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Abstract Title: Effect of Needle Age on Hg Concentration in Pinus pinaster Temperate Forests from southwest Atlantic Europe
Presenter Name: Melissa Méndez-López
Company/Institution: Universidade de Vigo
Session: Mercury in the Terrestrial Ecosystems
Co-Authors: Melissa Méndez-López

Abstract Information :

Forest foliage has been found to be highly efficient in removing Hg from the atmosphere accumulating it in leaves/needles. Since Hg accumulation increases with foliar aging, coniferous species with multi-year needles could contribute to the greater deposition of Hg to soil surface once foliar biomass is shed. Moreover, Hg deposition to soil can also increase as direct and indirect effects of precipitation. The present study assesses the effects of needle age and oceanic influence on Hg concentration in needle samples collected from thirty-one Pinus pinaster stands spread on a 30.000 km2 area in NW Spain. This area shows a decreasing influence of the oceanic climatic characteristics from coastal to inland areas. Pine needles were separated in four age classes: y0 (sprouted in 2009), y1, y2 and y3 (sprouted in 2008, 2007 and 2006, respectively). Total Hg (THg), as æg kg-1, increased as needle got older: y0 (9.1ñ3.1) < y1 (22.1ñ6.4) < y2 (29.5ñ6.5) < y3 (33.6ñ8.3). However, the Hg accumulation rate diminished with needle age due to reduced photosynthetic activity and in turn lower capacity to uptake atmospheric Hg. Proof of this is the percentage of Hg accumulated by y0, y1, y2 and y3 needles compared to the highest THg values reported (28, 40, 24 and 8%, respectively). On a spatial scale, needles from pine stands located near the Atlantic coast registered higher THg values than those from inland stands. This is consistent with the decrease in mean annual precipitation with increasing distance from the study stand to the coastal line, a fact linked to the general pattern of atmospheric circulation in southwest Atlantic Europe. In fact, rainfall accumulated during needle lifetime accounted for 68% of the variance of THg in pine needles.

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