Effects of changes in precipitation patterns and stream flow on stream DOC and NO3− concentrations in a headwater catchment in a subtropical region of southern China

Study region

The Guantian headwater watershed is located in the subtropical region of South China.

Study focus

This study examined how changes in precipitation and consequent shifts in streamflow affect dissolved organic carbon (DOC) and nitrate ($N{O}_3^{-}$) concentrations in a headwater stream.

New hydrological insights for the region

The results indicate that stream DOC and $N{O}_3^{-}$ concentrations decrease from spring to winter (0.16 mg/L/month for DOC and 0.18 mg/L/month for $N{O}_3^{-}$) and have a generally positive relationship with streamflow (p < 0.05). Changes in precipitation-concentration, precipitation-amount and consequent shifts in streamflow remarkably affect stream DOC and $N{O}_3^{-}$ concentrations. When precipitation events are more heavily concentrated (when precipitation concentration index (PCI) changed from 12.81 to 18.33) from May to July, the stream DOC and $N{O}_3^{-}$ concentrations tend to increase from May to July but decrease before and after this period. In addition, an increase in precipitation-amount tends to increase stream DOC and $N{O}_3^{-}$ concentrations before the occurrence of peak flow and in the dry period from September to December, but decreases them in the wet period from June to September. When the precipitation-amount decreases, the trend of the change in concentration is exactly the opposite. These findings suggest that stream DOC and $N{O}_3^{-}$ concentrations in the headwater stream are highly chemodynamic: they are transport-limited before the occurrence of high flow and in the dry period from September to December, while they are supply-limited in the June-September period.