*Article* **Ammonium Nitrogen Streamflow Transport Modelling and Spatial Analysis in Two Chinese Basins**

**Jingchen Yin <sup>1</sup> , Haitao Chen <sup>1</sup> , Yuqiu Wang 1,\*, Lifeng Guo 2,\*, Guoguang Li <sup>3</sup> and Puzhou Wang <sup>4</sup>**


<sup>4</sup> Synthego Corporation, Redwood City, CA 94063, USA; puzhou.wang@synthego.com

**\*** Correspondence: yqwang@nankai.edu.cn (Y.W.); guolifeng@hhbhjg.mee.gov.cn (L.G.)

**Abstract:** Ammonium nitrogen (NH<sup>4</sup> + -N), which naturally arises from the decomposition of organic substances through ammonification, has a tremendous influence on local water quality. Therefore, it is vital for water quality protection to assess the amount, sources, and streamflow transport of NH<sup>4</sup> + -N. SPAtially Referenced Regressions on Watershed attributes (SPARROW), which is a hybrid empirical and mechanistic modeling technique based on a regression approach, can be used to conduct studies of different spatial scales on nutrient streamflow transport. In this paper, the load and delivery of NH<sup>4</sup> + -N in Poyang Lake Basin (PLB) and Haihe River Basin (HRB) were estimated using SPARROW. In PLB, NH<sup>4</sup> + -N load streamflow transport originating from point sources and farmland accounted for 41.83% and 32.84%, respectively. In HRB, NH<sup>4</sup> + -N load streamflow transport originating from residential land and farmland accounted for 40.16% and 36.75%, respectively. Hence, the following measures should be taken: In PLB, it is important to enhance the management of the point sources, such as municipal and industrial wastewater. In HRB, feasible measures include controlling the domestic pollution and reducing the usage of chemical fertilizers. In addition, increasing the vegetation coverage of both basins may be beneficial to their nutrient management. The SPARROW models built for PLB and HRB can serve as references for future uses for different basins with various conditions, extending this model's scope and adaptability.

**Keywords:** Poyang Lake Basin; Haihe River Basin; SPARROW; ammonium nitrogen; nutrient transport
