Latin American Journal of Sedimentology and Basin Analysis ISSN: 1669-7316 [email protected] Asociación Argentina de Sedimentología Argentina

Fonseca DUARTE, Alejandro; GIODA, Adriana INORGANIC COMPOSITION OF SUSPENDED SEDIMENTS IN THE RIVER, AMAZON BASIN, Latin American Journal of Sedimentology and Basin Analysis, vol. 21, núm. 1, 2014, pp. 3- 15 Asociación Argentina de Sedimentología Buenos Aires, Argentina

Available in: http://www.redalyc.org/articulo.oa?id=381739311002

How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative LATIN AMERICAN JOURNAL OF SEDIMENTOLOGY AND BASIN ANALYSIS | VOL. 21 (1) 2014, 3-15 © Asociación Argentina de Sedimentología - ISSN 1851-4979

INORGANIC COMPOSITION OF SUSPENDED SEDIMENTS IN THE ACRE RIVER, AMAZON BASIN, BRAZIL

Alejandro Fonseca DUARTE 1 and Adriana GIODA 2

1 Federal University of Acre (UFAC), Department of Natural Sciences, CEP: 69.920-900, Rio Branco, AC, Brazil, [email protected] 2 Pontifical Catholic University (PUC-Rio), Department of Chemistry, CEP: 22.451-900, Rio de Janeiro, RJ, Brazil, [email protected]

Abstract: The purpose of this study was to determine the chemical and mineralogical composition of suspended sediments from the Acre River, located in the Purus Basin, upper Amazon basin, a region associated with the Fitzcarrald Arch. The elemental and mineralogical compositions of the sediments were assessed by using mass and atomic spectroscopy, and X-ray diffraction. A total of 46 samples were collected between 2008 and 2011 from four sites in the study area during wet and dry seasons. The suspended sediments contained feldspar, kaolinite, illite and quartz as well as the elements Hg, Zn, V, Ti, Si, Pb, Ni, Na, Mn, Mg, K, Fe, Cu, Cr, Cd, Ca, Al, S, and P in different proportions that were associated with the various weathering reactions linked to physical, chemical and biological processes in the region. The obtained results represent the first set of values and relationships regarding the mineralogy and chemical identification of the suspended sediments in the Acre River and can be used as a reference for the geochemical characteristics of the Purus Basin. Such regional studies will become increasingly necessary to observe the impacts of climate change and human activities on the suspended sediment load and composition of the Amazon River.

Keywords: chemistry of sediments, Amazon Basin, Acre River Basin.

km2 (Filho, 2005), and that of the Purus basin is INTRODUCTION 370,000 km2 (Paiva and Collischonn, 2012). The The Amazon River flows from the Andean begins in Peru at an altitude of 400 – Mountains to the Atlantic Ocean. The Amazon 500 m a.s.l. and runs for 3,300 km with a mean rainforest is the largest hydrographic basin in water discharge of 10,499 m3 s-1 (ANA, 2011). The the world and has been described in terms of its drainage area of the Acre River basin covers 35,000 dimension, biodiversity, floods, droughts, rainfall km2, and its discharge varies between 30 and 1,200 variability (Villar et al., 2009) and projected climate m3 s-1. change (Chen et al., 2010; Fekete et al., 2010; The Acre River basin is affected by forest fires, Salazar and Nobre, 2010). Suspended sediment logging, agriculture and cattle production, which (SS) composition and flux (Bouchez et al., 2011), are the principal branches of the local economy. The as well as water quality are highly important for annual average rainfall in the region is 1,956 ± 223 ecological equilibrium (Berry et al., 2003), which mm, according to 1971 – 2000 climatology (Duarte, involves aquatic, terrestrial, atmospheric, oceanic 2006). The climate of the Amazon is characterized and estuarine interactions. by the occurrence of two principal meteorological The drainage area of the Amazon basin is 6.4·106 systems: the Intertropical Convergence Zone (ITCZ)

Received August 31, 2013 - Accepted April 12, 2014 3 Alejandro Fonseca DUARTE and Adriana GIODA

Figure 1. Map of the Amazon basin showing the Fitzcarrald Arch, Solimões (Juruá, Purus) and Madeira basins. Inset: Acre River basin is shown in detail. B, X, P, R refers to the sampling location: Brasileia (B, 11°1.4ʼ S; 68°44.0ʼ W), (X, 10°38.9ʼ S; 68°30.4ʼ W), Rio Branco (R, 9°58.7ʼ S; 67°48.4ʼ W) and Porto Acre (P, 9°34.5ʼ S; 67°31.9ʼ W).

