New insights into the variation of dissolved organic matter components in different latitudinal lakes of northeast China

Dissolved organic matter (DOM) plays a key role in the carbon cycle of freshwater ecosystems. We explored DOM composition from six lakes encompassing a typical latitudinal gradient of lakes in northeast of China (41.9°N–48.6°N). Generally, the relative contents of protein-like components decreased while humic-like components increased with increasing latitude. Additionally, the results from modified two-dimensional correlation spectroscopy indicated that humic-like components with relatively simple structure were formed earlier than those with relatively complex structure. Furthermore, structural equation models suggested that at higher latitude, lake DOM tended to stabilize as protein-like component was transformed into humic-like component. We also found that nutrients (e.g., nitrogen and phosphorus) were key factors affecting DOM composition in lowlatitudinal lakes, whereas temperature was the key factor affecting DOM composition in high-latitudinal lakes. In conclusion, this study identified the factors which explained the observed latitudinal pattern of DOM in northeast lakes of China. This study provided a theoretical basis for DOM management of lakes at different latitudes.