Naoko Ueda

Screening analysis of hundreds of sediment pollutants and evaluation of their effects on benthic organisms in Dokai Bay, Japan

Dokai Bay in Kitakyushu, Japan, is polluted with complex mixtures of micro-pollutants originating from the extensive industry and urbanization. In order to evaluate effects of these micro-pollutants on benthic organisms in this almost completely enclosed bay, we screened for the occurrence of approximately 900 organic chemicals and heavy metals, and in addition quantified the density and biomass of benthic animals. For the chemical analysis, we used a newly developed comprehensive analytical method using an automated identification and quantification system with a GC-MS database. We detected 184 organic chemicals in the sediments. Since their concentrations, as well as those of metals, increased with proximity to the innermost part of the bay, their source seem to be factories and a sewage treatment plant located in this area. Confirming this, the identified pollutants in this area are characteristic of industrial chemicals and residues, as well as household chemicals, fecal matter and sewage effluent. Several polycyclic aromatic hydrocarbons (PAHs) and metals had concentrations higher than the effects range-median of the sediment quality guidelines of National Oceanic and Atmospheric Administration. The species richness and abundance of benthic animals were lowest in areas where concentrations of metals, PAHs and other organic pollutants were high, suggesting that these contaminants are having an adverse effect on benthic animals in the bay.

Impacts of Oxygen-Deficient Water on the Macrobenthic Fauna of Dokai Bay and on Adjacent Intertidal Flats, in Kitakyushu, Japan

Abstract Dokai Bay is surrounded by the city of Kitakyushu, Japan. We assessed the chemical conditions of its waters and sediments, and carried out quantitative samplings of the macrobenthic fauna of the bay and on adjacent intertidal flats from 1992 to 1993. Large amounts of organic matter were deposited on the floor of the bay and intertidal flats due to eutrophication, and resulted in the occurrence of oxygen-deficient water from the bottom to the middle layer during the summer. On the tidal flats, the sediments were kept oxygenated and accessible to benthic animals throughout the year. However, the macrobenthos declined markedly in summer. The oxygen-deficient water of the bay seemed to temporarily upwell onto the intertidal flats causing a catastrophic environmental disturbance. Following this, only a few polychaete species survived, in extremely low densities.

Recovery of the marine bottom environment of a Japanese bay

Abstract Dokai Bay lies adjacent to Kitakyushu city, one of Japans major cities with a population of more than 1 000 000. In this city, various heavy chemical-industrial plants have been established since the 1900s. Waste water from the factories and untreated sewage effluent from the city have heavily polluted the water and marine bottom environment of the bay. In the 1960s, this bay was called the ‘dead sea’ owing to the apparent absence of aquatic organisms. Since 1970, environmental recovery projects have been carried out by the local government. The effluent and waste water have been severely regulated. The polluted bottom sediments of the bay have been dredged. Consequently, in the past two decades, the environmental conditions of the bay have dramatically recovered. Since 1989, we have assessed the water and benthic conditions of the bay to describe the recovery of the benthic ecosystems, and to monitor the effects of environmental recovery projects on the bottom environment of the bay since 1970. The results of these studies indicate a drastic decrease in the levels of heavy metals in the bottom sediments and the recolonization of various benthic organisms, although the innermost areas of the bay remain seriously organically polluted. In these areas, in the summer, the benthic communities are seriously damaged owing to the occurrence of anoxic water masses. Prior to 1993, there was no regulation of the amount of nutrient salt loading present in factory waste water and city sewage. Overloading of nutrient salts generates large amounts of primary production by phytoplankton, and results in the overloading of organic matter at the bottom environment in the innermost areas of the bay. For further recovery of the ecosystem it is necessary to control the total amount of loading of nutrient salts to the bay system.

Estimation of particulate organic carbon flux in relation to photosynthetic production in a shallow coastal area in the Seto Inland Sea

Sediment trap experiments were carried out three times from 1999 to 2000, in the western part of the Seto Inland Sea (Suo-Sound), Japan. We investigated both the particulate flux and the composition of chemical substances in the sediment trap samples. Based on the results, we discuss the origin of particulate organic carbon (POC) collected by the sediment traps in a coastal area. Moreover, we purposed to estimate the flux of the portion of the POC that is derived from phytoplankton photosynthesis. The fluxes of POC varied between 677 and 3424 mgC m(-2) d(-1). Significant positive correlations between POC and aluminum (Al) fluxes suggested that these components show almost the same behaviour. The mean value of the Al flux was about eight times higher than that of Al burial rates on the sediment surface. Therefore, it seems that the POC flux observed with the sediment traps was considerably overestimated. Moreover, judging from the fact that Al is a typical terriginous element, it seems that most of the POC collected in the sediment traps derived from the re-suspended surface sediment or sediment transported laterally from shallow flanks such as intertidal mudflats. The fluxes of chlorophyll a (Chl a) were independent of the POC fluxes, and a relatively consistent correlation was found between Chl a abundance in the water column and the Chl a flux. Moreover, surface sediment Chl a content was approximately 100 times lower than that of suspended matter. Therefore, resuspension and terriginous contributions to Chl a collected in sediment traps are likely to be negligible. The POC content in the trap samples varied between 22.4 and 70.7 mg g(-1) dry weight. The variations of POC contents were positively correlated with the Chl a contents: POC(mg g(-1))=76.5 x Chl a(mg g(-1)) + 26.0 (r=0.95, p<0.01, n=9). This result shows that POC contents strongly corresponded with phytoplankton and their debris. It was also considered that the fraction of POC derived from phytoplankton primary production could be estimated as Chl a content times a certain factor. In this study, we estimated the flux of the portion of the POC originating from phytoplankton production by multiplying the Chl a fluxes by 76.5 (the mean POC:Chl a ratio in the trap samples). These values varied between 308 and 758 mgC m(-2) d(-1), and accounted for 35.1+/-21.2% of total POC flux. Although the amount of POC that originates from phytoplankton photosynthesis was a small portion of total POC flux, it seems to be a large portion of potential primary production in the water column.

Decrease in anthropogenic nutrients and its effect on the C/N/P molar ratio of suspended particulate matter in hypertrophic Dokai Bay (Japan) in summer

Biologically important nutrient concentrations in Dokai Bay have declined as a result of reductions in anthropogenic inputs of total nitrogen and total phosphorus. A decrease in nutrient concentrations affects phytoplankton growth, thereby changing the biochemical characteristics of autochthonous particulate matter. We therefore investigated changes in the C/N/P molar ratio of suspended particulate matter (SPM) in the summer, when phytoplankton growth is vigorous, before environmental quality standards (EQSs) were attained (1995–1998) and afterward (2006–2009). We found that the ratio of particulate organic nitrogen (PON) to particulate phosphorus (PP) changed in conjunction with changes in the ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus (DIP) that resulted from reductions in nutrient loading. Furthermore, we suggest that because the DIP concentration in seawater was high before EQSs were attained, inorganic phosphorus was possibly adsorbed onto SPM. After the attainment of EQSs, however, the DIP concentration fell, and PON/PP was high. Phosphorus limitation of phytoplankton growth in the mouth of the bay may explain the high PON/PP ratios after EQS attainment.