## 3 Results and Discussion  
A significant decrease in water depth was observed in September (late dry season, Tables S1 and S2) for most sampling points, except IR 1 and D3 (Tables S1 and S2). Most physicochemical characteristics did not vary among sites or seasons (Tables S1 and S2). The Blanco River showed a higher conductivity than the other water bodies (50 \(\upmu\)S cm\({}^{-1}\) as compared to a mean of 27 \(\pm\) 4 \(\upmu\)S cm\({}^{-1}\) for the Itenez River and 20 \(\upmu\)S cm\({}^{-1}\) for San Martin), and this value increased during the late dry season (80 \(\upmu\)S cm\({}^{-1}\)). Quantities of SPM showed a mean value of 5.6 \(\pm\) 1.1 mg/L with minor variations along the Itenez river in June (Table S1). In September, the quantities of SPM along the Itenez River were significantly higher (\(p\) = 0.005) than in June (Figure 2A). For point IR6 (Vuelta Grande), the value obtained in September more than doubled the value measured in June (12.4 mg/L in September compared to 5.7 mg/L in June, Table S1). Such an increase can be related to the resuspension of sediments by physical factors or bioturbation since the water column at this point became very shallow (0.9 m) [15]. In June, SPM values for the Itenez lakes were similar to those obtained for the river (Figure 2A); this is in agreement with the fact that, during the high water level season, rivers and lakes are connected. No significant difference for SPM in the Itenez lakes was observed between September and June, except for lake IL9, which showed a strong increase of suspended matter (from 4.8 mg/L in June to 100.2 mg/L in September, Table S1). In September, the connections between the river and the lakes were interrupted, and most floodplain lakes of Itenez showed slightly lower concentrations of SPM than the river, probably because of a sedimentation process and the fact that they did not receive new particulate material. Lake IL9 became very shallow in September (1.70 m), and resuspension phenomena can explain the very high value of SPM (Table S1). Two of the sampled tributaries of Itenez, a river from Brazilian territory that crosses highly deforested areas and the Colorado stream, which is influenced by gold mining showed in June the highest values for SPM (20.7 mg/L and 15.2 mg/L, respectively) (Table S2). However, the other tributaries directly influenced by anthropic activities showed values similar to those of the Itenez river. In September, the Asunta Stream showed a very high value (36.7 mg/L) for SPM, but the other two streams influenced by the \"San Simon\" goldmine had low values (6.4 and 9.7 mg/L). On the other hand, in June, Blanco river, which drains white waters, contained higher amounts of particulate matter than Itenez river (27.7 mg/L), while San Martin, a clear water river, and its lakes, showed the lowest values (2.9 mg/L, Table S2). Both rivers cross territory with little anthropic influence [11]. In September, however, concentrations of SPM in San Martin increased strongly (up to 19.9 mg/L), probably due to  
Figure 2: Comparison of suspended particulate matter (**A**) and particulate mercury concentration by volume (**B**) for the Itenez River and associated lakes in the two seasons. the resuspension of sediments [15], while this was not the case for Blanco. Although deforestation and mining give rise to disturbance of the upper horizons of soil and cause an increase in the loads of solid particles that reach water bodies [9; 10], factors not related to anthropic intervention must also be taken into account in order to determine the causes of high SPM. The concentration of particulate mercury by water volume ([Hg]\({}_{\rm v}\)) followed the same pattern as particulate suspended matter, showing little variations along the Itenez river (mean value 1.10 \(\pm\) 0.19 ng/L) and its associated lakes in June (mean value 1.26 \(\pm\) 0.23 ng/L, see Table S1). In September, the Itenez river had significantly higher [Hg]\({}_{\rm v}\) than in June (\(p\) = 0.0129) (Figure 2B), as was observed for SPM.