Organically enriched sediment tends to be deposited on the sea floor in the inner parts of enclosed coastal seas throughout the world, due to phytoplankton blooming by eutrophication, increase of discharge of organic matter, and so on. The benthic environment with an organically enriched sediment often suffers from the occurrence of hypoxic bottom water and the development of reduced conditions in the sediment in summer, when the decomposition of the organic matter in the sediment is accelerated under high temperature conditions. To treat the organically enriched sediment is, therefore, very important for the environmental conservation of enclosed coastal seas. We have developed techniques for bioremediation of the organically enriched sediment, using a small polychaete, Capitella sp. I, which specially favors areas with organically enriched sediment. In this paper, we review the background and outline of the bioremediation techniques.
Since the discovery of an extremely high abundance of viruses in marine environments in late 1980's, their ecological roles and scientific importance have been of great interest. Most marine viruses are considered to be bacteriophages and cyanophages, which have significant impact on the global biogeochemical cycle. Marine viruses also include viruses infectious to eukaryotic microalgae (=algal viruses). The genomic and physiological analysis of algal viruses showed that they are remarkably different from previously known viruses; hence, poverty in the marine virus sequence database has been a problem. On the other hand, their potential importance as genetic resources has recently been highlighted. Algal viruses are also important for controlling phytoplankton dynamics, especially for bloom-forming species. In addition, marine viruses have been studied from the viewpoint of industrial applications, e.g. microbiological agents for eliminating harmful blooms and fish diseases caused by bacteria. Marine virus study is still in its infant stage; further intensive research will shed light on the importance of viruses in marine environments.
Thraustochytrids are estuarine to marine protists and serve as both decomposers and secondary producers in the marine detritus food chain. They degrade refractory organic matter such as cellulose derived from terrestrial refuse, whose ecological function has been attributed mainly to bacteria. Thraustochytrid cells, are 5-20μm in diameter, which is ten or more times greater than bacterial cells, which shorten trophic links in a food chain and thus yield more biological production at higher trophic levels. Higher C/N ratios (>10) of thraustochytrid cells, compared to bacterial C/N (<6), may contribute to carbon cycling, despite their low abundance (-103 cells 1-1) compared to bacterial abundance (-106 cells 1-1) in marine water columns. Thraustochytrids also produce and accumulate biologically active polyunsaturated fatty acids such as eicosapentaenoic and docosahexaenoic acids, and thus may be exploited for biotechnological puroposes.
The objective of this study is to investigate the effect of belowground biomass reduction on the stability of eelgrass shoots in sediment in order to clarify the factors responsible for the outflow of eelgrass shoots even with little wave disturbance in Nagatsuraura Bay, Japan. We also investigated environmental conditions in the vicinity of eelgrass with and without root death. Loss of roots without dying-back symptoms led to a decrease in the stability of eelgrass shoots in sediment, and allows for the uprooting of shoots with little disturbance. The decay of healthy root biomass of eelgrass was associated with high sulfide concentration in sediment and/or low photosynthetic activity. In sulfide concentrations between 0.5mg g D.W.-1 and 1.5mg g D.W.-1, eelgrass with high photosynthetic activity tended to display fewer stunted roots compared to shoots for which photosynthetic rates were low. This result suggests that eelgrass with high photosynthetic activity seemed to prevent sulfide intrusion by supplying oxygen to belowground tissues to maintain an oxic microsphere around the roots and re-oxidizing it to a harmless sulfate.
This research aimed to develop a technique for non-point pollution source utilizing the fresh-water clam as water purification material. The fundamental abundance of fresh-water clams was investigated at first. However, we studied neither the direct nor short-term effect on water purification, but rather focused on the indirect and long-term effect on water purification of fresh-water clams. The biological characteristic and population density of fresh-water clams were quantified. It was confirmed that various kinds of useful and harmful elements are included in fresh-water clams from the result of chemical components tests. Based on these results, calculation results of the indirect water purification effects due to the growth of fresh-water clams was indicated using phosphorous as an example of a water pollutant. It was suggested that the utilization of fresh-water clams as one kind of bio-remediation technique is expected to be a great development for the restriction of non-point pollution sources. However, the fresh-water clam focused on in this research was considered an exotic species, so further accumulation of various information, such as the condition of distribution and research concerned to ecological aspects, would be necessary.
