The publisher regrets that some corrections were not incorporated during proofreading. We wish to apologise to the authors and to the readers for any inconvenience caused. The corrections are listed below and the paper has been updated online.
Figure 1 caption
Figure 1 | Geological map of Jinan spring area. Where, 1 = exposed and semi-exposed Ordovician limestone-Cambrian FengshanFormation limestone; 2 = Cambrian Changshan Formation limestone-Zhangxia Formation limestone; 3= magmatic rock; 4 = section; 5 = spring group; 6 = fault; 7 = river; 8 = the river recharge area; 9 = water sample collection point; 10 =place; 11=Discharge areas; 12=Direct recharge areas; 13=Indirect recharge areas.
Table 1 heading
Indirect recharge area, Direct recharge area, Discharge area
Projection pursuit algorithm (PPA) model of groundwater quality evaluation
Under Equation (6), the sentence:
Thirdly: The optimization algorithm is used to search the best projection direction. The optimal projection direction of the evaluation index; that is, the optimal weight value, can be obtained by optimizing Equation (6).
Figure 2 key and caption
Figure 2 | Geological profile of Jinan spring area (I-I'). Where, 1 = Ordovician; 2¼ Cambrian Zhangxia formation; 3 = Cambrian Fengshan formation; 4 = Cambrian Gushan and Changshan formation; 5 = Cambrian Mantou formation; 6 = Limestone; 7 = Maristone; 8 = Olomitic Limestone; 9 = Oolitic Limestone; 10 = wormkalk; 11 = Diorite; 12 = Quaternary clay; 13 = streamline; 14 = springs; 15 = groundwater level; 16= Archean Eonothem Taishan Group metamorphic rock.