Patrick Seyler

The Amazon River: behaviour of metals (Fe, Al, Mn) and dissolved organic matter in the initial mixing at the Rio Negro/Solimoes confluence

We studied the changes in major elements and organic carbon concentrations during the initial stage of the mixing of the black (Rio Negro) and the White (Rio Solimoes) waters in the Amazon River basin to understand the geochemical processes that could control the redistribution between particulate and dissolved fractions. Water samples were collected at six stations including the Rio Negro and the Rio Solimoes and four stations downstream from the confluence. The relative contributions of the two tributaries were determined using a triple tracer approach (d 18 O, dD, Cl � ). Particulate (>0.2 Am) and dissolved (<0.2 Am) concentrations of major elements (Ca, Mg, Fe, Al, Si) and organic carbon (POC and DOC) were measured. Major elements in the particulate fraction were found to have a nonconservative behaviour in the initial stage of the mixing due to mineral removal. In the dissolved fraction, only the DOC, Fe, and Mn behaved nonconservatively. The Fe losses could be due to preferential removal of Fe bound to N-rich organic matter (OM) and/or to preferential removal of Fe oxyhydroxides. The increasing dissolved manganese content in the dissolved phase is explained by a reductive dissolution of manganese oxides due to massive inputs of phenolic-rich OM from the Rio Negro. The amount of DOC removed from the water column in the initial stage of the mixing would represent 4% of the total annual DOC flux of the Amazon River at the reference gauging station of Obidos. D 2002 Elsevier Science B.V. All rights reserved.

Isotope studies in large river basins: A new global research focus

Rivers are an important linkage in the global hydrological cycle, returning about 35%of continental precipitation to the oceans. Rivers are also the most important source of water for human use. Much of the worlds population lives along large rivers, relying on them for trade, transportation, industry, agriculture, and domestic water supplies. The resulting pressure has led to the extreme regulation of some river systems, and often a degradation of water quantity and quality For sustainable management of water supply agriculture, flood-drought cycles, and ecosystem and human health, there is a basic need for improving the scientific understanding of water cycling processes in river basins, and the ability to detect and predict impacts of climate change and water resources development.

Rapid neodymium release to marine waters from lithogenic sediments in the Amazon estuary.

Rare earth element (REE) concentrations and neodymium isotopic composition (ɛNd) are tracers for ocean circulation and biogeochemistry. Although models suggest that REE release from lithogenic sediment in river discharge may dominate all other REE inputs to the oceans, the occurrence, mechanisms and magnitude of such a source are still debated. Here we present the first simultaneous observations of dissolved (<0.45 μm), colloidal and particulate REE and ɛNd in the Amazon estuary. A sharp drop in dissolved REE in the low-salinity zone is driven by coagulation of colloidal matter. At mid-salinities, total dissolved REE levels slightly increase, while ɛNd values are shifted from the dissolved Nd river endmember (−8.9) to values typical of river suspended matter (−10.6). Combining a Nd isotope mass balance with apparent radium isotope ages of estuarine waters suggests a rapid (3 weeks) and globally significant Nd release by dissolution of lithogenic suspended sediments.

Hidroquímica do rio Solimões na região entre Manacapuru e Alvarães: Amazonas - Brasil

Este trabalho discute as caracteristicas fisico-quimicas das aguas dos rios Solimoes, Purus e seus afluentes, coletadas em novembro de 2004 no Estado do Amazonas, entre as cidades de Manacapuru-Alvaraes e Anama-Pirarauara. Foram realizadas analises fisico-quimicas (temperatura, pH, condutividade eletrica, turbidez, Ca2+, Na+, K+, Mg2+, HCO3-, SO42-, Cl-), de elementos-traco (Li, B, Al, Sc, V, Cr, Mn, Fe, Co, Cu, Zn, As, Se, Rb, Sr, Mo, Cd, Sb, Cs, Ba, Pb, La, Ce e U) e isotopos de estroncio. Os parâmetros analisados e a composicao quimica mostram que as aguas dos rios e igarapes da regiao central da Amazonia sao quimicamente distintas entre si. As aguas brancas do Solimoes sao calcicas-bicarbonatadas e as do Purus bicarbonatadas, os respectivos afluentes sao sodico-potassico-bicarbonatados e sodico-potassico-sulfatados. Isso acarreta aguas brancas fracamente acidas a neutras e mais condutivas, enquanto as pretas sao menos mineralizadas, mais acidas, especialmente as do Purus. O Ba, Sr, Cu, V e As mais elevados diferenciam as aguas brancas do Solimoes das do Purus, bem como os afluentes do primeiro em relacao ao segundo. Esse conjunto de caracteristicas indicam que tanto o Solimoes, como o Purus e os respectivos afluentes, estao submetidos a condicoes geologicas/ambientais distintas. A influencia do aporte de sedimentos dos Andes e diluida ao longo da bacia do Solimoes e se reflete na formacao das varzeas dos Solimoes e Purus. Por outro lado as rochas crustais, representadas pelos escudos das Guianas e Brasileiro tambem contribuem, mas em menor proporcao.

