Nutrient baselines of Cerrado low-order streams: comparing natural and impacted sites in Central Brazil
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The aquatic systems responsible for water supply in the Brazilian Federal District (FD) have been threatened by anthropogenic pressures, especially considering the expressive demographic increase in the region during the last decades. The purposes of this research were: (a) to assess the water quality in streams located in the FD by monitoring physical–chemical variables; (b) to define baselines for these variables among different ecological status categories. The 14 investigated streams were sampled between 2006 and 2009, in the dry (August–September, 2006, 2008, 2009) and rainy (March–April, 2008, 2009) seasons. All sampling sites were classified in four categories (“very impacted”, “impacted”, “in transition” and “natural”) using an adaptation of a rapid habitat assessment protocol. Differences in water quality among sites were generally well predicted in the four ecological status categories defined by the protocol, which showed a gradient in nutrient concentrations from reference sites classified as “natural” (medians: electrical conductivity = 7.3 μS cm−1; nitrate = 0.040 mg L−1; ammonium = 0.039 mg L−1; soluble reactive phosphorus (SRP) = <0.001 mg L−1; total phosphorus (TP) = 0.006 mg L−1; ) to those classified as “very impacted” (medians: electrical conductivity = 87.7 μS cm−1; nitrate = 0.247 mg L−1; ammonium = 0.219 mg L−1; SRP = 0.010 mg L−1; TP = 0.035 mg L−1). Point sources inputs were the main factor for water quality deterioration. The nutrient baselines reported were relatively low when compared to data collected from reference areas in Brazil (e.g., São Paulo State) or temperate regions, especially for TP.
KeywordsMonitoring Nutrients Reference conditions Savanna Tropical limnology
This work was supported by Fundo Nacional do Meio Ambiente (FNMA) (Process 02000.005571/2005-89). We thank the Catholic University of Brasília (UCB) for the scholarships granted to undergraduate students and for the chemical analyses (especially to the environmental engineers Rafael Morgado and Rodrigo Zolini); the Department of Ecology of the University of Brasília (UnB) for the transport during field work, especially the driver Mr. Mardônio Timo; the administration and staff of Águas Emendadas Ecological Station for their support within this conservation unit. We are also grateful to colleagues involved in field and laboratory work, specially the undergraduate students.
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