No abstract

This study estimated Hg emission factors (EFs) and total Hg loading to the Jaguaribe Estuary, NE Brazil, from intensive shrimp farming, and compares this with other local anthropogenic activities. The EF reached 83.5 mg ha(-1) cycle(-1) (about 175 mg ha(-1) year(-1)), resulting in an annual Hg load to the estuary of 0.35 kg. The calculated EF is comparable to Hg EFs from urban wastewaters (200 mg ha(-1)) and solid waste disposal (400 mg ha(-1) year(-1)) from cities located in the estuary's basin. However, due to the smaller area of aquaculture (2,010 ha), total annual loads are much lower than from these other sources (75 and 150 kg year(-1), respectively). Since shrimp farming effluents are released directly into the estuary, the estimated high EF raises environmental concerns with this expanding industry, suggesting the inclusion of this element in ongoing environmental monitoring programs.

In this study, the Hg distributions in water and sediments from a mangrove creek that receives intensive shrimp farming effluents were determined. The average dissolved and particulate Hg concentrations in the water varied from 3.1 to 9.2 ng L(-1) and from 4.4 to 9.4 ng L(-1), respectively. However, the Hg concentrations in the suspended particulate matter and the bottom sediments varied from 95.4 to 115.7 ng g(-1) and from 1.6 to 10.3 ng g(-1), respectively. A Ward quadratic distance cluster analysis based on the Hg concentrations and hydro- and geochemical parameters (oxygen, salinity, temperature, pH, and organic matter and aluminum content) showed the effects of shrimp farming effluents on the Hg distribution pattern. Furthermore, these results were supported by the Hg distribution in the sediment cores. This study emphasizes the necessity of including Hg as a potential pollutant when monitoring the environmental impacts of intensive shrimp farming.

Abstract:The semi-arid coast of Brazil is being strongly affected by regional land use and global climate changes, resulting in decreasing continental runoff to the ocean and increasing the water residence time in estuaries and expanding mangrove areas; these in turn may induce an increase of particulate Hg accumulation within the estuaries and increase the export of dissolved Hg to the ocean. This is, paradoxically, what is presently happening in Arctic rivers due to increasing, not decreasing, continental runoff associated with global climate changes.Keywords: Mercury; estuaries; bioavailability; regional and global changes. ResumoO litoral semiárido do nordeste brasileiro vem sendo afetado fortemente por alterações regionais nos usos do solo e pelas mudanças climáticas globais, resultando em diminuição do aporte continental ao mar, aumentando o tempo de residência da massa de água fluvial nas regiões estuarinas e provocando uma expansão nas áreas de manguezais. Isto por sua vez, vem aumentando a acumulação de Hg particulado nos estuários e a exportação de Hg dissolvido para o mar. Paradoxalmente, este processo é similar ao que atualmente ocorre nos rios que deságuam no Oceano Ártico, porém devido ao aumento e não à diminuição do aporte continental. Palavras-chave:Mercúrio; estuários; biodisponibilidade; mudanças regionais e globais.