Fig. 1  Relationship between spatial patterns of nitrate isotopes in the Taihu Lake Basin and urbanization

Fig. 2  Redistribution of particles and sieved transport of bioavailable phosphorus under hydrodynamic disturbance

Unidentified sources of pollutants and undetermined discharge reduction targets have become the major bottleneck for formulating pollutant discharge reduction policies in the Taihu Lake Basin. Currently, NHRI Center for Eco-Environment Research has achieved important progress in tracking the sources, transformation and transport of nitrogen (N) and phosphorus (P) loads in the Taihu Lake Basin. The sources and spatial patterns of N at basin level were analyzed by the technology of dual stable isotopes of nitrate with consideration of hydrological regime and land utilization of the Basin. Hot spot areas with heavy point source of N pollution were identified, and the pollutant transformation process and transport routes were revealed. P spatial distribution at basin scale was analyzed as well. Moreover, a new mechanism of particle separation and P redistribution under strong hydrodynamic disturbance from activities like navigation was innovatively proposed, according to the hydrological and hydraulic characteristics of plain river networks.

The results of this study revealed that the spatial load of N and P corresponded well to the urbanization level from upstream rivers to downstream rivers in the research area. The nitrogen cycle was associated with the hydrological regime. Nonpoint sources constituted the major proportion of total nitrogen load during the high flow period, while point sources accounted for the major inputs among all sources during the low flow period. P load was relatively stable during all seasons, while the bioactivity of P sediments was increased from upstream rivers to downstream rivers in the Basin. The research has clarified the source mechanism of nutrition structure and limitation in the Taihu Lake Basin on the one hand. Furthermore, it has solved the scientific problems of relationships between N and P control and point and nonpoint source control, which have been argued for a long term, on the other hand. This study has provided important scientific basis for optimizing the pollutant reduction scheme in the Taihu Lake Basin, as well as for formulating policies of ecological restoration in the Taihu Lake. Relevant outcomes of this study have been published in the top journal of environmental science field, Environmental Science & Technology (EST) in 2017, receiving high evaluations from quite a few review experts. The links for the full paper are listed as following:

Tracking Nitrogen Sources, Transformation, and Transport at a Basin Scale with Complex Plain River Networks：http://pubs.acs.org/doi/abs/10.1021/acs.est.6b06278

Sieved Transport and Redistribution of Bioavailable Phosphorus from Watershed with Complex River Networks to Lake: http://pubs.acs.org/doi/abs/10.1021/acs.est.7b02710