Dissolved rainfall inputs and streamwater outputs in an undisturbed watershed on highly weathered soils in the Brazilian cerrado

Abstract

Abstract:The cerrados of Brazil cover 2 million km 2 . Despite the extent of these seasonally dry ecosystems, little watershed research has been focused in this region, particularly relative to the watersheds of the Amazon Basin. The cerrado shares pedogenic characteristics with the Amazon Basin in draining portions of the Brazilian shield and in possessing Oxisols over much of the landscape. The objective of this research was to quantify the stream water geochemical relationships of an undisturbed 1200 ha cerrado watershed for comparison to river geochemistry in the Amazon. Furthermore, this undisturbed watershed was used to evaluate stream discharge versus dissolved ion concentration relationships. This research was conducted in the Córrego Roncador watershed of the Reserva Ecológica do Roncador (RECOR) of the Instituto Brasileiro Geografia e Estatística (IBGE) near Brasilia, Brazil. Bulk precipitation and stream water chemistry were analysed between May 1998 and May 2000. The upland soils of this watershed are nutrient poor possessing total stocks of exchangeable elements in the upper 1 m of 81 š 13, 77 š 4, 25 š 3, and 1 š 1 kg ha 1 of K, Ca, Mg, and P, respectively. Bulk precipitation inputs of dissolved nutrients for this watershed are low and consistent with previous estimates. The nutrient-poor soils of this watershed, however, increase the relative importance of precipitation for nutrient replenishment to vegetation during episodes of ecosystem disturbance. Stream water dissolved loads were extremely dilute with conductivities ranging from 4 to 10 µS cm 1 during periods of high-and low-flow, respectively. Despite the low concentrations in this stream, geochemical relationships were similar to other Amazonian streams draining shield geologies. Discharge-concentration relationships for Ca and Mg in these highly weathered soils developed from igneous rocks of the Brazilian shield demonstrated a significant negative relationship indicating a continued predominance of groundwater baseflow contributions these cationic elements.

Soil changes under different land-uses in the Cerrado of Mato Grosso, Brazil

“…The measured low water conductivity (<10 µS·cm -1 ) supported previous studies at deeply weathered, weakly buffered Cerrado sites (Markewitz et al, 2006;Parron, 2004;Silva et al, 2011;Wantzen, 2003). We expected electrical conductivity to increase due to inverse dilution effects (i.e.…”

Influence of land use changes on water chemistry in streams in the State of São Paulo, southeast Brazil

“…Therefore, the concentration of dissolved oxygen was higher in streams located in Capão Bonito followed by streams in Teodoro Sampaio and Piracicaba and Santa Rita do Passa Quatro ( Figure 3). The values found in stream 6 (located at Santa Rita do Passa Quatro) were lower if compared to other streams in state parks since this area is located under savanna region with presents highly weathered soils and poor nutrient concentrations (Markewitz et al 2006) that reflected in all parameters of water chemistry evaluated in this work (see above). Silva et al (2007) evaluating undisturbed stream in this area reported that land use changes such as sugar cane and eucalyptus contribute to a decrease of physicochemical conditions in savanna watersheds.…”

Effects of land cover on chemical characteristics of streams in the Cerrado region of Brazil

“…Low ion concentrations previously observed in Cerrado region streams under natural cover are a result of the highly weathered soils and their associated low nutrient concentrations (Markewitz et al 2006). Given these low background concentrations, it was hypothesized that increases in dissolved solute loads under anthropogenic land covers would be readily observed.…”