Global climate change interacts with regional alterations of land use in coastal basins and promotes rapid changes in the biogeochemistry of the coastal zone. These changes are generally stronger in extreme environments such as polar and semiarid regions. In these environments, biogeochemical changes result in a greater transfer of pollutants from the continent to the sea with resultant contamination of marine biota. In semiarid regions, there is a reduction in continental runoff and bulk pollutant transport, but paradoxically, there is an increase in the export of more bioavailable pollutants, resulting in higher contamination of the marine biota. In tropical latitudes, mangroves dominate coastal and estuarine environments and respond rapidly to environmental changes. The semiarid coast of Brazil is strongly affected by climate change. A major environmental response is altered hydrodynamics, generally involving decreasing continental runoff to the ocean, caused by reducing annual rainfall and damming of rivers. Also, strengthening of marine forcing due to heat accumulation in the South Atlantic Ocean and rising sea level pushes shelf and coastal waters into estuaries. Basin and oceanic processes undergo positive feedback, which causes an increase in the water residence time in estuaries, an extension of saline intrusion landward, accumulation of sediments in the inner reaches of estuaries, and the expansion of mangrove areas, particularly over the past 50 years. Expansion of mangroves means an expansion of sulfate reduction metabolism, which produces large amounts of dissolved organic carbon, characterized by a high capacity for forming organo-metallic complexes of high environmental significance. Dissolved and particulate Hg concentrations and fluxes are greater from the river to the estuary than from the estuary to the sea, producing an accumulation of particulate Hg in the estuary. Particulate Hg export may occur only during extremely rainy periods, and Hg is eventually deposited is shelf sediments, displaying low bioavailability. Export of dissolved, reactive, and DOC-bound Hg is practically nonexistent during rainy periods but increases by two orders of magnitude during the progressively longer dry periods. These highly bioavailable forms of Hg will enter food webs in the lower estuary and coastal areas, increasing contamination of the biota and human exposure to Hg.
Recebido em 17/7/06; aceito em 18/12/06; publicado na web em 30/7/07 PHOSPHORUS GEOCHEMISTRY AS A PROXY OF ENVIRONMENTAL ESTUARINE PROCESSES AT THE JAGUARIBE RIVER, NORTHEASTERN BRAZIL. Sedimentation of different phosphorus geochemical fractions can characterize the natural or anthropogenic processes dominant in the watershed. Selective chemical extraction of different phosphorus geochemical forms in estuarine sediments showed the predominance of inorganic over organic forms suggesting an increase in inorganic phosphorus input from anthropogenic sources. Local hydrochemistry favors the dominance of inorganic ferric and carbonatic phosphorus. Ongoing changes in the estuarine throphy, from mesothrophic to euthrophic, may decrease the immobilization of these forms, increasing dissolved phosphorus and favoring euthrophy. Detritic phosphorus suggests a fluvial origin of this fraction and acts as a tracer of river influence upon the estuary.Keywords: environmental proxy; phosphorus; sediments INTRODUÇÃONos últimos anos, em virtude do acelerado crescimento urbano-industrial das cidades, tem aumentado substancialmente o aporte de cargas poluentes para os ecossistemas aquáticos costeiros, como lagoas, lagos e estuários 1,2 , que são ecossistemas de grande relevância para a manutenção de diversas espécies de animais e plantas. Os efeitos deletérios ocasionados pelo aporte de poluentes comprometem a qualidade ambiental dos ecossistemas 3 , tornando necessário o uso de indicadores e/ou índices para avaliação dessas alterações. Há pouco uso desses indicadores e índices para climas tropicais, dificultando a avaliação dos ecossistemas, por exemplo, da costa brasileira 4 . Os estuários servem como filtros de materiais continentais em direção ao mar, atuando como zonas de deposição para alguns compostos químicos. No entanto, é importante salientar que estes podem não ser depósitos definitivos, em virtude de alterações geoquí-micas do meio sedimentar ou aquático, ou como resposta a processos erosivos que resultam em remobilizações dos materiais depositados 5 . Dentre estes materiais, encontra-se o fósforo que é um nutriente essencial para a manutenção da vida, fazendo parte de diversas moléculas dos organismos vivos (e.g. ATP, ácidos nucléicos, fosfolipídios). Este elemento é, também, considerado um nutriente limitante para a produção primária das células fitoplanctônicas dos sistemas aquáticos costeiros 6,7 e tem sido considerado como principal responsável pela eutrofização artificial em águas continentais 8 . O fósforo presente ou emitido para os estuários por fontes naturais ou antrópicas pode ser de origem orgânica ou inorgânica.São fontes naturais significativas de fósforo o intemperismo das rochas fosfáticas (apatita detrítica), as chuvas e a lixiviação dos solos pelas águas das chuvas, sendo que a fluorapatita carboná-tica autigênica também representa um importante depósito em sedimentos marinhos para o fósforo reativo presente em águas oceâ-nicas. Por outro lado, a fração orgânica de fósforo encontrada em sedimentos estua...
