Remote estimation of gross primary production and light use efficiency at a boreal bog and an abandoned peatland pasture in western Newfoundland, Canada

Gillani, Syed Shah Mohioudin (2018) Remote estimation of gross primary production and light use efficiency at a boreal bog and an abandoned peatland pasture in western Newfoundland, Canada. Masters thesis, Memorial University of Newfoundland.

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Abstract

The pristine peatlands store approximately 1/3 of the global soil carbon (C) pool and function as a climate cooling mechanism. A peatland’s production is persistently larger than its decomposition due to its high soil water content. However, peatlands disturbed via drainage have been identified as a potential C source. Gross primary production (GPP) and light use efficiency (LUE) are two critical indicators for studying the C budget in terrestrial ecosystems. However, the knowledge of GPP and LUE values in boreal peatlands is still limited because so few measurements have been carried out in peatlands. Field measurements in boreal peatlands cover less than 0.01% of global peatlands; this significantly limits our capacity to understand the C budget of global peatlands. Normally, estimation of the C budget for global peatlands requires field-based measurements to be up-scaled from the field level to the global level. Another commonly-adopted approach for estimating the C budget for global peatlands is to estimate the C budget based on the remotely sensed measurement with global coverage. This approach needs to use the algorithm derived from field measurements. However, there are significant uncertainties over the field-based algorithm used to estimate the GPP and LUE in boreal peatlands due to the very limited availability of field measurements. Moreover, none of the field-based estimations of GPP and LUE were done for drained peatlands. Therefore, more studies are needed to estimate the GPP and LUE for both pristine peatlands and disturbed peatlands based on field measurements. To fill this gap, I conducted a study to estimate GPP and LUE using eddy covariance tower (EC) measurements and MODIS satellite data in a boreal bog and an adjacent abandoned peatland pasture. I have assessed the relationships of GPP with photosynthetic active radiation (PAR) alone, vegetation indices (normalized difference vegetation index [NDVI] and enhanced vegetation index [EVI]), and their products (PAR×EVI, PAR×NDVI) at both research sites during both study years. The relationship between GPP and the product of vegetation indices and PAR performed better in both study sites, with a greater value of determination coefficient R² (0.70 to 0.90), than those calculated from PAR and vegetation indices alone (R² ranged from 0.56 to 0.79). The abandoned peatland pasture had greater LUE capacity than the boreal bog. At the start and end of the growing season, the LUE value was minimum, but in the middle of the growing season, the LUE value peaked at both study sites. The LUE of the abandoned peatland pasture showed greater variations between the study years 2014 and 2015 compared to the boreal bog site. Air temperature and water table depth were the main environmental factors regulating LUE during the growing season in both study years. Research in this thesis will help to estimate the GPP and LUE in boreal bog and drainage pasture peatlands. This research is important for GPP modeling, and spatial and temporal simulation of GPP and LUE in peatland ecosystems, because both PAR and vegetation indices are readily available from the remotely sensed data. This work will improve our understanding of how GPP and LUE vary over space and time and contribute to C cycle budget and global climate change perceptivity.

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