Sources and fates of particulate organic matter in inland waters with complex land use patterns

Elucidating the sources of particulate organic matter (POM) is the foundation for understanding their fates and the sea-sonal variation of their movement from the land-to-ocean aquatic continuum (LOAC). The POM from different sources has different reactivity, which determines their fates. However, the key link between the sources and fates of POM, es-pecially in the complex land use watersheds in bays is still unclear. Stable isotopes and contents of organic carbon and nitrogen were applied to reveal them in a complex land use watershed with different gross domestic production (GDP) in a typical Bay, China. Our results showed that the POMs preserved in suspended particulate organic matter (SPM) were weakly controlled by assimilation and decomposition in the main channels. Source apportionments of SPM in the rural area were controlled by soil (46 % -80 %), especially inert soils eroded from land to water due to precipi-tation. The contribution of phytoplankton resulted from slower water velocity and longer residence time in the rural area. The soil (47 % -78 %) and manure and sewage (10 % -34 %) were the two major contributors to SOMs in the developed and developing urban areas. The manure and sewage were important sources of active POM in the ur-banization of different LUI, which showed discrepancies in the three urban areas (10 % -34 %). Due to soil erosion and the most intensive industry supported by GDP, the soil (45 % -47 %) and industrial wastewater (24 % -43 %) were the two major contributors to SOMs in the industrial urban area. This study demonstrated the close relationship between the sources and fates of POM with complex land use patterns, which could reduce uncertainties in future es-timates of the LOAC fluxes and secure ecological and environmental barriers in a bay area.

Automated summary

This study revealed the close relationship between the sources and fates of particulate organic matter (POM) in a typical Bay in China with complex land use patterns. The results showed that POM in rural areas mainly came from soil, while POM in developing and developed urban areas came from soil, manure, and sewage. POM in the industrial urban area primarily originated from soil and industrial wastewater.