Factors influencing the achievement of steady state in mercury contamination among lakes and catchments of south-central Ontario

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Abstract:

Mercury (Hg) concentrations in recent (0.5–1cm) and preindustrial (>30cm) sediments were examined across lakes in south-central and eastern Ontario, Canada (45.53°N, 82.41°W to 44.15°N, 76.25°W), to determine whether Hg exported from watersheds is at steady state with atmospheric deposition. An examination of headwater lakes revealed that Hg enrichment was not uniform among watersheds but that the enrichment factor (EF= [Hg]presentday/[Hg]preindustrial, standardized for organic matter) decreased as a function of drainage ratio (Ad/Ao, watershedarea/lakearea). Furthermore, the model fit was improved after accounting for differences in sulfate concentrations and pH among lakes: EF = (Ad/Ao)–15.96 – 0.07(SO42–)– (3.55(pH>8.3)) (R2 = 0.458, p = 0.0001). Hg concentrations in preindustrial sediments of headwater lakes showed a positive linear relationship with drainage ratio (partial t = 4.83, p< 0.0001, n = 66) that was strengthened following an adjustment for mean annual runoff (MAR) ([Hg]preindustrial = 0.011± 0.002(Ad/Ao)+ 0.0008± 0.0003(MAR) (R2 = 0.108, F[1,66] = 8.01, p = 0.006)). Our results suggest that Hg export from watersheds may be currently lagging behind atmospheric Hg deposition, in which case, Hg export would increase into the future, even as Hg deposition from the atmosphere stabilizes.

Nous avons mesuré les concentrations de mercure (Hg) dans les sédiments récents (0,5–1 cm) et préindustriels (>30 cm) dans des lacs répartis dans tout le centre-sud et l’est de l’Ontario, Canada (45.53°N, 82.41°O à 44.15°N, 76.25°O) afin de déterminer si le Hg exporté des bassins versants est en équilibre avec les retombées atmosphériques. Un examen des lacs d’amont des bassins versants indique que l’enrichissement en Hg n’est pas uniforme dans tous les bassins, mais que le facteur d’enrichissement (EF) ([Hg]actuelle / [Hg]préindustrielle; corrigé pour tenir compte de la matière organique) décroît en fonction du rapport de drainage (Ad/Ao; bassinsurface/ lacsurface). De plus, l’ajustement du modèle s’améliore si on tient compte des différences de concentrations de sulfates et de pH entre les lacs: EF = (Ad/Ao)–15.96 – 0.07(SO42–)– (3.55(pH>8.3)) (R2 = 0.458, p = 0.0001). Il existe une relation linéaire positive entre les concentrations de Hg dans les sédiments préindustriels des lacs d’amont et le rapport de drainage (t partiel= 4,83, p< 0,0001, n= 66) qui est renforcée si on fait un ajustement pour tenir compte du ruissellement annuel moyen (MAR) (Hgpréindustriel= 0,011± 0,002 (Ad/Ao)+ 0,0008± 0,0003(MAR) (R2 = 0.108, F[1,66] = 8.01, p = 0.006)). Nos résultats laissent croire que l’exportation de Hg des bassins versants peut être actuellement décalée par rapport aux retombées atmosphériques de Hg; dans ce cas, l’exportation de Hg devrait augmenter dans le futur, même s’il y a une stabilisation des retombées de Hg de l’atmosphére.

Document Type: Research Article

Publication date: February 1, 2009

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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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