Novel insights into sources identification of fluvial dissolved organic matter in intricate plain river networks...

Plain river networks are a complicated reciprocating flow system, posing significant challenges for tracing the transport processes of dissolved organic matter (DOM) in aquatic environments.

In this study, source contributions were investigated from intricate river networks in Jiashan Plain using UV-visible spectroscopy and excitation-emission matrix fluorescence spectroscopy with grey influence analysis (GINA) and end-member mixing analysis (EMMA). Overlying water samples were collected from Hongqi River (HQR), Sandian River (SDR) and Baishui River (BSR). Five potential end-members were simultaneously collected from Jiashan County, i.e., soil, riparian plant, aquaculture effluent, domestic sewage and groundwater. Based on the GINA, E₂/E₃, percentage of microbial secretions, degradation index (DIX) and biological index (BIX) could be defined as suitable descriptors to identify DOM sources. Two dual-optical-index groups, i.e., DIX-E₂/E₃ and BIX-E₂/E₃ were optimal for identifying contribution rates from either a given river or each sampling site. According to EMMA, the contribution of domestic sewage (62.38 % ± 17.43 %) was the highest in HQR, followed by aquaculture effluent (10.83 % ± 7.32 %), groundwater (9.60 % ± 3.69 %), soil (9.17 % ± 3.66 %) and riparian plant (8.02 % ± 3.99 %). Likewise, domestic sewage and aquaculture effluent exhibited high contributions both at SDR and BSR. For each end-member, substantial variations of contribution rates occurred at the sites both in HQR and SDR, probably resulting from significant aquaculture effluent inputs in upstream reaches of these rivers.

Identifying DOM sources by the optical indices, a simple and reliable method, might be conducive to understanding the factors impacting DOM dynamics in intricate river networks.