This work reviews the limnology of the largest multi-use reservoir in NE Brazil, the Castanhão Reservoir in Ceará State, during 5 years of an extended drought when the reservoir's volume decreased from 88% to about 30%. Major physical and chemical parameters of the water column, phytoplankton community, trophic state and sediment geochemistry were monitored, as well as the impact from extensive aquaculture. Water quality of the full reservoir was maintained due to hydrodynamics, which transport nutrients to the hypolimnion of a stratified water column, rendering an oligotrophic state to the reservoir, notwithstanding the large nutrient inputs from aquaculture and irrigated agriculture. However, with the extension of the drought period, the reservoir volume reduced, decreasing water depth leading to breaking of the thermocline due to wind forcing, and mixing the entire water column. This increased turbidity, nutrient availability and primary productivity, also changed phytoplankton functional groups. As a result, at the end of the monitoring period, when the reservoir attained its lowest volume, its trophic state became eutrophic. Under a scenario of climate change, where annual precipitation is decreasing, human uses of reservoirs in the semiarid should be very restricted to maintain water quality proper for human use.
We present here the first results of Hg concentrations in three small shark species (Rhizoprionodon lalandei, R. porosus and Mustelus higmani) from the SE Brazilian coast. Mercury concentrations in R. lalandei ranged from 21.5 to 280.0 ng.g -1 dry weight (d.w.) (average 74.6 ng.g -1 d.w.; 17.9 ng.g -1 wet weight). In R. porosus, concentrations ranged from 7.6 to 90.5 ng.g -1 d.w. (average 42.2 ng.g -1 d.w., 9.4 ng.g -1 wet weight), whereas in M. higmani, concentrations ranged from 13.0 to 162.8 ng.g -1 d.w. (average 54.9 ng.g -1 d.w., 13.4 ng.g -1 wet weight). These concentration ranges are very low compared with values reported for other large shark species of the Southwestern Atlantic Ocean. There was a significant positive correlation between Hg concentrations and individual size, suggesting that biomagnification is occurring in these animals.Key words: mercury, sharks, biomagnification, SE Brazil. RESUMO Conteúdo de mercúrio em espécies de tubarão da costa Sudeste do BrasilSão apresentados os primeiros resultados sobre a concentração de Hg em três espécies de pequenos tubarões da costa SE brasileira (Rhizoprionodon lalandei, R. porosus e Mustelus higmani). As concentrações de Hg em R. lalandei variaram de 21,5 a 280,0 ng.g -1 em peso seco (p.s.) (média de 74,6 ng.g -1 p.s.; 17,9 ng.g -1 em peso úmido). In R. porosus, variaram de 7,6 a 90,5 ng.g -1 p.s. (média de 42,2 ng.g -1 p.s., 9,4 ng.g -1 em peso úmido), enquanto em M. higmani variaram de 13,0 a 162,8 ng.g -1 p.s. (média de 54,9 ng.g -1 p.s., 13,4 ng.g -1 em peso úmido). Estas faixas de concentração são muito baixas quando comparadas com valores encontrados em espécies de grandes tubarões da costa do Atlântico Sul-Ocidental. Foi verificada uma correlação positiva, significativa entre a concentração total de Hg e o tamanho dos indivíduos. Isto sugere a ocorrência de biomagnificação do Hg nesses animais.Palavras-chave: mercúrio, tubarões, biomagnificação, Brasil sudeste.
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