Forests present themselves as the best land use for maintaining the quality of
natural surface water, providing ecosystem services of provision and regulation for
this resource. The conversion of forests to anthropogenic uses tends to reduce the
quality of waters due the nutrients and sediment inputs from moving and soil
management. The presence of vegetation in the riparian area can reduce these
effects by providing some services as the protection of water bodies. The aim of this
study was to detect the influence of riparian vegetation on water physico-chemical
composition in agricultural watersheds. The work was divided into two parts, the first
sought to evaluate the state of the forest vegetation in the study area and its potential
in providing services and the second part to assess the effect of vegetation on
physico-chemical parameters of the water. The study units were defined in
Corumbataí river basin, from a mapping of the land use in 2000 by adaptive sampling
method, where the units should have a minimum 70% matrix and 10% forest cover.
Were selected six units of 16 km2, three units with pasture matrix and three units with
sugar cane matrix. With the units defined mappings were performed by
photointerpretation for five dates (1962, 1978, 1995, 2000 and 2008), from this
mapping was possible to calculate the changes in land use and some indices for
forest fragments. Were also used maps of soils and geology, and the mapping of
relief for recognition of physical and chemical aspects of the terrain. Seven
watersheds, from first to second order, were selected and water samples were
collected during one year, biweekly, for the analysis of physico-chemical parameters
of the water. Differences in occupation of land use and the trajectory of forest
fragments between matrices were evaluated using analysis of variance and
differences between water variables were assessed using the nonparametric
Wilcoxon-Mann-Whitney test. The results showed that the forest vegetation cover
has increased in recent years, giving evidence the beginning of a regeneration
phase, known as the second stage of forest transition, but only future studies can
confirm this analysis. The matrices exhibit similarity to the area occupied by forest,
however, the trajectories of these forests were different. The potential of services by
these forests in relation to protection of streams is relatively low, which through the
methodology it was observed that only 1/3 of the forest has been considered
appropriate for the provision of services. The sugar cane promotes the increase of
nitrogen in the stream, while the pasture has higher concentration of dissolved
organic carbon. The riparian forest is essential to the maintenance of the aquatic
ecosystem. The forests are contributing to the increase in the concentration of some
nutrients in the water.
