Estudos da APA – Biblioteca Digital Itupararanga

Menu

Paleolimnological evidence of environmental changes in seven subtropical reservoirs based on metals, nutrients, and sedimentation rates

Este trabalho é somente para uso privado de atividades de pesquisa e ensino. Não é autorizada sua reprodução para quaisquer fins lucrativos. Esta reserva de direitos abrange a totalidade dos dados do documento bem como seu conteúdo. Na utilização ou citação de partes do documento é obrigatório mencionar o nome da pessoa autora do trabalho.

Evidências paleolimnológicas de mudanças ambientais em sete reservatórios subtropicais com base em metais, nutrientes e taxas de sedimentação

ABSTRACT

Paleolimnological research can shed light on a broad range of environmental concerns; however, such studies are scarce in reservoirs. To address this lack of knowledge, a paleolimnological investigation was conducted to determine historical changes in sedimentation rates (SR), using 210Pb geochronology, and concentrations of nutrients and metals (Cr, Cu, Ni, Pb, Zn, Al, Mn, Fe) in seven subtropical reservoirs (S˜ao Paulo, Brazil). Sediment cores were collected in the dam areas. Increasing SR was observed in all reservoirs and was mainly attributed to eutrophication and changes in land use and occupation. Considering the total nitrogen and/or phosphorus, the sediment could be considered polluted at the Broa, Barra Bonita, Salto Grande, and Rio Grande reservoirs. Decreasing values were observed for Pb when the use of tetraethyl lead as an additive in gasoline was forbidden (1990). According to the applied indices, no significant enrichment, contamination, or ecological risk for metals were registered, except at the Rio Grande reservoir. At this reservoir, a moderate enrichment of Mn was observed since 1999, which was mainly associated with municipal wastewater and erosive processes, as indicated by a significant correlation between Mn and SR (r = 0.73, p < 0.0001). A very high enrichment of Cu was observed. The accumulation of Cu in this reservoir peaked in 2006 to 6183.0 mgCu/kg, a value 412-fold higher than the background. Even during a period before intense industrialisation, concentrations of Cu were 49-fold higher than background levels. The increase of Cu in bottom sediments could be attributed to vertical migration according to a series of complex mechanisms; however, further research will be needed to improve the understanding of Cu dynamics. This work makes an important contribution to understanding the paleolimnology of reservoirs, and the findings could also 

RESUMO

A pesquisa paleolimnológica pode lançar luz sobre uma ampla gama de preocupações ambientais; no entanto, tais estudos são escassos em reservatórios. Para abordar essa falta de conhecimento, uma investigação paleolimnológica foi conduzida para determinar mudanças históricas nas taxas de sedimentação (TS), usando geocronologia de 210 Pb e concentrações de nutrientes e metais (Cr, Cu, Ni, Pb, Zn, Al, Mn, Fe) em sete reservatórios subtropicais (São Paulo, da dinâmica do Cu. Este trabalho traz uma contribuição importante para a compreensão da paleolimnologia de reservatórios, e as descobertas também podem ser aplicadas em outros contextos, uma vez que o impacto da contaminação por metais em corpos d’água é um problema de escala global. (Brasil). Testemunhos de sedimentos foram coletados nas áreas das barragens. O aumento da SR foi observado em todos os reservatórios e foi atribuído principalmente à eutrofização e às mudanças no uso e ocupação do solo. Considerando o nitrogênio e/ou fósforo total, o sedimento pode ser considerado poluído nos reservatórios de Broa, Barra Bonita, Salto Grande e Rio Grande. Valores decrescentes foram observados para Pb quando o uso de chumbo tetraetila como aditivo na gasolina foi proibido (1990). De acordo com os índices aplicados, nenhum enriquecimento significativo, contaminação ou risco ecológico para metais foi registrado, exceto no reservatório de Rio Grande. Neste reservatório, um enriquecimento moderado de Mn foi observado desde 1999, que foi principalmente associado a águas residuais municipais e processos erosivos, conforme indicado por uma correlação significativa entre Mn e SR (r = 0,73, p < 0,0001). Um enriquecimento muito alto de Cu foi observado. A acumulação de Cu neste reservatório atingiu o pico em 2006, atingindo 6.183,0 mgCu/kg, um valor 412 vezes superior ao nível de referência. Mesmo durante um período anterior à industrialização intensa, as concentrações de Cu eram 49 vezes superiores aos níveis de referência. O aumento de Cu nos sedimentos de fundo pode ser atribuído à migração vertical, de acordo com uma série de mecanismos complexos; no entanto, mais pesquisas serão necessárias para aprimorar a compreensão.

Introduction

Paleolimnology can provide important information about the dynamics of ecosystems, establishing reference conditions for water bodies and enabling the assessment of current impacts (Smol, 2008, Hollert et al., 2018, Stivrins et al., 2018). It can also provide important ecological information in the absence of long-term monitoring data (Bennion and Battarbee, 2007, Smol, 2008, Stivrins et al., 2018). Although viable, there has been little application of paleolimnological techniques to reservoirs, so the sediments of these ecosystems have rarely been used to track environmental changes (Shotbolt et al., 2006, Tse et al., 2015). This is because reservoir sediments are more susceptible to disturbances due to fluctuations in the water level, making historical reconstruction more complex (Shotbolt et al., 2006). However, the stratigraphy of undisturbed sediments can be observed in deeper reservoir areas, providing long-term environmental information that can be used in management programs (Tse et al., 2015) and to improve the understanding of ecological processes.

