Regional geochemical baselines for sedimentary metals of the tropical São Francisco estuary, NE-Brazil.
Regional geochemical baselines for sedimentary metals of the tropical São Francisco estuary, NE-Brazil.
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DOI：
10.1016/j.marpolbul.2009.01.011
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发表时间：
2009-04
影响因子：
5.8
通讯作者：
E. Sabadini-Santos;B. Knoppers;Eliane Padua Oliveira;T. Leipe;R. Santelli
中科院分区：
文献类型：
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作者：
E. Sabadini-Santos;B. Knoppers;Eliane Padua Oliveira;T. Leipe;R. Santelli
潮湿热带地区的河流集水区将世界上大量的悬浮颗粒物和相关元素输送到沿海地区（Hay，1998年; Meybeck，1993年）。沿着这条运输途径的河口和红树林生境将一部分河流携带的微粒和金属转化、保留和积累在沉积物中（Lee，1995年; Jennerjahn和Ittekkot，2002年;马查多和Lacerda，2004年）。金属优先被细粒沉积物掩埋，并且还受到矿物学和有机物质含量的影响（Hornberger等人，1999年）。沿海系统中的许多金属累积研究侧重于建立地球化学基线，以评估系统中自然和/或人为金属负荷的程度。巴西的热带和亚热带沿海地区受到多种金属污染研究，研究对象是海湾、河口、沿海泻湖和这些系统中的红树林生境，这些生境受到不同程度的多重人类影响，如城市化、工业化、毁林、土地侵蚀和农业做法（Patchineelam等人，1988; Lacerda等人，1992，1999，2006; Marins等人，2004年）。然而，一致的地球化学基线仍然相对缺乏，实际上也只能在区域基础上建立，因为巴西热带河流悬浮物的粒度、矿物学和化学成分根据流域的区域气候、地质地貌和基质、沉积学、植被覆盖和人类土地使用情况而变化很大（Tintelnot，1995年; Knoppers等人，1999; Leipe等人，1999; Leão和Dominguez，2000; Souza和Knoppers，2003; Jennerjahn等人，2006).本研究建立了区域地球化学基线的金属铁，锰，铬，铜，镍，铅和锌的表面样品和岩心采取的几个沉积环境的圣弗朗西斯科弗朗西斯科河口，东北部巴西。它采用了金属浓度相对于该地区主要的保守粒度代表的标准化程序，并通过显示浓度散点图计算富集因子（Loring，1991年; Schropp等人，1990; Loring和Rantala，1992; Covelli和Fontolan，1997; Abraham，1998; Covelli等人，2006; Mil-Homens等人，2007年）。这些发现被认为是一个独特的例子，一个热带潮湿的河口附近，完全受到河流大坝的影响，自70年代末以来，在中低半干旱地区的圣弗朗西斯科（SF）河流域（拉特。10 360 S，长型。36 230 W; Ab= 634 103 km 2，L= 2840 km）。大坝梯级调节河流流量恒定Qr为2060 m3 skirl 1，并保留了水库中94%以上的悬浮泥沙。河口浑浊的沃茨已经变得透明和贫营养。水坝下游的物资补给几乎可以忽略不计，人类活动仅限于稻田农业和小城市住区的污水在当地扩散。SF河中下游流域嵌入在由松散的富铁冲积沉积物组成的“晚第三纪Barreiras组”的形态单元中，该单元与整个巴西东部和东北部海岸线接壤。SF河口的第四纪河流三角洲（A= 800 km 2，宽度= 50 km）由
River catchments of the humid tropics deliver a large amount of the world’s particulate suspended matter and associated elements to the coastal zone (Hay, 1998; Meybeck, 1993). The estuaries and mangrove habitats set along this transport pathway transform, retain and accumulate a fraction of the river-borne particulates and metals in their sediments (Lee, 1995; Jennerjahn and Ittekkot, 2002; Machado and Lacerda, 2004). The metals are preferentially buried with fine-grained sediments and also affected by the mineralogy and content of organic matter (Hornberger et al., 1999). Many metal accumulation studies in coastal systems focused on the establishment of geochemical baselines for the evaluation of the degree of natural and/or anthropogenic metal loadings in the system. The tropical and sub-tropical coastal zone of Brazil has been subject to manifold metal contamination studies of its embayments, estuaries, coastal lagoons and mangrove habitats embedded in these systems affected by a varying degree of multiple human impacts, such as urbanization, industrialization, deforestation, land erosion and agricultural practices (Patchineelam et al., 1988; Lacerda et al., 1992, 1999, 2006; Marins et al., 2004). However, consistent geochemical baselines are still relatively scant and in practice may also only be established on a regional basis, as the grain size, mineralogical and chemical composition of suspended matter of Brazils tropical rivers varies greatly in accordance to the regional climate, geological relief and matrix, sedimentology, vegetation cover and human land-uses of the drainage basins (Tintelnot, 1995; Knoppers et al., 1999; Leipe et al., 1999; Leão and Dominguez, 2000; Souza and Knoppers, 2003; Jennerjahn et al., 2006).This study establishes a regional geochemical baseline for the metals Fe, Mn, Cr, Cu, Ni, Pb and Zn from surface samples and cores taken in several sedimentary environments of the São Francisco river estuary, NE-Brazil. It adopts the normalization procedure of metal concentrations against the dominant conservative grain size proxy of the region and the calculation of enrichment factors with display of concentration scatterplots (Loring, 1991; Schropp et al., 1990; Loring and Rantala, 1992; Covelli and Fontolan, 1997; Abraham, 1998; Covelli et al., 2006; Mil-Homens et al., 2007). The findings are regarded as a unique example of a tropical humid estuary near to solely impacted by river dams constructed since the late seventies in the middle-lower semi-arid reaches of the São Francisco (SF) river basin (Lat. 10 360S, Long. 36 230W; Ab= 634 Â 103 km2, L= 2840 km). The dam cascade regulated river flow to a constant Qr of 2060 m3 sÀ1 and retained over 94% of the suspended sediments in their reservoirs. The estuaries turbid waters have become transparent and oligotrophic. Material replenishment downstream of the dams is near to negligible and human activities are restricted to rice field agriculture and local diffuse inputs of effluents from small urban settlements. The middle-lower SF river basin is embedded in the morphological unit denominated as the ‘‘Late Tertiary Barreiras Formation” comprised of unconsolidated iron-rich alluvial sediments, which borders the entire Brazilian eastern and northeastern shoreline. The Quarternary river delta (A= 800 km2, width= 50 km) of the SF estuary is comprised