Impacts of Sugarcane Expansion on Water Resources in Areas of São Paulo State

Title: Impacts of sugarcane expansion on water resources in areas of São Paulo State.

Keywords: ethanol, sugarcane impacts, water resources, time-series analysis.

Abstract

The expansion of sugarcane cropping for bioethanol production can impact both the quantity and the quality of water resources in the region where it occurs. Land use changes and different management practices can modify the runoff processes in the watersheds and the river flows (TUCCI and CLARKE, 1997). The consumption of water resources associated to sugarcane and ethanol production has decreased during the last years. This has been possible due to the use of fertirrigation and due to the reduction of water withdraws for the industrial phase through the optimization of some processes and water reuse (ELIA NETO et al., 2010). However, the vinasse and the use of agrochemicals can contribute to the pollution of water bodies (GOLDEMBERG et al., 2008).

This abstract is based on the master’s thesis of the first author which evaluated whether it is possible to observe impacts of sugarcane expansion both on the quantity and the quality of water bodies. For this research, data of water monitoring in the state of São Paulo were used; these database is publically available and this was a premise for defining the research: what can be understood from the data publically available?

Data used were those from the monitoring stations regarding precipitation, discharge and quality parameters; they are provided by the Brazilian Water Agency (ANA), Department of Water and Energy (DAEE) and Brazilian Commission for the Environment (CONAMA).

The selection of studied areas was made considering the monitoring stations with the longest historical series (above 15 years), with less than 10% of failures, and located in areas with significant expansion of sugarcane over the years. Stations located near hydroelectric plants were avoided and small scale rivers basins were prioritized. To evaluate the water quality impacts, an additional criterion used was the availability of parameters related to agrochemical inputs and vinasse.

The selection of studying sites was limited by the unavailability of long time series of discharge and variables of water quality in areas with growing sugarcane cultivation. Besides the unavailability of long time series, many data of gauging stations have several failures, mainly in small scale catchments.

In Brazil, the implementation of a water monitoring network was motivated by the importance of hydroelectric plants. This explains the shortage of gauging stations in basins with less than 500 km2 (PAIVA and PAIVA, 2003). The methodology for evaluating the effects of land use change in river flow is more conclusive in small-scale basins (COSTA, 2003). However, the hydrological monitoring network in small-scale basins has constrains, and data is available for just few years or the series have several failures.

The selection of areas to assess the potential impacts on water quality was also constrained by the shortage of time series during long periods for many parameters related to agrochemical inputs and stillage, as potassium and nitrogen series. Among the 80 water quality monitoring stations preselected, approximately 25 stations have data for nitrogen concentration along six years, and less than 10 have registered parameters for potassium. The stations with registers of potassium correspond to information for three large rivers, and the monitoring of this parameter started only in 2001.

Based on the procedure described above, three studying sites in São Paulo State were chosen: the regions of Jaú, Pontal and Ribeirão Preto.

The Jaú River basin, located at the central part of São Paulo State, has an area of 417 km2. In this area, it was only possible to evaluate the discharge between 1982 and 1999. During these eighteen years, the area planted with sugarcane increased 20% (regarding the total area) followed by a reduction of pasture area. In the 1990s, sugarcane cropping area represented more than 50% of the total area of the region. The ethanol and sugarcane production is very important to the economy of the cities in the region of Jaú. Three mills of sugar/ethanol are placed close to the Jaú River.

In the regions of Pontal e Ribeirão Preto, with drainage watershed of 12.445 km2 and 10.679 km2, respectively, both the river discharge and the water quality parameters of the Pardo River were analyzed. In those areas, the area planted with sugarcane grew 40% during the period of evaluation of the streamflow (between 1974 and 2011). In 2010, more than 60% of the total area of the Pontal region and around 50% of Ribeirão Preto region were occupied by sugarcane cropping. Seven sugar/ethanol mills are located near the discharge and water quality stations analyzed.

The historical time series provided by the monitoring stations were analyzed using nonparametric procedures. The Mann-Kendall’s test was applied to detect trends, as well as Pettitt’s test to determine abrupt changes. Discharge data were correlated with the sugarcane planted area in each studied region over the years. The main water quality variables analyzed were potassium, total phosphorus, nitrate, nitrite, and ammonium. The concentrations of these parameters were correlated to sugarcane planted area and to the population growth.

According to the test, no trend and no changing point were detected in total annual discharge of the rivers analyzed. In fact, all these time series present better correlation to precipitation series. No significant correlation was observed between sugarcane growth and the river flows.

The quality parameters series in Pardo River showed significant increasing trends, except the potassium concentration for which no trend was observed. However, the parameters evaluated are not only influenced by the agrochemical inputs and vinasse containing nitrogen, as well as phosphorus and potassium due to sugarcane production. The increase on concentrations can be associated to the fertilizers leaching, as well as to the discharge of sewage and industrial effluents without appropriated treatment from urban areas.

Despite the use of appropriate procedures for the analysis of hydrological data, the research results are inconclusive. Among the biggest sugarcane producers, São Paulo State is supposed to be the one with the largest water monitoring network. But even in this case, time series are poor for analyzing the relationship between land use changes and its effects on water resources.

The stations with the largest time series correspond to meso- or large-scale basins. In these areas, several anthropogenic, climatic and geographical factors impact on water resources. So, it is difficult – and in some cases impossible – to isolate the effects of sugarcane expansion on catchment hydrology.

Impact assessments on water quality were also constrained by the shortage of important monitoring parameters related to agriculture practices and to residues from urban areas and from industrial activities. The bulk of quality monitoring stations are in large rivers, and several time series have failures that constrain the assessment along the time. Therefore, based on the database available to São Paulo State it was not possible to determine the impacts of sugarcane expansion on the water resources.

For the proper evaluation of impacts on water resources caused by the expansion of sugarcane activity, using statistical procedures, it would be necessary to monitor specific areas in small-scale watersheds. This would allow proper data gathering in regions where the influence of other factors could be reduced. To make this possible, investments are required for the installation of new gauging stations to expand the network of water controlling stations.

References

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ELIA NETO, A.; ZOTELLI, L.C.; DONZELLI, J.L. Cenários de demanda de água industrial para o setor sucroenergético nas bacias hidrográficas do estado de São Paulo. In: II Congresso Estadual de Comitês de Bacia; 2010. Anais... São Paulo.

GOLDEMBERG, J.; COELHO, S.T.; GUARDABASSI, P. The sustainability of ethanol production from sugarcane. Energy Policy, v. 36, p.2086 - 2097, 2008.

PAIVA, J. B. D., PAIVA, E. M. C. D.(Org.) Hidrologia Aplicada à gestão de pequenas bacias hidrográficas. Porto Alegre: ABRH, 2003. 628 p.

TUCCI, C.E.M., CLARKE, R.T. Impacto das mudanças da cobertura vegetal no escoamento: revisão. Revista Brasileira de Recursos Hídricos, RBRH. V.2, n.1, p. 135-152, 1997.