城市化背景下白洋淀入湖营养盐负荷模拟研究

过量的营养盐输入导致白洋淀富营养化程度较高。雄安新区建设伴随着快速城镇化进程，将可能进一步增加入湖营养盐负荷。为摸清新区建设背景下白洋淀入湖营养盐负荷的变化趋势及削减量，基于入湖营养盐负荷模型计算了历史不同时期（1995-2015年）白洋淀入湖营养盐盐负荷，预测了土地利用、农业管理和污水处理系统变化下入湖营养盐负荷的变化趋势。结果表明，白洋淀历史时期入湖总氮和总磷年平均负荷分别为2018 t和313 t，主要来源分别是耕地和畜禽粪便排放。就土地利用变化而言，以2010年为基准，2050年白洋淀入湖总氮和总磷负荷在建设用地快速增长（RAP）情景下增长率最高，分别增长了56%和60%，主要原因在于城镇人口增加，从而增加了畜禽需求量和生活污水排放。就农业管理而言，削减化肥使用有利于降低入湖总氮负荷，控制畜禽粪便排放更有利于入湖总磷负荷的降低。2050年，生活污水将成为白洋淀入湖营养盐的重要来源，因此，在制定未来社会经济发展路径时，应重点提高农村地区生活污水收集率和处理效率。PCLake模型对不同入湖负荷下湖泊营养状态演变的模拟发现，削减入湖总磷负荷是白洋淀水质恢复的关键。白洋淀水质达到III类和IV类标准时，入湖总磷负荷阈值分别为2.1和2.6 mg P m^-2 d^-1。在建设用地快速增长情景下，若使白洋淀水质达到III类标准，入湖总磷负荷应减少131 t。

Modelling nutrient loadings to the Baiyangdian Lake under the background of urbanization

Rapid socio-economic development related to population growth, food production, and waste management has led to the increasing river export nutrient inputs to the Baiyangdian Lake (BYD), causing severely anthropogenic lake eutrophication. Look ahead, these human-induced nutrient inputs will continue to increase due to the construction of Xiong''an new area. It is thus crucial to provide information on future trends of nutrient loading and its implications for lake restoration. Here we quantified nutrient loadings to the BYD Lake in the different periods during 1995-2015 and assessed their future trends (2050) under changes in land use, agricultural management, and sewage systems. The results showed that multi-year averaged total nitrogen and total phosphorus loadings to the BYD Lake were 2018 ton year^-1 and 313 ton year^-1, respectively. Cropland and directly discharged animal manure were the main sources of total nitrogen and total phosphorus loads, respectively. In terms of land-use change, the growth rates of total nitrogen and total phosphorus loads to the BYD Lake were the highest in 2050 under the scenario of the rapid growth of construction land, increasing by 56% and 60% compared with the baseline scenario in 2010, respectively. The increases are driven by the increasing demands of animal production and wastewater discharge from the growing urban population. As for agricultural management, reducing synthetic fertilizer application was conducive to reducing total nitrogen loadings to the BYD Lake, while controlling directly discharged of animal manure was more helpful for reducing total phosphorus loadings. In 2050, wastewater will become the dominant sources of both total nitrogen and total phosphorus loadings to the BYD Lake. Hence, improving the collection rate and removal efficiency of sewage systems, especially in rural areas, should be put more efforts for the formulation of effective policies for improving the water quality of the BYD Lake. The critical nutrient loads were estimated by the load-response curves from the PCLake model. Knowing the difference between future nutrient loadings and critical nutrient loads is important for lake restoration. The results indicated that reducing the total phosphorus loadings is the key to restore water quality for the BYD Lake. The critical total phosphorus loadings for the III level and IV level of water quality standard are 2.1 mg P m^-2 d^-1 and 2.6 mg P m^-2 d^-1, respectively. To meet the III and IV level of water quality standard, the total phosphorus loadings to the BYD Lake need to be reduced 67 and 131 tons in the scenario of rapid growth of construction land, respectively.