Snow cover dynamics and plant phenology documentation using digital camera images and their relation with CO2-fluxes at Stordalen mire, northern Sweden
Abstract: This report investigates the utilization of digital camera images (DCIs), sensitive in the visible part of the spectrum, for documentation of seasonal and inter-annual variations in snow cover and plant phenology. The DCIs used were transformed to orthographic images (ortho-image) from ordinary oblique DCIs taken between January 2001 and December 2003 at a sub- arctic mire (Stordalen) in northern Sweden. Snow depletion- and ablation curves and a greenness index (GI) together with climatic parameters were produced to examine the relationship with Net Ecosystem Exchange (NEE) measured with eddy covariance technique (EC). The snow cover length ranged between 183 and 190-days/ year and showed effect on the flux as the driving force on the length of the seasons. The accumulated temperatures during shoulder seasons (spring and fall), especially the fall, are closely correlated to the accumulated carbon fluxes. The length of the summer season is correlated to the accumulated fluxes for the same period. Inter-annual comparisons points out the mire as an increasing carbon (CO2) sink over the analysed years. The accumulated temperature at Stordalen decreases and becomes warmer during the years of investigation. The creation of a GI was proved functional but a large variation reduces the applicability for vegetation analysis. The method applied on the data was successful but developing the method would improve the results. By raising the camera, the tilt angel is enlarged and the area of focus improved. This action would make the images usable for a larger area of the mire. If the camera is modified, removing the infrared (IR) filter or installing a new camera with a spectral resolution bridging the IR spectra and preferable with possibilities to save images as raw data (without algorithms and filters and without normalisation for incoming light) would improve the vegetation monitoring. In spite of this, it is possible to conclude that the mire acts as a larger sinks during long summer seasons. But in the same time, shorter winter seasons produce larger effluxes from the mire. Thus, the shoulder seasons are of high importance for the whole year carbon (CO2) budget. This work exclude fluxes from CH4, VOC, and lateral fluxes e.g. DOC from the analysis, as these fluxes generally are important in wetlands carbon budgets, they would if included probably change the (mire) ecosystem from a net sink to a net source.
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