and the South Atlantic Convergence Zone (SACZ), Wang et al., 2011). Biomass burning, deforestation which are modulated by the natural inter-annual and fertilization produce materials entering the river variability related to El Niño and La Niña (Pizarro system and contributing to the composition of the and Montecinos, 2004; Marengo, 2008; Chiessi et al., suspended sediment (Zhang et al., 1999; Druffel 2009; Jury, 2009; Meehl et al., 2009). et al., 2005; Figueiredo et al., 2010). In the upper Townsend-Small et al. (2008) attributed the Amazon basin and particularly in the Madeira basin, Andean sediment loads (particularly those of gold-mining operations release large quantities of Hg organic sediments) to episodic events of heavy into the atmosphere, water and soils (Diaz, 2000; rainfall or storms. The mechanical erosion rate and Maurice-Bourgoin et al., 2000; Fillion et al., 2006). sediment fluxes due to weathering are related to Furthermore, the transport of particulate matter via precipitation, runoff, temperature, winds, humidity, rivers could be altered by dam constructions in the basin morphology and other climatic and physical Amazon basin (Kemenes et al., 2012). influences (Hurtrez et al., 1999; Gartner et al., 2008; The Acre River originates in Peru, then delimits Zoccatelli et al., 2011; Govin et al., 2012). Persson Peru, Bolivia and Brazil and runs through the State of (2008) confirmed that as a general rule, sediment Acre to join the Purus River, which is the main river samples increase in roundness, sphericity and that drains the Fitzcarrald Arch (Fig. 1). Riverbank- quartz content downstream from the Andes. erosion processes, transport and deposition of Elements such as Si, Mg, Fe, Al, Ca, Ti, and K are sediment in the floodplains and sediment re- found in river bed and in the suspended sediment in entrance in the river flux play fundamental roles different proportions (Mcdonough, 2000; Govin et al., in the geochemistry of suspended matter due to 2012), depending on geographical distribution and the structural dynamics of the region. According to redistribution factors, such as geological formations, Guyot et al. (2007), most of the suspended sediment parental rocks, mineralogy, soils, topography, land originates in the Andes Mountains and crosses the use, land cover, climate and climate change (Zhang Amazon floodplains before reaching the Atlantic et al., 1999; Liu et al., 2007; Yoshikawa et al., 2008; Ocean. The geological formation of the Purus

4 LATIN AMERICAN JOURNAL OF SEDIMENTOLOGY AND BASIN ANALYSIS | VOL. 21 (1) 2014, 3-15 Inorganic composition of suspended sediments in the Acre River, Amazon Basin, Brazil basin corresponds to the Cenozoic Solimôes (sub- Wet SS (mg L-1) Dry SS (mg L-1) Andean trough and Andean foreland in Central P 13/11/08 502 P 11/07/08 501 Amazon). Thus, in this region, the mineralogical P 28/11/08 503 P 24/10/08 140 and chemical composition of the SS should have common characteristics. The SS particularities are R 30/11/08 500 X 25/10/08 500 better established for Solimões and Madeira Rivers P 10/12/08 336 B 25/10/08 210 than for the Purus River; therefore, the objective R 27/12/08 500 R 30/10/08 501 of the present paper was to determine the SS load, seasonality and, mineralogical and chemical P 20/01/09 500 R 28/05/09 494 composition of the Acre River (Purus basin) as well X 24/01/09 381 P 06/06/09 122 as its regional connection. R 30/01/09 502 R 28/06/09 410 R 25/02/09 375 P 25/07/09 142 P 13/03/09 500 R 30/07/09 415 MATERIALS AND METHODS R 31/03/09 546 P 15/08/09 114 The study area comprises the Acre River basin R 29/04/09 507 R 25/08/09 154 (part of the Purus basin, Fitzcarrald Arch), bordered R 24/11/09 501 R 28/09/09 149 by the Andean Mountains and the Juruá, Solimôes P 09/12/09 512 P 10/10/09 457 and Madeira Rivers (Fig. 1). The white waters of R 23/12/09 551 R 20/10/09 156 the Amazon River begin in the elevated parts of the Fitzcarrald Arch, initiating the erosion processes R 20/01/10 161 R 20/05/10 77 and high sediment load that muddies the rivers. R 23/02/10 226 R 20/06/10 502 The study area contains the following classes of R 22/03/10 437 R 20/07/10 102 soil: cambisols, vertisols, luvisols, acrisols, ferralsols R 20/04/10 75 R 20/08/10 92 and plinthosols (Amaral, 2003; EMBRAPA, 2006; R 20/11/10 502 R 20/09/10 35 FAO, 2007). The sampling procedures have been R 20/12/10 500 R 20/10/10 336 previously described (WMO, 1994). Surface water samples were collected during the wet (rainy) and dry R 20/01/11 325 seasons from four sampling sites (Fig. 1): Brasileia, P 24/01/11 354 Xapuri, Rio Branco and Porto Acre. The sampling R 20/02/11 287 points were located in a well-mixed reach of stream R 20/03/11 227 whose width, depth and velocity ranged from 100 to 200 m, 2 to 12 m, and 0.5 to 1.8 m s-1, respectively. Table 1. Suspended sediment concentration in the Acre River Samples were collected with 1-L plastic bottles that in the dry and wet seasons between 2008 and 2011. B, R, P, were immersed 15 to 30 cm under the water surface. and X as in figure 1. Depth-profiling of SS was not measured. A total of 46 samples were obtained: 25 in the wet season and 21 in the dry season. The sediment yield QS (mega resultant solution was diluted 5 to 100 times for tons per year) was calculated using the following elemental analysis (Tessier et al., 1979; Gioda et al., formula: 2006; Gioda et al., 2011). The chemical composition of the samples was determined using inductively QS (Mt y-1) = SS (g l-1) R (Gm3 y-1) (1) coupled plasma mass spectroscopy (ICP-MS - Elan 6000, Perkin Elmer, USA) to measure the total Hg where: SS is suspended sediment concentration level and using inductively coupled plasma optical (grams per liter) and R is the integral water discharge emission spectrometry (ICP-OES - Optima 4300 DV, (giga cubic meters per year). Perkin Elmer, USA) for the other elements. Hg was The suspended sediment in the river water was measured as a total because this species is volatile, dried (50 – 60ºC) for approximately 15 h. Next, and certain losses could have occurred between the material was homogenized and weighed. The sampling and analysis. For Ti, the acid digestion sediments were digested by adding 2.5 mL HNO3, with HNO3 was inefficient, extracting approximately heating for 5 h at 80ºC and centrifuging. The 5%. Therefore, for these elements (Hg and Ti), the

