Pluriannual Watershed Discharges of Hg into a Tropical Semi-Arid Estuary of the Jaguaribe River, NE Brazil

Luiz D Lacerda,Francisco J S Dias,Rozane V Marins,José Marcos O Godoy,Maria Luiza D P Godoy,Talita M Soares

doi:10.5935/0103-5053.20130216

Luiz D Lacerda, Francisco J S Dias + Show 4 more

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https://doi.org/10.5935/0103-5053.20130216

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Abstract

Mercury fluxes were measured during the dry and rainy seasons (2005 to 2009) at the Jaguaribe River estuary, which discharges into the Equatorial Atlantic Ocean in NE Brazil. During rainy periods, the water masses exhibited a short residence time within the estuary (0.8 days). During dry periods, seawater choked the fluvial discharge, resulting in longer residence times (3.1 days). Dissolved (< 0.7 µm) and particulate Hg concentrations and fluxes were greater from the river to the estuary than from the estuary to the sea, producing accumulated particulate Hg in the estuary. Particulate Hg export (1.8 to 12.6 mg s-1) to the ocean occurred during extremely rainy periods, while dissolved Hg export was practically nonexistent during rainy periods and increased up to 0.45 mg s-1 during dry periods. Because continental runoff in semi-arid regions is affected by land use and global climate changes, the increasing accumulation of particulate Hg in the estuaries and increasing export of dissolved Hg to the ocean are expected.

Highlights

Meso- and macro-tidal estuaries with semi-arid climates tend to accumulate sediments of fluvial origin, which may be washed out to the ocean during short but intensive rain periods.[1]
The continental flux to the ocean is extremely difficult to estimate due to the varying residence time of fluvial waters induced by the strong seasonality of semi-arid rivers, as materials originating in the continental shelf can be imported to estuaries during the long dry season
We present an estimate of the Hg mass balance in the Jaguaribe Estuary based on pluriannual analyses and simultaneous determinations of river fluxes at the river-estuary and estuary-sea interfaces, which were used to estimate Hg export to the continental shelf off of the Jaguaribe coast and understand its variability and response to hydrodynamics

Summary

Introduction

Meso- and macro-tidal estuaries with semi-arid climates tend to accumulate sediments of fluvial origin, which may be washed out to the ocean during short but intensive rain periods.[1]. The continental flux to the ocean is extremely difficult to estimate due to the varying residence time of fluvial waters induced by the strong seasonality of semi-arid rivers, as materials originating in the continental shelf can be imported to estuaries during the long dry season. In the case of dammed rivers, the exportation of continental materials can depend on dam operation rather than on the natural variation of the fluvial flux.[4] To properly assess continental fluxes to the ocean, studies covering longer period of time are required, in particular in regions highly sensitive to climate and land use changes, such as in the semiarid coast of northeastern Brazil

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