Long-Term (∼57 ka) Controls on Mercury Accumulation in the Souther

Dec 29, 2014 - Natural archives have been used to reconstruct mercury atmospheric deposition at different spatial and temporal scales during the Holoc...
3 downloads 3 Views 2MB Size
Subscriber access provided by SELCUK UNIV

Article

Long-term (~57 ka) controls on mercury accumulation in the Southern Hemisphere reconstructed using a peat record from Pinheiro mire (Minas Gerais, Brazil) Marta Pérez-Rodríguez Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 29 Dec 2014 Downloaded from http://pubs.acs.org on January 5, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Environmental Science & Technology

This document is confidential and is proprietary to the American Chemical Society and its authors. Do not copy or disclose without written permission. If you have received this item in error, notify the sender and delete all copies.

Long-term (~57 ka) controls on mercury accumulation in the Southern Hemisphere reconstructed using a peat record from Pinheiro mire (Minas Gerais, Brazil)

Journal: Manuscript ID: Manuscript Type: Date Submitted by the Author: Complete List of Authors:

Environmental Science & Technology es-2014-04826d.R2 Article 29-Dec-2014 Pérez-Rodríguez, Marta; Universidade de Santiago de Compostela, Edafoloxía e Química Agrícola Horák-Terra, Ingrid; ESALQ/ Universidade de São Paulo, Departamento de Ciência do Solo Rodríguez-Lado, Luis Manuel; University of Santiago de Compostela, Departamento : Edafología y Química Agrícola. Fac. Bioloxia Aboal, Jesus; Univ. Santiago de Compostela, Biologia Celular y Ecologia Martínez-Cortizas, Antonio; Faculty of Biology, University of Santiago de Compostela, Soil Science and agricultural chemistry

ACS Paragon Plus Environment

Page 1 of 32

Environmental Science & Technology

Long-term (∼57ka) controls on mercury accumulation in the Souther Hemisphere reconstructed using a peat record from Pinheiro mire (Minas Gerais, Brazil) Marta P´erez-Rodr´ıguez,∗,† Ingrid Hor´ak-Terra,‡ Luis Rodr´ıguez-Lado,† Jes´us R. Aboal,¶ and Antonio Mart´ınez Cortizas† Departamento de Edafolog´ıa y Qu´ımica Agr´ıcola,Universidad de Santiago de Compostela, Spain, Departamento de Ciˆencia do Solo, Escola Superior de Agricultura Luiz de Queiroz ESALQ/ USP,Piracicaba-SP, Brazil, and Ecolog´ıa,Universidad de Santiago de Compostela, Spain E-mail: [email protected]

Abstract 1

Natural archives have been used to reconstruct mercury atmospheric deposition at

2

different spatial and temporal scales during the Holocene in the Northern Hemisphere.

3

In this study we present the results from a Brazilian mountain mire (Pinheiro mire,

4

Minas Gerais, SE Brazil), extending back to ∼57 ka. The core was analyzed for mercury ∗

To whom correspondence should be addressed Departamento de Edafolog´ıa y Qu´ımica Agr´ıcola, Facultad de Biolog´ıa, Campus Sur s/n, Santiago de Compostela, Spain ‡ Departamento de Ciˆencia do Solo, Escola Superior de Agricultura Luiz de Queiroz ESALQ/ USP, Av. P´ adua Dias, 11, 13418-900, Piracicaba-SP, Brazil ¶ Ecolog´ıa, Facultad de Biolog´ıa, Campus Sur s/ n, Santiago de Compostela, Spain †

1

ACS Paragon Plus Environment

Environmental Science & Technology

5

concentration, organic matter content, organic carbon isotopic composition and tracers

6

of mineral matter flux. Principal components analysis followed by principal components

7

regression enabled us to determine the evolution of the weight of the latent processes

8

governing the accumulation of mercury through time. We show that climate change

9

was the main driver for the variations of mercury concentrations, either indirectly by

10

i) enhancing soil erosion in the mire’s catchment, which led to a decrease in mercury

11

concentration due to dilution by low mercury-containing mineral matter, ii) increasing

12

regional dust deposition, which resulted in increased concentrations; or directly, by

13

long-term changes in atmospheric wet deposition (arid vs humid periods). Internal

14

peat processes (i.e. decomposition and mass loss) had a minor influence at the time

15

scale represented by the core.

Introduction 16

Mercury is a metal of environmental concern because of its high volatility, long atmospheric

17

residence time and the toxicity of its methylated forms. 1 Elemental mercury (Hg0 ) is the

18

dominant species in the atmosphere, 2,3 with a mean residence time of 1-2 years. This means

19

that a substantial fraction of mercury can be transported over long distances from the emis-

20

sion sources. Eventually, elemental mercury is oxidized into mercury ions, Hg(II), in the

21

atmosphere, which are washed out by rainfall. 4 Hg(II) is the dominant species in precipita-

22

tion. 5 Particulate mercury represents a minor fraction of the total mercury in the atmosphere

23

and can be dispersed over tens to hundreds of kilometers. 3 Methylated forms of mercury are

24

most toxic, and bioaccumulate and become enriched at the higher trophic levels. Hammer-

25

schmidt and Fitzgerald 6 found that, at continental scale, mercury deposition was correlated

26

to the concentrations of mercury in fish.

