Although watershed nutrient exports have been well studied and modelled, the dynamic changes in the contributions of individual nutrient sources to reservoirs are less certain under changing land use and climate. The intensification of agriculture has led to expansion in plantation areas and the corresponding increased use of chemical and organic fertilisers in many headwater catchments in recent decades in China. Nutrient yields are potentially substantial because of the expansion of agricultural ecosystems. Here, in combination with biogeochemical nutrient budgets, we developed a synthesis model to quantify daily nutrient yields in terms of dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON), dissolved inorganic phosphorus (DIP) and dissolved organic phosphorus (DOP). We also identified their

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Agricultural cropping systems in coastal areas of China have experienced significant shifts, and nitrogen (N) and phosphorus (P) losses via surface runoff from fields have considerably increased. However, it is unclear how changes in cropping systems coupled with rainfall-runoff affect nutrient losses in coastal areas. In this study, in-situ daily rainfall-runoff events in agricultural fields in the Dagu River watershed (a coastal area of Shandong Province, Southeastern China) were observed and the dissolved nutrient losses measured. The fields comprised three cropping systems-wheat-maize rotation (W-M), vegetable-maize rotation (V-M) and vegetable-vegetable rotation (V-V). The runoff yields of total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) in V-V (10.4 ± 0.8 kg N ha À1 year À1 and 3.90 ± 0.1 kg P ha À1 year À1 ) and V-M (6.52 ± 0.31 kg N ha À1 yr À1 and 2.12 ± 0.08 kg P ha À1 year À1 ) were significantly higher than those in W-M (1.51 ± 0.15 kg N ha À1 year À1 and 0.84 ± 0.08 kg P ha À1 year À1 ), and the nutrient export coefficients were 291-1271 and 146-489 kg ha À1 year À1 m runoff À1 for TDN and TDP, respectively. Remarkable shifts in cropping systems coupled with varied rainfall-runoff are dominant factors responsible for agricultural nutrient losses. TDN and TDP losses would increase by 70.0% and 59.8%, respectively, if the watershed traditional cropping system of W-M is completely replaced by V-V. The TDN and TDP losses would increase by 36.36%-46.97% under the SSP2-4.5 and SSP5-8.5 climate scenarios until 2100 with a 50% of the watershed area of traditional agricultural plantation converted to modern plantation. This study can enhance our understanding of the effects of cropping system changes coupled with varied rainfall-runoff on nutrient losses in coastal areas of China.