Yasushi Seike

First investigation of ultraoligotrophic alpine Lake Puma Yumco in the pre-Himalayas, China

Lake Puma Yumco is a typical alpine lake (altitude 5030 m) located in the pre-Himalayas of Tibet, China, and this study was the first limnological investigation ever conducted on it. Lake Puma Yumco (28°34″N, 90°24″E) has the following morphometric properties: maximum length 31 km, maximum width 14 km, mean width 9 km, shoreline 90 km, surface area 280 km2, and shoreline development 1.5. Transparency was approximately 10 m, even in the thawing season. The extinction coefficient of the lake water was calculated as 0.15 m−1. Annual maximum transparency was estimated from the depth of the Chara zone to be 30 m. Dissolved oxygen was 7 mg O2 l−1 and showed saturated values, and salinity was 360 mg l−1. The chemical type of the lake water was Mg-Ca-HCO3-SO4, and it was slightly alkaline in character. Total nitrogenous nutrients (sum of ammonia, nitrite, nitrate, and urea nitrogen), phosphate, and silicate were extremely low at 1, 0.02, and 9 µM, respectively. Dissolved organic carbon, nitrogen, and phosphorus concentrations were 160, 11, and 0.08 µM and the molar ratio was calculated as 2100 : 140 : 1. Chlorophyll a concentration was 0.2 mg m−3. Phytoplankton and zooplankton were dominated by Aphanocapsa sp. and Diaptomidae. Both nitrogen and phosphorus appear to be the limiting parameters for phytoplankton growth. Organic carbon and nitrogen contents in lake sediments were low and the sediments contained a large amount of CaCO3. The grain size of sediment was that of silt-sand in most cases. The present results indicate that the pre-Himalayan alpine freshwater Lake Puma Yumco is an ultraoligotrophic lake.

Nitrous oxide in brackish Lakes Shinji and Nakaumi, Japan

Abstract 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.

Seasonal and areal features of the lagoonal environment in Lake Nakanoumi, a shallow coastal lagoon in Japan

Lake Nakanoumi is a shallow coastal lagoon connected with the Japan Sea by a narrow channel. Over the past decade, land reclamation resulted in a 33% reduction of the lagoons surface area. The remaining water basin of Lake Nakanoumi is scheduled to be artificially freshened to supply irrigation water for the newly reclaimed lands. This paper deals with the seasonal and areal features of the lagoonal environment prior to the beginning of the artificial desalinization.

Distribution of aquatic plants and absorption of radionuclides by plants through the leaf surface in brackish Lake Obuchi, Japan, bordered by nuclear fuel cycle facilities

We investigated the distribution of aquatic plants and the absorption of radionuclides by them in the brackish Lake Obuchi, Japan, which is bordered by nuclear fuel cycle facilities. We studied 5 species of submerged plants: Zannichellia palustris, Ruppia maritima, Potamogeton pectinatus, Zostera japonica, and Z. marina. The plants contained many elements, including radionuclides. The concentrations of 238U, 137Cs, and 90Sr in Z. marina were 11.3-12.4, 0.000-0.144, and 0.151-0.202 Bq.kg-1 dw, respectively. Those in Z. japonica were 5.2-8.8, 0.000-0.267, and 0.081-0.175 Bq.kg-1 dw, respectively. The concentrations of these radionuclides in the plants tended to be higher in higher-salinity regions than in lower-salinity regions of the lake. We found a close relationship between photosynthetic activity and the absorption of stable Sr by plants in the laboratory. Salinity, illumination, and water temperature influenced the photosynthetic activity of the plants and the consequent absorption of elements.

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

Abstract 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 (N2ON) increased markedly with decreasing concentrations of DO. Low DO (10%–30% saturation) induced high N2ON. In contrast to nitrification, N2O-producing activity by denitrification (N2OD) 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.

Evaluating the Contribution of Long-Range Transport of Heavy Metals from the Asian Continent to Their Concentrations in Sediment Cores from Lake Shinji, Western Japan

The historical trend of heavy metal pollution recorded in sediment cores from Lake Shinji, western Japan, was investigated to evaluate the contribution of increasing long-range transport of heavy metals from the Asian continent in recent years. The concentrations of Cd, Co, Cr, Cu, Ni, Pb, Sb, and Zn and lead isotope ratios were determined for sediment cores collected at two sites in the lake. Among the metals, Cd, Sb, and Zn showed markedly high concentrations since the 1970s. Moreover, a high Pb concentration and less radiogenic lead isotope ratios have been observed since the 1980s in the core from a site close to the mouth of a major river. Air masses from the Asian continent, including China, Russia, and South Korea, have less radiogenic lead isotope ratios than those from Japan. This suggests that the recent increase in Pb concentration in the sediment core is primarily due to the long-range transport of heavy metals from the Asian continent, followed by their deposition in the catchment area of the river. The concentration ratios of Pb/Cd, Pb/Sb, and Pb/Zn of the sediment around 2000 were calculated on the basis of the metal concentrations in excess of those before 1940. They were then compared with the volume-weighted annual average concentration ratios of Pb/Cd, Pb/Sb, and Pb/Zn of rain samples collected on the shore of the lake for 1999–2001. The result showed that the ratios of the former to the latter are 1.0 for Cd, 0.69 for Sb, and 0.31 for Zn. Thus, it is likely that the long-range transport of Cd and Sb from the Asian continent also contributes significantly to the recent increase in the concentrations of these metals in the sediment core from Lake Shinji. For Zn, however, the contribution from the Asian continent was evaluated to be small, suggesting the importance of local sources such as effluent discharges.

