Abstract
The spatial distribution of dissolved organic matter (DOM) concentrations and characteristics were examined to elucidate its controlling factors in four rivers draining into the Kesennuma Bay. Ultraviolet absorbance of 254-nm light, an indicator of humification of DOM, and the relative fluorescence intensity of fulvic acid-like and protein-like substances determined by the excitation-emission matrix fluorescence spectra were used to characterize DOM.
Stepwise multiple regression analysis revealed that current land use was the key factor in determining riverine DOM. DOM derived from humic substances increased with an increased proportion of broadleaved deciduous forest and agricultural land areas to the total watershed areas. A proportion of proteinlike substances that originating from aquatic microbes to riverine DOM increased with urban area, which may be attributed to mixing of treated water containing a high proportion of protein-like DOM, and the growth of phytoplankton in nutrient-enriched sewage water column. Salt marsh was newly formed due to the Great East Japan Earthquake and following tsunami attack and ground subsidence in the coastal area of one of our study basins. This salt marsh contained high DOM derived from fulvic acid-like and protein-like substances and affected DOM concentration and characteristics in the river mouth. This result suggests that the earthquake can make a large impact on the concentration and quality of DOM outflow from the land to sea.
