Major Ion Chemistry in a Freshwater Coastal Lagoon from Southern Brazil (Mangueira Lagoon): Influence of Groundwater Inputs |
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Authors: | Isaac R Santos Maria I Machado Luis F Niencheski William Burnett Idel B Milani Carlos F F Andrade Richard N Peterson Jeffrey Chanton Paulo Baisch |
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Institution: | 1.Department of Oceanography,Florida State University,Tallahassee,USA;2.Departamento de Geociências,Funda??o Universidade Federal do Rio Grande,Rio Grande,Brazil;3.Departamento de Química,Funda??o Universidade Federal do Rio Grande,Rio Grande,Brazil |
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Abstract: | This paper characterizes major ion distributions and investigates whether groundwater exerts a major control on the chemical
functioning of Mangueira Lagoon, a large (90 km long), shallow (∼4–5 m deep), and fresh coastal lagoon in southern Brazil.
Water volumes equivalent to ∼80% of the total annual input are used in the summer for irrigating nearby rice plantations,
the most important regional economic activity. While Na+ and Cl− are the major ions in local groundwater, Na+ and HCO3− are the most enriched ions in lagoon water. The ion concentrations measured in Mangueira Lagoon were homogeneous, except
for a few samples affected by rainwater and groundwater inputs. A shore-normal transect starting at the pump house of a rice
irrigation canal indicated strong groundwater input at this canal. In spite of the small volume contribution (∼2% of precipitation),
groundwater discharge accounts for 50–70% of major ion inputs into the lagoon, with ∼70% of the groundwater inputs being anthropogenically
derived (e.g., from the rice irrigation canals). This may have serious implications for the management of the coastal water
resources from Mangueira Lagoon and other similar areas as groundwater associated with agricultural systems may be contaminated
by fertilizers and pesticides. The results imply that groundwater should not be neglected in dissolved species’ budgets even
when its volume contribution is small. |
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Keywords: | Submarine groundwater discharge Biogeochemistry Permeable sediments Coastal lagoons Hydrogeochemistry |
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