Nitrous oxide in brackish Lakes Shinji and Nakaumi, Japan

Nitrous oxide (N₂O) was measured monthly from September 1997 to August 1998 in the brackish Lakes Shinji and Nakaumi, Japan. N₂O (5–37 μg N l⁻¹) was supersaturated in the overlying water on lake sediments from October 1997 to January 1998. The N₂O concentration in the hypolimnion was higher than that in the epilimnion on 17 October 1997, when N₂O was first observed in a water column of Lake Nakaumi. Afterward, N₂O was almost uniform throughout the water column and then disappeared on 16 February 1998. On the one hand, large amounts of N₂O were found throughout the year in the interstitial water in Lake Shinji, where a high concentration of nitrate was discharged from the Hii River. On the other hand, in Lake Nakaumi, stratified by halocline, a high concentration of N₂O was observed in the interstitial water only from winter to spring. N₂O concentrations in the interstitial water were about 10 to 1000 times as large as those in the overlying water. These results imply that N₂O was mainly produced at the sediment-water interface and was diffused to the overlying water. It was also suggested that the accumulation of N₂O in the sediment-water system was accelerated by a high concentration of hydrogen sulfide. Received: July 6, 2000 / Accepted: November 30, 2000     

Long-term change in water transparency before and after the loss of eelgrass beds in an estuarine lagoon,Lake Nakaumi,Japan

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.     

Limnological characteristics of subtropical Lakes Phewa, Begnas, and Rupa in Pokhara Valley, Nepal

Limnological characteristics were studied and analyzed in the subtropical Lakes Phewa, Begnas, and Rupa of Pokhara Valley, Nepal, from 1993 to 1997. The annual water temperature ranged from 12° to 29°C in all lakes. Lake Phewa and Lake Begnas were monomictic and anoxic in the hypolimnion during thermal stratification from April to September. Dissolved oxygen was drastically depleted in April and/or May in shallow Lake Rupa when the macrophyte community began to decompose. NH₄ ⁺-N accumulated below 5 m during March–September when dissolved oxygen was depleted in Lakes Phewa and Begnas. The PC : PP ratio was higher, but the PC : PN and PN : PP ratios were close to the Redfield ratio (106C : 16N : 1P) in Lakes Phewa and Begnas, denoting that P was limited. Annual net primary production showed that the lakes were productive but will tend to become heterotrophic in the future. The seasonal variation of chlorophyll a concentration was high, but its annual variation was low. Ceratium hirundinella and Peridinium spp. in Lake Phewa, Microcystis aeruginosa and Aulacoseira granulata in Lake Begnas, and Tabellaria fenestra in Lake Rupa were the dominant species. The zooplankton population and species varied irregularly. On the basis of chlorophyll a concentration in the euphotic zone and phytoplankton species composition, the lakes seem to be oligoeutrophic and to have some characteristics of temperate lakes rather than tropical lakes. Received: April 26, 1999 / Accepted: September 20, 1999     

Population genetic structure of Potamogeton anguillanus in Lake Shinji, Japan

Enzyme electrophoresis was performed to investigate the genetic variation of Potamogeton anguillanus Koidz. in Lake Shinji, Shimane Prefecture, Japan. The collection was made in six local populations along the coast of the lake, and a total of 78 shoot samples were obtained. No variation among samples occurred in the six enzymes analyzed, and the whole population in Lake Shinji was proved to consist of only a single multienzyme phenotype. Clonal growth without sexual reproduction may have resulted in the genetic uniformity. The implication of the lack of genetic variation is briefly discussed from the viewpoint of conservation of the species in Lake Shinji. Received: July 11, 2000 / Accepted: October 5, 2000     

Distributional survey of large branchiopods of rice paddies in Shiga Prefecture,Japan: a Lake Biwa Museum project based on lay amateur participation

