Coupled effects of biogeochemical and hydrological processes on C, N, and P export during extreme rainfall events in a purple soil watershed in southwestern China

- The effects of extreme weather events on C, N, and P transport from inland watersheds.
- Discovering how C, N, P export would be affected by the size of the watershed.
- Changes in biogeochemical processes in storm runoff in contrast to those in base flow.

SummaryAs global warming and extreme weather events increase and intensify across the globe, it becomes ever more urgent to study and understand the effects of extreme rainfall events on carbon (C), nitrogen (N), and phosphorus (P) export from terrestrial to riverine ecosystems. There is still much to learn regarding C, N, and P non-point source discharge that results from extremely heavy rainfall as well as their effects on downstream ecosystems. This study aimed to shed light on C, N, and P biogeochemical and hydrological coupling processes. Long-term and short-term water composition monitoring research was carried out within a purple soil watershed in China's Sichuan Province. This study captured both base flow from long-term observations and dynamic runoff under extreme rainfall events that took place during the 2012 rainy season. Dissolved total nitrogen (DTN) was the largest percentage of total nitrogen (TN) in storm runoff. DTN exceeded particulate nitrogen (PN), which itself exceeded dissolved organic nitrogen (DON). Under site conditions, particulate phosphorus (PP) formed the largest constituent of total phosphorus (TP) followed by dissolved total phosphorus (DTP) and dissolved organic phosphorus (DOP). Furthermore, results showed that C, N, and P loads increased sharply in response to heavy rainfall. Although P abundance in purple soils is limited, it was nevertheless shown that C:N:P ratios measured during rainstorms corresponded much more closely to the Redfield ratio than to ratios measured in base flows. This adds to the evidence that suggests that increased storm runoff will increase eutrophication likelihood in ecosystems further downstream.