Abstract
AIM: The aim was to verify the geochemical composition of sediments samples (riverbed and bank) and the relationship of the following elements: Al, As, Cd. Cr, Cu, Fe, Mn, Ni and Zn with the zooplankton community. METHODS: Bank and riverbed sediments were collected in four sampling points along the studied area, in June/2010 (dry season) and March/2011 (rainy season). Three types of analysis were performed: granulometric, mineralogical (by X-Ray diffractometer) and geochemical (by ICPOES), where for the last two types, only a fraction of silt/clay (<0.062 mm) was used, and the results were compared with the following reference values: Local Reference Value (Costa et al., 2010), Quality Reference Values (São Paulo, 2005), PEC and TEC values (MacDonald et al., 2000). For identification of the zooplankton community, riverbed and bank samples were collected in polyethylene bottles, suspended with deionized water (bank sample only), stained with Rose Bengal and preserved in formalin at 4%. RESULTS: As concentrations at Col sampled point were 18 times greater than the Local Reference Value (3.84 mg.kg-1). Cd concentrations were greater than the values established by the QRV (<0.5 mg.kg-1) and PEC (4.98 mg.kg-1) in almost all the sampled points, regarding seasonality. The following zooplanktonic species were identified: Arcella costata (Ehrenberg, 1847), Arcella discoides (Ehrenberg, 1843), Arcella vulgaris (Ehrenberg, 1830), Centropyxis aculeata (Ehrenberg, 1838), Centropyxis ecornis (Ehrenberg, 1841), Difflugia sp., Difflugia acuminata (Ehrenberg, 1838), Euglypha laevis (Perty, 1849), Trynema enchelys (Ehrenberg, 1938), Asplanchna priodonta (Gosse, 1850), and Bedelloida, with, approximately 81% belonging to the Protozoa group. CONCLUSIONS: The studied area, with the exception of the Tripuí point, was found to be impacted by historical gold exploration in the region, as well as by the growing urbanization. Within the elements considered to be the most toxic to the biota, As and Cd violated all their reference values. In spite of high concentrations of major and trace elements encountered at downstream points, testacea species were identified, suggesting that this group has the capacity to adapt to adverse situations.
Highlights
Anthropic interventions in any natural system could cause impacts in the environment such as: alteration of texture of recent sedimentary deposits causing liberation of gases; availability and/or retention of nutrients and trace elements; and reduction or loss of local biodiversity (Tundisi and Tundisi, 2008)
The mineralogy found in the riverbed sediment matches that which was found in the bank sediment, suggesting a proximity to the area source of the sediments
In spite of the high concentrations found at the downstream points (Pra and Col), zooplankton species were encountered, of which testaceas were the most abundant, suggesting that they could developed mechanisms to adapt to adverse situations
Summary
Anthropic interventions in any natural system could cause impacts in the environment such as: alteration of texture of recent sedimentary deposits causing liberation of gases; availability and/or retention of nutrients and trace elements; and reduction or loss of local biodiversity (Tundisi and Tundisi, 2008). This mine produced around 35 tons of gold during its active lifetime, discharging the effluents directly into Ribeirão do Carmo (Costa et al, 2010; Borba, 2004) As this exploration went on for three centuries, it created a significant environmental impact by contaminating the surface water and sediments of the stream. Riverbed sediment is considered to be the main compartment of accumulation, availability and interaction of major and trace elements, the sediment on the banks is important because it represents the link between land and water environments (Cotta et al, 2006), being the habitat for a variety of aquatic organisms (Esteves, 1988) It is an important data source for assessing environmental quality, as it bears the pollution history of the area. The richness may be considered similar as a biodiversity index, and can be used as a comparison, reflecting the stability of terrestrial environments that have suffered some impact and the natural ones (Li et al, 2010)
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