A distributional survey of the large branchiopod crustaceans of the rice paddies of Shiga Prefecture, Japan, was conducted by the Lake Biwa Museum in May and June of 1999 and 2000. Collecting kits were issued to over 100 lay Field Reporters, who returned all samples, usually dried, to the museum for processing. Their 242 species-lots were augmented by 146 from Grygier, 46 from Ida, and 41 from other museum staff. Apart from this survey, 50 additional records in 1997–2000 were also taken into account. Seven species were recorded in the prefecture's southern half: Branchinella kugenumaensis (Ishikawa), Caenestheriella gifuensis (Ishikawa), and Lynceus biformis (Ishikawa) with wide distributions; Triops longicaudatus (LeConte) and Leptestheria kawachiensis Uéno limited to paddy areas around the south end of Lake Biwa; and Eulimnadia sp. mostly in remnant paddy areas threatened with urban development in Otsu city, with Triops granarius (Lucas) at a single such site in Otsu. In the prefecture's northern half, only B. kugenumaensis and C. gifuensis occurred to a limited degree. Possible reasons for these differences are discussed. Data pertaining to species co-occurrence and occurrence relative to the ongoing program of paddy field consolidation in the prefecture are presented and discussed. Success of the survey was due to the use of Field Reporters, who were able to provide a high degree of coverage of the study area, as well as the clearly defined habitat, the low number and easy recognizability of species, and the collection of voucher material from all sites. Conservation-related results included the listing of Eulimnadia sp. as a `rare' species by Shiga Prefecture.     

<Emphasis Type="Italic">Oncorhynchus kawamurae</Emphasis> “Kunimasu,” a deepwater trout,discovered in Lake Saiko, 70 years after extinction in the original habitat,Lake Tazawa,Japan

Oncorhynchus kawamurae (Osteichthyes: Salmonidae) (common name “Kunimasu”), a species endemic to Lake Tazawa, Akita Prefecture, Japan, was believed to have been extinct since 1940. However, nine specimens were discovered in March and April 2010 in Lake Saiko, Yamanashi Prefecture, one of the lakes to which eyed eggs of the species were introduced in 1935. These were identified as O. kawamurae because of having 47–62 pyloric caeca, 37–43 gill-rakers, a black-colored body, and spawning at 30–40 m depth in early spring, which are unique characteristics within Oncorhynchus. Furthermore, the distinctiveness of Kunimasu from sympatric kokanee (O. nerka) was supported by microsatellite DNA data.     

Stereotyped sequence of mating behavior in the Far Eastern catfish, Silurus asotus, from Lake Biwa

 Mating behavior of the Far Eastern catfish, Silurus asotus (Siluriformes: Siluridae), was observed in a ricefield system facing the shore of Lake Biwa in mid-May to early June in 1990–1997. A set behavioral sequence similar to those of two other silurid fishes, S. biwaensis and S. lithophilus, both endemic to the Lake Biwa system, was observed: “chasing,”“clinging,”“enfolding” while “squeezing” by the male, and “circling” by the spawning pair. This form of mating behavior is quite different from that of S. asotus reported from the Ooi River system in Kyoto Prefecture, which mainly spawns in running water in ditches. Received: April 10, 2001 / Revised: November 5, 2001 / Accetped: November 20, 2001     

Stonogobiops yasha, a new shrimp-associated goby from Japan

A new shrimp-associated goby, Stonogobiops yasha sp. nov., is described on the basis of nine specimens collected from the Ryukyu Islands, Japan. This species is easily distinguished from other congeneric species in having reddish-orange stripes on a white body and only two median cephalic sensory pores on the head. Received: July 21, 1999 / Revised: July 10, 2001 / Accepted: July 26, 2001     

Phosphorus release and sedimentation in three contiguous shallow brackish lakes, as estimated from changes in phosphorus stock and loading from catchment

In situ phosphorus release rates in three contiguous shallow brackish lakes were calculated by considering the amount of water inflow, changes in salinity and phosphorus stock, and loading from phosphorus inflow based on monthly data. The annual amount of sedimental phosphorus relative to that of phosphorus inflow was different for each of the three water bodies: 16% for Lake Shinji, 3% for the Honjo area, and −8% for Lake Nakaumi, as estimated in a 10-year period from January 1993 to December 2002. During the warm season, the quantity of phosphorus released surpassed sedimentation in these three water bodies. The low annual sedimentation ratio in Lake Nakaumi is related to a large seawater backflow resulting in phosphorus removal, in addition to a stable stratified structure promoting phosphorus release from sediment due to oxygen depletion in the lower layer. In Lake Nakaumi, field data shows that if dissolved oxygen at the sediment surface falls below 2.54 mg L⁻¹, phosphorus release from the sediment begins to be accelerated.     

