Seasonal changes of carbon and nitrogen stable isotope ratios for dominant species: chironomid larvae, phytoplankton, and benthic diatom inhabiting strongly acidic Lake Katanuma

Lake Katanuma is a colcanic, strongly acidic lake (average pH of 2.2), located in Miyagi prefecture, Japan. Only a few spieccies are found in Katanuma; Chironomus acerbiphis larvae as benthic invertebrate, Pinnularia baunii as benthic diatom, and Chlamydomonas acidophila as phytoplnkton. We tried analyzing seasonal changes of carbon and nitrogen stable isotope raios foethese spicies in Lake Katanuma. Food souece analysis by isotope ratios clearly showed main food source for Chironomus acerbiphilus larvae was P.braunii (benthic diatom). δ1C values of P.braunii varied seasonally, while those of POM (mainly phytoplankton) remained fairly stable. The difference of stable isotope ratios in these orfanisms discussed.Article信州大学山地水環境教育研究センター研究報告 2: 25-28(2004)departmental bulletin pape

Environmental fluctuations of the Lake Chany complex in western Siberia based on NOAA images

The Lake Chany complex, located in Western Siberia, consists of the large shallow lakes with an average depth of about 2m. The lake area fluctuates according to water level that depends closely on the amount of inflow( snow-melt) and the evaporation, since the lake complex has no outflow river. Based on NOAA/AVHRR satellite normalized difference vegetation index (NDVI) data of the ice-free periods in 2000 and 2001, we evaluated the seasonal changes in the lake area and the surroundingu vegetations of the Lake Chany complex. In late April or early May, the maximum lake area was abserved and the lake area decreased drastically until late May or early June. Then, the lake area decreased gradually from early June to late August. The lake area in August was about 70% of the maximum. Then, the area tends to increase by early October. Compared with the ground truth in August 2001, the seasonally fluctuated areas on NOAA images corresponded to the vast vegetations with several km in width of reed (Phragmites communis) stands which seem to be influenced by the inflow of snow meltwater and the growth of reeds.Article信州大学山地水環境教育研究センター研究報告 2: 1-4(2004)departmental bulletin pape

Isotopic evidence for the spatial heterogeneity of the planktonic food webs in the transition zone between river and lake ecosystems

Resources and organisms in food webs are distributed patchily. The spatial structure of food webs is important and critical to understanding their overall structure. However, there is little available information about the small-scale spatial structure of food webs. We investigated the spatial structure of food webs in a lake ecosystem at the littoral transition zone between an inflowing river and a lake. We measured the carbon isotope ratios of zooplankton and particulate organic matter (POM; predominantly phytoplankton) in the littoral zone of a saline lake. Parallel changes in the δ 13C values of zooplankton and their respective POMs indicated that there is spatial heterogeneity of the food web in this study area. Lake ecosystems are usually classified at the landscape level as either pelagic or littoral habitats. However, we showed small-scale spatial heterogeneity among planktonic food webs along an environmental gradient. Stable isotope data is useful for detecting spatial heterogeneity of habitats, populations, communities, and ecosystems

The influence of paddy soil drying on Tc insolubilization by bacteria

Tc insolubilization in four soils samples was compared by pre-incubating them in both dry and wet states, then measuring Tc concentrations in solution when the samples were saturated with an excess of water spiked with 99-Tc. Soils pre-incubated in a dry state showed higher Tc insolubilization than soils incubated in a wet state. To clarify the difference in Tc insolubilization, Eh, bacterial abundances, and bacterial species compositions in the dry and wet ponding water samples were determined. For the wet ponding water samples, Eh values were forced to decrease, but no increase in Tc insolubilization was observed. The dry and wet ponding water samples had similar numbers of bacteria. However, denaturing gradient gel electrophoresis analysis revealed that they had different bacterial species compositions. These results suggested the difference in bacterial species compositions would account for the difference in Tc insolubilization

Responses of the bacterial community to chronic gamma radiation in a rice paddy ecosystem

Purpose: Public concern about radiation protection of the environment and non-human species is increasing. The potential impact of chronic gamma radiation on the bacterial community in a rice paddy ecosystem was investigated.Materials and methods: Paddy field microcosm samples were continuously exposed at a dose rate of 1 Gy day-1 for 5 days after which the bacterial community structures in them were compared with those of unirradiated control samples by denaturing gradient gel electrophoresis (DGGE) of the 16S ribosomal ribonucleic acid (rRNA) gene. Dissolved ions in ponding waters of the microcosm samples were determined by ion chromatography.Results: The DGGE band profiles were clearly different between the control and exposure samples. Sequencing of selected DGGE bands revealed that a specific species of the genus Clostridium and of the genus Massilia were grown under radiation exposure. Additionally, the concentrations of sulfate ion in the ponding water of the microcosm samples increased under radiation exposure. Concentrations of Na+, Ca2+, and F- inversely decreased.Conclusions: The data presented suggest that chronic gamma radiation affects the bacterial community structure and material cycles in the rice paddy ecosystem

Ontogenetic dietary shifts of largemouth bass do not increase trophic position in a shallow eutrophic lake in Japan

The trophic positions of top predators can provide useful information for estimating the length of food chains and for assessing the impacts of invasive species or the bioaccumulation of harmful compounds. In aquatic ecosystems, large carnivorous fishes may change their trophic positions ontogenetically. We used stable carbon and nitrogen isotope ratios to test the hypothesis that the trophic positions of largemouth bass, top predators in Lake Izunuma, Japan, would increase with total length (TL) as a result of ontogenetic shifts in diet. Results from a stable isotope analysis in R mixing model indicated that largemouth bass <100 mm TL fed mostly on zooplankton and small omnivorous fishes, while individuals from 100 to 199 mm TL size class relied more heavily on small omnivorous fishes. Red swamp crayfish Procambarus clarkii were a major food source for largemouth bass ≥200 mm TL. However, the trophic positions of largemouth bass did not increase with the dietary shift from zooplanktivory to piscivory, and actually decreased when larger fish shifted towards feeding on red swamp crayfish. In Lake Izunuma, the trophic positions of small omnivorous fishes and red swamp crayfish were not higher than those of zooplankton. This explains why the largest largemouth bass occupied lower trophic positions than smaller individuals. Our results suggest that the body size of carnivorous fishes should be taken into consideration when using their trophic positions as top predators to evaluate aquatic systems.Trophic positions of largemouth bass Micropterus salmoides in Lake Izunuma, Japan, did not increase with the dietary shift from zooplanktivory to piscivory, and actually decreased when larger fish shifted towards feeding on red swamp crayfish. Consequently, largemouth bass ≥300 mm TL occupied lower trohic positions than smaller individuals