In 2006, the secondary reed bed treatment system has been constructed to treat sewage from milking parlor in the northern Hokkaido. This system which efficiently uses natural purification abilities has got much attention as a waste treatment facility. However, there are only a few studies about the effects of the treated effluent having high environment loads from the system on surrounding lotic environments and their biota. Therefore, we investigate the effects on stream environments and biotic communities having the effluent through biota studies and survival experiments. These experiments were done by using three representative species, that is, oriental weather fish Misgurnus anguillicaudatus, lake prawn Palaemon paucidens, and Jesogammarus jesoensis. The biota of the study area was poor, and a species of the family Chironomidae was dominant, and no fish species was found. The survival rates of experimental animals were higher in the two upstream sections than those of the two downstream sections in which the effluent flow. The survival rates of experimental animals significantly correlated with concentrations of DO and NH₄⁺ , and COD. Moreover, concentrations of DO were lower, and NH₄⁺ and COD were higher in the two downstream sections than those of the two upstream sections. As a result, it appears that the poverty of biota in the two downstream sections has been caused by anoxic conditions and ammonia toxicity due to the effluent of the waste treatment system.

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We investigated the influence of water level fluctuation on the spatial distribution of deposited sediment and soil environment in the wetland between dam reservoir and its incoming river, called "ecotone" in this study. The target reservoir was Sagae Dam in Yamagata Prefecture, where the range of annual water level fluctuation rises up to 50m and a relatively large area of the wetland is dried out in summer and autumn. In the ecotone we set five lateral transects (Line-1 to -5) and sampled the sediment, interstitial water and surface water in June, August and October in 2009 and October in 2010. When water level was relatively high (June), a clear longitudinal change was not observed regarding size distribution and organic matter content of the surface soil. In contrast, when the ecotone turned into a riverine zone having low water level (August and October), a clear longitudinal shift of sediment and the downstream transects were observed and characterized by fine sediment with rich organic matter at Line-3 to -5. In October such sediment contained reductive interstitial water with the lowest ORP of - 19 to - 35 mV at Line-4. Stepwise multiple regression analysis found that ORP is negatively correlated with fine organic matter content and relative height. The relation of such sediment property to interstitial water quality is possibly determined by the fact that the sediment containing rich fine organic matter has low permeability and high water content. Overall, the results indicates that the fine sediment containing rich fine organic matter maintains the reductive condition in the soil layers deeper than 30 cm even though sediment has been exposed to atmosphere for two months. It implies that such sediment together with anaerobic organic matter decomposition may promote methane production in the ecotone at the upstream end of reservoir.

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The objective of this research is to demonstrate the antioxdant ecological response of Vallisneria asiatica to the heavy metal Cu²⁺ pollution which is recently a serious problem in the lakes. Batch experiments with five different concentrations of Cu²⁺ (0, 5, 10, 20, 40, 80 mg· L^-1) were carried out. After the 12^th day, the roots and leaves of Vallisneria asiatica dipped in the solution with Cu²⁺ were removed and the physiological and biochemical indexes, chlorophyll, protein and malondialdehyde (MDA) content, superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activity were measured. After the experiment; the roots and leaves cultivated in the 0 mg·L^-1 of Cu²⁺ group showed chlorophyll and protein content reduced while the MDA content, POD and SOD activity were increased notoriously. Compared with the 0 mg·L^-1 of Cu²⁺ group, the 5 mg·L^-1 of Cu²⁺ group showed chlorophyll and protein content increase, SOD and POD activity showed also a slight increase, while MDA content decreased. However, for the 10 mg·L^-1 of Cu²⁺ group, the decrease of chlorophyll and protein content and the increase of MDA content were observed. Also a sharp increase of SOD and CAT activity compared with the 5 mg·L^-1 group were found; for over 10 mg·L^-1 of Cu²⁺ concentration, chlorophyll content and protein content fell off, whereas increase of MDA became considerable, CAT raised up steadily and POD showed a decrease trend. The results showed that, both insufficiency and overabundance of Cu²⁺ in water environment can affect the anti-oxidation function of Vallisneria asiatica which can be observed by the value of SOD, CAT and POD activity. Therefore, the measurement of anti-oxidation activity, protein content and MDA as a forecast and judgment indicator of Cu²⁺ contaminations in the water environment can be considered in the future.

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[in Japanese]

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A stream that was severely damaged by heavy rainfall was restored using large woody debris and boulders from the site. The experimental site was a natural stream of the Horonai River system in northern Hokkaido, where intense rainfall triggered debris flow and flooding in 1998. Several types of woody structures were installed to stabilize sediment and gravel. A series of low check dams (log dams) constructed from large woody debris was installed along the main channel to prevent movement of new debris deposits. Complex grids of woody structures (debris catcher) were also constructed along alternating sides of the shore to capture drifting wood. Large boulders were selected, attached to steel wires, placed along the bottom of the channel, and buried (boulder cluster). Construction was carried out in 2000, and changes in the geomorphological characteristics, debris movement, vegetation recovery, and influence on stream-dwelling fishes were monitored until 2008. Most of the log dams were functional, and although evidence of minor lateral scouring was observed, no serious damage had occurred. The log dams were effective at creating deep plunge pools while maintaining a variety of water currents and substrates. The debris catcher captured drifting logs as well as provided rearing habitat for juvenile masusalmon (Oncorhynchus masou). The boulder clusters stabilized the stream channel, enabling tree seedlings to establish. Significantly more juvenile masu salmon were seen in June and October at the log dam section and in October at the debris catcher compared to the reference section. A similar result was observed for sculpin (Cottus nozawae) except in October. Generally, a large concrete dam is constructed after a flooding disaster, which seriously damages stream ecosystems. Given our results, we suggest that a combination of wood and boulder structures is an attractive alternative to concrete dams from ecological, economical, and landscape perspectives.

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The captured Inversiunio jokohamensis individuals and their inhabiting environment were investigated in the east side ditch (Site 1, drying up ditch) and the west side ditch (Site 2, not drying up ditch) in a valley after a period of temporary drying up to assess the influence of drying up on the Inversiunio jokohamensis individuals in Site 1 and consider ditch structure to relieve the influence on September 18 and October 24, 2010. As a result, the ratio of dead individuals and the body length distribution had a significant difference between both sites P < 0.01 ). In addition, dead individuals of all body length sizes were confirmed in Site 1. The number of individuals has decreased accompanying growing of the body length in Site 1. Methods to modify the ditch structure to relieve influence of temporary drying up are considered essential to maintain the population.

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