FIGURE 6 | (A) Hybrid NCA–MRMR–CTree network with dissolved oxygen (x1) and SPM (x2) ruling out the trophic state. (B) Trophic state classification in terms of dissolved oxygen and DIN concentrations. (C) Hybrid NCA–MRMR–CTree network with arsenic (Var1) ruling out the water contamination level. (D) Water contamination level classification in terms of cadmium and arsenic