13C and the distance from the seawater entrance was attributed to changing δ13C of DIC sources used by autochthonous phytoplankton, because sediment N:P reflected the dominant phytoplankton inputs in each lagoon. These results suggest that autochthonous primary production controlled organic matter supply to sediments in both lagoons.

Filter-feeding bivalves often predominate the benthic biomass of estuaries, although their population size may drastically fluctuate due to physical and biological disturbances. To examine the recovery of a mussel population after periods of severe predation and anoxia, and to estimate the amount of nutrients removed from the system through mussel production, we surveyed, over 2 years, the Musculista senhousia population in the estuarine lagoon, Lake Nakaumi, Japan. Predation by diving ducks (Aythya fuligula, Aythya ferina and Aythya marila) during winter dramatically reduced the mussel biomass in both years, but recruitment of juvenile mussels sustained the population. Anoxia during the second summer severely reduced the mussel population, resulting in less biomass than in the autumn of the previous year. Potential annual removal of nitrogen and phosphorus from the lagoon water through burial of M. senhousia shells under oxic conditions was estimated to be 7.1 and 5.1 tons, respectively. These are equivalent to 0.7% and 4.9% of the nitrogen and phosphorous annual load entering the lagoon via the main river. Under anoxic conditions, removal would decrease to only 5.6% of the potential amount.

We have conducted a continuous measurement of temperature and water quality in a littoral zone of a brackish lake, Lake Shinji, where filter-feeding bivalves (Corbicula japonica) are densely populated. Daytime heating and nighttime cooling created density gradients that drove strong horizontal mass exchange. Simultaneous measurement of Chlorophyl a. concentration suggests that this circuration, especially during cooling period, mainly supports feeding of phytoplankton by bivalves which are habited at the lake bottom, and thus controls natural purification process through benthic-pelagic coupling.

A rapid technique is presented for measuring organic C and N in carbonate-bearing sediments. Organic C and N were determined with a Yanaco MT-5 CHN analyzer after removing carbonate by acidification of samples in ceramic sample boats with HCI vapor. This procedure eliminates loss of acid-soluble organic matter during carbonate dissolution. The accuracy of this new technique and two earlier methods of determining organic C and N concentrations was verified with standard chemicals and carbonate-bearing sediments (>80 wt% CaCO 3 ). With the new technique there was no contamination or loss of organic C and N. The method is suitable for acidifying sediments with a wide range of carbonate content.

Social and ecological systems around the world are becoming increasingly globalized. From the standpoint of understanding coastal ecosystem behavior, system boundaries are not sufficient to define causes of change. A flutter in the stock market in Tokyo or Hong Kong can affect salmon producers in Norway or farmers in Togo. The globalization of opportunistic species and the disempowerment of people trying to manage their own affairs on a local scale seem to coincide with the globalization of trade. Human-accelerated environmental change, including climate change, can exacerbate this sense of disenfranchisement. The structure and functioning of coastal ecosystems have been developed over thousands of years subject to environmental forces and constraints imposed mainly on local scales. However, phenomena that transcend these conventional scales have emerged with the explosion of human population, and especially with the rise of modern global culture. Here, we examine five broad questions of scale in the coastal zone: (1) How big are coastal ecosystems and why should we care? (2) Temporal scales of change in coastal waters and watersheds: Can we detect shifting baselines due to economic development and other drivers? (3) Are footprints more important than boundaries? (4) What makes a decision big? The tyranny of small decisions in coastal regions. (5) Scales of complexity in coastal waters: the simple, the complicated or the complex? These questions do not have straightforward answers. There is no single "scale" for coastal ecosystems; their multiscale nature complicates our understanding and management of them. Coastal ecosystems depend on their watersheds as well as spatially-diffuse "footprints" associated with modern trade and material flows. Change occurs both rapidly and slowly on human time scales, and observing and responding to changes in coastal environments is a fundamental challenge. Apparently small human decisions collectively have potentially enormous consequences for coastal environmental quality, and our success in managing the effects of these decisions will determine the quality of life in the coastal zone in the 21st century and beyond. Vigilant monitoring, creative synthesis of information, and continued research will be necessary to properly understand and govern our coastal environments into the future. (C) 2011 Elsevier Ltd. All rights reserved.