The physical factor inducing spawning of the Biwa catfish, Silurus biwaensis

The physical factor inducing spawning of the Biwa catfish, Silurus biwaensis (Siluriformes: Siluridae), an endemic species of Lake Biwa, was investigated on the basis of field observations on 150 nights at the spawning site, the rocky shore of the Seta River, the lake's outlet, and environmental data from April to July in 1989–1994. The catfish gathered at the spawning site when the water level of the river rapidly rose and the rocky shoal became submerged, within a wide range of water temperature (15.0°–30.0°C); their spawning was induced in relation to increases in the submerged portion of the rocky shoal. This observation suggests that water level control operations in Lake Biwa might critically affect the spawning of this and other fish species. Received: December 17, 1999 / Revised: September 13, 2000 / Accepted: January 16, 2001     

Fishes and fisheries of Lake Nubia,Sudan

Developing lake conditions in Lake Nubia were found to offer good commercial fisheries potential. This prospect initiated fishery research since 1967.In this study, 26 fish species belonging to 10 families were recorded. Compared with previous studies the total number has decreased and some of the species that were commercially important during the early years of the lake formation, are now negligible in occurrence (Distichodus, Citharinus, Bagrus). The species widely distributed in the lake are Labeo niloticus, Lates niloticus, Sarotherodon niloticus, Hydrocynus forskallii, Alestes baremose and Eutropius niloticus. Their highest production occurs during two periods: February to May and July to September. The dominant fish species feed on different items in a balanced equilibrium with the ecological and biological conditions.     

Occurrence of arbuscular mycorrhiza on aged Eucalyptus

Eucalyptus despite the fact that Eucalyptus seedlings do form both endomycorrhiza and ectomycorrhiza early during their developement. In the present study, all the structures of arbuscular mycorrhiza were observed within roots of four Eucalyptus species of 15, 17 and more than 50 years old at three different sites in northern Algeria. Arbuscular mycorrhiza frequency was assessed in roots of 15-years old Eucalyptus camaldulensis species, during two periods in 2 consecutive years (July and November of 1996 and 1997). Intensity of root colonization was dependent on the time of sampling and attained 42% in July 1997. Accepted: 17 September 1999     

Natural hybridization and gene flow between twotridentiger gobies in lake hinuma (ibaraki prefecture, japan)

Of 851 specimens ofTridentiger obscurus andt. brevispinis collected from Lake Hinuma (Ibaraki Prefecture, Japan) from July 1996 to February 1998, 49 (5.8%) comprised F₁ hybrids and backcross progeny of the two species. Since the mitochondrial DNA haplotypes of the F₁ hybrids reflected those ofT. brevispinis, most instances of hybridization are thought to have occurred between maleT. obscurus and femaleT. brevispinis. Although both allozyme and mitochondrial DNA analyses indicated backcrossing and introgression of mitochondrial DNA, the frequency of backcross progeny was relatively low, suggesting the existence of a natural selection to backrossing.     

MIXOTROPHY IN THE ANTARCTIC PHYTOFLAGELLATE,PYRAMIMONAS GELIDICOLA (CHLOROPHYTA: PRASINOPHYCEAE)1

Grazing by the planktonic phytoflagellate, Pyramimonas gelidicola McFadden (Chlorophyta: Prasinophyta), and heterotrophic nanoflagellates (HNAN) in meromictic saline Ace Lake in the Vestfold Hills, eastern Antarctica was investigated in the austral summers of 1997 and 1999. Up to 47% of the P. gelidicola population ingested fluorescently labeled prey (FLP). Ingestion rates varied with depth. In January 1997 and November 1999, maximum P. gelidicola ingestion rates of 6.95 and 0.79 FLP·cell^?1·h^?1, respectively, were measured at the chemocline (6–8 m) where a deep chl maximum composed of phototrophic nanoflagellates (PNAN DCM), predominantly P. gelidicola, persisted all year. During the summers of 1997 and 1999, the grazing P. gelidicola community removed between 0.4% and approximately 16% of in situ bacterial biomass, equivalent to between 4% and>100% of in situ bacterial production. Because of their higher abundance, the community clearance rates of HNAN in Ace Lake generally exceeded those of P. gelidicola, but HNAN removed approximately only 3%–4% of bacterial biomass, equivalent to between 28% and 32% of bacterial production. Pyramimonas gelidicola growth rates were highest at the PNAN DCM concomitant with the highest ingestion rates. It is estimated that during the summer P. gelidicola can derive up to 30% of their daily carbon requirements from bacterivory at the PNAN DCM. This study confirms mixotrophy as an important strategy by which planktonic organisms can survive in extreme, polar, lacustrine ecosystems.     

