Takuo Nakajima

Seasonal variations of Microcystis populations in sediments of Lake Biwa, Japan

Seasonal variations of colony numbers of Microcystis aeruginosa(Kütz.) Kütz. and M. wesenbergii(Komárek) Komárek in N. V. Kondrat. in sediments of Lake Biwa were investigated over a period of 1 year. At two stations located in the shallow South Basin of Lake Biwa (ca. 4 m water depth), the colony number of Microcystisfluctuated seasonally. The number had a tendency to gradually decrease from winter to early summer, while it increased through mid-summer and autumn. Since the Microcystispopulation in sediment was rather small, intensive growth and accumulation in the water column should be important for the formation of Microcystisblooms in Lake Biwa. Microcystiscolonies in the sediment samples after June were observed to be floating in a counting chamber under a microscope. The observation suggests that the recruitment of Microcystis colonies into the water column mostly occurs in early summer. The number of Microcystiscolonies in the deep North Basin of Lake Biwa (70 – 90 m water depth) was larger than in the South Basin. Because the seasonal variation of colony numbers was not observed in the North Basin, and Microcystiscells do not have gas vesicles, these colonies will not return into the water column. The colonies isolated from the sediment of the North Basin were able to grow in cultured conditions, in the same way as those from the sediment of the South Basin. Therefore, Microcystiscolonies may survive for a long time under stable conditions of low temperature (ca. 8 °C) and darkness, in the sediment of the deep North Basin, accumulating gradually each year.

Vertical distributions of sulfate-reducing bacteria and methane-producing archaea quantified by oligonucleotide probe hybridization in the profundal sediment of a mesotrophic lake

Abstract Vertical distributions of sulfate-reducing bacteria and methane-producing archaea were investigated in the profundal sediment of a freshwater lake using membrane-immobilized small subunit rRNA hybridization with group- and genus-specific oligonucleotide probes. The annual average of the relative abundance of small subunit rRNA hybridized with all probes for sulfate-reducing bacteria to total small subunit rRNA was 2.3% at 0-2 cm and increased with depth up to 22.9% at 8-14 cm where sulfate concentration was less than 10 nmol ml(-1) in interstitial water, suggesting that these bacteria may survive on alternative metabolisms. The signal of probe Dsv687 (the family Desulfovibrionaceae and some Geobacteraceae) was the main factor in this increase. The relative abundance of methane-producing archaea to total small subunit rRNA was highest (7.8%) at 8-14 cm, dominated by the order Methanosarcinales. The metabolic rates measured in the sediments demonstrated that the peaks of sulfate reduction and methane production were separated vertically, and were not linked to their small subunit rRNA distributions. Our data indicate that sulfate-reducing bacteria can coexist with methane-producing archaea from 0 to 20 cm in the freshwater lake sediment.

Denitrification by the sessile microbial community of a polluted river

Denitrification by the sessile microbial community of the River Tamagawa was studied in laboratory experiments. Inorganic nitrogen loss was observed when river water was incubated with sessile microbial community of the river in a continuously circulating system. It was confirmed by the 15N tracer technique that both sessile microbial communities of unpolluted and polluted areas had denitrifying activity, even though they were incubated in oxygenated river water. The denitrification rate of the sessile microbial community taken from a polluted area, measured by the 15N tracer technique, was 8–16 mg N/m2/day in October and December, 1977, and it was enhanced 10-fold by raising the water temperature from 14 to 30° C. Denitrification in the river was also suggested by determining the N2: Ar ratio of gases evolved from the river bed.

Chemical composition of labile fractions in DOM

Dissolved organic matter in natural water was classified into a labile and a refractory fraction according to the decomposition properties for microorganisms. In decomposition experiments of dissolved organic matter from an eutrophic small lake in Japan, dissolved amino acids and dissolved carbohydrates fractions could be confirmed to be the labile fractions of dissolved organic matter.

Denitrification activities in epilimnetic sediments in littoral wetland areas of Lake Biwa

The ecotone, which lies between land and water, shows characteristics ofboth freshwater and terrestrial ecosystems. The ecotone ecosystem comprises a wide diversity of environments due to various factors such as changes o f water level in the lake, wave erosion, chemical characteristics of inflow water and density of large emergent plants. In the wetlands in ecotone regions oflakes, the chemical state ofbioelements and organic matter in incoming water is significantly changed by biological functions such as the uptake of nutrients by large emergent plants, decomposition of organic matter by benthic microorganisms, and reduction in nitrate through denitrification under anaerobic conditions. Therefore, in lake ecosystems, the littoral wetlands play a significant ro le as a natural buffer, holding back incoming water. In this way, lakes maintain the stability of their biogeochemical cycle. The aim ofthe present study was to clarify the contribution of denitrification by littoral wetlands of Lake Biwa to the nitrogen cycle ofthe lake. The denitrification process involves a biochemical reduction that emits nitrogen as nitrogen gas. Studies of denitrification have previously been conducted in a large number ofwetlands, mainly focusing on the relationship between denitrification and differences in sediment environments or root zones o f emergent plants (REDDY et al. 1989, KERN et al. 1996). However, few investigations have focused on the contribution of denitrification by littoral wetlands to the nitrogen cycle o f a lake. Eutrophication in Lake Biwa has rapidly advanced since the 1960s due to increasing economic activities. Thus, denitrification is considered to play a major role in purification ofthe lake by reducing nitrate concentrations. The waterside ecotone of Lake Biwa has many wetlands separated from the main body of water by sandy beaches. Since these wetlands are dominated by large emergent plants, their sediments are covered with an abundance of detrital organic matter. An enormous biomass of microorganisms is supported by the rich organic matter, which is decomposed by numerous microorganisms, creating anoxic conditions. This feature o f wetland is thought to intensify the denitrification in littoral wetlands of the lake. This study reports on the relationships between the denitrification rates (in silu and potential) and the environmental parameters in littoral wetlands of Lake Biwa.

