## 3 Results
### Response of Karsi Groundwater Quality Indicators to Changes in Porosity
#### 3.3.1 Changes in pH of Groundwater at Various Depths under Different Porosity Conditions
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Depth/(m)**} & \multicolumn{3}{c}{**Porosity**} \\ \cline{2-4}  & **0.60** & **0.55** & **0.50** \\ \hline
0.1 & 6.16 & 6.28 & 6.29 (_max_) \\
0.2 & 6.02 & 6.10 & 6.15 \\
0.3 & 5.91 & 6.02 & 6.03 \\
0.4 & 5.91 (_min_) & 5.9  
3.3.3. Changes in COD (Chemical Oxygen Demand) of Groundwater at Various Depths under Different Porosity Conditions  
Indoor experiments under different soil porosity conditions tested the chemical oxygen demand (COD) values of groundwater at various depths, as indicated in Table 11 and Figure 12.  
(i) As shown from the results, in the soil surface karst zone with different porosity rates, the range of chemical oxygen demand (COD) values in groundwater fluctuated between 7.19 and 28.78, with a variance of 21.59. This significant fluctuation suggests that the groundwater in this karst surface zone generally has a high COD, indicative of substantial pollution. \begin{table}
\begin{tabular}{c c c c} \hline \multirow{2}{*}{**Depth/(m)**} & \multicolumn{3}{c}{**Porosity**} \\ \cline{2-4}  & **0.60** & **0.55** & **0.50** \\ \hline
0.1 & 8.76 & 10.76 & 13.02 \\
0.2 & 7.62 & 8.25 & 12.65 \\
0.3 & 7.19 (_min_) & 10.28 & 18.83 \\
0.4 & 10.44 & 11.65 & 21.49 \\
0.5 & 16.24 & 24.35 & 28.78 (_max_) \\ Average value E & 10.05 & 13.06 & 18.95 \\ Range R & 9.05 & 16.10 & 16.13 \\ \hline \end{tabular}
\end{table} 
Table 11: The COD values of different depths of groundwater under different porosity conditions. Figure 12: The COD curve for different depths of groundwater under different porosity conditions. (ii) In the soil surface karst zone soil layer, with smaller porosity, the fluctuations in groundwater COD values are also reduced, indicating increased stability. (iii) As demonstrated in Figure 12, throughout the entire soil surface karst zone, the overall trend shows that groundwater COD values tend to increase with increasing soil depth, exhibiting a non-linear positive correlation. 3.4 Changes in TBC (Total Bacterial Count) of Groundwater at Various Depths under Different Porosity Conditions  
Indoor experiments under different soil porosity conditions tested the total bacterial count (TBC) of groundwater at various depths, as indicated in Table 12 and Figure 13.  
(i) As shown in the results, in the soil surface karst zone, under varying porosity rates, the Total Bacterial Count (TBC) values of groundwater fluctuated between 109,275 and 186,367 CFU/mL, with a range of 77,092. These significant fluctuations suggest that the groundwater in this karst surface zone generally experiences severe TBC exceedance, indicative of serious microbial pollution. (ii) Within the soil layer of the soil surface karst zone, with smaller porosity, the groundwater TBC values increase, with the average being approximately 1.5 times higher than in looser soil layers, and fluctuations are larger and more unstable. (iii) As demonstrated in Figure 13, across the entire soil surface karst zone, as soil becomes denser or the soil particle size decreases, the general trend is for groundwater TBC values to increase with increasing soil depth, typically exhibiting non-linear changes. In contrast, when the soil layer is looser or the soil particle size is larger, changes in groundwater TBC values with increasing depth are relatively smaller. 3.5 Changes in TEC (Total _Escherichia coli_) of Groundwater at Various Depths under Different Porosity Conditions  
Indoor experiments under different soil porosity conditions tested the total _Escherichia coli_ (TEC) values of groundwater at various depths, as indicated in Table 13 and Figure 14.