Evidence of long term biogeochemical interactions in carbonate weathering: The role of planktonic microorganisms and riverine bivalves in a large fluviokarst system.

The infiltration of organic-rich surface waters towards groundwaters, is known to play a significant role in carbonate weathering and in contributing to the atmospheric continental carbon sink. This paper investigated biogeochemical interactions in karst critical zones, with strong surface water /groundwater interactions, and in particular the role of planktonic microorganisms and riverine bivalves through the analysis of particulate organic matter (OM) oxidation on carbonate weathering. In the large Val d'Orléans fluviokarst aquifer (France), a 20-year monthly dataset of Nitrates, Dissolved Oxygen (DO), dissolved inorganic and organic Carbon (DIC and DOC) fluxes was gathered. The surface water-groundwater comparison of geochemical trends showed that planktonic microorganisms had drastically decreased in surface waters, related to the proliferation of Corbicula bivalves spreading and a decrease in nutrients. This decrease in planktonic microorganisms was followed by a DO increase and an DIC decrease at the karst resurgence. The degradation of planktonic microorganisms consumes DO and produces NO3, dissolved inorganic carbon (DIC) and a proton that in turn, dissolves calcite and produces DIC. Without the input from planktonic microorganisms, the fluviokarst has lost 29 % of this nitrification and 12 % of the carbonate dissolution capacities. Thus, the oxidation of particulate organic matter of planktonic microorganisms, which is part of heterotrophic respiration, appears to be a significant source of the inorganic carbon flux in riverine ecosystems. This shows how weathering can remain active under waters saturated versus calcite and suggests that the oxidation of organic matter can be a more appropriate mechanism than autotrophic respiration to explain the relationship between global warming and DIC flux change in rivers. Through the consumption of plankton, the animal life in rivers thus influences the inorganic carbon in groundwaters, creating a negative feedback in the carbon cycle.

Amazon River dissolved load: temporal dynamics and annual budget from the Andes to the ocean.

The aim of the present study is to estimate the export fluxes of major dissolved species at the scale of the Amazon basin, to identify the main parameters controlling their spatial distribution and to identify the role of discharge variability in the variability of the total dissolved solid (TDS) flux through the hydrological cycle. Data are compiled from the monthly hydrochemistry and daily discharge database of the "Programa Climatologico y Hidrologico de la Cuenca Amazonica de Bolivia" (PHICAB) and the HYBAM observatories from 34 stations distributed over the Amazon basin (for the 1983-1992 and 2000-2012 periods, respectively). This paper consists of a first global observation of the fluxes and temporal dynamics of each geomorphological domain of the Amazon basin. Based on mean interannual monthly flux calculations, we estimated that the Amazon basin delivered approximately 272 × 10(6) t year(-1) (263-278) of TDS during the 2003-2012 period, which represents approximately 7 % of the continental inputs to the oceans. This flux is mainly made up by HCO3, Ca and SiO2, reflecting the preferential contributions of carbonate and silicate chemical weathering to the Amazon River Basin. The main tributaries contributing to the TDS flux are the Marañon and Ucayali Rivers (approximately 50 % of the TDS production over 14 % of the Amazon basin area) due to the weathering of carbonates and evaporites drained by their Andean tributaries. An Andes-sedimentary area-shield TDS flux (and specific flux) gradient is observed throughout the basin and is first explained by the TDS concentration contrast between these domains, rather than variability in runoff. This observation highlights that, under tropical context, the weathering flux repartition is primarily controlled by the geomorphological/geological setting and confirms that sedimentary areas are currently active in terms of the production of dissolved load. The log relationships of concentration vs discharge have been characterized over all the studied stations and for all elements. The analysis of the slope of the relationship within the selected contexts reveals that the variability in TDS flux is mainly controlled by the discharge variability throughout the hydrological year. At the outlet of the basin, a clockwise hysteresis is observed for TDS concentration and is mainly controlled by Ca and HCO3 hysteresis, highlighting the need for a sampling strategy with a monthly frequency to accurately determine the TDS fluxes of the basin. The evaporite dissolution flux tends to be constant, whereas dissolved load fluxes released from other sources (silicate weathering, carbonate weathering, biological and/or atmospheric inputs) are mainly driven by variability in discharge. These results suggest that past and further climate variability had or will have a direct impact on the variability of dissolved fluxes in the Amazon. Further studies need to be performed to better understand the processes controlling the dynamics of weathering fluxes and their applicability to present-day concentration-discharge relationships at longer timescales.