Diel changes in the concentration of nitrogen species [ammonium, nitrite, nitrate, dissolved organic N, and particulate organic N (PON)] and some biological parameters were monitored in the water column of Lake Shinji, a shallow estuarine lake in Japan. The sediment of the lake was densely inhabited by the filter-feeding bivalve Corbicula japonica. An overlying water sampler showed that PON at the sediment-water interface (less than a few millimeters above the sediment) was not depleted; nevertheless, active uptake of PON by C. japonica (10.4 mg-atoms N m −2 d −1 ) is reported. Dissolved and particulate N species showed vertically uniform profiles at night, which we attributed to nocturnal water mixing associated with cooling surface water. These observations suggest benthic-pelagic coupling between filter-feeding bivalves and phytoplankton which enables the removal of nitrogen from the eutrophic lake through fisheries yield of bivalves

Uptake of particulate nitrogen and nutrient excretion by the filter-feeding bivalve Corbicula japonica in Lake Shinji was measured simultaneously by two methods: a continuous flow laboratory incubation with an intact sediment and an in situ measurement with a benthic chamber. The excretion rate of ammonium by C. japonica estimated from the in situ measurement exceeded the uptake rate of particulate organic nitrogen (PON), suggesting the involvement of bioturbation or other nonmetabolic process in the upward flux of ammonium. On the other hand, the results from the continuous incubation method agreed well with the growth rate of C. japonica under natural conditions. In the natural habitat of Lake Shinji, C. japonica excreted 4.5 mg-atoms N m-2 d-l as ammonium and 4.6 mg-atoms N m-2 d-l as feces and pseudofeces while taking up PON at a rate of 10.4 mg-atoms N m- 2 d-l. These results suggest that C. japonica plays an important role in stimulating primary production by maintaining rapid recycling of nitrogenous materials.

To better understand topography-dependent characteristics of suspended particulate matter (SPM) in a tropical shallow estuary during dry season, the physical factors causing an increase in SPM and the sources of SPM were investigated at the western coast of Thailand. Single and multiple regression analyses using physical parameters as independent variables indicated that periodic tidal current-driven resuspension, episodic wind-driven resuspension, and river-borne inputs were the most important factors controlling SPM increases in areas surrounded by sand bars, areas directly facing the ocean, and areas close to the river mouth, respectively. The assessment of the origin of increased SPM over the background levels estimated from the chemical signatures (delta(13)C and C/N ratio) at all investigated locations and for each event responsible for an increase in SPM confirmed the results of the multiple regression analyses. The results suggested that specific characteristics of SPM at each location were highly contributed by sedimentary materials and could be rather consistent through the season under similar weather conditions., Marine Environmental Research. 68(2), pp. 59-70; 2009

A sediment trap experiment was carried out in the West Caroline Basin, located in the equatorial western Pacific between influences of the Asian monsoon and the open ocean. Annual mass flux at the shallow trap at Site 1 was 57.10 g m(-2)yr(-1). Generally, the higher flux of organic matter was associated with higher activities of biogenic opal-producing and carbonate-producing plankton communities. In addition, as the organic matter content increases, the organic carbon/carbonate carbon ratio shows a tendency to increase. Carbonate-producing plankton was predominant during periods 1 and 3 (May to July and November to the beginning of December), which could be due to limited silica supply to the euphotic zone. On the other hand, surface sea water was more nutrient-rich during periods 2 and 4 (August to October and the end of December to April) at Site 1. These high total mass fluxes could be stimulated by wind. The amount of biogenic components collected in the sediment traps and the accumulation in surface sediments at Site 1 could be compared with primary productivity values. Carbonate and biogenic opal fluxes were 99 % and 90 % less, respectively, in the surface sediments compared to those in the shallow sediment trap. This could be due to the reaction of sinking particles with undersaturated deep sea water just above the sea floor, rather than with the water column during sinking. About 20 % of the organic matter was decomposed between the shallow and deep sediment traps and more than 98 % between the deep sediment trap and final burial in the surface sediments. The relative amount of organic carbon preserved in surface sediments was about 0.10 % of annual primary productivity., Des pièges à sédiments ont été déployés dans le bassin des Carolines Occidentales (ouest du Pacifique équatorial), entre la zone d'influence de la mousson d'Asie et l'océan ouvert. À la station 1, le flux annuel au piège le moins profond est 57, 10 g m-2 an-1. Les flux élevés de matière organique sont généralement associés au développement des communautés planctoniques à test silicieux et carbonaté. De plus, le rapport carbone organique/carbone minéral tend à augmenter avec la teneur en matière organique. Le plancton carbonaté prédomine pendant les périodes 1 et 3 (de mai à juillet et de novembre au début décembre), probablement en raison de l'apport limité en silice dans la couche euphotique. L'eau superficielle est enrichie en éléments nutritifs pendant les périodes 2 et 4 (d'août à octobre et de la fin décembre à avril) à la station 1. Ces flux eleves pourraient être favorisés par l'action du vent sur la surface océanique. La quantité de composés biogéniques collectés dans les pièges à sédiments et leur accumulation dans les sédiments superficiels du site 1 peuvent être comparées aux valeurs de productivité primaire. Les flux de carbonate et d'opale biogènes dans les sédiments de surface sont inférieurs, de 99% et 90% respectivement, aux flux dans le piège à sédiment le moins profond; probablement par réaction des particules avec l'eau sous-saturée, à proximité du fond, plutôt que durant la chute des particules dans la colonne d'eau. Environ 20% de la matière organique est décomposée entre les deux niveaux de pièges à sédiments, et plus de 98% avant l'incorporation au sédiment. Le carbone organique préservé dans les sédiments superficials représente environ 0, 10% de la productivité primaire annuelle.