Spatiotemporal changes in distributions of the two dominant bivalve species in an estuarine river connecting two brackish lakes,Japan

Spatiotemporal changes in the biomass and abundance of the two dominant bivalve species Corbicula japonica and Arcuatula senhousia were investigated at 14 stations positioned along the Ohashi River from November 2005 to August 2007. Corbicula japonica predominantly inhabited the upstream section of the primary branch and Kensaki stream of the Ohashi River, whereas A. senhousia predominantly inhabited the downstream section of the Ohashi River. However, the distributions were highly variable among stations and seasons. Intrusions of saline water from Lake Nakaumi varied with astronomical and climatological factors, and consequently, the halocline of the Ohashi River is subject to spatiotemporal changes. Changes in distributions of C. japonica and A. senhousia occurred in relation to a flood event, indicating that environmental disturbances affect the distributions of the two bivalve species. Responses of the two species to continual saline water intrusion were also observed during the period of normal flow conditions. We suggest that the distribution of the two species is closely related to the dynamics of the ambient saline water, which is the most important factor correlated to changes in the distributions of C. japonica and A. senhousia in the Ohashi River.     

Two new species of Amanita from Japan

 Two new species from Japan, Amanita areolata and Amanita griseoturcosa, are described. The former, found in a broad-leaved forest in Aichi Prefecture, is a medium- to large-sized mushroom characterized by an areolate, brownish pileus, a nonstriate and appendiculate margin of the pileus, and amyloid basidiospores. The latter, found in forests with Fagaceae or Pinaceae in Tokyo, Chiba Prefecture, and Miyagi Prefecture, is a medium-sized mushroom characterized by a grayish-turquoise pileus, a nonstriate margin of the pileus, a saccate volva, an apical membranous annulus, and amyloid basidiospores. Received: July 10, 2001 / Accepted: June 5, 2002     

A new species of <Emphasis Type="Italic">Pseudomaseus</Emphasis> (Coleoptera: Carabidae: Pterostichini) from Greece

A new species of carabid beetles, Pterostichus hejkali sp. n. is described from Northwest Greece (type locality: Epirus District, Ioannina Prefecture, Ioannina Lake environs). Diagnostic characters include distinctive shape of the median lobe of aedeagus, of right paramere and of sexual modification on last visible sternum in males as well as shape of pronotum and size of body. Members of the new species are most similar to P. minor. A key to the identification of the Balkan taxa of Pseudomaseus is presented.     

Nitrous oxide in brackish Lake Nakaumi, Japan II: the role of nitrification and denitrification in N2O accumulation

In order to understand the role of nitrification and denitrification in the accumulation of nitrous oxide (N₂O) in the hypolimnetic water of brackish Lake Nakaumi, the effects of dissolved oxygen (DO) concentration on these activities were investigated by incubation experiments. N₂O was produced during the oxidation of NH₄ ⁺ to NO₂ ⁻ in nitrification and during the reduction of NO₃ ⁻ to N₂ in denitrification. N₂O-producing activity by nitrification (N₂O_N) increased markedly with decreasing concentrations of DO. Low DO (10%–30% saturation) induced high N₂O_N. In contrast to nitrification, N₂O-producing activity by denitrification (N₂O_D) decreased with decreasing concentrations of DO. Little N₂O was accumulated during denitrification under low-level conditions of DO (10%–30%), because of further reduction of N₂O to N₂. It can therefore be assumed that N₂O produced as the by-product of nitrification is concurrently reduced to N₂ by denitrification under low-DO conditions. This would result in no substantial accumulation of N₂O during active nitrification in the hypolimnetic water of Lake Nakaumi. Received: July 6, 2001 / Accepted: December 10, 2001