Quantifying the Water Quality Impacts of Intensive Farming in China : A Satellite Data Approach

The absence of temporally consistent data on nonpoint source pollution has long hindered the efforts to quantify the environmental and economic impacts of intensive farming in China. We compile a unique satellite-derived panel dataset to investigate the impacts of cropland areas on the outbreak of Harmful Algal Blooms (HABs) in China between 2003 and 2019. Our results indicate that a 1% increase in cropland leads to a 0.5 percent increase in the size of HAB in a lake greater than 20 km2. Cropland changes not only affect the size of HABs but also significantly prolong their duration on average, with a 1% increase in cropland coverage yielding a 0.24% increase in the duration of HABs. Additionally, our econometric analysis provides strong evidence supporting the presence of a legacy effect of cropland on the intensity of HABs and uncovers a distinctive “U-shape” relationship between cropland area and HABs. Among all staple crops in China, corn planting generates the most significant impact on the formation of HABs. We show that the nationwide fertilizer reduction policy released in 2015 has successfully dampened the intensity of HABs in non-reservoir lakes during the initial three years of implementation. However, the long-term impacts of the policy remain questionable. The study highlights the potential of satellite imaging data for economic analysis on nonpoint source pollution in China. Proactive measures and continuous monitoring are essential for mitigating nutrient pollution and protecting water quality in China