Intra and interannual variability in the Madeira River water chemistry and sediment load

Abstract

Concentrations of cations (Na ? , Ca 2? , Mg 2? , K ? , NH 4 ? ), anions (HCO 3 -, Cl -, NO 3 -, SO 4 2-, PO 4 3-) and suspended sediments in the Madeira River water were determined near the city of Porto Velho (RO), in order to assess variation in water chemistry from 2004 to 2007. Calcium and bicarbonate were the dominant cation and anion, respectively. Significant seasonal differences were found, with highest concentrations occurring during the dry season, as expected from the drainage of Andean carbonate-rich substratum. Interannual variations were also observed, but became significant only when annual average discharge was 25% less than normal. Under this atypical discharge condition, bicarbonate was replaced by sulfate, and higher suspended sediment concentrations and loads were also observed. Compared to previously published studies, it appears that no significant changes in water chemistry have occurred during the last 20-30 years, although differences in approaches and sampling designs among this and previous studies may not allow detection of modest changes. The calculated suspended sediment load reported here is close to the values presented elsewhere, reinforcing the relative importance of this river as a sediment supplier for the Amazon Basin. Seasonality has a significant control on the chemistry of Madeira River waters, and severe decrease in discharge due to anthropogenic changes, such as construction of reservoirs or the occurrence of drier years-a plausible consequence of global climate change-may lead to modification in the chemical composition as well in the sediment deliver to the Amazon River.

Phosphorus transport by the largest Amazon tributary (Madeira River, Brazil) and its sensitivity to precipitation and damming

“…Discharges in the Madeira River vary considerably between low and high waters ( The drainage area of the Madeira River until Porto Velho (elevation = 42 m asl) is estimated in 976,000 km 2 . At this point, the Madeira River annually transports 319 x 10 6 tons of suspended sediments (Leite et al 2011). At Porto Velho, the average discharge is 19,100 m 3 s -1 (this study), the channel width ranges between 0.6-5.9 km, the depth varies between 7-24 m, and flow velocities range between 0.28-1.23 m s -1 (Bonthius et al 2012).…”

“…With an area of 1.4 x 10 6 km 2 , it covers 23% of the Amazon basin and drains 35% of the Andean Amazon (Guyot et al 1996). The headwaters are located in the Peruvian and Bolivian Andes, where the strong annual variability in precipitation (Villar et al 2009) creates clearly defined flood pulses (Leite et al 2011). Discharges in the Madeira River vary considerably between low and high waters ( The drainage area of the Madeira River until Porto Velho (elevation = 42 m asl) is estimated in 976,000 km 2 .…”

“…Like in the majority of large Amazonian rivers, discharge varies substantially over the year in the Madeira River (Leite et al 2011). As a result, the river water seasonally overflows the banks, depositing nutrient-rich sediments onto the floodplains, ultimately boosting primary production and supporting high biological diversity (McClain and Naiman 2008).…”

Métodos e técnicas de pesquisa em bacias hidrográficas

“…Isso demonstra a importância da vegetação na entrada de nutrientes nos ecossistemas fl orestais até alcançar o solo (LOPES, 2001;TOBÓN;SEVINK;VERSTRATEN, 2004;PROTIL;MARQUES;PROTIL, 2009). O enriquecimento das diferentes formas de Nitrogênio iniciase a partir de processos que ocorrem na atmosfera; no entanto, alguns estudos sugerem que a maior contribuição se dá nos estratos do dossel que contribuem para o enriquecimento na PI (LEITE et al, 2011;HOFHANSL et al, 2011). Na área de fl oresta, o ET foi a via de maior enriquecimento das formas de Nitrogênio, enquanto no sistema cacau-cabruca a principal via foi a PI (p < 0,05).…”

“…O aumento dos nutrientes (NH 4 + e NOD) após a passagem pelo dossel e consequente aumento no rio pode ser explicado pela dissolução na água da chuva de compostos depositados através da lixiviação das copas das árvores (PARKER, 1983;LEITE et al, 2011;JOST et al, 2011;HOFHANSL et al, 2012).…”