Enhanced soil erosion threatens fluvial tufa landscapes after an Ms 7.0 earthquake in the Jiuzhaigou World Heritage Site, southwestern China

Tufa is a porous freshwater deposit comprising primarily calcite (CaCO₃) and organic matter. Massive tufa depositions can spread for up to several kilometers, forming tufa landscapes that have been recognized as national parks and World Heritage Sites. Previous studies have suggested that enhanced soil erosion owing to human activities (e.g., deforestation and agriculture) is one of the major causes of fluvial tufa decline in many places worldwide. In 2017, an Ms 7.0 earthquake occurred in Jiuzhaigou, which greatly increased soil erosion in the catchment. We compared the water chemistry and tufa deposition before and after the earthquake to understand the impact of soil erosion on tufa landscapes in Jiuzhaigou. After the earthquake, we found that high turbidity greatly reduced the aesthetic value of the lakes. Enhanced soil erosion increased NO₃^-, dissolved organic carbon (DOC), and PO₄^3- concentrations in surface water, which may worsen the problems of increased algal biomass and marsh development. Enhanced soil erosion reduced alkalinity, HCO₃^-, and the saturation index of calcite (SIc), thereby decreasing the potential to generate new calcite. Enhanced soil erosion may also increase the annual tufa deposition rates by increasing the soil and organic materials in the sediment. In addition, the tufa sediment affected by enhanced soil erosion was loose, highly porous, and contained numerous diatoms. This study provides observational data to explain the impact mechanisms of soil erosion on tufa landscapes and assess the necessity and achievements of artificial soil erosion control.