Abstract: Modern canal projects realize inter-basin water system connections and improve navigation capacity.Artificially channelized riverways reconstruct the hydrological pattern of river networks and watersheds,and combined with land use evolution,they jointly alter nitrogen and phosphorus transport processes across watersheds.The multi-tributary confluence pattern and artificially regulated hydrodynamic conditions formed by canals differ significantly from natural river channels.Existing single-scale water environment models fail to clarify the spatial transport rules of nitrogen and phosphorus and quantitative pollution source contributions in such project areas,and the response mechanisms of nutrients under various land use scenarios remain unclear.Taking the Pinglu Canal,the first river-sea connecting canal constructed in China,as the research object,this study established a coupled SWAT-SPARROW simulation framework for nitrogen and phosphorus transport.Aiming at the challenges of adjusted monitoring sites and scarce measured data caused by project construction,this paper quantitatively analyzed nitrogen and phosphorus pollution source contributions and the driving effects of land use from multi-scales of watershed,sub-watershed,and canal project.The results show that the determination coefficients of runoff,total nitrogen (TN) and total phosphorus (TP) simulated by the coupled model are all higher than 0.72.Source apportionment reveals that agricultural chemical fertilizer is the primary contributor to TN (46.59%),while livestock breeding acts as the major contributor to TP (74.65%).TN loads increase remarkably with the rising proportion of cultivated land and construction land,yet decrease continuously with the expansion of forest and grassland.For sub-watersheds along the canal with forest coverage exceeding 50%,TN in 58.75% of units meets the Class I standard for surface water.When the proportion of cultivated land and construction land surpasses 60%,nearly half of the sub-watersheds degrade to inferior Class V in terms of nitrogen water quality.This study quantifies the interception and reduction effects of forestland on nitrogen and phosphorus under the reconstructed river network of canal projects and identifies differentiated zonal control targets.It can provide scientific support for constructing a collaborative governance system integrating agricultural non-point source control,livestock pollution treatment,and forest ecological conservation for inter-basin canal projects and offer a methodological reference for multi-scale simulation of nitrogen and phosphorus in artificial canals with scarce measured data.