Spatial-temporal variation of dissolved inorganic material in the Amazon basin / Variação espaço-temporal do material inorgânico dissolvido na bacia Amazônica

The Amazon River basin is important in the contribution of dissolved material to oceans (4% worldwide). The aim of this work was to study the spatial and the temporal variability of dissolved inorganic materials in the main rivers of the Amazon basin. Data from 2003 to 2011 from six gauging stations of the ORE-HYBAM localized in Solimões, Purus, Madeira and Amazon rivers were used for this study. The concentrations of Ca2+, Na+, K+, Mg2+, Cl-, SO4 -2, HCO3 - and SiO2 were analyzed. At the stations of Solimões and Amazon rivers, the concentrations of Ca2+, Mg2+, HCO3 - and SO4 -2 had heterogeneous distribution over the years and did not show seasonality. At the stations of Madeira river, the concentration of these ions had seasonality inversely proportional to water discharge (dilution-concentration effect). Similar behavior was observed for the concentrations of Cl- and Na+ at the stations of the Solimões, Amazon and Madeira rivers, indicating almost constant release of Cl- and Na+ fluxes during the hydrological cycle. K+ and SiO2 showed almost constant concentrations throughout the years and all the stations, indicating that their flows depend on the river discharge variation. Therefore, the temporal variability of the dissolved inorganic material fluxes in the Solimões and Amazon rivers depends on the hydro-climatic factor and on the heterogeneity of the sources. In the Madeira and Purus rivers there is less influence of these factors, indicating that dissolved load fluxes are mainly associated to silicates weathering. As the Solimões basin contributes approximately 84% of the total flux of dissolved materials in the basin and is mainly under the influence of a hydro-climatic factor, we conclude that the temporal variability of this factor controls the temporal variability of the dissolved material fluxes of the Amazon basin.

A bacia do rio Amazonas é importante no aporte de material dissolvido para o oceano (4% a nível mundial). O objetivo deste trabalho foi estudar a variabilidade espaço-temporal do material inorgânico dissolvido nos principais rios da bacia Amazônica, para o qual foram utilizados dados entre 2003 e 2011 de seis estações hidrológicas do ORE-HYBAM localizadas nos rios Solimões, Purus, Madeira e Amazonas, analisados Ca2+, Na+, K+, Mg2+, Cl-, SO4 -2, HCO3 - e SiO2. Nas estações do rio Solimões e Amazonas as concentrações de Ca2+, Mg2+, HCO3 - e SO4 -2 tiveram distribuição heterogênea ao longo dos anos e não apresentaram sazonalidade. Nas estações do rio Madeira a concentração desses íons mostraram sazonalidade inversamente proporcional à vazão (efeito diluição-concentração). Comportamento similar tiveram Cl- e Na+ nas estações dos rios Solimões, Amazonas e Madeira, indicando liberação quase constante desses fluxos ao longo do ciclo hidrológico. K+ e SiO2 apresentaram concentrações quase constantes ao longo dos anos e entre as estações, indicando que seus fluxos dependem da variação da vazão. Portanto, a variação temporal do fluxo de material inorgânico dissolvido no rio Solimões e Amazonas depende do fator hidroclimatológico e da heterogeneidade das fontes. Nos rios Madeira e Purus há menor influência desses fatores, o que evidencia maior aporte dos silicatos. Como a bacia do Solimões aporta aproximadamente 84% do fluxo total de material dissolvido na bacia e está sob influência, principalmente, do fator hidroclimático, pode-se concluir que a variabilidade temporal desse fator controla a temporalidade dos fluxos do material dissolvido na bacia Amazônica.

Geoquímica de rios de água preta do sudeste do Amazonas: origem, fluxo dos elementos e consumo de CO2 / Geochemistry of black water rivers from the southeastern of the Amazonas State: source, element fluxes and consumption of CO2

This work examined the chemical composition of waters from tributaries of the right bank of the Madeira River which drain silicaterocks of the Brazilian Craton. The study was conducted at the municipalityof Apui, in the southeastern of the Amazonas State, Brazil. There were analyzed pH, conductivity, SiO2 and dissolved ions (Na+, K+, Mg2+ e Ca2+, HCO3-, Cl-, NO3- and SO4(2-)) in the four pluviometric seasons of the Amazon region: rainy, transition to the dry, dry and transition to the rainy. The waters are diluted, have high HCO3-and SiO2 concentration and represent the typical environment of intense leaching that affects the rocks in the Amazon. Although the chemical composition reveals seasonal influences, it was identified variation due to lithological composition. The rate of exportation of cations and the chemical erosion are low in consequence of the tectonic stability of the region and the weathering mantle, which hinders the interaction of water with the bedrock.

Neste trabalho foi examinada a composição química das águas dos afluentes da margem direita do rio Madeira que drenam as rochas do Escudo Brasileiro. O estudo foi realizado no município de Apuí no sudeste do estado do Amazonas, Brasil. Foram analisados pH, condutividade, as concentrações de SiO2 e de íons dissolvidos (Na+, K+, Mg2+, Ca2+, HCO3-, Cl-, NO3- e SO4(2-)) em quatro épocas do ano segundo o índice pluviométrico: chuvosa, transição para a estiagem, estiagem e transição para a chuvosa. As águas são diluídas, mais concentradas em HCO3- e SiO2 e representam o típico ambiente de intensa lixiviação que afeta as rochas na Amazônia. Apesar da química das águas terem influência da sazonalidade, foram identificadas variações em função da litologia. As taxas de exportação de cátions e de erosão química das rochas são baixas e refletem a estabilidade tectônica da região e o manto intempérico que dificulta a interação da água com o substrato rochoso.