Urea decomposing activity of fractionated brackish phytoplankton in Lake Nakaumi

Abstract The influence of brackish phytoplankton cell classes upon the response of urea decomposition was investigated in Lake Nakaumi. The urea decomposition rate was 5 to 350 μmol urea m−3 h−1 in the light and 3 to 137 μmol urea m−3 h−1 in the dark. The urea decomposition rates in the light were obviously higher than in the dark. An extremely high rate (350 μmol urea m−3 h−1) was observed in Yonago Bay. The rate in the smaller fraction (<5 μm) exceeded that in the middle (5–25 μm) and larger fractions (>25 μm). The chlorophyll- and photosynthesis-specific rates for urea decomposition in the light were 0.5 to 3.9 μmol urea mg chl.a−1 h−1 and 0.3 to 1.3 μmol urea mg photo.C−1. The specific urea decomposing activities were higher in the smaller fraction than in the other two fractions. The present results suggest that in brackish waters urea decomposition occurred with coupling to the standing crop and photosynthetic activity of phytoplankton.

Characteristics of CO2, CH4 and N2O emissions from a multi-soil-layering system during wastewater treatment

Abstract In the present study, characterization of greenhouse gas emissions, such as CO2, CH4 and N2O, from a multi-soil-layering (MSL) system during wastewater treatment was conducted, using a laboratory scale system (width 50 × depth 10 × height 120 cm). Net fluxes of CO2, CH4 and N2O from the system were in the range of 21.2–48.0 g m−2 day−1, −66.4–0.02 mg m−2 day−1 and 41–246 mg m−2 day−1, respectively. Carbon dioxide emission generally increased as the air temperature increased. The net flux of CO2 was not appreciably different among the treatments, even though the hydraulic loading rates (HLR) differed widely. These findings indicated that the decomposition of organic matter loaded through wastewater was more efficient in the low HLR treatments. Mean CH4 emission was lower than the amount of CH4 brought by the influent. Methane was consumed in the MSL system during most of the study period, and the consumption tended to be more efficient in the treatments at high HLRs. Wastewater quality was not markedly related to the characteristics of the CO2 and CH4 emissions. Nitrous oxide was mainly released into the treated water as dissolved gas. Nitrous oxide emission per 1,000 L of wastewater decreased as the HLRs increased in the wastewater containing a high level of contaminants (HWW), while in the case of wastewater containing a low level of contaminants (LWW), such a decrease in the emission was not observed. Mean N2O conversion rates of the LWW treatments ranged from 1.10 to 1.79% and were higher than those of the HWW treatments, which ranged from 0.19 to 1.95%. Nitrous oxide emission could be reduced in the HWW treatments.

Second record of Cyclopina kiraensis, a small, brackish-water cyclopoid copepod, in Japan

Abstract In the monthly zooplankton survey in Lake Nakaumi, Shimane Prefecture, conducted since July 1997, Cyclopina kiraensis occurred in the samples in July 1997 and July 1998. This species had not been recorded since the original description from the mouth of the Yahagi-furukawa River, Aichi Prefecture, in 1984. This paper is the second record of the species and is the first report of the species from the coast of the Sea of Japan. We describe environmental conditions of the habitat and the characteristics distinguishing this species from the morphologically allied species, Paracyclopina nana, which co-occurred in Lake Nakaumi.

Adsorptive removal of cadmium by natural red earth: equilibrium and kinetic studies

Natural red earth (NRE), an iron-coated sand found in the north western part of Sri Lanka, was used to examine the retention behaviour of cadmium, a heavy metal postulated as a factor of chronic kidney disease in Sri Lanka. Adsorption studies were conducted as a function of pH, ionic strength, initial Cd loading and time. The Cd adsorption increased from 6% to 99% with the pH increase from 4 to 8.5. The maximum adsorption was reached at pH>7.5. Cadmium adsorption was not changed over 100-fold variations of NaNO3, providing evidence for the dominance of an inner-sphere bonding mechanism for both 10-fold variation of initial Cd concentrations. Surface complexation modelling suggests a monodentate bonding mechanism. Isotherm data were fairly fitted to a two-site Langmuir isotherm model and sorption maximums of 9.11×10−6 and 3.89×10−7 mol g−1 were obtained for two surface sites. The kinetic study reveals that Cd uptake by NRE is so fast that the equilibrium was reached within 15 min and ∼ 1 h for 4.44 and 44.4 μM initial Cd concentrations, respectively, and the chemisorption was the dominant mechanism over intra-particle diffusion. The study indicates the potential of NRE as a material for decontaminating environmental water polluted with Cd.