Haruo Fukuhara

Enhancement of inorganic nitrogen and phosphate release from lake sediment by tubificid worms and chironomid larvae

The effects of chironomid larvae and tubificid worms on the release of inorganic nitrogen and phosphorus from a eutrophic freshwater lake sediment were evaluated experimentally using mud-water microcosms. The larvae of Chironomus plumosus L. and Limnodrilus spp. caused an enhancement of inorganic nitrogen release (mainly ammonium nitrogen) from lake sediment. Increasing densities of tubificids markedly influenced release rates. Apparent diffusion coefficients of ammonium at the mud-water interface in microcosms with Limnodrilus spp. increased from 3.5 to 24 x 10-5 cm2 S-1 over a range of 5 densities from 0 to 72500 worms m-2, while that for microcosms with C. plumosus increased from 2.6 to 48 x 10-5 cm2 s-1 over a range of 5 densities from 0 to 6800 larvae m-2. Chironomids and tubificids also had an accelerating effect on phosphate release. Phosphate release rates became greater with an increasing density of organisms. Chironomids induced some enhancement of the release rate at low densities but caused a suppression at high densities. The excretion: release ratios indicated the importance of bioturbation for ammonium release and the importance of excretion for phosphate release.

Ammonium excretion by some freshwater zoobenthos from a eutrophic lake

Relationships between the ammonium excretion rate of zoobenthos and temperature were examined for two chironomids, Chironomus, plumosus and Tokunagayusurika akamusi, one chaoborid, Chaoborus flavicans, and two tubificids, Limnodrilus spp. and Branchiura sowerbyi, which often dominate in eutrophic lakes. The representative Q10 value and excretion rate at 15° C for each species were as follows: C. plumosus, 1.67, 1.40, (µg N mg dry w.−1 d−1 ); T. akamusi, 1.02 (< 15° C), 0.33; C. flavicans, 1.49, 2.87; Limnodrilus spp., 2.98, 0.59; and B. sowerbyi, 3.15, 0.79.

Community structure of microorganisms associated with reddish-brown iron-rich snow.

Reddish-brown colored snow, containing spherical brown particles, has been observed in several mires in Japan. In order to characterize this remarkable phenomenon, the microbial community and chemical species in snow were analyzed. A core sample of snow which had a colored region was investigated and it revealed vertical shifts in physicochemical characteristics and the microbial community structure. The abundance of particles peaked within the colored layer, and correlated with the amount of reducible Fe(III). The interstitial water of the colored layer was enriched with Fe(II), and characterized by reduced concentration of dissolved methane. The bacterial community in the colored region was characterized by higher relative abundance of iron-reducing bacteria and methanotrophs. Aggregates of the brown particles were found as precipitates in snow melt pools, and were subjected to cloning analyses targeting several different genes. The majority of bacterial 16S rRNA gene clones belonged to the class Betaproteobacteria or the phylum Bacteroidetes. No snow algae were detected in the eukaryotic small subunit rRNA gene clone library. As a possible carbon source to sustain the community in the snow, involvements of carbon dioxide and methane were investigated by analyzing the genes involved in their assimilation. In the analyses of genes for ribulose-1,5-biphosphate carboxylase/oxygenase, clones related to sulfur oxidizers were obtained. The analysis of particulate methane monooxygenase genes indicated dominance of Methylobacter species. These results emphasized the uniqueness of this phenomenon, and iron reducers of the genus Geobacter are suggested to be the key organisms that could be investigated in order to understand the mechanism of this phenomenon.

The effect of tubificids and chironomids on particle redistribution of lake sediment

The effects of chironomid larvae,Chironomus plumosus, and tubificid worms,Limnodrilus spp., on particle redistribution in lake sediment were investigated experimentally using pots containing sediments obtained from Lake Suwa, Japan. The chironomids and tubificids increased the water content of surface sediment. The chironomid larvae had no effect on particle size distribution, while tubificids continuously accumulated small particles on the surface sediment through their selective feeding activity. Particles larger than 0.125 mm were buried at a sediment depth of 6 cm. In Lake Suwa, long diatom frustules, large plant debris and blue-green algal flocs were found to accumulate in the deeper layer of the lake sediment inhabited by tubificids at high density.

