RIASSUNTO
ABSTRACT
Increasing concentration of NO3-N in Kumamoto's water possibly due to infiltration of toxic elements (e.g. fertilizers) has become a big concern. Some lactic acid bacteria (LAB) have the capability to absorb some metals. The main objective of this research is to detect suitable LAB strain (TOKAI strain) to adopt the biosorption capability of LAB to reduce the amount of NO3-N in Kumamoto's water. Different incubation conditions are applied and concentrations of NO3-N of samples are measured. Several TOKAI strains have been found to be effective in reducing NO3-N.
INTRODUCTION
Kumamoto is located on the Kyushu island in the southwest part of Japan and was hit by a magnitude 7.3 earthquake in 2016. Kumamoto is very famous for its bays, especially for its contribution to fisheries and seaweed culturing. Kumamoto bay area (i.e. Ariake Bay and Isahaya Bay) is famous for owning majority of Japan's remaining tidal flats and its sea resources. Ariake Bay is the largest bay of Kyushu area, located in the west coast of the island. However, the bay has witnessed frequent red tides since the 1960s (Tsutsumi et al, 2015). The number of red tides has especially increased since the second half of the 1990s. It is a phenomenon that occurs due to excess of nutrition in the water that leads to overpopulation of algae. The numerous algae discolor the water making it red and deplete oxygen and some algae also release toxin. The lack of oxygen and presence of toxins disrupt the coastal ecosystem by imposing harm on the sea creatures and human beings. In the subtidal areas of the Ariake Bay, a noticeable increase in the amount of the autumn bloom of the phytoplankton has been observed as red tides have covered the inner part of the bay regularly.
The nutrient input from land to bay has fluctuated through years in Kumamoto. However, nutrients have regularly flowed to the bay through the major rivers of Kumamoto for the past three decades. Especially in the year 2000 and 2002, the Nori (Japanese seaweed of the red algae genus Pyropia) culture was severely damaged by large-scale autumn red tide (Tsutsumi, 2006). Since the year 2001, hypoxic water (water lacking in adequate oxygen) has been detected in the bottom layer of Ariake Bay in early summer which has caused huge ecological disturbance. According to Tsutsumi (2006), these occurrences occurred due to the stratification in the salinity level of the water in the bay which had progressed since the last part of 1990s. The Isahaya Bay Reclamation Project to reclaim the tidal flats of approximately 3,500 ha has been underway since 1986 (Tsutsumi, 2006). A decrease in the tidal current in the west part of the bay was noticed after the gates of the dike were closed in 1997's April. The hydrographical changes resulted from these actions could be related to the development of stratification in water level in Ariake Bay. This type of eutrophication, stratification and ecological imbalance make it imperative to research about the nutrient levels in the water of Kumamoto.