Seasonal dissolved rare earth element dynamics of the Amazon River main stem, its tributaries, and the Curuaí floodplain

We present a comprehensive dissolved rare earth element (REE) data set for the Amazon River and its main tributaries, Rio Negro, Solimoes, and Madeira, as well as the Curuai floodplain. The two-year time series show that REE vary seasonally with discharge in each of the tributaries, and indicate a hydrologically dominated control. Upper crust normalized REE patterns are relatively constant throughout the year, with Ce/Ce* anomalies being positively related to discharge. We propose revised annual dissolved REE fluxes to the surface Atlantic Ocean based on an integration of the seasonal data. For Nd (<0.22 μm) this results in an average flux of 607 ± 43 T/yr, which is at least 1.6 times larger than the previous estimate of 374 T/yr (<0.45 μm) based on low water stage data. Moreover, during the high water season the maximum Nd flux measures 1277 t.yr−1, constituting 30% of the required flux to the Atlantic Ocean (Tachikawa et al., 2003). Consequently, a smaller contribution of Nd from atmospheric and river particle desorption is required than was previously suggested. A mass balance of Amazon tributaries and observed fluxes at Obidos indicates that dissolved LREE behave quasi-conservatively. Conversely, the HREE mass balance presents a deficit during the high water stages, which could be related to the passage of water through the floodplain system accompanied by solid/dissolved phase transfer.

Synergistic effects of mining and urban effluents on the level and distribution of methylmercury in a shallow aquatic ecosystem of the Bolivian Altiplano

Lake Uru Uru (3686 m a.s.l.) located in the Bolivian Altiplano region receives both mining effluents and urban wastewater discharges originating from the surrounding local cities which are under rapid development. We followed the spatiotemporal distribution of different mercury (Hg) compounds and other metal(oid)s (e.g., Fe, Mn, Sb, Ti and W) in both water and sediments during the wet and dry seasons along a north-south transect of this shallow lake system. Along the transect, the highest Hg and metal(oid) concentrations in both water and sediments were found downstream of the confluences with mining effluents. Although a dilution effect was found for major elements during the wet season, mean Hg and metal(oid) concentrations did not significantly differ from the dry season due to the increase in acid mine drainage (AMD) inputs into the lake from upstream mining areas. In particular, high filtered (<0.45 μm) mono-methylmercury (MMHg) concentrations (0.69 ± 0.47 ng L-1) were measured in surface water representing 49 ± 11% of the total filtered Hg concentrations (THgF) for both seasons. Enhanced MMHg lability in relation with the water alkalinity, coupled with abundant organic ligands and colloids (especially for downstream mining effluents), are likely factors favoring Hg methylation and MMHg preservation while inhibiting MMHg photodegradation. Lake sediments were identified as the major source of MMHg for the shallow water column. During the dry season, diffusive fluxes were estimated to be 227 ng m-2 d-1 for MMHg. This contribution was found to be negligible during the wet season due to a probable shift of the redox front downwards in the sediments. During the wet season, the results obtained suggest that various sources such as mining effluents and benthic or macrophytic biofilms significantly contribute to MMHg inputs in the water column. This work demonstrates the seasonally dependent synergistic effect of AMD and urban effluents on the shallow, productive and evaporative high altitude lake ecosystems which promotes the formation of natural organometallic toxins such as MMHg in the water column.