Abstract:

Chromophoric Dissolved Organic Matter (CDOM) is optically active compounds in aquatic systems, which absorb light in the ultraviolet and visible domains, controlling the water leaving radiance or remotelysensed reflectance. It is important to the carbon cycling in inland waters as the photochemical processes of CDOM producing CO2 or CO. Previous studies have focused on the CDOM absorption properties in specific water ecosystems, limiting the knowledge of biogeochemical dynamics of CDOM in different waters. For example, CDOM may suffer from changes in absorption spectra with the temperature, potential sources and residence time of water, and so on. The significant issue is to analyze the properties of CDOM absorption in inland waters at different latitudes and trophic states, which is useful to construct the IOPs database and provide spatial and temporal variations of CDOM absorptions from water color. Based on the field CDOM absorptions in Taihu Lake, Shitoukoumen Reservoir, Chaohu Lake and Poyang Lake, the temporal and spatial changes of CDOM absorption at 412 nm (aCDOM(412)) was analyzed. We found that Shitoukoumen Reservoir at the highlatitude showed highest aCDOM(412) than those at lowlatitude, including Taihu Lake, Chaohu Lake and Poyang Lake. CDOM absorptions in the lakes at highlatitude exhibited significant spatial heterogeneity in terms of trophic states, for example, aCDOM(412) in the oligotrophic lake (Poyang Lake) was lower than the eutrophic lakes (Taihu Lake and Chaohu Lake). It is noted that average of aCDOM(412) in Chaohu Lake was higher than Taihu Lake, although they both are hyper eutrophic inland waters. We also found that changes in absorption spectra of CDOM as the influence of massive phytoplankton blooms with two distinct absorptions at 320 nm and 600 nm. The spectral slopes S reveals the potential sources and fates of CDOM and may negatively correlate with CDOM absorptions. We calculated the S in different wavebands and observed that spectral slopes from the UVA (315-400 nm) showed high correlation with aCDOM(412) in different water regions. The SA/aCDOM(412) was used to detect the sources of CDOM in the four water areas. The results revealed a useful proxy, SA/aCDOM(412), to determine the potential sources and fates of CDOM in inland water ecosystems. Future work will focus on how the regulatory factors (such as, temperature, light, hydrology, etc.) characterize the CDOM absorption properties in aquatic ecosystems