LATIN AMERICAN JOURNAL OF SEDIMENTOLOGY AND BASIN ANALYSIS | VOL. 21 (1) 2014, 3-15 5 Alejandro Fonseca DUARTE and Adriana GIODA detected concentrations may be underestimates. The accuracies of the employed methods were evaluated using spiked blanks of known metal concentration and a standard reference material (SRM, MESS-1, NRC Institute for National Measurement Standards). The recovery efficiency ranged from 40% (Mn and V) to 90 – 100% (Pb and Zn). The average recovery for most of the metals was 70 – 80%. A calibration check was performed after each set of 14 samples. The detection limit ranged from 0.02 to 0.80 ng L-1. The mineralogical composition of the samples was analyzed using X-ray powder diffraction (XRD - Diffractometer Ultima IV, Rigaku Americas Corporation, USA). Qualitative analysis of the samples was performed via continuous records (5o o o ≤ 2θ ≤ 80 , Δ2θ = 0.05 ) using Cu Kα radiation (λ = 1.540562 Å) and a Kβ Ni filter. The minerals were identified by comparison of the XRD experimental patterns with standards in the Mineralogy Database Figure 2. Seasonality of SS concentration in the Acre River (http://webmineral.com/) and the literature (Albers from 2008 to 2011. Gray bars denote the dry season interval, et al., 2002). from May to October, when the lowest SS concentrations were frequently observed.

RESULTS

The seasonal SS concentration values are shown also presented strong correlations: the Pb, V and in table 1. The SS was significantly greater during Ni levels were correlated (r = 0.8), and the levels the wet season than in the dry season according to of V and Ni were also strongly correlated with Cr, the results of a t-test at the 0.05 significance level. Cd, and Cu (r = 0.6 – 0.9). However, Hg showed no The seasonal behavior of SS concentration is not correlations with these species. Fe, Al, Mg, and Si uniform as shown by the distribution of values in are predominant in silicate minerals, but there was figure 2. no correlation among the concentration of these elements in the SS samples, with the exception of Mg and Al (r = 0.9). Chemical and mineralogical composition For all the studied sites, the X-ray diffractograms The chemical composition of the suspended of the SS samples display characteristic peaks of sediment of the Acre River is shown in table 2. The quartz, kaolinite, and illite, as illustrated in figure major elements were Fe, Al and Ca, with average 3. Quartz, kaolinite and illite were previously found concentrations of 27,232 mg kg-1, 10,808 mg kg-1, in suspended sediment, in the Purus and Juruá and 5,354 mg kg-1, respectively. In contrast, the basins (Martinelli et al., 1993; Carvalho et al., 2005). lowest concentrations were measured for Hg, Cd, Minerals as feldspar, Na-plagioclase, Ca-plagioclase and Ti with values of 1.54 mg kg-1, 1.91 mg kg-1, and and smectite-vermiculite were also found in the SS 3.33 mg kg-1, respectively. Other elements detected in Amazonian rivers (Allard et al., 2002). in high concentrations were Mg, K, Mn, Si, P, and S. The ratio of X/Al (where X = Mg, Ca, Na and K) Strong correlations among certain elements denotes the weathering index as a function of Al/Si, suggest similar sources, as noted for P and S (r = which exhibits the linear trend shown in figure 4, 0.9), as well as for Ca and Mg (r = 0.9). Phosphorus where the slopes of the lines are close to zero. The in SS indicates anthropogenic origin. Fertilizers are Pearson correlation coefficient indicates a strong a source of P to water courses through leaching and association of the Mg/Al and Ca/Al ratios with the runoff, especially for Al- and Fe-rich soils, which are Al/Si and a weak association of the Na/Al and K/Al characteristic of the Purus Basin. Other elements ratios with the Al/Si. Bouchez et al. (2011) had been