Various proxies can be used to reconstruct past environmental conditions (Smol, 2008). For example, metals, nutrients, and sedimentation rates (SRs) may be viable proxies, especially for urban reservoirs that are highly susceptible to the impacts of rapid urbanisation and industrialisation. Metal pollution in aquatic ecosystems is of great concern and is an increasing global problem (Kucuksezgin et al., 2008, Väänänen et al., 2018) . Metals, such as chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), and zinc (Zn), are of considerable environmental interest due to their toxicity, persistence, bioavailability, biomagnification in the food chain, and potential threat to ecological systems and human health (Luoma and Rainbow, 2008). Information about the dynamics of metals in aquatic ecosystems can be obtained using paleolimnological studies, as shown by Cardoso-Silva et al., 2016a, Korosi et al., 2018, Lintern et al., 2018, Thienpont et al., 2019, and Soares-Silva et al. (2020).

Analyses of macronutrients, such as phosphorus, nitrogen, and carbon, in sediments can shed light on eutrophication processes, although caution is required in interpreting the data (Boyle, 2001). It is important to consider these three main elements because under eutrophic conditions, phosphorus released from the sediment may often be intense, even if external loading is low, because of high internal loading that does not reflect the trophic state in the water column (Cardoso-Silva et al., 2018). However, nitrogen is considered a superior indicator of primary aquatic productivity (Dai et al., 2007), enabling the assessment of anthropogenic impacts. Carbon can provide important information about the diagenetic processes affecting organic matter (OM), and together with concomitant analyses of nitrogen and phosphorus, it can indicate the origins of the material (Meyers, 1994) and possible contamination by phosphorus (Cardoso-Silva et al., 2018).

The SR can also be used as an important proxy to understand environmental processes and to assess urbanisation impacts. Sedimentation processes affect the metabolism of the aquatic ecosystem, which in turn influences the regeneration of nutrients in the epilimnion, the removal of particulate matter to the bottom, and control of the supply of nutrients to the benthic community (Bloesch and Uehlinger, 1986). The SR is closely related to the hydrologic flow pattern and the topography of the basin, which affects the hydrodynamic regime (Navas et al., 2009). SRs are specific for each water body and depend on the nature of the river basin but can be influenced by anthropogenic activities, which may result in increased erosive processes and SRs associated with eutrophication (Moss et al., 2003, Scharf et al., 2010). The transport and deposition of eroded sediments can directly affect adjacent urban settlements, for example, by reducing the storage capacity of surface reservoirs (Rahmani et al., 2018). The 210Pb dating technique is of great importance for studying sedimentation processes, since it can provide both geochronological information and accurate SR data, using cores of sediment younger than 150 years (Moss et al., 2003).

Long-term records of the chemical states and ecological conditions of reservoirs are absent in many regions worldwide, including tropical and subtropical areas in Brazil. This can complicate the implementation of effective and realistic environmental remediation strategies. Furthermore, the lack of information for aquatic ecosystems in tropical and subtropical areas hinders international access to information, thus restricting the understanding of processes and phenomena on a global scale.

The present paleolimnological study was undertaken to fill this knowledge gap, with the following goals: 1) elucidate temporal changes in SRs using 210Pb geochronology and determine of metal and nutrient concentrations in seven subtropical reservoirs in São Paulo State; 2) propose background values for Cr, Cu, Ni, Pb, Zn, Mn, Al, and Fe; 3) investigate metal contamination and toxicity potential by analysing different indices and using empirical sediment quality guidelines; 4) evaluate quality gradients and spatial heterogeneity in the reservoirs.

The hypothesis was that the metal concentrations and SR would exhibit increases over the course of time because anthropogenic impacts have increased in the watersheds of the reservoirs. The data obtained shed light on natural and anthropogenic changes in reservoirs during the recent past. The findings represent an important contribution of paleolimnology to the understanding of subtropical reservoir environments.

Section snippets

Study area

Sediment cores were obtained at seven reservoirs in São Paulo State, Brazil: Broa (sampled on June 11, 2015), Barra Bonita (June 18, 2015), Salto Grande (June 25, 2015), Itupararanga (September 10, 2015), Igaratá (September 24, 2015), Atibainha (October 1, 2015), and Rio Grande (Billings Complex) (October 8, 2015) (Fig. 1). The Broa reservoir was the smallest of the seven reservoirs and is impacted by inputs of untreated domestic sewage, resulting in high trophic levels (Tundisi et al., 2015, 

General characteristics of the sediments and analysis of nutrients

The sediments from all reservoirs displayed uniform coloration, with no clear variation according to depth. The silt and clay fractions (<63 μm), which provide important binding sites for metals (Chapman et al., 1999, Cardoso-Silva et al., 2016b), were only predominant in the sediment from the Broa reservoir (60.04 ± 19.15%) (Table 3). The sediments could be considered organic with LOI values > 10% (Ungemach, 1960) (Table 3).

Sedimentation rate and dating with 210Pb

Figures 2a and 2b present the vertical profiles obtained for the

Conclusions and final considerations

All seven reservoirs displayed anthropogenic impacts of various magnitudes, which tended to increase in recent years. Increases in SRs in these reservoirs were mainly attributed to eutrophication and changes in land use and occupation. Signs of eutrophication were especially evident in the Broa, Barra Bonita, Salto Grande, and Rio Grande reservoirs, where the sediments were polluted by TP and TN, with low C:P molar ratios.

Analyses of the metals enabled the establishment of background values,

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors are grateful to the Postgraduate Program in Environmental Sciences, at the Sorocaba campus of UNESP, and to the Ecology Department of the Institute of Biosciences, at the University of São Paulo. We are also grateful to Cláudia H. Watanabe M.Sc for her help with the laboratory analyses. Financial support for this work was provided by FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo, grants 2014/22581-8, 2016/17266-1, and 2016/15397-1) and CAPES (Coordenação de

References (103)

There are more references available in the full text version of this article.