General characterization of the hydrological data series
The historical series of daily precipitation and flow of the three experimental catchments have different extents because data records began in 2009 in the C1 catchment and in 2013 in C2 and C3. Although precipitation was the same for the three catchments, there were differences in the dynamics and values of flow and baseflow (Figure 3). These differences were expected as the hydrological response to precipitation events is influenced by vegetation characteristics, including management practices, and by the physical characteristics of the catchment (Brown, Zhang, McMahon, Western, & Vertessy, 2005; Sun et al., 2004), which differed between the catchments studied (Table 1, Figure 2).
The average daily flows recorded in the C1, C2 and C3 catchments were 0.55 mm, 0.27 mm and 0.58 mm, respectively. The shares of baseflow in the average daily flow were 79%, 55% and 70%, respectively, in C1 (0.43 mm), C2 (0.15 mm) and C3 (0.41 mm). Thus, it can be noted that, although the average daily flow followed the decreasing order C3>C1>C2, the daily average values of baseflow followed the decreasing order C1>C3>C2. Although surface runoff is usually governed by the slope of the terrain, forests commonly reduce surface runoff due to increased roughness (Kalantari et al., 2014), and subsurface runoff can be increased by maintenance or improvement in the infiltration capacity of forest soils (Neary, Ice, & Jackson, 2009; Price, 2011), thereby increasing the chances of underground recharge. For this reason, although the C1 catchment has higher average slope compared to the others (Table 1), it had greater share of baseflow in the flow.
In relation to the concentrations of total suspended solids in the catchments (Figure 4), C3 had a higher and significantly different (p<0.05) median (5.7 mg L-1) compared to the medians of C2 (4.0 mg L-1) and C1 (3.5 mg L-1). Regarding nitrate concentrations, the three catchments differed significantly (p<0.05), and C2 had the highest value (0.60 mg L-1), followed by C3 (0.50 mg L-1) and C1 (0.30 mg L-1) (Figure 4). The C1 catchment had the lowest values for the two parameters analyzed. Differences between the studied catchments were expected because even catchments that are close and similar may have different water quality parameters as a result of small variations in geology, soils or shading of streams, for example (Binkley & Brown, 1993; Feller, 2005). Nevertheless, in general, the concentrations of total suspended solids and nitrate recorded in the three catchments (Figure 4) are within the range of values reported in studies conducted in catchments with forest management (Aust & Blinn, 2004; Baillie & Neary, 2015; Binkley & Brown, 1993; Grace, 2005) and corroborate the fact that usually the water quality of forest landscapes is superior to that of other types of land use, such as agricultural use (Binkley, Burnham, & Lee Allen, 1999; Boggs, Sun, Jones, & McNulty, 2013; Da Silva et al., 2007; Diaz-Chavez, Berndes, Neary, Elia Neto, & Fall, 2011; Grace, 2005; Sun et al., 2004; Van Dijk & Keenan, 2007).