6 LATIN AMERICAN JOURNAL OF SEDIMENTOLOGY AND BASIN ANALYSIS | VOL. 21 (1) 2014, 3-15 Inorganic composition of suspended sediments in the Acre River, Amazon Basin, Brazil explained the dilution processes in a mineralogical mixing with quartz and clay minerals, such as illite, kaolinite, alkali-feldspar and others.

DISCUSSION

Seasonality and composition of suspended sediment

The seasonal SS concentration in the Acre River follows the annual behavior of rainfall and water discharge. The maximum values ranges from 450 to 550 mg L-1 during the wet season when the water discharge ranges from 800 to 1200 m3 s-1, and the minimum values were measured during dry season, Figure 3. X-ray diffractograms of the Acre River SS with when the water discharge ranges from 30 to 450 m3 peaks of quartz (qtz), kaolinite (kln) and illite (ill). Identical s-1. The high water discharge induces erosion of patterns were obtained for all the sampling sites. the river borders and soils and also promotes the re-entrance of the floodplain sediments into the river, increasing the SS load in the wet season. Lack sediment chemical concentration were Fe, Al, Ca, of uniformity in SS seasonality had been noticed Mg, K, Mn, Si, P, and S. In contrast, the lowest by Meade (1994) in relation to large rivers, but in concentrations were measured for Hg, Cd, and Ti. the case of the Acre River, it can be influenced by The measured concentrations of Hg, Pb, Fe, S, and P anthropogenic movement of matter into the river were significantly greater in the dry season than in system due to suppression of the vegetation in the wet season. The high concentrations of elements areas adjacent to the river (Machado, 2011). The in SS are evidence of severe weathering of Amazon reported mean yearly R values of the Acre River in soils. Weathering processes follow deforestation Rio Branco and at the confluence with the Purus and burning with multiple responses. As referenced River are 8.9 and 13.7 Gm3, respectively (Duarte, by Lindgren and Röttorp (2009) the influence of 2010). Using eq. (1), the QS in Rio Branco is 2.7 Mt deforestation disturbances on soil erosion and y-1, and at the confluence with Purus River, the QS leaching of substances are complex and dependent is 4.1 Mt y-1. The Purus River discharge is 10 – 15 on each specific site and factors such as soil times greater than that of the Acre River. According texture, topography, vegetation, land management to the proportionality between the sediment load history, climate, atmosphere deposition, etc. Forest and discharge, the load of sediment carried by dynamics in the Amazon show different influences the Purus River is approximately 25 – 40 Mt y-1. on chemical element mobilization, such as slash Observations conducted at the mouth of the Amazon and burn agriculture, intense rainfalls, forest to River indicate a broad interval for estimated values pasture conversion, leaching and surface runoff between 0.6 and 1.3 Gt y-1 of sediment load (Filizola and erosion, elevated export of solids and solute, et al., 2009; Villar et al., 2011). Erosion of rocks volatilization of S, alteration in the P cycle, reduced containing quartz and clay minerals and weathering soil acidity and increased concentrations of Ca and of cambisols, vertisols, luvisols, acrisols, ferralsols, of the trace elements Cu, Pb, Hg, and Ni (Lindell, and plinthosols, in conjunction with deforestation 2011). It has been observed that Hg does not have and use of slash and burning to transform vegetation an appreciable presence in the region (Mascarenhas into pasture for cattle and agriculture, as well as et al., 2004; Siqueira and Aprile, 2012). The Hg water transport, are the sources of the chemical concentration in the SS of the Acre River could be composition and diversity of concentration of the a result of atmospheric deposition following the SS, characterizing the sediment particles in the open-air amalgamation step of gold mining through upper Amazon of the Acre River, Purus Basin. which up to 170 t y-1 of Hg vapor is released to the The major elements present in the suspended Amazon atmosphere (Diaz, 2000). In addition, the