27

The use of natural archives such as peatlands, 7–29 ice-cores 30–32 and lake-sediments 22,23,33–49

28

to reconstruct mercury atmospheric deposition trends on a local, regional and global scale

29

has increased over the last two decades. However, large differences in the estimated back2

ACS Paragon Plus Environment

Page 2 of 32

Page 3 of 32

Environmental Science & Technology

30

ground fluxes exist between lake-sediments and peat cores, 44 hampering our understanding

31

of emission sources, atmospheric processes, rates of exchange between terrestrial and ocean

32

and atmospheric pools. 50–52

33

It has been argued that different factors, such as organic matter degradation and mass loss

34

associated to the evolution of the peat, 13,44,53,54 control mercury accumulation in peatlands.

35

Climate may also play a significant role, either by controlling the re-emission of part of the

36

accumulated mercury 8 or by inducing changes in peat decomposition. 54 These considerations

37

are almost exclusively based on Holocene records and only a few studies extended their

38

conclusions back to the Pleistocene. For example, Roos-Barraclough et al. 12 studied a 14500-

39

year peat record from the Swiss Jura Mountains and found a 5 fold increase in mercury

40

concentration during the Younger Dryas (9550-11050 BP). This increase was attributed either

41

to higher particle scavenging or to an increase in the oceanic productivity, which led to higher

42

mercury emissions from the oceans under cold climatic conditions. Jitaru et al. 55 also found

43

elevated mercury concentrations in sections of Antarctic ice cores corresponding to glacial

44

periods over the last 672,000 years BP, attributing them to mercury depletion phenomena

45

in the polar atmosphere and increased atmospheric dust loads. More long-term records of

46

mercury deposition are needed in order to fully understand the various processes that can

47

influence emission, deposition and accumulation of mercury in continental ecosystems.

48

Additionally, most of the studies which have investigated the processes controlling mer-

49

cury concentrations in peat and in most other natural records are located in the Northern

50

Hemisphere, while there is only a limited amount of quite heterogeneous information avail-

51

able for the Southern Hemisphere. 10,13,16,30,35,36,46,48,49,56

52

In this study, we analyzed a peat core sampled in a Brazilian mountain peatland (Pinheiro

53

mire, Minas Gerais, SE Brazil), extending back to ∼57 ka. We analyzed it for mercury

54

concentration, organic matter content (C, N), degree of decomposition (C/N ratios) isotopic

55

composition (δ 13 C) of the organic matter, and tracers of mineral dust deposition (Si, Ti, Zr,

3

ACS Paragon Plus Environment

Environmental Science & Technology

56

Y, Th). The objectives of the research were i) to determine the main factors that controled

57

peat mercury concentrations over long time scales; ii) to quantify their relative effect; and

58

iii) to establish a chronology of the changes in mercury fluxes.

59

Material and Methods

60

Location and sampling

61

Pinheiro (18◦ 03’44.42” S 43◦ 39’42.37” W) is a minerogenic, valley mire located in Serra do

62

Espinha¸co Meridional, state of Minas Gerais (Brazil) (Figure 1 and in supporting informa-

63

tion Figure S1). Higher elevations (1300-1320 m a.s.l.) are found at the northwestern and

64

southern slopes of the catchment and the mire’s valley, which drains from SW to NE, is sit-

65

uated between 1270 and 1230 m a.s.l. Although minerogenic, the location of the mire on the

66

mountain summit and the rather small catchment area (∼140 ha) makes it quite sensitive to

67

variations in rainfall. The background lithology corresponds to the Galho do Miguel Forma-

68

tion, and comprises pure and thin quartzites (∼ 90%), thin micaceous quartzites and gray

69

or greenish metargilites (∼ 5 a 10%). 57 According to the K¨oppen classification, the present

70

climate is tropical mountainous, with mean annual temperature and annual accumulated

71

precipitation values of 18.7◦ C 58 and 1500 mm respectively. 59 Rainfall is controlled by the

72

South Atlantic Convergence Zone (SACZ), which is one of the most prominent features of

73

the South Atlantic Monsoon System (SAMS) during the austral summer and it is associated

74

with intense convective activity in the Amazonian region. 60 The SACZ extends in a south-

75

eastern direction from the interior of the continent to the South Atlantic Ocean. 61 May to

76

October are characterized by extremely low rainfall coinciding with the end of the monsoon

77

period. Natural vegetation is similar to a typical Cerrado biome (savanna), but with patches

78

of trees (seasonal semi-deciduous forest and Cerrad˜ao), known locally as “Cap˜oes”, which

79

appear as small islands among grassland formations within the mire.

80

The core was sampled in 2010 using a vibracore 62 to a depth of 324 cm. It is composed of 4

ACS Paragon Plus Environment

Page 4 of 32

Page 5 of 32

Environmental Science & Technology

81

quartzitic sands below 220 cm, sapric peat layers from 220 to 8 cm (with strongly decomposed

82

peat at 212-220, 190-198, 136-157 and 8-58 cm), and an upper (