4.3.2 Suspended Solids
The highest values for suspended solids were recorded in the T1
treatment (Figure 3C), when compared to T2 (Figure 3D). In February, all
values were larger than 100 mg l-1 (milligrams per litre), with an
average of 252 mg l-1 for that month. The same happened with the values
of October, 222 mg l-1, and in December, with an average of 416 mg
l-1. In T2, the values were more uniform, with averages of 126, 163
and 107 mg l-1, with only a peak of 696 mg l-1 observed in October 2012
(Figure 3D), though still below the peaks recorded for T1 with a peak of
884 mg l-1 observed in in October 2006, and another of 1850 mg l-1 in
December 2003 (Figure 3C).
The results of suspended solids for the rainy season were lower than
those described by Setzer (1985), who evaluated soil losses and their
relation to turbidity, as well as water parameters in several watersheds
in the state of São Paulo. Setzer’s results expressed average annual
rates for suspended solids in the rivers of São Paulo as slightly lower
than 150 mg l-1, rising to almost 300 mg l-1 in the rainiest months, and
lowering to less than 50 mg l-1 in the driest months.
The results of the work show that there was a significant decrease in
suspended solids after the adoption of conservationist practices and the
restoration of agricultural properties. Rodrigues et al. (2015)
documented that the runoff coefficient was low in the presence of
vegetation, resulting in larger infiltration and better flow regularity;
also, they observed that erosion and carried sediments increased on
unprotected soils, changing the dynamics of water on the soil.