Trends of soil acidification in the Hangjiahu Plain

Table 5-3 shows the proportion of sample points within the pH range of various levels of surface soil surveyed in the Hangjiahu Plain in 1990 and 2002, and the soil pH values ??predicted in 2012 and 2022 based on this.

Use a linear change model for prediction. First, calculate the annual average change in soil pH value ΔpHj, α for analysis sample cell number j from 1990 to 2002, that is,

ΔpHj, α = (pHj, 2002-pHj, 1990) ∕12 (1) < /p>

The predicted soil pH value of analysis sample grid number j 10 years later (2012) and 20 years later (2022) is

pHj, n=pHj, 2002+n×ΔpHj, α/2 (n=10, 20) (2)

Table 5-3 The number and percentage of soil samples with different acidity and alkalinity (pH) in the Hangjiahu Plain in 1990 and 2002

It can be seen from the data in the table that the area of ??acidic soil in the Hangjiahu region increased greatly from 1990 to 2002. Calculations show that the soil pH dropped by 0.3 units on average, and the acidification trend is very obvious. Areas with rapid acidification are mainly concentrated in Jiaxing area (accounting for 41% of Jiaxing area), Huzhou area, and Xiaoshan-Shaoxing area (Plate V-2).

Analysis of the causes of soil acidification suggests that soil acidification in the Hangjiahu Plain is related to acid rain deposition, irrational application of chemical fertilizers and other factors, resulting in a significant increase in the proportion of strongly acidic soil area year by year, while the area of ??neutral and alkaline soil The proportion is declining year by year. In addition, soil acidification may also be related to human disturbance factors such as urbanization and industrial area sewage (alkaline wastewater). The soil in a few areas has a tendency to change toward alkalinity. The polarized development of strong acidification and strong alkalinization, as well as the reduction in the proportion of neutral and acidic soil areas, will inevitably have an adverse impact on the soil ecological environment, which is reflected in the suitability of the soil for agricultural cultivation, soil microbial populations and quantities, heavy metals and Activation leaching of harmful elements such as aluminum and their impact on the water environment (related to strong acidification), leaching or fixation of nutrients, etc.

Based on the change in pH value of the corresponding surface soil analysis cells in the Hangjiahu Plain in Zhejiang Province between 1990 and 2002, a linear model was used to calculate the pH values ??10 years later (2012) and 20 years later (2022). ) The predicted value of pH value for each analytical sample unit (area 4km2) of surface soil in Hangjiahu area (Table 5-3).

According to the soil pH classification standard (Table 5-3), the measured value distribution map of the surface soil pH value in the Hangjiahu Plain in 1990 and 2002 and the predicted value distribution map in 2012 and 2022 can be drawn (Plate V -3). As can be seen from the figure, soil acidification is mainly distributed in Jiaxing area, Huzhou area, and Xiaoshan-Shaoxing area.