Kouji Tsushima

NITRATE LOSS FOR DENITRIFICATION DURING HIGH FREQUENCY RESEARCH IN FLOODPLAIN GROUNDWATER OF THE TAMA RIVER

This study aims to identify the possible roles of a floodplain inbiogeochemical nitrogen cycles, based on analysis of groundwaterdynamics of inorganic nitrogen species. Groundwater samples collected from boreholes made of poly vinyl chloride located onthe floodplain in the middle reach of the Tama River, Nagata district were analyzed for dissolved organic carbon, dissolved oxygen, inorganic nitrogen compounds, major anions and the stableisotope ratio of nitrate-nitrogen.Dissolved oxygen in groundwater samples collected from marked borehole (G-5) was low (50 ± 16 μM) and nitrate decreasedfrom 63 μM to < 10 μM during our research period. Concentrations of nitrate, nitrite and nitrous oxide decreased one after the other. These decreases in concentration, combinedwith 15N-enrichment of groundwater nitrate suggest denitrification as a significant nitrate sink, yielding an isotopic fractionation of nitrate-nitrogen with an enrichment factor (ε= –17.9‰) that is comparable tothose in various soil and groundwater systems. This study provesthat floodplains can perform as nitrogen sinks for groundwaterin river catchments.

Assessing ecological risk of zinc in Japan using organism- and population-level species sensitivity distributions.

In Japan, the Environmental Quality Standard for zinc, established in 2003, was the first standard for the protection of aquatic species. To achieve this environmental criterion, the National Effluent Standard was lowered from 5 mgL(-1) to 2 mgL(-1) in 2006. However, some industries were permitted to apply a provisional effluent standard until 2011, when the provisional standard will revert to the national standard. Therefore, discussion about the environmental management of and countermeasures for the risk of zinc continues in Japan. The aim of this paper is to present the current status of the risk of zinc. Using long-term monitoring data for zinc from more than 3000 monitoring sites in Japan, both freshwater and marine, we found that the geometric mean concentration of zinc at freshwater sites was about 10.8 microgL(-1) and that the annual mean concentrations have been generally decreasing. We identified sites where zinc concentrations were high, and we also identified the most likely sources of zinc responsible for the high concentrations. The ecological risk of zinc was estimated at the conventional individual level and at the population level. Individual-level risk was detected at about 20% of freshwater sites, and population-level risk at about 2%. The risks were lower in more recent years; however, they remain at unacceptable levels. Our results show the necessity of risk reduction strategies. We propose a new approach for risk management and countermeasures that consider both individual- and population-level risks.

Potential bioavailability of phosphorus in citrus orchard soil to Microcystis aeruginosa

Algal blooms in eutrophic water bodies are controlled by inputs of phosphorus (P) as the growth-limiting nutrient. Runoff particulate P associated with soil from fields often predominates among P fractions. Here, an algal bioassay to investigate the potential bioavailability of particulate P in soil collected from a citrus orchard was conducted. Microcystis aeruginosa was cultured in medium containing soil as the sole source of P. The P in the soil was not notably solubilized after autoclaving. Analyses of chlorophyll-a, suspended solids, particulate organic carbon, and particulate organic nitrogen showed that M. aeruginosa could utilize some of the P present in the soil, perhaps that in particulate form, but this form of P was not sufficient to maintain optimum growth.

Flow path and material cycle for groundwater of floodplain in the Nagata district of the Tama River

Possible role of floodplains in nitrogen dynamics in the middle reach of the Tama River, Tokyo is discussed based on analyses of groundwater flow and water chemistry.