Na Wen, Yue Wang, Beibei Ding, Yiwen Han, Junyu Qi, Srinivasulu Ale, Puyu Feng, De Li Liu, Raghavan Srinivasan, Yong Chen
Abstract
Phosphorus (P) loss from agricultural lands is a major contributor to surface water quality deterioration. Elevated atmospheric CO2 concentrations (eCO2) may affect P loss directly by altering hydrological processes and indirectly by influencing soil P cycling. However, the combined effects of these two mechanisms on P loss remain considerably uncertain. This study employed a more physically-based SWAT-CO2 model, which incorporates a nonlinear gs-CO2 and a LAI-CO2 function, to project P loss from corn fields in the macro-scale watershed (∼500,000 km2) of the Upper Mississippi River Basin (UMRB) under eCO2 and future climate change. Results showed that the modified SWAT-CO2 model predicted 7.9 % less total phosphorus (TP) loss than the original SWAT at 825 ppm CO2 during the baseline (1985–2014). Future TP loss projections deviated between models compared to the baseline (30.3 % increase by the modified SWAT-CO2 vs 40.1 % increase by the original SWAT under high emission scenario in the 2071–2100 period). Moreover, different forms of P loss exhibited distinct change patterns over time for both models. Soluble phosphorus (SOLP) loss increased 16.5 %-58.8 %, while organic phosphorus (ORGP) loss changed from −11.1 % to 38.8 % across all SSP scenarios. As a result, economic costs for reducing TP loss to low risk were projected to rise, with costs during the 2071–2100 period exceeding those during both 2041–2070 and the baseline periods, particularly under SSP5-8.5 scenario. These findings highlight the importance of eCO2 in predicting P loss and underscore the need for increased economic investment to achieve P-related sustainable environmental development goals.
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