Hiroshi Hirotani

Microbial indicators in natural biofilms developed in the riverbed

Microbial indicators such as heterotrophic bacteria, total coliforms, and Escherichia coli in naturally developed riverbed biofilms were investigated. Pebbles covered with natural biofilm were sampled directly from the riverbed at sampling stations ranging from the upstream region within a quasi-national park to the midstream in the urban district. Heterotrophic bacteria densities in biofilm positively correlated with stream discharge. E. coli densities in biofilm positively correlated with temperature, which suggests the growth in the biofilm. It was considered that the attachment of planktonic bacteria to biofilm was negligible. The biofilm may serve as an internal source of false positive indication of fecal contamination in the water column.

Predicting the summer chlorophylla concentration in a reservoir based on the environmental conditions of the preceding spring

From a monthly survey over a ten-year period (1983–1992) of the Ishitegawa Reservoir, Japan, two multiple regression equations describing the mean chlorophylla (Chl-a) concentration at 0.5 m depth during July, August and September (CS) and the maximum Chl-a concentration in the photic zone, including its subsurface maximum during this period (CM), were obtained. The conductivity at 0.5 m depth in May and the mean air temperature during May or during May and June were used as independent variables. These equations were calculated using seven years of data (1983–1988 and 1992). From 1989 to 1991 two impermeable plastic-coated sheet fences were installed across the upper end of the reservoir along the top 5 m of water column. The equations were used to determine the effectiveness of this flow regulation on the summer Chl-a concentration. In 1989 and 1991, when the fences were in place from June to August, no effects were found on the observed CS and CMvalues. In 1990, when the fences had been in place since October 1989, the observed values were lower than the predicted values.

Destruction of fecal coliphages during the composting process of porcine feces

Abstract Application of sewage sludge to agricultural land has been a common practice for many years. There is, however, a potential hazard of pathogen spread through food and drinking water, since the pathogens concentrate in the sludge (JONES and WATKINS 1985; SHIMOHARA et al. 1985) and remain in the sludge for a long period of time (TIERNEY 1977). Anaerobic digestion of sludge destroys the indigenous pathogens owe to the high temperature generated by the microbial activity in the course of digestion (BERG and BERMAN 1980). However viruses have been recovered from sludges digested during a prolonged period of time at 37 or 50°C (LUND 1976). Anaerobic digestion of sludge is associated with health risks caused by virus spread.

Fluctuation of densities of bacteriophages and Escherichia coli present in natural biofilms and water of a main channel and a small tributary

Fluctuation of bacteriophage and Escherichia coli densities in naturally developed riverbed biofilms were investigated for a 1-year period. E. coli ranged from 1,500 to 15,500 most probable number (MPN)/100 mL and from 580 to 18,500 MPN/cm(2) in the main channel in the river water and biofilms, respectively. However, the fluctuations were much greater in the tributary, ranging from 0.8 to 100 MPN/100 mL and from 0.3 to 185 MPN/cm(2) in water and biofilms, respectively. The fluctuations of coliphages were also greater in the tributary than in the main channel. FRNA phage serotyping results indicated no significant differences in the source type of the fecal contamination in the main channel and tributary sampling stations. Significant correlations between phage groups in biofilms and water were found at both main channel and tributary. It was assumed that natural biofilms developed in the streambed captured and retained somatic phages in the biofilms for a certain period of time in the main channel site. At the location receiving constant and heavy contamination, the usage of phage indicators may provide additional information on the presence of viruses. In the small tributary it may be possible to estimate the virus concentration by monitoring the E. coli indicator.

Chlorophyll sedimentation in a deep reservoir in Japan

Sedimentation of phytoplankton has an important ro le in lake ecosystems as a source o f nutrient regeneration and algal recruitment. Positive correlations are found among many lakes between epilimnetic chlorophyll concentration and sedimentary chlorophyll content (GORHAM et al. 1974 ), and between primary production and sedimentation of organic carbon (GALYEZ & NIELL 1993 ). However. in an interannual comparison in the Ishitegawa Reservoir, Japan, we could not find any significant correlations between epilimnetic chlorophyll concentration and sedimentary ch!orophyll content (KAGAWA et al. 2000). In the present study we reinvestigate this relationship, taking into consideration redistribution of bottom sediment.

Effects of plastic-coated sheet fences crossing the upper end of a reservoir on summer lake chlorophyll a concentration

Pre-reservoirs are used as a way of redueing nutrient loading in lakes and reservoirs (e.g. FIALA & VASATA 1982, HOEHN 1994). The dominant proeesses in norma! pre-reservoirs are nutrient uptake by algae and sedimentation, so surfaee release is reeommended at the outlet of a pre-reservoir (BENNDORF & PDTz 1987). However, as a eountermeasure against eutrophieation of a darn reservoir, KAGAWA (1989) proposed a method of subsurfaee release involving an impermeable fenee erossing the reservoir in the upper part near the inflowing river, extending down from the water surfaee to the upper hypolimnion. The intent was to form a strong interflow or underflow of river water below the fenee to faeilitate the release of the hypolimnetie water.