Energy balance closure, water balance, carbon exchange, and water use efficiency : observed and modeled outcomes for a managed, hemiboreal forest in Southern Sweden

Abstract

The claims for the potential of boreal and sub-boreal forests to combat negative effects of climate change have been substantial with over half of Earth’s primary forests found within boreal and temperate regions of the Northern Hemisphere.

Given the likely occurrence of more extreme climate events in the future, ascertaining a better understanding of how climate effects, such as profound fluctuations in precipitation, decreases in yearly snow, faster snow melt rates, variability in evapotranspiration due to environmental stress, and related changes in the energy, hydrological, and carbon cycles will change these northern, boreal landscapes is crucial.

Energy, water, and ecosystem level carbon biosphere-atmosphere exchange were examined over a two-year study period from January of 2015 to December of 2016 at a managed forest site in southern Sweden. The energy balance was initially evaluated for closure, and to see which energy components had the largest influence on this system. Initial energy balance closure before energy storage correction was 0.75 and improved by about twenty percent after energy storage was modeled. Shortcomings in the energy balance were outlined by looking at closure during varying atmospheric conditions. The best EBR values prior to correction happened during daytime hours when friction velocities were higher than 0.8 m s-1 and windspeeds were higher than 4 m s-1 for stable-neutral and unstable conditions. Closure of the energy balance was then used to validate later calculations of evapotranspiration. Substantiated evapotranspiration fluxes were used to determine the nature of the water balance and water use efficiency. Looking at the water balance revealed the extent of the drought that occurred in 2016, which had less precipitation and higher temperatures than 2015. Temporal investigation of the individual water balance components described when the drought was most severe and which components were most affected. This decrease in incoming water had the largest effect on soil water storage and ground water storage. Diurnal patterns for the radiation components, evapotranspiration, CO2 fluxes and ecosystem exchanges were then evaluated. All of which were highest during daytime hours of the growing season. Integrated water use efficiency at the ecosystem level was determined and productivity of carbon sequestration for biological growth was gauged. Water use efficiency and the carbon exchanges indicated high productivity during the study period primarily during daytime hours of the growing season when the forest acted as a carbon sink. During nighttime and non-growing season periods it released more carbon than it took up. Aggregate, annual gross primary production was surprisingly higher in 2016 at 291 g C m-2 year-1, which was unexpected given the environmental strain placed upon this ecosystem due to drought stress. The implications of this suggest that drought stress would need to be more severe to make a lasting, negative effect on forest productivity.

Popular Abstract

When one hears the phrase “climate change” it often invokes a sense of fear or bewilderment since the phenomenon is characterized as an extreme threat with its effects far reaching to all corners of the planet. While rightfully alarming, there have been claims that northern forests may be able to help combat some of negative effects of climate change.

Given the likely occurrence of more extreme climate events in the future, gleaning a better understanding of what this will look like for these northern regions, and thus the rest of the world, is crucial.

In this study energy, water, and ecosystem level carbon biosphere-atmosphere exchange were examined over a two-year study period from January of 2015 to December of 2016 at a managed forest in southern Sweden. The energy balance measurements were initially evaluated for completeness, and to see which of them had the largest influence on the forest. Initially, the energy balance before corrections were made was not great. Fortunately, after corrections were made, the balance improved a lot. From this, the shortcomings in the energy balance were outlined by looking at closure during varying conditions. It appeared that the balance was closest to closure during daytime hours when windspeeds were higher. The corrected energy balance was then used in calculations for the water balance and water use efficiency. Looking at the water balance revealed the extent of the drought that occurred in 2016, which had less precipitation and higher temperatures than 2015. Investigation of the individual water balance components over time described when the drought was most severe and which components were most affected. This decrease in incoming water had the largest effect water within the soil and ground. Daily patterns for some of the energy, water, and carbon cycles were evaluated. All of which were highest during daytime in non-winter months. Forest water use efficiency was determined and productivity of carbon uptake for plant growth was gauged. Water use efficiency and the carbon uptake indicated high productivity for the study years primarily during daytime in non-winter months when the forest took in more carbon than it released. During nighttime and winter months it released more carbon than it took up. Plant growth productivity was surprisingly higher in 2016, which was unexpected given the drought that took place that year. The implications of this suggest that drought stress would need to be more severe to make a lasting, negative effect on forest productivity.

• author: Avila, Linsey Marie
• supervisor: Harry Lankreijer
• organization: Dept of Physical Geography and Ecosystem Science
• course: NGEM01 20192
• year: 2019
• type: H2 - Master's Degree (Two Years)
• subject: Earth and Environmental Sciences
• keywords: Energy balance, energy balance closure, energy balance ratio, net radiation, sensible heat, latent heat, turbulent fluxes, ground heat flux, energy storage, available energy, Bowen ratio, evaporative fraction, latent heat of vaporization, water balance, evapotranspiration, precipitation, water storage, water discharge, gross primary production, ecosystem respiration, net ecosystem production, carbon exchange, water use efficiency
• publication/series: Student thesis series INES
• report number: 497
• language: English
• id: 8998010
• date added to LUP: 2019-11-21 16:19:01
• date last changed: 2019-11-21 16:19:01