# A Review of the Artificial Neural Network Models for Water Quality Prediction
## 2 Methods  
This review focuses on the application of ANNs to water quality variables prediction excluding drinking water from 2008 to 2019. The papers to be reviewed were selected using the following steps:  
1. First, we identified ANN-related papers in influential water-related and environmental-related journals to ensure that high-quality papers are included in the review. These papers are mainly from journals whose subjects are environmental science and ecology, water resources, engineering and application.
2. Thereafter, a keyword search of the ISI Web of Science was then conducted for the period 2008-2019 using the keywords; water quality, river, lake, reservoir, WWTP, groundwater, pond, prediction, and forecasting, accompanied by the names of ANN methods (one or more), such as neural network, MLP, RBFNN, GRNN, RNN, to name but a few.
3. Then, through the search process from 1 to 2, 151 articles in English relevant to our focus were selected. The basic information of the papers, including authors (year), locations, water quality variables, meteorological factors, other factors, output strategy, data size, time step, data dividing, methods, and prediction lengths are provided in Appendix A.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Abbreviations** & **Full Name** & **Abbreviations** & **Full Name** & **Abbreviations** & **Full Name** & **Abbreviations** & **Full Name** \\ \hline AH & air humidity & EC & Electrical conductivity & ORP & Oxidation reduction potential & TCC & total chromium concentration \\ AODD & August, October, December, data & Evap & evaporation & Q & discharge & TIC & total iron concentration \\ AP & air pressure & FIT & flow travel time & pH & Pondus & total anions and \\ AT & air temperature & Fe & iron & Precip & precipitation & TNs & total nutrients \\ As & Arsenic & F & flow & P & phosphate & TA & total alkalinity \\ B & boron & HCO\({}_{3}\) & bicarbonate & RH & relative humidity & TP & total phosphorus \\ BOD & Biochemical & & & & & Redox potential & Tur & turbidity \\  & Oxygen & HA & & Amine & RP & & total dissolved \\  & Demand; & & & & & & solids \\ C & carbon & ICs & ionic concentrations & & RO & runoff & TDS & total silsides \\ Cl & chloride & K & potassium & RF & rainfall & TN & total nitrogen \\ Cu & Copper & Lon & longitude & RainP & Rainy period & TH & total hardness \\ Ca & calcium & Lat & latitude & SR & solar radiation & TOC & total organic carbon \\ CO\({}_{3}\)\({}^{2}\) & Carbonate & LV & lake volume & & & sunshine time & & total suspended \\  & & & & & & hours & TSS & solids \\ Coli & Coliform & MDHM & & month, day, hour, minute & SD & transparence & VP & volatile phenol \\  & Chemical & & & & & sodium & \\ COD & Oxygen & Mn & manganese; & SAR & absorption & WL & Water Level \\  & Demand & & & & ratio & & water \\ COD\({}_{\text{Mn}}\) & & & & & & & temperature \\  & & & & & & soil & \\ Chl-a & Chlorophyll a & Na & sodium & ST & soil & & wind speed \\  & dissolved & & & & & temperature & WD & wind direction \\ DO & oxygen & & & & & & the year \\ DOY & day of year & NO\({}_{2}\) & nitrite & S & salinity & YMDH & numbers \\ \hline \hline \end{tabular}
\end{table}
Table 1: The abbreviations in this review.