Water streamflow decreases in response to acid deposition in a subtropical forest watershed in China

The acid deposition simulation in the DBR watershed was initiated in June 2009. Two acid intensities were simulated with solution pH values of 4.0 (pH4.0) and 3.0 (pH3.0). Plots applied local lake waters with a pH was about 4.5 and were selected as the control group (CK). Each treatment had three replicated plots and thus, nine plots (10m × 10m) were established. The simulated acidic solution was prepared by mixing H₂SO₄ and HNO₃ at a 1:1 mole ratio into the lake water. At each application time, 40 liters was applied to each plot at an interval of two weeks throughout the experimental period. Tree foliage was collected in each treated plot in December 2020. Foliar samples were divided into two parts. One part was used for stomatal density and guard cell length measurements, and the other was oven-dried at 60 °C for subsequent nutrient content analysis.