Nutrient and manure management to improve water quality in urbanizing Baiyangdian

Lake Baiyangdian provides water in northern China. Agriculture contributes to nutrient pollution in this lake. This especially holds for livestock production with poor nutrient and manure management. Furthermore, a new urban area is currently developing in the basin. This increases demand for food in cities and feed for animals. This study aims to explore sustainable options to reduce nutrient losses from livestock production systems to Lake Baiyangdian between 2012 and 2050, taking urbanization into account. We used the MARINA-Lakes model to analyze future trends in nutrient pollution at the sub-basin scale, using four scenarios that consider nutrient management and intensified crop and animal production. Model results show that between 2012 and 2050, river export of nutrients to Lake Baiyangdian almost doubled in our baseline scenario without improved nutrient and manure management. As a result, the lake is expected to receive 9,623 Mg of total dissolved nitrogen and 448 Mg of total dissolved phosphorus in 2050. Additional restrictions to livestock production did not reduce the projected river export of nutrients to the lake much. Increased recycling of manure could decrease the river export of nutrients by 40% by 2050. The river export of all nutrients is projected to decrease to one-third to half of the 2012 export in our optimistic nutrient management scenario, which assumes that the available animal manure is reallocated to areas where crop demand for nutrients is high. This avoids direct discharges of animal manure to rivers. Our study shows that additional policies are needed to effectively recycle animal manure in crop production systems. Effective sewage treatment is also important for pollution control in the lake, given the anticipated urbanization.