Modified MAGIC model to assess and predict acidification effects on water chemistry changes in Taihu lake, China

Abstract

Acid deposition, nitrogen (N) fertilizer and wastewater discharge are multiple stressors producing great impacts on natural water chemistry. However, few studies have quantitatively estimated effects of these stressors on Taihu water chemistry. Here, MAGIC model was used to simulate and predict lake water chemistry change at long term scale after adaptive modifications. Long term historical water chemistry data and our field data of soil properties were used to calibrate the model. The result indicated that Cl-, Na+, and SO42- were the most sensitive to wastewater discharges, resulting in around 80% increase of Cl- and Na+; and after “wastewater calibration” the modelled result was in good agreement with calculated ones. Modelled Ca2+ and Mg2+ losses were well consistent with measured result before 2000, and acid deposition induced effect was no difference from combined effect of acid deposition and N fertilization application; while after that base cation losses caused by the dual acidification were significantly higher than those simply caused by acid deposition, which well matched the N fertilizer consumption and SO2 emissions. The Modelled result indicated that after 2000, annual loss of Ca2+ and Mg2+ caused by double acidification (acid deposition and N fertilization) was 27% and 11% higher than that caused by acid deposition, respectively. The MAGIC prediction based on different scenarios showed that reduction of wastewater discharge would effectively inhibit the increase of Cl-, Na+, and SO42-, while effect of acidification would last longer than expected even under SO2 reduction. This work is expected to provide a scientific basis for an integrated watershed management and recovery planning.