Senichi EBISE’s research while affiliated with Setsunan University and other places

In East Asia, high levels of atmospheric nitrogen are deposited onto land. This could elevate the nitrate levels in coastal waters via river runoff, even from areas where anthropogenic sources are minimal. It is important to identify NO3⁻ sources in river water and the mechanisms involved in NO3⁻ runoff. Yakushima Island, Japan, is a Natural World Heritage site featuring numerous watersheds with diverse topography and rivers. The area receives significant precipitation, with up to 10 000 mm in mountainous regions. Its proximity to coastal urban areas in China (∼800 km) leads to substantial atmospheric nitrogen wet and dry deposition in the island's forests. The study aimed to clarify regional water quality characteristics by conducting long-term monitoring of dissolved ion components (Na⁺, K⁺, Mg²⁺, Ca²⁺, F⁻, Cl⁻, NO3⁻, and SO4²⁻) in river waters, and to determine the effects of NO3⁻ sources and watershed topography on NO3⁻ behavior. Dissolved ion concentrations were obtained from a long-term monitoring (2011–2014) dataset. Cluster analysis classified runoff water from the central mountainous region into three groups: western region, other regions, and groundwater. The average NO3⁻ concentration in the western region was 10.2 μmol L⁻¹, which was higher than the 6.24 μmol L⁻¹ observed in the other regions. Stable isotope analysis in December 2018 showed that river water NO3⁻ (1.39 μmol L⁻¹) in the western region had a high proportion of atmospheric NO3⁻. Topographic analysis indicated that NO3⁻ and atmospheric NO3⁻ increased in smaller watersheds and steeper terrain. This study conclude that NO3⁻ output is controlled by topography.

The prevailing westerlies and winter northwest monsoon that blow from the China Continent across the Japanese archipelago carry acidic depositions to six solitary islands and four higher mountains in Japan facing the Sea of Japan and the East China Sea. Ten areas having their acid rain observation sites within 20 km from their central mountains receive much of the long-range air pollutant load. All their mountain streams were observed in the stable low-water runoff stages. Due to the concentration ratios and correlations between wet deposition and stream waters for seven inorganic ions and molar ratios of Na⁺/Cl⁻, their ion weights in the load from discharge sources could be made clear. The concentrations of SO4²⁻ and K⁺ showed statistically good correlations between wet deposition and stream waters. Though concentration ratio of the latter to the former for NO3⁻+NH4⁺–N were about 1.0 with intake by plant, almost those of mineral ions were larger than 2.5 by leaching out from soil, rock and plant. The ratios of two large streams in Shimo-Tsushima Is., having the site in their upstream catchment, showed larger than those of lower small streams. On Yakushima Is. which had observation data of wet deposition and four stream waters in their neighborhood of catchments at the northern area during nineteen years, the both correlations and the coefficients of variation for their yearly changes and the concentration ratios of the seven ions in four streams were analyzed statistically. The analytical results showed that they were supplied from air pollutants, sea-salt and mineral. It is shown that the concentration ratios were influenced by the elevation and direction of wet deposition observation site and the topography of catchment area.

The Yodo River, which has a large discharge area, is a source of tap water for fourteen million citizens in the Kinki area. It is also an inflow river supplying the largest pollutant load into Osaka Bay. The flow of the Yodo River, which has the Lake Biwa basin and seven dams in its upper reaches, its flow is usually stable and large water quality changes occur only during flooding stages. During our highly frequent routine observation (once every three days) , eleven events of the ordinary flooding in 2005-2006 and one of the superflooding due to the 1318 typhoon were observed in our past observation period. For superflooding the highest concentrations of T-COD, TOC, and SS, and the largest loadings of all pollutants were observed during the observation period of 1995-2013. The results may be useful reference data for automation operation systems in water supply plants and for the estimation of the impact of inflow pollutants on Osaka Bay. The shares of loads, discharged during the superflooding stage to the annual total load in 2013 were estimated. The differences between the regression equations of total loads of pollutant for the six largest flooding events, included the superflooding event, and all twelve events were clarified. Annual total loads of pollutants were estimated using L-Q equations on the basis of the highly frequent observations in 2013 and ΣL-ΣQ equations for the six flooding events. The total loads in the Yodo River could be estimated with high precision using by the regression equations.

