Nobutada Nakamoto

Population dynamics of Propsilocerus akamusi and Chironomus plumosus (Diptera: Chironomidae) in Lake Suwa in relation to changes in the lake's environment

Lake Suwa is a shallow eutrophic lake in central Japan. We have investigated the long-term population dynamics of chironomids in this lake. The objective of this study was threefold: (1) clarifying temporal variations in the emergence pattern of P. akamusi midges, (2) assessing dynamics in density, biomass and distribution pattern of Propsilocerus akamusi and Chironomus plumosus larvae in this lake, and (3) determining key factors that may affect these variations, as well as comparing the results of this study to those of previous reports. Emergence periods of P. akamusi midges from the lake have tended to become shorter in recent years. Furthermore, the mean daily catch of midges exhibits a clear decrease over time. In contrast, average densities of P. akamusi and C. plumosus larvae in the lake were 73.3±48.0 (SD) and 3.2±9.4 individuals per m2, respectively. Compared to 1986, this amounts to a decrease of about 1/70 and 1/130, respectively. Finally, the organic matter in the upper layer of the sediment has also been decreasing. This suggests that the basic conditions necessary for chironomid larvae habitats, especially quality and quantity of food, seem to be changing in Lake Suwa as water quality improves.

Field Study on Acoustic Response of Chironomid Midges (Diptera: Chironomidae) Around a Hyper-Eutrophic Lake in Japan

Abstract A new method was developed to control adult chironomid midges, Chironomus plumosus (L.) and Einfeldia dissidens (Walker), using their acoustic responses to sound traps in the field. Trials were conducted in 1999 from 2 to 7 June (during emergence period of E. dissidens ) and from 2 to 7 September (emergence period of C. plumosus ) near hyper-eutrophic Lake Suwa in central Japan. Swarms of E. dissidens were formed at 1–3 m above the terrain and were observed from 1900 to 1930 hours. More than 97% of E. dissidens trapped from the swarms were males. In cylindrical sound traps, optimal trapping of swarming males occurred at a frequency of 240 Hz at 21.9 ± 2.3°C. Swarms of C. plumosus were formed at 1 m to >5 m above ground, and were observed from 1830 to 1900 hours. More than 88% of C. plumosus caught from the swarm were males, and optimal trapping of swarming males occurred at frequencies of 300–360 Hz at 20.7 ± 0.5°C. We compared our results with those of other chironomid species and attempted to clarify the relationship between female wing length and ambient air temperature. There was no correlation between the most attractive frequency and female wing length. However, a positive correlation existed between the most attractive frequency and air temperature. It is concluded that the most attractive frequency differed among species (interspecific) according to air temperature. These mechanisms may play an important role in isolation during chironomid swarming.

Grain size distribution of particulate matter and sediment in extensive freshwater bodies in pre-Amazonian floodplain, Baixada Maranhense, Brazil

The limnology of the Amazon River and its floodplain ecosystems has been vigorously studied (FISHER & PARSLEY 1979, SIOLI 1984, FoRSBERG et al. 1988, MELACK & FISHER 1990, RICHEY et al. 1990, DEVOL et al. 1995, JUNK & WEBER 1996, IBANEZ 1997, JUNK 1997, BOZELLI & GARRIDO 2000, CARNEIRO et al. 2002, FARJALLA et al. 2002, ROLAND et al. 2002, GUENTHER & BOZULL 2004). The freshwater bodies in floodp1ains provide high productivity and biodiversity, which are sustained with various biogeochemica1 cycling. We a1so have some data from rivers and 1akes in the pre-Amazonian floodplain (REm & TuRNER 1988, BARBIERI et al. 1989, IBANEZ et al. 2000). The limnological knowledge of this aquatic system, especially the grain-size configuration of particulate matter and bottom sediment, however, has been limited. The aim of this study was to clarify the characteristics of fine size distribution o f particulate matters and bottom sediments in the Turiacu, Pericuma, and Pindare aquatic systems, in a typica1 pre-Amazonian floodplain ecosystem, Baixada Maranhense, Maranhao, Brazíl, which 1ies in the southem part of the Amazon River estuary.

Emergence Composition and Seasonal Change of Crane Flies (Diptera: Tipulidae) from Slow Sand Filter Beds in Japan

ABSTRACT We studied seasonal change in adult crane fly emergence from slow sand filter beds in an inland climate area of Japan and identified a total of 12 genera and 20 species belonging to two families. Crane fly fauna in filter beds was dominated by two species Antocha (Antocha) bifida and Antocha sp. 1. Emerging adults of the two main species showed a significant seasonal change in body size (determined by wing length), which decreased steadily from spring to summer and increased again in fall. We speculate that water temperatures influenced the decline in the wing length of crane flies on such filter beds.

Oxygen production and bubble formation by algal mat on the bed in a slow sand filter pond

A slow sand filter pond for drinking water, similar in shape to a swimming pool with a water depth of about l m, was used in this study. The bottom was composed of a sand layer for filtration. There was a constant downward current, the speed of which was normally about 4-5 m/day (10-20 em/h), and a constant nutrient supply to the filter basin from an intake of water. There was sufficient radiation for photosynthesis on the shallow bottom and photosynthetic organisms grew in this environment. However, phytoplankton did not grow due to the presence of a water current and only some filamentous algae grew on the bottom under these conditions (NAKAMOTO & EzuRE 1989). A heavy algal bloom of filamentous diatoms was observed in the pond in which the intake water contained enough nutrients to allow algal growth. Bubbles were formed by photosynthesis in the algal mat on the sand surface. The algal mat was easily lifted up to the surface due to the buoyancy of the bubbles, and then disappeared through the scum outlet. The slow sand filter acted as a continuous culture system for filamentous algae. This paper describes the formation of oxygen bubbles and its role in this system.