The eutrophication history of a tropical water supply reservoir in Brazil

Author(s)

Fontana, Luciane ^[1] ; Albuquerque, Ana Luiza S. ^[2] ; Brenner, Mark ^{[3, 4]} ; Bonotto, Daniel M. ^[5] ; Sabaris, Tatiani P. P. ^[6] ; Pires, Maria A. F. ^[7] ; Cotrim, Marycel E. B. ^[7] ; Bicudo, Denise C. ^[1]

Affiliation

^[1] Inst Bot, Dept Ecol, BR-04301012 Sao Paulo - Brazil

^[2] Univ Fed Fluminense, Inst Quim, Dept Geoquim, BR-24020015 Niteroi, RJ - Brazil

^[3] Univ Florida, Dept Geol Sci, Gainesville, FL 32611 - USA

^[4] Univ Florida, Land Use & Environm Change Inst, Gainesville, FL 32611 - USA

^[5] Inst Geociencias & Ciencias Exatas, Dept Petrol & Metalogenia, BR-13506900 Rio Claro, SP - Brazil

^[6] Univ Santa Cecilia, Unisanta, BR-11045097 Santos, SP - Brazil

^[7] IPEN CNEN SP, Ctr Quim & Meio Ambiente, BR-05508000 Sao Paulo - Brazil

• Document type: Journal article
• Source: JOURNAL OF PALEOLIMNOLOGY; v. 51, n. 1, p. 29-43, JAN 2014.
• Web of Science Citations: 25

Abstract

Guarapiranga Reservoir is the second most important public water supply in So Paulo, Brazil and has been eutrophic for several decades. We inferred the major ecological shifts for the period 1919-2010 related to multiple stressors (forest flooding, hydrological change, use of algicide and eutrophication), using geochemistry (TOC, TN, TP, C/N, delta N-15, delta C-13) and diatom assemblages in a short (75-cm) sediment core. Thirty-two diatom species were abundant in the core and stratigraphically constrained incremental sum of squares analysis enabled identification of three diatom zones and four subzones, i.e. depths at which marked changes in species composition occurred. Early diatom assemblages were dominated by benthic, oligotrophic taxa, mainly Eunotia, influenced by flooded vegetation after dam construction. A shift to dominance by a planktonic species (Eunotia tukanorum) occurred ca. 1932, during the period of initial physical disturbance and early use of the water body as a public water supply. Diatoms and geochemical variables show that the reservoir was oligotrophic from similar to 1919 to 1947. Eutrophication began similar to 1975 and by the early 1980s the reservoir had become eutrophic, in response to an explosive increase in human population in the watershed. Severe cultural eutrophication has persisted since similar to 1990. Higher concentrations of copper in the sediments, beginning in 1991, reflect the increased use of copper sulfate to control cyanobacteria blooms and provide a chronological marker. Higher delta N-15 values in recent sediments indicate greater sewage inputs and low C/N values reflect the predominant contribution of algae to sediment organic matter. Eutrophic taxa Cyclotella meneghiniana and Nitzschia sp. dominate recent diatom assemblages, along with Aulacoseira granulata, a species that is tolerant of copper sulfate. Diatom assemblages reflect multiple stressors, however, geochemical information provides a better understanding of the early phase of the reservoir. Paleolimnologically documented trophic state changes in this important drinking water supply are largely attributable to increased urbanization of the drainage basin and inputs of sewage. Management efforts should focus on mitigating this nutrient source. (AU)

• FAPESP's process: 09/53898-9 - Paleolimnological reconstruction of Guarapiranga Reservoir and diagnosis of water and sediment current quality of SPMR water supply reservoirs facing their management
• Grantee: Carlos Eduardo de Mattos Bicudo
• Support Opportunities: Research Projects - Thematic Grants