Statistical Analysis and Review of Event Mean Concentrations in Stormwater Runoff from Agricultural Nonpoint Source Pollution among Different Land Use Types

Abstract

Objectives : In this study, the characteristics of stormwater runoff from agricultural nonpoint pollution sources investigated under various experimental conditions were evaluated among different land use types (e.g., paddy, field, field (alpine), and vinyl house), and event mean concentrations (EMCs) for each water quality parameter were statistically analyzed. These results can be used in calculating the contribution of stormwater runoff to water quality of receiving water body by performing quantitative and qualitative analysis. The unit loads calculated were compared with Ministry of Environment TMDL (2019) to secure the reliability of the calculated unit loads.Methods : EMCs and unit loads investigated in various studies were classified in terms of paddy, field, field (alpine), and vinyl house. Among various land use types, EMCs and unit loads were statistically analyzed quantitatively and qualitatively. For EMCs, a null hypothesis is that ‘EMCs of water quality parameters among different land use types are not different at a statistically significant level (α=0.05)’. Based on the results of statistical analysis, heteroscedasticity (p<0.05) and Welch-test method were consequently applied, and post hoc test was performed using the Games-Howell method. Finally, unit loads was compared and reviewed against the TMDL (2019) unit loads of the Ministry of Environment.Results and Discussion : Various EMCs in all water quality parameters were found among different land use types (i.e., paddy, field, field (alpine) and vinyl house). For most water quality parameters, EMCs tended to decrease in the order of field (alpine) > field > vinyl house > paddy. The coefficient of variance (CV) values of all water q uality parameters were 0.5 or greater. Based on these results, EMCs in agricultural nonpoint source pollution are very diverse and deviated due to the combination of natural and artificial factors. Post hoc test results indicated different statistical significance among all water quality parameters. In addition to the land use types, both natural factors (i.e., season, rainfall, antecedent rainfall day, and, rainfall runoff rate) and artificial factors (i.e., cultivator manipulation, emission route, type of crop, and amount of compost) affect the characteristics of stormwater runoff. In particular, in the case of field (alpine) with prominent topographical feature of slope, and EMCs were statistically greater than those from other land use types in all water quality categories (p<0.05).Conclusions : Countermeasures for field (alpine)with greater EMCs than paddy, field and vinyl house, should be performed priority. EMCs were affected by a complex interaction between natural factors (i.e., season, rainfall, antecedent rainfall day, and, rainfall runoff rate) and artificial factors (i.e., cultivator manipulation, emission route, type of crop, and amount of compost), and additional data and research are required for further study to elucidate these complex interactions.