Nitrate dynamics in a reed belt of a shallow sand dune lake in Japan: Analysis of nitrate retention using stable nitrogen isotope ratios

A stable nitrogen isotope analysis was used to clarify the relative importance of denitrification and nitrate uptake by plants in the nitrate reduction in a reed belt of L. Kamisagata (N 37°49′, E 138°53′, alt. 4.5 m, depth 30–80 cm, area 0.025 km2), one of about 20 sand dune lakes in Japan. A very high concentration of NO3 −-N with 19.0 ±5.9 mg N l−1 in spring sources decreased during passage through the reed belt along two set transect lines about 120 m long in any season, whereas progressive enrichment in 15N-NO3 − in flowing water was detected. Loss rate of nitrate ranged from 38.4 to 73.1% with an average of 56.7 ±11.6%. Enrichment factors calculated using a Rayleigh curve method ranged from - 1.03 to -5.12%.. The contribution of denitrification to nitrate loss ranged from 6 to 28%, with a mean of 19.5% (±7.0), whereas that of plant uptake was from 72 to 94%, with a mean of 80.5% (±7.0), indicating the importance of vegetation in a sand dune riparian zone. A technique using the variation of natural abundance of 15N may provide useful information on the nitrate dynamics in artificial or natural wetlands under a nondestructive condition.

The antagonistic relationship between chlorophyll a concentrations and the growth areas of Trapa during summer in a shallow eutrophic lake

The relationship between concentrations of chlorophyll a in an open water area and growing areas of the macrophytes Trapa spp. and Nelumbo nucifera was investigated to clarify the role of macrophytes in phytoplankton growth in summer in a eutrophic shallow sand lake, Lake Honsagata, Japan. The chlorophyll a concentrations formed peaks in June 2007 and July 2008 in summer with cyanobacterial blooms composed of mainly Microcystis, Anabaena, Phormidium, and Oscillatoria, which decreased toward August and were maintained at different annual levels. The decline of blooms in August was caused by the rapid growth of macrophytes. The composition of phytoplankton and the level of bloom development in summertime differed characteristically from year to year. Also the total vegetation area of N. nucifera and Trapa spp. showed annually marked changes. A significant negative correlation between the concentrations of chlorophyll a and the growth areas of Trapa spp. in August was detected, indicating that the floating-leaved plants, Trapa spp., produced irregular, clear and turbid water states in this shallow eutrophicated lake. These antagonistic relations are explained based on a likely scenario of allelopathic effects on the development of cyanobacteria by Trapa spp. vegetation and the nutrient absorption competition among them. Our study demonstrated the potential of Trapa spp. to control cyanobacterial blooms producing harmful toxins.

Spring red snow phenomenon ‘Akashibo’ in the Ozegahara mire, Central Japan, with special reference to the distribution of invertebrates in red snow

lt has been noted extensively from the earliest days that the surface of snow is frequendy colored red, pink, yellow, green o r b laek in the Arctic and Antarctic Zones or the high mountains, and also in glaciers. The colored snow patches usually contain many species of algae, bacteria and fungi (FUKUSHIMA 1963, KOL 1964, 1968). The comprehensive literature available on red snow idenrifies Chlamydomonas as the main alga in the Northern and Southern Hemispheres (NEWfON 1982, LING 1996, MULLER et al. 1998). The shade of red snow patches varies from mild pink to deep blood red (NEwrON 1982). Some invertebrates, a very low number of species of aquatic insects, crustaceans, rotifers, tardigrads and oligochaetes in red snow with algae are known as cryobionts, i.e. living in/on ice or snow and in pools of ice melt such as cryoconite-holes (TYNEN 1970, MAciNTYRE 1984, KoHSHIMA 1984, 1994, K:!KUCHI 1994). Red-colored snow patches, or so-called Akashibo (meaning red dirt or dark-red ooze), have been known in several parts in the Ozegahara mire, Central Japan by a few alpinists or skiers. They appear very briefly during 2 or 3 weeks when snow is rapidly melting under strong sunny conditions in late spring around May or June. In this season the Akashibo snow patches are colored deep red (from brown to black-red) and contain snow algae, and many species of small invertebrates at a high density on/in the snow or in small pools forming on the snow surface. lt was found that the dominant algae and invertebrates at high density in the Akashibo snow patches were different to those reported in other areas of typical red snow. Another distinctive character of the Akashibo compared to other red snow is that a redcolored substance remains on the peat even after the snow has disappeared entireJy. KOBAYASHI & FUKUSHIMA (1952a,b) speculated that the cause of the coloration of the Akashibo snow in the Ozegahara mire was not algal color but ferric oxides oozing out from the peat onro the snow surface. However, they had not conducted cryophytological studies when searching for the origin of the Akashibo phenomenon. This phenomenon in the Ozegahara mire have been investigated from many aspects chemical, biological, geographical, ecological and limnological since the research by KOBAYASHI & FuKUSHIMA (1952a). This srudy offers a preliminary description of the red snow phenomenon, the so-called Akashibo, in the Ozegahara mire in Central Japan with special reference to the invertebrates distributed in the Akashibo snow patches.