Dynamic changes of organic content over time in the sea sludge collected from the Gobo/Hidaka coastal area in Wakayama, southwest Japan

Abstract

The Gobo/Hidaka coastal area is known for its pristine nature and biodiversity, but recent urban developments might have affected its environmental condition. In previous study, we found a relatively low amount of organic matter from the Hidaka Port samples. In this study, we determine the possible cause of such an anomalous low organic matter content. Sludge samples were collected from the bottom of the sea of Hidaka Port monthly for one year (July 2016 to June 2017). The result showed the lowest content of organic matter in July 2016 (0.89%) and almost repeated in November 2016 (1.47%), February 2017 (1.08%), and May 2017 (1.42%). Meanwhile, the highest record was in June 2017 (3.93%). The fluctuating organic contents are in congruent with the water temperature data. The possible interactions among the seawater temperature, monthly rainfall amount of the corresponding months, possible abundance of marine microbes, and farming in the surrounding area might have caused the fluctuations. Our result would certainly be useful to infer the interrelationships of anthropogenic activities and other biotic and abiotic factors to the sea sludge, and eventually, the oceanic environment. Future studies needed to analyze inorganic content and data collections over multiple years.