LATIN AMERICAN JOURNAL OF SEDIMENTOLOGY AND BASIN ANALYSIS | VOL. 21 (1) 2014, 3-15 7 Alejandro Fonseca DUARTE and Adriana GIODA P 83.42 506.27 447.64 470.43 450.51 609.09 443.79 878.84 498.54 427.13 508.79 456.39 339.47 485.23 375.74 465.46 469.75 492.48 518.25 576.17 717.88 540.24 579.31 464.93 498.28 S 14.36 238.00 161.88 396.22 200.08 467.47 225.56 920.13 335.86 154.22 264.96 128.55 130.24 135.81 132.81 276.43 194.48 245.72 216.94 445.44 512.46 259.04 219.69 238.30 238.01 Al ND 9410.96 8989.38 8390.19 9030.98 9897.58 9075.72 8739.16 11153.33 11839.75 10572.30 12519.20 12484.17 13222.07 10617.39 10804.25 12406.09 12656.22 10794.17 15089.98 10656.39 10259.81 13757.35 12252.59 12790.06 Ca ND 4985.89 5729.46 4917.37 5353.84 4575.03 6447.51 4351.09 5131.17 4591.98 5908.39 4770.76 5393.12 6241.61 4527.05 5057.79 7142.69 4841.66 4522.13 5737.97 6399.34 5069.01 5181.10 4793.84 4518.18 Cd ND 1.95 2.42 1.25 2.16 1.21 2.04 1.10 2.62 1.47 2.06 1.18 2.24 1.80 1.92 1.17 2.05 2.00 2.02 1.40 2.58 2.33 3.50 1.13 1.22 Cr ND 13.61 15.32 10.81 15.37 10.34 14.60 10.10 12.87 13.51 15.27 10.43 15.21 15.31 14.62 12.46 14.57 14.80 15.65 12.29 14.49 15.21 16.19 10.35 12.27 Cu ND 15.04 18.92 18.96 18.11 19.81 17.94 23.96 18.67 22.05 16.79 19.67 19.45 19.93 15.01 19.31 22.73 20.23 20.11 18.91 32.96 23.51 22.02 18.54 17.21 Fe 23130.31 26007.10 24816.47 34609.03 23479.03 27777.77 22071.06 24191.14 22666.56 26712.89 21769.63 25212.90 24934.11 24182.17 30290.48 21952.44 22753.72 26331.38 25426.71 28000.71 37796.58 25723.32 28482.46 22305.72 23618.71 K ND 973.55 997.01 982.13 936.40 929.22 1152.11 1311.21 1176.98 1018.69 1427.40 1646.51 4329.29 1248.56 1035.10 1343.89 1064.05 1284.46 1534.08 1296.84 1175.59 1338.98 2165.01 2565.99 1723.32 Mg ND 2334.58 3045.00 2546.50 2558.68 2394.28 2621.09 2259.99 2193.75 2500.54 2788.90 2545.24 2719.63 3126.07 2376.53 2675.87 3777.66 2529.84 2506.29 2566.53 3154.77 2801.04 2525.88 2287.44 2259.15 ND Mn 849.70 789.97 580.81 781.83 971.89 709.86 976.07 929.08 784.88 646.79 773.84 741.03 832.78 921.68 751.85 982.42 973.34 643.47 883.35 1173.43 1056.74 1231.77 1060.31 1020.74 Na ND 36.66 53.73 80.33 51.50 46.11 50.77 16.62 43.75 40.10 20.89 88.40 27.67 39.76 36.39 124.31 162.36 106.85 139.36 137.70 134.66 133.98 160.32 121.33 132.55 Ni ND 20.55 23.19 17.83 18.74 16.48 20.53 18.20 23.10 17.85 24.22 19.27 23.20 20.98 19.37 18.91 23.74 22.01 21.30 19.63 21.68 25.20 22.52 15.86 16.86 Pb ND 11.05 11.54 13.16 14.51 12.21 11.12 10.96 14.64 10.32 17.52 11.21 13.08 10.86 15.74 19.21 12.63 12.21 13.53 11.56 11.84 20.19 16.89 10.66 15.04 Si ND 97.06 111.24 112.18 114.95 141.55 224.65 146.23 257.81 155.75 220.22 115.87 125.55 703.50 125.62 136.85 129.28 152.57 144.42 138.62 605.38 137.18 158.48 122.09 124.41 ) of suspended sediment in the Acre River in the wet and dry seasons between 2008 2011. Note: ND – Not determined. ) of suspended sediment in the Acre Ti -1 ND 2.28 3.37 2.18 4.38 3.11 3.35 2.64 2.73 4.17 2.99 2.82 2.67 3.44 2.31 2.80 3.10 3.00 0.82 3.36 2.80 2.54 1.46 1.64 23.49 V ND 20.42 24.23 21.44 24.17 20.96 27.59 18.73 28.90 19.90 23.46 20.51 23.59 22.93 21.26 21.13 24.64 25.36 23.34 28.43 28.39 24.27 25.73 19.62 20.54 Zn ND 55.46 66.00 55.86 54.33 54.86 62.37 51.51 70.36 49.28 59.01 54.98 64.21 58.52 52.92 56.19 68.87 68.19 60.60 78.64 68.02 67.56 68.13 51.35 52.45 Hg ND ND ND ND 1.71 0.18 3.66 0.00 5.52 2.43 0.84 0.80 1.77 0.02 0.74 0.83 0.36 0.14 0.02 0.96 0.62 1.24 0.63 0.71 0.02 Wet 13/11/08 20/11/10 28/11/08 30/11/08 20/01/11 24/01/11 20/02/11 20/03/11 20/12/10 10/12/08 27/12/08 20/01/09 24/01/09 24/11/09 30/01/09 25/02/09 13/03/09 31/03/09 29/04/09 09/12/09 23/12/09 20/01/10 23/02/10 22/03/10 20/04/10 P P P P P P P R R R R R R R R R R R R X R R R R R Table 2. Chemical concentration (mg kg Table

