Stable isotope modeling of the groundwater discharge in complex
watersheds of the State of São Paulo, Brazil
Abstract
The increasing pressure on water resources demands integrated
multidisciplinary approaches to deal with environmental, scientific, and
social issues related to water availability in watersheds. In large
watersheds, many factors control hydrological processes, requiring the
application of a methodology capable of describing water dynamics in
complex situations. This study uses stable isotope (2H and 18O) modeling
to characterize groundwater contribution in an area of heterogeneous
hydrogeological framework and advanced anthropization, located in the
Piracicaba-Capivari-Jundiaí (PCJ) and Tietê-Jacaré (TJ) water management
units – central-eastern portion of the State of São Paulo, Brazil.
Groundwater dynamics is controlled by the direct interaction of the
rainfall regime with hydrogeological domains. The modeling performed in
this study indicates that a portion ranging from 60 to 80% of the total
volume of streamflow comes from groundwater discharge (for studied
year). However, in the crystalline domain, the aquifer capacity of
storing surplus water is smaller, increasing the importance of rainfall
for the generation of direct runoff and maintenance of the streamflow.
In most of the PCJ unit, there is a greater dependence on surface water
and vulnerability to prolonged droughts. On the other hand, in the
sedimentary areas, the contribution of groundwater discharge is around
80%, showing that the aquifer storage capacity guarantees
homogenization of the discharge throughout the year, and ensures water
security in drought periods. This study attests to the successful
application of stable isotope modeling to large basins, as the method is
able to describe natural hydrological processes occurring in watersheds
with a heterogeneous hydrogeological framework and the effects of the
anthropogenic action. It is concluded that the use of stable isotopes
can aid water resources management in expanding the capacity of
monitoring surface and groundwater resources to identify negative
effects on water availability.