Hydrological analyses
Flow data were integrated over time to obtain the daily and annual flow (Q), as well as the data of precipitation (P). Annual evapotranspiration (ET) was estimated based on the difference between annual P and Q (simplified equation of water balance). Water yield (Q:P) was calculated from the ratio of Q by P for the monthly and annual scales. The monthly water yield was compared by the Kruskal-Wallis test, and the differences were analyzed by the Mann-Whitney pairwise test.
Baseflow index (BFI) was calculated on the annual scale by the method of Lyne and Hollic (1979) described by Grayson (1996) using a digital filter. The flow duration curve (FDC) was constructed from the daily flow data (Gordon et al., 2004), from which the following percentiles were obtained: Q10, representative of the maximum values, Q50 representative of median values and Q90 representative of the minimum values of flow for each catchment.
The data of total suspended solids (TSS) and nitrate (NO3) concentrations obtained in the C1, C2 and C3 catchments during the entire study period were analyzed using the Kruskal-Wallis and Mann-Whitney pairwise tests to detect differences between the data sets.
Table 2 shows the data periods for the 3 catchments, the indicators and the analysis scales used. For general characterization of the effects of forest management throughout the period in the 3 catchments, the daily variation of flow, baseflow and precipitation was analyzed. For water quality, medians of TSS and N were compared. The effect of age was assessed with data of the C1 catchment, from September 2009 to August 2019. The average age of the plantation in each water year was calculated by the average age of the plots weighted by the area of each plot. The comparison of the hydrological regime between restoration (C2) and commercial planting (C3) was performed for the period of two water years, from September 2017 to August 2019, and compared with the C1 catchment, considered as reference. The hydrological regime in the initial years of development of regrowth and post-replanting, for the period from May 2014 to April 2016 (regrowth) and from May 2017 to April 2019 (post-replanting), was analyzed from the data of the catchments C2 and C3.