8 LATIN AMERICAN JOURNAL OF SEDIMENTOLOGY AND BASIN ANALYSIS | VOL. 21 (1) 2014, 3-15 Inorganic composition of suspended sediments in the Acre River, Amazon Basin, Brazil P 90.91 711.26 984.70 458.40 736.16 657.97 830.96 607.46 397.76 403.90 492.04 726.51 806.20 375.47 607.92 366.56 895.94 761.48 624.19 431.70 1023.73 S 69.57 929.84 216.07 529.28 623.13 802.50 791.92 172.05 177.81 213.04 555.54 823.14 121.36 408.62 127.59 560.51 340.60 463.65 388.87 269.42 1553.50 Al 2124.11 9904.86 9449.53 8197.30 9740.67 9367.85 8757.46 11099.89 11863.69 11362.03 10118.13 11732.07 11296.52 12077.99 10779.13 10433.50 10704.70 12352.51 10195.05 14287.41 13097.61 Ca 1165.68 6112.09 6031.81 6727.93 4881.61 6560.85 5943.70 5293.54 5837.73 4542.34 5433.32 5229.23 6201.40 6893.82 6633.28 4796.31 5253.02 5043.03 5494.16 5703.84 4951.52 Cd 3.48 2.89 2.52 1.52 1.32 2.72 2.65 0.61 2.08 2.09 2.49 1.73 1.61 2.46 1.24 1.21 1.25 1.44 3.14 1.60 1.18 Cr 1.91 11.89 11.42 15.14 16.34 14.18 13.17 12.06 13.58 13.75 14.63 14.31 12.47 13.01 14.53 13.91 12.23 13.62 12.00 14.24 12.74 Cu 4.92 25.11 33.87 24.50 18.23 47.49 21.89 25.03 17.53 20.35 27.10 18.15 39.81 19.14 23.41 20.23 16.93 20.81 16.83 18.94 32.41 Fe 31624.72 28808.91 25863.66 33227.27 25933.88 25336.45 38587.39 36429.02 24998.05 27326.01 31893.60 24745.02 30370.35 24359.91 27265.19 26644.19 23649.40 27688.25 22924.86 40033.25 30704.35 K 282.19 1114.65 1611.75 1107.06 1311.71 1136.51 1883.16 1295.48 2843.16 1778.08 1818.37 1322.45 1469.52 1297.90 1907.58 1568.68 1368.89 1886.85 1029.15 1045.05 1785.31 Mg 474.69 2517.38 2356.89 2998.65 3092.65 2446.64 2491.93 2450.57 2889.57 2789.85 2236.15 2780.60 3813.41 3272.85 2451.25 2805.25 2144.27 2355.14 2319.92 2527.51 2509.24 Mn 711.32 776.41 740.05 898.93 935.16 176.25 845.74 682.75 754.01 647.00 853.08 800.45 903.93 855.84 1139.60 1125.09 1364.09 2028.82 1021.40 1291.03 1236.42 Na 7.42 76.11 27.93 84.82 96.67 50.61 89.52 55.30 70.91 80.61 55.98 68.13 133.66 178.84 128.59 123.08 104.10 166.83 126.67 162.34 183.44 Ni 2.45 28.65 26.24 18.43 17.34 29.30 24.30 21.14 21.39 19.93 22.51 20.47 21.98 21.66 15.38 21.42 18.31 17.88 14.75 15.83 20.42 Pb 3.10 11.96 20.19 18.06 13.04 14.51 28.43 14.39 14.43 13.38 15.31 14.37 20.57 12.94 18.26 12.06 21.32 15.38 18.94 15.80 17.13 Si 28.99 117.30 110.02 110.42 172.94 172.93 136.14 187.35 135.17 134.93 196.15 436.85 190.36 136.52 495.37 130.36 622.09 160.24 233.17 1688.23 1810.82 Ti 2.11 5.38 5.53 2.63 1.38 1.24 5.05 4.03 0.84 2.82 2.78 3.00 2.40 3.02 2.99 2.06 1.10 3.63 2.69 1.86 5.92 V 6.43 27.11 39.68 33.62 25.65 22.04 32.31 31.40 30.21 22.14 21.17 24.35 23.66 20.45 26.33 26.04 20.77 26.48 27.25 23.47 30.17 Zn 8.68 91.31 61.97 58.46 60.67 71.22 60.68 61.54 59.64 58.46 62.91 57.97 63.25 67.51 55.04 51.27 53.08 62.12 59.63 68.06 253.37 Hg ND ND ND ND ND ND ND 3.43 1.67 0.97 4.00 1.71 2.26 0.72 2.82 0.82 0.18 1.95 0.02 8.24 1.95 Dry 11/07/08 24/10/08 20/10/10 20/09/10 25/10/08 30/10/08 28/05/09 20/05/10 20/06/10 25/10/08 06/06/09 25/08/09 28/09/09 20/10/09 10/10/09 28/06/09 15/08/09 20/07/10 30/07/09 20/08/10 25/07/09 P P P P P P R R B R R R R R R R R R R R X Table 2. Continuation. Table

