Ra and Rn isotopes as natural tracers of submarine groundwater discharge in the patagonian coastal zone (Argentina): an initial assessment

Submarine groundwater discharge (SGD) is herein recognized as a significant pathway of material transport from land to the coastal SW Atlantic Ocean and thus, it can be a relevant factor affecting the marine biogeochemical cycles in the region. This paper focuses on the initial measurements of 226Ra, 228Ra and 222Rn made in Patagonia’s coastal zone of Chubut and Santa Cruz provinces (42°S–48°S, Argentina). 226Ra activity ranged from 2.9 to 73.5 dpm 100 L−1, and 228Ra activity ranged from 11.9 to 311.0 dpm 100 L−1 in groundwater wells. The radium activities found in Patagonia’s marine coastal regions and adjacent shelf indicate significant enrichment throughout the coastal waters. Groundwater samples presented the largest 222Rn activity and ranged from 2.66 to 1083 dpm L−1. Conversely, in the coastal marine environment, the 222Rn activity ranged from 1.03 to 6.23 dpm L−1. The Patagonian coastal aquifer showed a larger enrichment in 228Ra than in 226Ra, which is a typical feature for sites where SGD is dominant, probably playing a significant role in the biogeochemistry of these coastal waters.Fil: Torres, Américo Iadran. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Andrade, Carlos F.. Fundação Universidade Federal do Rio Grande; BrasilFil: Moore, Willard S.. University of South Carolina; Estados UnidosFil: Faleschini, Mauricio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Esteves, Jose Luis. Fundación Patagonia Natural; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Niencheski, Luis F. H.. Fundação Universidade Federal do Rio Grande; BrasilFil: Depetris Gallino, Pedro Jose. Academia Nacional de Ciencias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Influência de um cultivo de camarão sobre o metabolismo bêntico e a qualidade da água Influence of shrimp cultivation on the benthic metabolism and water quality

Atividades de cultivo de camarão tendem a aumentar a taxa de sedimentação de matéria orgânica nos corpos hídricos receptores de seus efluentes, devido à excessiva produção de produtos de excreção e sobras de ração. Dependendo das condições ambientais, o sistema pode não apresentar condições de autodepuração, gerando um grande acúmulo de nutrientes ao longo da camada sedimentar e intensificação do metabolismo bêntico levando, muitas vezes, o ambiente a um processo de eutrofização e possível situação de anoxia. Utilizaram-se, no presente estudo, incubações in situ com câmaras bentônicas transparentes e opacas, para avaliar o metabolismo bêntico em uma área de cultivo de camarão no estuário da Lagoa dos Patos, RS. Ficou evidente a existência de uma clara interferência do cultivo nos processos de regeneração bêntica de nutrientes, incrementando os fluxos de nitrogênio (na forma de amônio) e fósforo (fosfato). Embora a interferência desta atividade se tenha mostrado de abrangência local e temporária (apenas 4 a 5 meses do ano), é conveniente salientar que ela ganha maior importância em locais rasos e de circulação restrita, como é o caso de baías e enseadas, locais em que o cultivo de camarão é desenvolvido no estuário da Lagoa dos Patos.Shrimp farming activities tend to increase the organic matter sedimentation rate, by extreme inputs of excreta products and shrimp food (commercial shrimp diet) into the environment. In certain environmental conditions, the auto-depuration system can be surpassed, generating a high production of nutrients at the sedimentary layer as a result of benthic metabolism intensification. Consequently the system can be induced to a eutrophication processes and anoxia. In the present study, in situ incubations with transparent and opaque chambers have been used to evaluate the benthic metabolism in semi-intensive shrimp farming areas in the Patos Lagoon Estuary (pen enclosures). Existence of clear interference of the cultivation in the processes of benthic regeneration of nutrients was evident, resulting in increases of phosphorus (phosphate) and nitrogen (in the ammonium form) fluxes. Even considering that this activity has a local and temporary distribution (only 4 to 5 months of the year), it is important to call attention to the sediment oxygen consumption and the input of nutrients deriving from the regeneration of organic matter, which is enhanced in shallow waters and restricted circulation areas (such as small bays), locations where shrimp cultivation is developed in the Patos Lagoon Estuary

Submarine groundwater discharge revealed by radium isotopes (Ra-223 and Ra-224) near a paleochannel on the Southern Brazilian continental shelf

Submarine Groundwater Discharge (SGD) has been recognized as an important component of the ocean-continent interface. The few previous studies in Brazil have focused on nearshore areas. This paper explores SGD on the Southern Brazilian Continental Shelf using multiple lines of evidence that include radium isotopes, dissolved nutrients, and water mass observations. The results indicated that SGD may be occurring on the Continental Shelf in the Albardão region, near a paleochannel located 50 km offshore. This paleochannel may thus be a preferential pathway for the delivery of nutrient- and metal-enriched groundwater and porewater into continental shelf waters