Evaluation of carbon storage process into marine sediment based on new optical technology: non-destructive measurement of belowground production and degradation of seagrass

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This project aims to establish a method for quantitatively estimating production and degradation rate of belowground parts of seagrass by adopting non-destructive optical measurement techniques developed in terrestrial ecosystem research. Firstly, an aquaculture experiment of eelgrass was conducted using indoor and outdoor aquaria to periodically monitor growth of rhizomes and roots using an optical scanner in non-destructive manner. It was revealed that the root biomass accounted ca. 3 % of a total biomass of eelgrass, but the whole belowground parts occupied 14% and contributed significantly as a sink of carbon in sediment. Secondarily, hyper spectral reflectance images of different-aged belowground parts of seagrass were captured at visible and near-infrared spectral region (446-894nm). The increase in age from 14-220 days reduced the reflectance of live fine roots mainly at visible spectral region. The dead seagrass parts showed low reflectance at whole spectral region. By developing the estimation model, root age and concentrations of carbon and nitrogen were predicted by the spectral reflectance at the error of 12-37% (rRMSE). In conclusion, it was shown that seagrass belowground production has clear seasonal cycle and contributes to blue carbon storage. It was firstly demonstrated that age of belowground parts, carbon and nitrogen balance can be determined non-destructively using spectral reflectance images.