LATIN AMERICAN JOURNAL OF SEDIMENTOLOGY AND BASIN ANALYSIS | VOL. 21 (1) 2014, 3-15 9 Alejandro Fonseca DUARTE and Adriana GIODA

Figure 4. a) Mg/Al, b) Ca/Al, c) Na/Al and d) K/Al vs. Al/Si in the Acre River basin during the wet and dry seasons. The Pearson correlation coefficient, the intercept and slope of the linear trend lines are shown.

Hg is remobilized due to the cultural practices of effects of weathering reactions that affect the soils deforestation in the Amazon. Slashing and biomass and floodplains compared to reactions affecting burning contribute to the atmospheric emission of the primary rocks. These authors report that little Hg estimated by Michelazzo et al. (2010) of 6.7 t y-1 information is available to date on the potential between 2000 and 2008 and by Roulet et al. (1999) of contribution of weathering reactions during between 6 and 9 t y-1 from burning of primary forest. riverine transport and transient storage to global weathering fluxes and that weathering reactions were responsible for downstream chemical Acre River and downstream suspended sediment changes in sediments from the Solimões varzea Weathering processes were extensively described (floodplain). These changes occurred through the by Bouchez et al. (2012), primarily in the context of loss of plagioclase, smectite and illite, the formation the sediments of large rivers in the Amazon basin, of kaolinite and a downstream shift in the mineral by introducing a weathering index to measure the assemblage dominating the clay fraction of Amazon

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Table 3. Acre River Suspended SSAc (mg kg-1) SSAm (mg kg-1) SSAm/SSAc Sediment (SSAc), and Solimões, Concentration SD Concentration SD Enrichment ratio Madeira and Amazon mainstreams Na 90 49 7,955 1,830 88 SS (SSAm). Chemical mean concentration, standard deviation Mg 2,596 492 8,219 2,271 3 and enrichment ratio. Al 10,808 2,088 79,733 23,977 7 Si 265 355 301,394 45,918 1,139 K 1,456 627 18,732 4660 13 Ca 5,354 971 8,068 2,818 1.5 Ti 3 3 4,799 1,531 1,441 Cr 13 2 68 22 5 Fe 27,232 4,596 42,769 11,565 1.6 Ni 20 4 31 8 1.6 Cu 22 7 29 16 1.4 Zn 64 31 129 47 2

