Effects of Chlorella ZJ Addition on Soil Carbon and Nitrogen Losses via Runoff and Sediment Under Simulated Rainfall

The application of microalgae to soil has gained attention due to their ability to improve soil fertility and sequester C, but the effects of their application on rainfall-induced runoff, sediment, and associated nutrient losses remain unclear. This study investigated the impacts of Chlorella ZJ application on soil properties, C and N accumulation, and the loss characteristics of C and N via runoff and sediment under simulated rainfall at intensities of 50 and 100 mm h−1. The results showed that applying microalgae significantly increased soil pH and the geometric mean diameter (GMD) of aggregates. It also promoted C and N accumulation, which increased by 11.28–23.79% and 13.42–24.62%, respectively, compared to the control. The contents of dissolved organic carbon, dissolved nitrogen, and nitrate nitrogen (NO3−-N) in the crusted soil decreased significantly due to soil disturbance. Under simulated rainfall, intact microalgae crusts reduced sediment loss but did not increase runoff yield. However, they substantially elevated N loss via runoff, with total nitrogen (TN) concentrations (5.85 to 20.31 mg L−1) exceeding surface water quality standards, indicating a high eutrophication risk. Overall, microalgae fertilizers have the potential to sequester C, enhance soil nutrients, and control soil erosion. However, reasonable management measures need to be implemented to prevent N pollution caused by runoff loss during their application.