Short-term responses to watershed logging on biomass mercury and methylmercury accumulation by periphyton in boreal lakes

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Abstract:

In the boreal forest, watershed logging may increase runoff, as well as chemical loading, including nutrient, dissolved organic carbon, and mercury, to lakes. Because they are exposed directly to nutrients and contaminants exported from the watershed, littoral communities such as periphyton may respond quickly to watershed disturbances. The objectives of this study were to evaluate the response of periphyton to watershed logging using a BACI (before–after control–impact) statistical approach and to develop a predictive tool to facilitate the elaboration of practical logging policies aimed at reducing Hg loading to lakes. In this study, we compare the periphyton biomass in 18 boreal Canadian Shield lakes, as well as their total mercury and methylmercury levels. During the ice-free season from 2000 to 2002, eight of these lakes were monitored before and after logging, with the other 10 lakes serving as controls. The BACI statistical analyses reveal a significant impact of logging on periphyton biomass (decrease; 0.6- to 1.5-fold) and methylmercury accumulation (increase; 2- to 9.6-fold). This study demonstrates that periphyton responds quickly to disturbances of the watershed. Our results suggest that the periphyton and watershed characteristics could serve as good management tools and that logging should be limited in watersheds with a mean slope below 7.0%.

En forêt boréale, la coupe forestière peut augmenter l'écoulement et l'apport d'éléments chimiques aux lacs tel que le carbone organique dissous et le mercure. Les communautés littorales, comme le périphyton, peuvent être exposées directement aux apports de contaminants exportés du bassin versant, et ainsi répondre rapidement aux perturbations de ce dernier. Les objectifs de cette étude étaient d'évaluer la réponse du biofilm périphytique aux coupes forestières en utilisant une approche statistique de type BACI, et de développer des outils prédictifs utiles pour l'élaboration de politiques forestières visant la réduction des apports de Hg dans les lacs. Dans cette étude, nous avons échantillonné 18 lacs boréaux du bouclier canadien et comparé la biomasse et les concentrations de mercure total et méthylmercure du périphyton. Durant la saison libre de glace de 2000 à 2002, huit lacs ont été échantillonnés avant et après la coupe alors que les autres ont servi de témoins. Les analyses statistiques BACI révèlent un impact significatif des coupes sur la biomasse (diminution; 0,6 à 1,5 fois) et sur les concentrations de méthylmercure (augmentation; 2 à 9,6 fois). Cette étude démontre que le périphyton répond rapidement à une perturbation du bassin versant. Nos résultats suggèrent que le périphyton et les caractéristiques du bassin versant peuvent être de bons outils de gestion et que la coupe forestière devrait être limitée lorsque la pente moyenne est inférieure à 7,0 %.

Document Type: Research Article

Publication date: August 1, 2006

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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