SS from illite-chlorite to kaolinite-smectite. grain-size distribution of suspended sediment with Comparison between the SS chemical river depth, i.e. the sediment-transport dynamics concentrations from the Solimões, Madeira and are essentially related to the movement of fine Amazon mainstreams (SSAm) (Bouchez et al., 2011) particles in a turbulent flow where the SS particles and that from the present study (SSAc), concerning are almost randomly distributed. Figure 5 shows the an integrated size spectrum of particles, indicates relationship of the chemical concentration of the the significant enrichment of Si, Ti, and Na, the alkali metal Na and alkali-earth metal Ca with respect moderate enrichment of K, Al, Cr, and Mg, and the to Al/Si ratio for the case of (SSAm) (Bouchez et al., low enrichment of Zn, Fe, Ni, Ca, and Cu in sediments 2011) and this study. The relationship indicates in the course from Acre to Amazon mainstreams, as the distribution of elements in particles of various shown in table 3. grain sizes, prevailing in the mixing of coarse SS The major Si enrichment occurs in coarse (low Al/Si ratios) and fine surface SS (high Al/Si sediments that are in deepest areas of the river. The ratios), respectively. In the Amazon River, the Al/Si relatively moderate content of Al in the Acre River SS ratio points toward low values (silicon rich coarse is a characteristic property of fine particles in samples. sediments) in bottom SS and high values (aluminum Bouchez et al. (2011) conducted observations in river rich fine sediments) in surface SS (Bouchez et al., profiles up to 25, 30 and 60 m in depth, different from 2011). In the Acre River, no significant differences in the Acre River depths between 2 and 12 m, where grain size and chemical composition were observed, only surface samples were collected. This difference as evidenced by the nearly constant relationship of explains the high dispersion (SD) of values for the the weathering index values X/Al as a function of the SSAm measurements compared to that encountered Al/Si (Fig. 4). for the SSAc data. The relative enrichment in the chemical concentration of SS and the prevalence of Perspectives of suspended sediment modification coarse or fine particles in both of the compared areas is also revealed from the corresponding Al/Si values: Amazon ecosystems are highly vulnerable to between 1 and 160 for SSAc and between 0 and 0.5 extreme events of climate and human interventions. for SSAm. For example, the concentration of Na in Such impacts occur through deforestation, seasonal coarse particles (SSAm) was 88 times greater than its changes in atmospheric composition, floods and concentration in fine particles (SSAc); it was more droughts. Moreover, the construction of highways than one thousand times for Si and Ti; and less than (Maldonado et al., 2012) and more than seventy dams two times for Ca, Fe, Ni and Cu (Table 3). Apparently, for hydropower generation in the Brazilian Amazon the Acre River does not show a clear chemical and (Kemenes et al., 2007; Burger, 2011; Kemenes et

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Figure 5. a) Downstream enrichment of Na concentration and b) of Ca concentration in SS. Comparison between SSAm from Bouchez et al. (2011) and SSAc (this paper). Circles represent grain size and element concentration: blue for SSAc and orange for SSAm. al., 2011; Kemenes et al., 2012; Pyper, 2012) and in (SS) from the Acre River was determined. The SS the Andean Amazon (Finer and Jenkins, 2012) will concentration of sediments was significantly greater have environmental impacts such as the release of during the wet season than during the dry season. significant amounts of methane and carbon dioxide In contrast, the concentrations of Hg, Pb, Fe, S, to the atmosphere, with implications for climate and P in the SS were significantly greater during change, natural cycles, soil loss, biodiversity loss the dry season than during the wet season. Quartz, and disturbances of river system loads and transport kaolinite and illite were observed in all the sampling of sediments. sites. The elements Zn, V, Ti, Si, Pb, Ni, Na, Mn, Influences on the suspended sediment load could Mg, K, Fe, Cu, Cr, Cd, Ca, Al, S, and P derive from be intensified due to the projected climate changes weathering reactions that affect the minerals and in Amazonia (Salazar et al., 2007), which predict a soils that are characteristic of the Fitzcarrald Arch loss of vegetation, a decrease in precipitation during geochemistry. A detailed chart of the geochemistry longer dry seasons and higher temperatures and, of the SS provides evidence of the distribution of as a consequence, additional droughts and fires. At element concentrations. Particles of various grain the same time, during the shorter wet seasons, the sizes, are present in the mixing of coarse SS (low rainfall is expected to intensify severe erosion events Al/Si ratios) and fine SS (high Al/Si ratios), and a in a landscape with poor vegetation coverage (Saxena downstream enrichment of chemical concentrations and Hildemann, 1996). These modifications could was observed. It was assumed that Hg reaches the increase the redistribution of nutrients, such as P, region via atmospheric transport and deposition and and of contaminants, such as Hg and Pb, and increase from gold mining in the Madeira basin. Erosion of the significance of water-sediment interactions and rocks and clay minerals, soil weathering, practice of their influence on river water quality (Walling and deforestation, use of slash and burning in agriculture, Kane, 1982). Situations such as extreme floods and as well as water transport determine the chemical droughts in the Amazon (Collier and Webb, 2002) composition and diversity of concentrations of are predicted as new climate behavior for the 21th suspended sediment in the Acre River in the Purus century. Basin. The obtained results represent the first set of values and relationships regarding the mineralogy CONCLUSION and chemical identification of the SS in the region The present study was developed in a portion of and can be used as a reference for future efforts the Purus Basin that is the least studied area in the to add spatial and temporal information about the region. The seasonality of the suspended sediment hydrological and geochemical characteristics within

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