Kumamoto city and its neighboring municipalities, which is more than 1,000 km² in area and have almost 1 million people, are considered a mesoscale region. This region is a special area in Japan and in the world because of the fact that all drinking water demand by most of its population is met using only groundwater. However, recently, nitrate-nitrogen (NO₃-N) contamination has been a source of concern. The goal of this study is to examine the groundwater contamination by NO₃-N in this area and to determine the factors of nitrogen load. NO₃-N concentration was higher than 4 mg·L^-1 in many wells, it was even higher than 10 mg·L^-1 in some wells in upstream areas of groundwater. In addition, most groundwater samples showed an upward trend in NO₃-N concentration in recent years. The Geographical Information System (GIS) technique using agricultural census data revealed that nitrogen emission from domestic animal waste significantly increased in the upstream areas of groundwater, which was coincident with the NO₃-N contamination of groundwater. The nitrogen stable isotope ratios (δ¹⁵N) of NO₃-N in groundwater were relatively high (9.6 to 15) in most of the wells, and especially higher (10<) in the upstream areas of groundwater. From these results, domestic animals waste and the application of organic fertilizers were identified by the effective combination of the GIS technique and δ¹⁵N analysis as the main contributors to NO₃-N contamination.

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Dissolved silicate (DSi) has been considered an important factor for determining dominant phytoplankton species in coastal ecosystems. However, there is little information on DSi discharged by human activities, especially factory activities. We measured DSi concentration in industrial wastewater samples collected from specified facilities in Fukuoka Prefecture, and calculated DSi loads to examine the effects of industrial effluents on environmental waters. Furthermore, we investigated DSi in freshwater, raw wastewater and wastewater in some selected facilities in order to confirm the increase/decrease in DSi concentration in both manufacturing and wastewater treatment processes. The results showed that DSi concentration in industrial effluents depended on the type of factory. 82% of all the samples contained DSi concentrations less than or equal to 20 mg·L^-1. Several working sites discharged high DSi emission loads of over 100 kg·d^-1, which indicates that these effluents may have a significant impact on aquatic ecosystems. Moreover, DSi concentrations in effluents are determined by augmenting freshwater and increasing/decreasing DSi concentration through manufacturing and wastewater exhausting processes.

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