## 1 Introduction
While field monitoring data are required to simulate N and P pollution in the whole basin, limited transboundary monitoring due to high data collection costs and a lack of desire, interest, and clarity in information sharing seriously constrain such environmental assessments. Additionally, prior research has mostly concentrated on evaluating water quality indicators at sample locations to reflect the broader water environment. However, this does not fully capture the extent of contamination in the entire basin. In order to model surface-source pollution, hydrological models might be a feasible alternative strategy [31]. The Soil and Water Assessment Tool (SWAT), a basin-scale ecohydrological model, was created by the USDA in Tamburlaine, Texas, and the Texas A&M University Research Office [32]. A number of factors with physical and semi-empirical characteristics are included in the SWAT model, which is a chemical, physical, and continuous-time dynamical model. By entering different spatial and attribute data, such as weather data, the Digital Elevation Model (DEM), soil, and LULC data, this model can simulate a watershed's hydrological cycle and nutrient loads [33]. It is possible to create the SWAT model without data using parameter transplanting factor transfer [34; 35]. The model has been used in numerous studies around the world. However, such studies are limited in Iraq, especially in the Shatt Al-Arab basin. Since the 1970s, the impact of LULC type on water quality has been a source of concern [36]. Previous research has demonstrated that LULC change driven by anthropogenic activities is the primary cause of declining water quality [37; 38]. By altering the qualities of the underlying surface and soil composition, improper LULC alteration affects the hydrological processes of a watershed [39; 40]. It may impact the watershed's runoff formation process, which may then have an effect on the movement and transformation of non-point source pollutants, particularly N and P [41; 42]. Some LULC types might enhance nutrient loading and decrease nutrient retention, causing eutrophication and hypoxia in the environment [37; 43]. Other research has shown that regulating LULC artificially or modifying LULC practices can reduce non-point source pollution and effectively promote ecological functions [44]. For instance, [PERSON] et al. [45] concluded that land cover changes, such as a reduction in agricultural land cover, could reduce nutrient loading. Moreover, agricultural practice modifications such as controlled-release fertilization can ensure that significantly higher levels of nutrients reach the crops, leading to higher yields with less fertilizer usage [46]. In addition to the effects of LULC change on nutrient discharge loads, climate change can also have an influence on river chemistry and nutrient discharge loads [47; 48]. The catchment hydrology (such as precipitation-runoff response), microbial processes (such as denitrification), and, accordingly, nutrient sourcing and retention will likely vary as a result of climate change and shifting precipitation patterns [49]. As SWAT was successfully used to simulate LULC impacts on flow volume, sediment, and nutrient loads [50; 51], this study used this model to simulate the N and P pollution in the entire Shatt Al-Arab basin to explore the effect of LULC and flow volume on water quality. The stability of the local societies in this basin and their quality of life depend greatly on maintaining good water quality. Thus, investigating how LULC patterns and water quality are related can help with LULC management, water contamination control, and assisting the government to safeguard the water resources in this basin and other basins. This study's major goals are:  
1. Observe LULC and landscape patterns in the Shatt Al-Arab river basin;
2. Assess water quality and simulate N and P contamination;
3. Investigate the correlations between N and P discharge loads, LULC, and flow volume.