Different impacts of natural and anthropogenic factors on dissolved organic matter chemistry in coastal rivers: Implications for water management.

The chemical composition of dissolved organic matter (DOM) exerts significant influence on aquatic energy dynamics, pollutant transportation, and carbon storage, thereby playing pivotal roles in the local water quality and regional-global biogeochemical cycling. However, the effects of natural climate change and local human activities on watershed characteristics and in-river processes have led to uncertainties regarding their contributions to DOM chemistry in coastal rivers, creating challenges for effective water management and the study of organic matter cycling. In this investigation, we employed a combination of stable isotopic analysis, optical techniques, and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to elucidate the sources, optical properties, and molecular composition of DOM in three South China coastal rivers.

Evaluating the impacts of biochemical processes on nitrogen dynamics in a tide gate-controlled river flowing into the South China Sea.

This study aimed to evaluate the nitrogen (N) dynamics in Lijiang River, a tide gate-controlled river flowing into South China Sea, and to quantify the biochemical processes affecting nitrate fate and transport during the closed-tide gate period. The continuous on-line water monitoring indicates a chemostatic NH-N pattern with respect to variable discharges in the upstream section. The survey via daily grab water sampling from July to December 2020 at four equidistant locations in the lower stretch showed that a gradual increase in NO-N and decrease in NH-N concentrations occurred along the river from upstream to downstream sections and with the time from September to December (the closed-tide gate period).