Amagasaki port, which is one of the most polluted sea areas, is located at the innermost region of Osaka Bay. The test structure was set as a vertical seawall for spontaneous environmental mitigation at our suggestion. We investigated the function of this structure for two years. As a result, the biomass of deposit feeder of the test structure is 5.3 times, that of the carnivore is 1.8 times, as many as the vertical structure at the bottom. Deposited bivalves and settling matter containing feces of bivalves ware caught on the shelf of the test structure. It was considered that organic matter was fed by deposit feeder and carnivore. These results show that this technology has some effects to decrease oxygen consumption by organic matter to improve the coastal environment on a continuous.
From the standpoint of practical application, we examined a concentration procedure for supernatant solutions of jellyfish suspensions using in-vacuo heating. The procedure precipitated high concentrations of Na (sodium) as NaCl (sodium chloride), thereby reducing the Na concentration in the solutions. A larger volume (500 ml) of raw supernatant solutions of Aurelia aurita was concentrated using different concentration ratios and heating temperatures. The rates of decrease for Na and those for other coexisting components were calculated. Results showed that 28-times concentration of the supernatant solutions in vacuo (70 hPa) at 40°C achieved a 69% decrease of Na, but N (nitrogen), P (phosphorus), and Ca (calcium) decreased 23-62% during the procedure. Chingensai plants (Qing geng cai, Brassica rapa var. chinensis) were cultivated using the concentrated solutions as a fertilizer to examine the effect of decreasing Na on chingensai growth. Decreased Na concentrations seemed to reduce the inhibitory effect of Na on the growth of vegetables.
A bioreactor packed with halo-tolerant microorganisms was investigated for the treatment of waste decomposing biological materials on a laboratory scale. The waste of sea water after complete decomposition of jellyfish by means of protease E77 were used as a model solution for this purpose. The waste mentioned above contained CODMn from 1,040 to 3,440 mg/L. Masses of halo-tolerant microorganisms were isolated from the enriched cultural solution including the waste, because these microorganisms utilized the waste as a source of substrates. The harvested microorganisms were encapsulated in the immobilized 3% agar pellets. A bioreactor packed with the pellets including microorganisms was circulated aerobically by the waste of sea water after the decomposing jellyfish at 32°C. 84% of CODMn was removed from the original value after the packed bioreactor was circulated over 4 days. Combined with coagulation-sedi-mentation and treatment of activated carbon adsorption, the CODMn content became almost zero. The yeast using jellyfish wastewater as a nutrient source was identified as Rhodotorula mucilaginosa by means of 28S rDNA-D1/D2 analysis. We determined six bands for bac-teria from the polymerase chain reaction and denaturing gradient gel electrophoresis (PCR-DGGE) on the basis of 16S rDNA.
This study aims to find ways for flushing with a little impact on fishery environment, by field observations and experiments, as the sediment flushing from Dashidaira dam at Kurobe River in December, 1993 caused serious problems for the local fishery. The impact caused by muddy water density depends on species. No dead case was found for Salvelinus leucomaenis, Oncorhynchus masou, Oncorhynchus keta, Nordotis discus hannai. A Rise in hemoglobin levels was observed for Salvelinus leucomaenis, Oncorhynchus masou, Oncorhynchus keta as muddy water density (SS concentration 8,000 mg/L) increases, while it recovered to normal levels on a day when the SS density decreases. On the other hand, evasive action was observed for Pagrus major, Seriola quinqueradiata, but it went back after the SS density decreased. Sillago japonica, Sebastes schlegeli didn't take any action. Based on these observations, we concluded that sediment flushing in a dam might be allowed under certain conditions.