pH response in stream water and buffering capacity of forested soil affected by clear-cutting

Leaf litter supply to the forest floor i s m ue h reduced after clear-cutting, which may affect the budget o forganic matter as well as meta\ elements in the forest ecosystem. Acid rain attacks soi! surtàce directly, and metalleaching is accelerated after felling. Aluminum and manganese released from forest soi! results in harmful effects to biota in aquatic environments (CHRISTOPHERSEN et al. 1990). Long-term measurements of some metals and pH in stream water are useful for estimating the impacts from clear-cutting. We measured the concentrations o f so m e meta! s (Al, Fe and Ca2-) and pH in stream water before and after clear-cutting and carried out experiments of meta! leaching from soi! ofthe forest floor by artificial rain water.

Denitrification and nitrous oxide production in a stream

Increases in anthropogenie nitrogen loading to riverine systems eause nitrate inereases in river water. By 2050, anthropogenic input to rivers is estimated to inerease more than 2 fold eompared to the 1998 1evel (KROEZE & SEITZINGER 1998). This situation has attraeted attention to the nitrogen-loss funetion of riverine eeosystems. Studies of eonditions eontrolling the nitrogen metabolism in small streams are important beeause rapid uptake and transformation of inorganic nitrogen oeeur in these reaehes (ALEXANDER et al. 2000, PETERSON et al. 2001). Using undisturbed natural samples is the preferred method for measuring denitrifieation rate in situ (SHEIBLEY et al. 2003). Many previous studies have used the natural biofilm method (NAKAJIMA 1979, SORENSEN et al. 1988, TEISSIER & ToRRE 2002), intaet sediment eores (HILL & SANMUGADAS 1985, COOKE & WHITE 1987, CHRISTENSEN & SORENSEN 1988, CHRISTENSEN et al. 1989 KESTER et al. 1997, PATTINSON et al. 1998) or sediment perfusion eores (SHEIBLEY et al. 2003). However, few studies have been eondueted in a sandy stream sueh as the middle reaeh o f the Kizu River, Japan. Nitrous oxide, whieh is produeed by denitrifieation and nitrifieation, is one o f the greenhouse gases and a regulator of atrnospherie ozone. Nitrous oxide emissions derived from rivers area net souree ofN20 to the atrnosphere (McELROY et al. 1978, CoLE & CARACO 200 l). More than 30% o f the anthropogenie N20 produetion on land was estimated to derive from rivers in 1998 (SEITZINGER & KROEZE 1998). Between 1990 and 2050, nitrous oxide emissions from rivers, estuaries and eontinental shelves are predieted to inerease by 2.6 times, 2/3 ofwhieh will eome from rivers (KROEZE & SEITZINGER 1998). In the present study, laboratory experiments with intaet eores from the middle reaeh o f the Kizu River were eondueted to determine the spatial and temporai variation in respiration ( oxygen flux ), the flux N20 from sediment to the overlying water body, and denitrifieation (aeetylene inhibition).

Effects of forest cutting on stream water quality

The watershed o f Lake Biwa is u p to 60% eovered by forest, and the river warer flowing imo rhe lake through the foresred watershed may signifieandy affeet the lake warer qualiry. The Asou Experimemal Area (AEA) was established at rhe head water region of the Ado river, flowing imo Lake Biwa and rhe forese was eur in o ne drainage basin to srudy rhe effeets on the lake water qualiry. The environmemal eonditions in the AEA signifieandy differ from rhe Hubbard Brook Experimemal Forest (LIKENS at al. 1977) in meteorology, vegetation, soi! texture and reeovery of soi! aeriviry afi:er clearfelling, ete. The coneemration of Al inereased with deereases in pH, and below a pH of about 5.0 the speeiation of Al was dominared by inorganie Al whieh is toxie to aquarie biota (BAILEY er al. 1995). In the AEA region, most of rhe preeipitation is aeidified (pH < 4.0) whieh has rhe potemial for leaehing of meta! elemems sueh as Al and Mn. An aeid deposition to forest watersheds includes deplerion of eations and the mobilizarion o f elevared eoneentrarions of Al from soi! to drainage warers (CRONAN & SCHOFIELD 1990). Al erosion by aeid rain from rhe soi! of forested areas in rhe US and Germany is an imporcam problem (ULRICH er al. 1980, SHORTLE & SMITH 1988). A high eoneenrrarion of Mn has rhe poremial for fish deformation (FRASER & HARVEY 1982). In the presem srudy, stream water of a rype similar to rhat of neighboring drainage basins was analyzed for some meta! elements (Ca, Mg, Al, Mn, Cu, Zn and Fe) and rhe beforeand after-clearfelling meta! eoneemrations were eompared.