Yodo River is an important source of tap water for 12 million people in Kinki area. The statistical characteristics in pesticide concentrations for R. Yodo and three major tributaries were made clear by high-frequency observations. The relationships between total pesticide loads during observation periods and the areas of river watershed and its paddy field became almost linear on a log-log graph. The mass balances of pesticide loads between the three major tributaries and R. Yodo during the downstream reach were calculated during the observation period. As the sums of total pesticide loads of the three major tributaries accorded to those of R. Yodo at Yodo River New Bridge during observation period in 2011, the decreases of pesticide loads by degradation during the downstream reach were considered to be very small. The frequency of routine observation was evaluated in order to precisely estimate the total runoff pesticide loads mainly during an irrigation period. The estimated total loads for three pesticides detected widely in long term during the monthly observation distributed widely in the range of 10 - 472% of those by every three days of observations. The weights of the three pesticides in DI value (detecting index value) were calculated as 27 - 88% of all pesticide species in the big rivers during the irrigation period.

The River Uji merges with the R. Katsura and R. Kidu at the same point and then becomes the Yodo River. We observed the Yodo River every three days at three transverse points and the other three rivers weekly at their downstream points, and estimated the runoff loading balance of Cl- during their flow downstream. The runoff characteristics of Cl- in the rivers and the detailed input and output loadings during the flow of the rivers downstream were clarified. By computing the Cl- loadings of the rivers outside of the observation periods using the regression equations between flow and loading, the mean Cl- loadings for one year were estimated and compared with the total mean Cl- loadings of the three upstream rivers and that of the Yodo River. By estimating the discharged Cl- loadings for one year for the watersheds of the rivers using the statistical data of the consumption of salts and the watershed characteristics and by comparing the estimated values with the values due to the regression equations and observation data, it was confirmed that the basic discharged loading method of Cl- can be applied to the analysis of the large watershed of the Yodo River.

The Yodo River, which has two big tributaries and an annual mean flow of 268m3/s, flows out of Lake Biwa, runs through the Amagase Dam and flows into Osaka Bay. Point and non-point pollutant loads in Kyoto City and its adjacent cities discharge into the river. The frequency of our routine observation (once every three days) during the period from late April to late November 2003-2005 was ten times that of official routine water quality monitoring in Japan. We also carried flooding-stage observations at three transverse points across the river during the routine observation period in 2005. The total pollutant loads during five flooding events were larger than those observed by the routine observation during the periods. The mean pollutant loads during observation periods of every three days, every six days, every nine days and semimonthly data were different from those derived from monthly data. The annual total loads of runoff pollutant in 2003-2005 were estimated by extrapolating to both sides of the observation period and by compensating during flooding-stages using regression equations between flow and pollutant loadings.

The application of a model of long-term runoff of herbicide mefenaset from paddy fields to a river was investigated. The model of long-term runoff of mefenaset to the river was constructed as follows. The change in the concentration of mefenaset in ponding water provided a pseudo-first-order rate, and a flow model provided the amount of the surface runoff in the paddy field of the tank model. For the model of long-term runoff, although there were little gaps, the characteristic of mefenaset from paddy fields of the runoff to a river was reproduced. From the simulation results, it is considered that it is possible to use it for a sufficiently precise forecast of the movement of applied pesticides in the environment and use it for runoff load reduction.

The runoff behavior characteristics of pesticides were analyzed every three days and five flooding-stage observations were carried out for five months at three traverse points in the Yodo River. The differences in pesticide concentretion among the three traverse points were particularly seen during the flooding-stages. The total runoff loads of pesticides for about five months from late April to late September were larger according to both the regular and flooding-stage observations than according to only the regular observation. The total runoff loads of many pesticides in 2005, which was a dry year, were smaller than in 2004, which was a rainy year and 2001, which had a average amount of rain among the three regular observations. Most pesticide loads estimated using monthly and bimonthly observations in 2005 were smaller than those estimated using observations every three days during the observation period. Those estimated using semimonthly and monthly observations were 0.5- to 2.0-fold those estimated every three days. The change in the DI of a tap water quality standard was found to be less than 0.37 in 2005 according to the every-three-day-observation data and the five-flooding-stage-observation data.

Yakushima, facing at 800 km east of Shanghai in the East China Sea, is a tall cone-shaped island with seven exceeding 1800 m peaks. The prevailing winds of westrelie on the island blow mostly fromnorthwest and west. It has been exposed to acid rain of pH 4.7 and precipitation 8000 mm in the central highland. More than sixty mountainous streams were observed at downstream points seasonally for past twelve years. The alkalinity of streamwaters in the southwestern part was lower than others. The concentrations of SO4²⁻ in the northwestern part were higher than others. The high concentrations of SO4²⁻, dissolved SiO2 and other ions in the southwestern part with high canopy density of evergreen broadleaved forest were caused by higher air temperature, less rainfall and higher evapotranspiration than other parts. The alkalinity, pH and EC in the catchment of north stream in the upstream branch of the R. Anboh became lower than those in the catchment of south stream. The height of catchment boundaries, the direction of the main axis of a catchment and the prevailing winds govern the influence of acid deposition on water quality of branch streams.