The impact of chamber transparency on estimation of peatland net ecosystem exchange

Marcin Stróżecki,Anshu Rastogi,Radosław Juszczak

doi:10.1051/itmconf/20182300033

Marcin Stróżecki, Anshu Rastogi + Show 1 more

Open Access

https://doi.org/10.1051/itmconf/20182300033

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Abstract

The purpose of this work was to quantify the variation of chamber transparency over the period of one month of measurements and its impact on estimates of peatland net ecosystem exchange. The automated transparent closed (non-steady-state) chambers are widely used for quantifying net carbon dioxide (CO2) fluxes exchanged between different canopies and the atmosphere. However, it is known that the transparency of the chamber, and hence the amount of radiation reaching the surface, is changing over time and depends on several factors, such as solar angle, obstacles, and cleanness of the chamber surface which is exposed to the environmental conditions. The objective of this research work was to determine if the material from which the measuring chamber is made maintains constant parameters for reduction of incoming radiation in the form of photosynthetic photon flux density (PPFD) inside the chamber. Based on the obtained results, it can be stated that during the specific atmospheric conditions, the average transparency of the measuring chamber of the automatic chamber system can drop even up to 20%. If not considered, it may lead to incorrect estimation of net ecosystem exchange (NEE). In case of our experiment, non-corrected NEE flux rates were five times higher than the same fluxes after corrections. For this reason, it is important to apply correction coefficients, which allow the selection of the appropriate value for PPFD during the NEE modelling process.

Highlights

IntroductionDue to simple methodology of measurements and the relatively low prices of manual measuring systems, the chamber technique is most commonly applied for determining the exchange of greenhouse gas (GHG) fluxes [1,2]
Due to anthropogenic activities, the climate is changing, an international agreement is reached to mitigate its impact, which gave rise to a need to understand and quantify greenhouse gas (GHG) exchange and its balances in all kinds of ecosystem, throughout the world.Due to simple methodology of measurements and the relatively low prices of manual measuring systems, the chamber technique is most commonly applied for determining the exchange of GHGs fluxes [1,2]
One of the biggest disadvantages of manual chamber approach is that measurements are often conducted during cloudless conditions [11, 15] and that is why some site and ecosystem specific short-term events like thawing [16], precipitation [17] or sudden weather changes are often not well represented, it is well known that they have significant impact on seasonal GHG budgets [18]

Summary

Introduction

Due to simple methodology of measurements and the relatively low prices of manual measuring systems, the chamber technique is most commonly applied for determining the exchange of GHGs fluxes [1,2] This method is widely used in ecosystems like: tundra [3,4], peatlands [5,6,7], forests [8,9] and croplands [10,11]. It is known that any obstacles, scratches, dust or condensation of water vapour on chamber walls may lead to significant reduction of PPFD reaching the canopy surface and inhibit photosynthesis It is not well addressed nor discussed in the literature, we assume that when CO2 fluxes are related to PPFD taken from the nearest weather station, the estimated net and gross fluxes are often significantly overestimated. Questions are 1) if chamber transparency is really so stable overtime and we can use the same light transmissivity factor for all measured data independently on time and season? 2) If PPFD values taken from the nearest tower well represent the conditions inside the chamber headspace?

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