## 4 Discussion  
The above was an experimental study on the reduction effects for single pollutants by each herbaceous riparian buffer strip. The overall reduction capacity of multiple pollutants by each herbaceous vegetation may be more instructive to engineering practice because various pollutants exceeding the standard may coexist in the runoff. According to the above experimental results, the total removal loads of TSS, TN, TP, NH\({}_{3}\)-N, and COD per unit area were calculated on different buffer strips. Although the calculation and analysis \begin{table}
\begin{tabular}{c c c} \hline \hline
**Plant Species** & **Concentration (mg/L)** & **Rate (\%)** \\ \hline _Cymodon dactylon ([PERSON].) Pers_ & 0.33 & 58.1 \\ _Dichondra repens Forst_ & 0.24 & 69.6 \\ _Zoysia mattrella_ & 0.27 & 65.7 \\ _Festuca elata Keng ex E. [PERSON]_ & 0.27 & 65.7 \\ _Lolium pereenne_ & 0.50 & 36.6 \\ bare soil & 0.63 & 20.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The comparison reduction capacity of five herbaceous vegetation buffer strips on TP. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Plant Species** & **Concentration (mg/L)** & **Rate (\%)** \\ \hline _Cymodon dactylon ([PERSON].) Pers_ & 63.0 & 27.6 \\ _Dichondra repens Forst_ & 65.0 & 25.3 \\ _Zoysia mattrella_ & 66.0 & 24.2 \\ _Festuca elata [PERSON] ex [PERSON]. [PERSON]_ & 65.0 & 25.3 \\ _Lolium pereenne_ & 71.0 & 18.4 \\ bare soil & 73.0 & 16.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: The comparison reduction capacity of five herbaceous vegetation buffer strips on COD. may deviate from the actual situation, it also reflected the total reduction capacity of plants to a certain extent [37]. The reduction effects for TSS, TN, TP, NH\({}_{3}\)-N, TP, and COD by five riparian herbaceous vegetation buffer strips (i.e., _Zoysia matrella, Cynodon dactylon ([PERSON].) Pers, Dichonda repens Forst_, _Festuca elata Keng ex [PERSON]. [PERSON]_ and _Lolium preenne_) are summarized in Table 8.  
Adding the reduction rates for various pollutants by the five riparian herbaceous vegetation buffer strips and converting them into total scores according to the percentage system can be roughly regarded as the comprehensive reduction capacity. In Table 8, we can find that the vast reduction capacity follows the order: _Dichondra repens Forst_ (45.0) > _Cynodon dactylon ([PERSON].) [PERSON]_ (44.5) > _Zoysia matrella_ (40.4) > _Festuca elata Keng ex [PERSON]. [PERSON]_ (38.2) > _Lolium preenne_ (26.8). _Cynodon dactylon ([PERSON].) [PERSON]_ and _Dichondra repens Forst_ exhibited the best comprehensive reduction effects on pollutants among the five riparian herbaceous vegetation buffer strips selected in this experiment because of the fastest growth of biomass. The other three herbaceous vegetation have poorer reduction ability. Meanwhile, the above five herbaceous buffer strips have better reduction ability for suspended solids, TN, and TP in the surface runoff but have lower reduction rates for NH\({}_{3}\)-N and COD. Five riparian herbaceous vegetation buffer strips significantly reduce pollutants more than bare soil, especially in reducing TSS and TN pollutants. Taking the better-performing _Cynodon dactylon ([PERSON]. [PERSON]_ and the weaker-performing _Lolium preenne_ as examples, _Cynodon dactylon ([PERSON]. [PERSON]_ has 21.5 times greater ability to reduce TSS than bare soil and 6.2 times greater ability to reduce TN than bare soil. In comparison, _Lolium preenne_ has 9.9 times greater ability to reduce TSS than bare soil and 3.3 times greater ability to reduce TN than bare soil. Based on the relevant research results, the interception effects on pollutants by ecological slope protection are affected by various factors, such as runoff, slope, and herbaceous vegetation coverage rate [18; 38]. In this study, the types of pollutants and herbaceous vegetation significantly influence the reduction effect under the same runoff velocity and slope.