Snowpack concentrations and estimated fluxes of volatile organic compounds in a boreal forest

H Aaltonen,J Pumpanen,T Vesala,S Rasmus,J Bäck,H Hakola

doi:10.5194/bg-9-2033-2012

Abstract

Abstract. Soil provides an important source of volatile organic compounds (VOCs) to atmosphere, but in boreal forests these fluxes and their seasonal variations have not been characterized in detail. Especially wintertime fluxes are almost completely unstudied. In this study, we measured the VOC concentrations inside the snowpack in a boreal Scots pine (Pinus sylvestris L.) forest in southern Finland, using adsorbent tubes and air samplers installed permanently in the snow profile. Based on the VOC concentrations at three heights inside the snowpack, we estimated the fluxes of these gases. We measured 20 VOCs from the snowpack, monoterpenes being the most abundant group with concentrations varying from 0.11 to 16 μg m−3. Sesquiterpenes and oxygen-containing monoterpenes were also detected. Inside the pristine snowpack, the concentrations of terpenoids decreased from soil surface towards the surface of the snow, suggesting soil as the source for terpenoids. Forest damages (i.e. broken treetops and branches, fallen trees) resulting from heavy snow loading during the measurement period increased the terpenoid concentrations dramatically, especially in the upper part of the snowpack. The results show that soil processes are active and efficient VOC sources also during winter, and that natural or human disturbance can increase forest floor VOC concentrations substantially. Our results stress the importance of soil as a source of VOCs during the season when other biological sources, such as plants, have lower activity.

Highlights

Volatile organic compound (VOC) emissions in boreal forests at the branch and canopy levels have been rather well characterized (Hayward et al, 2001; Hakola et al, 2003, 2006; Ruuskanen et al, 2005), in contrast to soil volatile organic compounds (VOCs) fluxes
Soil provides an important source of volatile organic compounds (VOCs) to atmosphere, but in boreal forests these fluxes and their seasonal variations have not been characterized in detail
The results show that soil processes are active and efficient VOC sources during winter, and that natural or human disturbance can increase forest floor VOC concentrations substantially

Summary

Introduction

Volatile organic compound (VOC) emissions in boreal forests at the branch and canopy levels have been rather well characterized (Hayward et al, 2001; Hakola et al, 2003, 2006; Ruuskanen et al, 2005), in contrast to soil VOC fluxes. VOC emissions from boreal forest soil are highest in the spring and autumn (Hellen et al, 2006; Aaltonen et al, 2011), but the processes behind the seasonal variations remain uncertain. Most likely they are related to changes in biological activity in forest floor, for example increased decomposition. In order to better understand the biological processes behind the VOC fluxes, and their role in air chemistry in the troposphere we need better understanding of wintertime forest floor VOC exchange

Methods

Discussion

Conclusion