Plastic transport from land to the oceans
This research aims to clarify plastic transport from land to the oceans by in-site survey and/or developing a technique for quantifying plastics on river and marine environment.
Moringoring of microplastics in aquatic environment
The numerical and mass concentrations of microplastics collected at 36 sites on the surfaces of 29 Japanese rivers were mapped and compared with four basin characteristics (basin area, population density, and urban and agricultural ratios) and six water quality parameters (pH, biochemical oxygen demand (BOD), suspended solids (SS), dissolved oxygen (DO), total nitrogen (T-N), and total phosphorus (T-P)) in each river basin. Microplastics were found in 31 of the 36 sites, indicating that some plastics fragment into small pieces before reaching the ocean. The microplastic concentrations are significantly correlated with urbanisation and population density, indicating that the microplastic concentrations in the river depend on human activities in the river basin. Furthermore, we found a significant relationship between the numerical and mass concentrations and BOD, which is an environmental indicator of river pollution. This result demonstrates that microplastic pollution in river environments has progressed more in polluted rivers with poor water quality than in rivers with good water quality, leading to the conclusion that the sources and inflow processes of microplastics in river environments are similar to those of other pollutants. Our findings can help identify potential sources (i.e., point and non-point sources) of fragmented microplastics to improve waste management in Japan and model the transport fluxes of fragmented microplastics in Japanese rivers using water quality parameters and basin characteristic.
Kataoka et al., 2019. Assessment of the sources and inflow processes of microplastics in the river environments of Japan. Environ. Pollut. 244, 958-965. 10.1016/j.envpol.2018.10.111
A technique for quantifying macro-plastics flowing on water surface
A new algorithm has been developed to quantify floating macro-debris transport on river surfaces that consists of three fundamental techniques: (1) generating a difference image of the colour difference between the debris and surrounding water in the CIELuv colour space, (2) detecting the debris pixels from the difference image, and (3) calculating the debris area flux via the template matching method. Debris pixels were accurately detected from the images taken of the laboratory channel and river water surfaces and were consistent with those detected by visual observation. The area fluxes were statistically significantly correlated with the mass fluxes measured through debris collection. The mass fluxes calculated by multiplying the area fluxes with the debris mass per unit area (M/A) were significantly related to the flood rising stage flow rates and agreed with the mass fluxes measured through debris collection. In our algorithm, plastic mass fluxes can be estimated via calibration using the mass percentage of plastics to the total debris in target rivers. Quantifying riverine macro-plastic transport is essential to formulating countermeasures, mitigating adverse plastic pollution impacts and understanding global-scale riverine macro-plastic transport.
Kataoka and Nihei, 2020. Quantification of floating riverine macro-debris transport using an image processing approach. Sci. Rep. 10, 2198. 10.1038/s41598-020-59201-1
Remote sensing of ocean wave in coastal region
This research aims to develop a technique for measuring ocean waves with high spatiotemporal resolution using high-frequency radars and to clarify a spatiotemporal flucutuation of ocean waves in coastal region.
Validation of significant wave height measured by high-frequency (HF) radar systems in estuary region
The significant wave heights (Hs) are measured using three HF radar systems, whose center frequency of the transmission signal is 24.515 MHz with 100 kHz of sweep bandwidth, in Ise Bay located in the center of Japan (Fig. 3). In Case 0, Hs fluctuated greatly in comparison with the observation data (see the blue line in Figs. 4c and 4d). Meanwhile, when removing the noises (Case 1), the measurement accuracy of Hs was successfully improved. This indicates that the technique for removing the noises is useful for measuring ocean waves using HF radars. Nevertheless, Hs was overestimated in the period after August 25 (Figs. 4c and 4d), corresponding to the reduction of the SSS, as shown in Fig. 4b.This indicates that the extent of freshwater near the HF radar station is critical for measuring ocean waves based on HF radar systems owing to the deterioration of the S/N in a broad area.
