Temporal and spatial accumulation of heavy metals in the sediments at Paiva Castro Reservoir (São Paulo, Brazil)

Abstract

The analysis of heavy metals in sediments, associated with geochronology, can identify the historical accumulation of these contaminants that occurred over time as a result of anthropogenic activities. A study was conducted at Paiva Castro Reservoir, a tropical reservoir in Brazil, to (1) establish baseline values for the metals Cd, Cr, Cu, Ni, Pb, Zn, Mn, Al and Fe; (2) investigate the history of heavy metal accumulation through geochronology using 210 Pb; and (3) identify the main variables that differentiate the sampled regions. A gravity corer was released twice in three reservoir areas. Each core was sliced at intervals of 2 cm and stored in a sealed plastic bag. One core was used for the determination of metals and for dating using the 210 Pb technique. The other core was used for the determination of organic matter and particle size. The baseline values for heavy metals were calculated according to the mean bottommost samples of the three core analysed. In terms of the levels of heavy metals, the greatest impacts in the region occurred during periods prior to the period of reservoir operation. In surface sediments, Cu exceeded several times (97.0 mg kg-1) the background (24.0 mg kg-1). This result may be a consequence of the application of copper sulphate for controlling algal blooms. A canonical discriminant analysis indicated that the variables that significantly differentiated the three sampled areas were related to the elements Al, Fe, and Mn and to particle size. These data indicate that the main differences are due to lithological variations and to the dynamic operation of reservoirs that provide a larger particle size fraction in the area where the uptake of water for the public water supply is located and in the area upstream from Paiva Castro, where there is higher flow energy. Evidence of the degradation of Paiva Castro Reservoir is already being reflected in the sediments. It is necessary that public policies are actually applied to counteract the degradation of this important ecosystem; otherwise, the reservoir's 'good quality' will be at risk.

Factors that control the spatial and temporal distributions of phosphorus, nitrogen, and carbon in the sediments of a tropical reservoir

“…6). These slight increases in C and P coincided with the period in which there was a significant increase in the copper concentration to around three times the background value, as reported by Cardoso- Silva et al (2016a), which was attributed to applications of copper sulfate as an algicide in the Cantareira system watershed. This period also coincided with record water scarcity in the region, when the Cantareira system reached 1% of its storage capacity (Whately and Cunha 2007).…”

“…Nevertheless, this does not imply that these activities did not influence the ecosystem. For the same period, Cardoso- Silva et al (2016a) observed a significant correlation between the copper content of the sediment and population increase, which was attributed to the application of algicides. The absence of a significant correlation between phosphorus concentrations and population numbers may be explained by the fact that the Paiva Castro reservoir experiences periods of mesotrophy.…”

“…Geochronology and sedimentation rate and results were presented in Cardoso- Silva et al (2016a). Vertical profiles of 137 Cs and ln ( 210 Pbxs) (unsupported) can be observed in Fig.…”

“…Greater turbulence in the fluvial and transition regions, together with shallower depths, would create an unstable depositional environment, as observed by Hou et al (2014) in Dalinouer Lake, China, and by Bartoszek and Tomaszek (2007) in Solina-Myczkowce Reservoirs, in Poland. In the dam area, however, the higher sedimentation rate (Cardoso- Silva et al 2016a) favors greater accumulation and retention of nutrients in the sediments (Jia et al 2017).…”

“…6). According to Cardoso-Silva et al (2016a), this increase could be attributed to two main events. Firstly, in 1981, two additional downstream reservoirs in the region entered into operation and the flow rate in the system increased from 11 to 33 m 3 /s, directly affecting the dynamics in the water body.…”