A systematic examination of the relationship between CDOM and DOC for various inland waters across China

Abstract. Chromophoric dissolved organic matter (CDOM) plays a vital role in aquatic ecosystems. Strong relationship has been proven between CDOM and dissolved organic carbon (DOC), which set the basis for remote estimation of DOC with remote sensing data. An algorithm has been developed to retrieve DOC via CDOM absorption at 275 and 295 nm with coastal waters. However, the relationship between DOC and a_CDOM(275) and a_CDOM(295) for different types of inland waters are still not clear. Further, is the relationship stable with different types of inland waters? In the current investigation, samples from fresh lakes, saline lakes, rivers or streams, urban water bodies, ice-covered lakes were examined. The regression model slopes range from 1.03 for urban waters to 3.13 for river water, with extreme low slope value for highly saline waters (slope is about 0.3); while coefficient of determinations (R²) range from 0.71 (urban waters) to 0.93 (winter waters). The specific CDOM absorption (SUVA254) showed the similar trend, i.e., low values were observed for saline water and waters from semi-arid or arid regions, where strong photo-bleaching is expect due to thin ozone layers, less cloud cover, longer water residence time and sunshine hours. In the contrast, high values were measured with waters developed in wetlands or forest in Northeast China, where inverse environmental settings were witnessed. The investigation also demonstrated that stronger relationships between CDOM and DOC were revealed when CDOM275 were sorted by SUVA254 (0.78 < R² < 0.98) or the ratio of CDOM250:CDOM365 (0.78 < R² < 0.99). Our results highlight that non-unified relationship exhibits for different types of inland waters, and remote sensing models for DOC need to be tuned with different inherent optical parameters obtained from various types of waters for quantification of DOC in inland waters.