Two species of ascidian, Didemnum molle Herdman and Lissoclinum voeltzkowi Michaelsen, were collected from a Fijian seagrass meadow. The primary production of their symbiont (Prochloron), the inorganic nitrogen metabolism and the filtration rate were measured to assess the nutritional coupling between the symbiont and the host animal. The loss of organic carbon due to the respiration of D. molle (1.1 �g at. C (mg dry wt)-1 day-1) was greater than that supplied through photosynthesis of the Prochloron (0.69 �g at. C (mg dry wt)-1 day,-1). The carbon supplied through filter-feeding appeared to supplement the ascidian's carbon budget. In contrast, organic carbon from the Prochloron of L. voeltzkowi appeared to meet the colony's respiration needs. The nitrogen budgets of both ascidian colonies were estimated from their respiration rates, the nitrogen requirement of the Prochloron, and the uptake of inorganic nitrogen and particulate organic nitrogen uptake from the water column. The nitrogen incorporated from the surrounding environment could contribute to the net nitrogen gain of the colony. However, our estimate of the nitrogen needed by the Prochloron was much greater than that which could be supplied externally. The amount of nitrogen released by the ascidians was also greater than that which could be supplied externally. This suggests that nitrogen is efficiently recycled within the symbiotic Prochloron-ascidian relationship.

Partitioning of the nitrogen stock in a Fijian seagrass bed dominated by Syringodium isoetifolium (Ascherson) Dandy and in an adjacent area bare of macrophytic vegetation was assessed to evaluate the effect of the presence of seagrass on coral sediment. Concentrations of major nutrients, such as nitrogen and phosphate, were as low in the water column at the seagrass bed and the bare area as they were in the open ocean. Concentrations of ammonium and dissolved organic nitrogen, however, were higher in the water within the seagrass canopy than they were in other waters. In sediments at the seagrass bed and the bare area, interstitial nitrogen, such as nitrate and dissolved organic nitrogen, was a minor component of the total nitrogen (0.3-0.05%). On the other hand, concentrations of total organic nitrogen in seagrass-bed sediment (about 70% of which was in the form of amorphous organic nitrogen and the rest of which came from living and dead seagrass) were more than three times higher than those in bare-area sediment. Concentrations of organic carbon from amorphous organic materials in seagrass-bed sediment showed no large change with depth, resulting in an apparent decrease in the carbodnitrogen atom ratio from 60 to 10. These results suggest some mechanisms to minimize the loss of nitrogen stock from the sediment of tropical seagrass beds.

To examine the polychaete fauna of Lake Shinji, an oligohaline and mesohaline brackish lake, quantitative sampling was carried out three times within a period of sixteen months. Some environmental factors including the chlorinity of the bottom water were measured at the same time. Throughout three samplings, three species of previously reported brackish forms (Prionospio japonica, Notomastus sp., Neanthes japonica) and an undefined species (Potamilla sp.) were always observed. Total numbers of species were seven in summer 1982 with 248 sampling stations and seven and six in spring and autumn 1983, respectively, with 62 sampling stations. The relationship between the densities or distributions of polychaetes and observed environmental factors could not be explained.

