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.