In order to determine the height and age of paleo sea level precisely, it is necessary to find suitable indicators. The tube worm Pomatoleios kraussii (BAIRD) was an excellent indicator of sea level stands on the southeast coast of Boso Peninsula. Studies of vertical distribution of P. kraussii, living and emergent at the time of the 1923 Taisho Earthquake, showed that the upper limit of the P. kraussii zone was located at 0.1±0.1m above mean sea level. At Hiraiso, the upper limit of the distribution of fossil P. kraussii emergent at the time of the 1703 Genroku Earthquake was 6.8m. Using the relationship between the upper limit of P. kraussii and mean sea level, paleo sea level prior to the Genroku Earthquake was estimated to be 6.7±0.1m.On dating radiocarbon ages of small samples such as P. kraussii tubes, the alternation of samples might lead to incorrect results. Three out of four radiocarbon ages of fossil P. kraussii tubes emergent at the time of the 1703 Genroku Earthquake were dated to be about 100-250 years older than the time of the earthquake. Observation of these tubes by scanning electron microscopy revealed that the tubes which gave the older ages had been recrystallized, and did not yield reliable ages.

Quantitative seasonal samplings of macrobenthos were carried out in two brackish lakes with different salinity in Kamikoshiki Island, Kagoshima Prefecture.At Lake Kazakiike, where chlorinity of the water was around 1 ‰ macrobenthic fauna was constructed mostly with chironomid larvae and oligochaetes, which were presumably fresh form, and some brackish and one marine species were added to the fauna. At Lake Kaiike, where surface water usually showed 10 ‰ chlorinity, all species were marine.The population density of macrobenthos was high in autumn and low in summer in both lakes. Dominant species changed at each depth among bivalves and polychaetes in Lake Kaiike.Common brackish species were characteristically absent in both Lake Kazakiike and Lake Kaiike. The author assumed that the absence of open waterways from the lakes into both fresh and marine region was responsible for the lack of brackish species in both lakes.

汽水性潟湖である宍道湖における魚類相の周年変化を,1994年10月から1995年9月にかけて毎月1回,定置網の1種であるます網を用いて調査した。汽水種であるコノシロやサッパはます網で大量に捕獲されていたが,宍道湖では水産資源として利用されず放棄されていた。また季節によって出荷されたり放棄されたりする魚種もあった。このことから,宍道湖では漁獲統計から優占種を推定することはできないことが分かった。また調査期間を含む1994年夏季から1995年冬季は例年よりも水温と塩分が高めに推移したが,このことが調査水域の魚類相に反映されていた。海産の漁獲対象種であるスズキの幼魚は,従来考えられていたよりもずっと早い時期である5月に,体長(全長)32±3.4mmで宍道湖に進入していた。その幼魚は9月には体長165±6.8mmに成長していた。スズキの餌となる汽水種のマハゼも,5月には32±2,1mmであった体長(全長)が,9月には114±16mmに成長していた。以上からスズキの初期成長にとって宍道湖は餌資源が豊富な,重要な水域であると推察された。

青森県下北半島の太平洋側中央部に位置する汽水湖尾駮沼におけるベントスの出現特性を2001年から2003年に至る期間,8地点において調査した。ベントスの個体密度は淡水河川の河口部と沼の沿岸部が湖心部と比較して多く出現した。出現が確認されたベントスの分類群は53種であり,大部分は軟体動物,環形動物および節足動物の分類群で構成されていた。優占種はヤマトスピオ,スピオ科のPolydorasp.,カワグチツボ,ホトトギスガイ,タカホコシラトリガイ,イソコツブムシであった。本研究の結果から,尾駮沼におけるベントスの歴史的変遷をみると,過去50年間において種構成の変化は小さかったが,近年環形動物のイトゴカイ,軟体動物のムラサキイガイやオオノガイなどの増加が示唆された。

大型植物の漁獲が富栄養化湖沼における栄養物質の削減対策としてどの程度の効果を期待できるのかを見積もるために,閉鎖性汽水域である中海の大型藻類の窒素・リン濃度を分析した。Gracilaria uerrucosa(オゴノリ)の窒素・リン濃度はそれぞれ3.1%drywおよび0.21%dry wであったことから,オゴノリの漁獲が盛んであった1960年当時の年間出荷量(551t dry w)には窒素とリンがそれぞれ17tおよび1.2t含まれていたと見積もられた。これは現在の宍道湖・大橋川・中海への窒素とリンの年間流入負荷量の0.56%および0.41%に相当した。1960年当時のオゴノリの漁獲量は生産量の約13%であったと推定されていたことから,年間漁獲量を5倍(年間生産量の65%)に増やせるとすると,宍道湖・大橋川・中海への窒素とリンの流入負荷に対して2.8%および2.0%を中海におけるオゴノリの漁獲だけで除去することが可能になると見積もられた。