Abstract
AbstractUnderstanding primary productivity is a core research area of the National Science Foundation's Long-Term Ecological Research Network. This study presents the development of the GIS-based Topographic Solar Photosynthetically Active Radiation (T-sPAR) toolbox for Taylor Valley. It maps surface photosynthetically active radiation using four meteorological stations with ~20 years of data. T-sPAR estimates were validated with ground-truth data collected at Taylor Valley's major lakes during the 2014–15 and 2015–16 field seasons. The average daily error ranges from 0.13 mol photons m-2 day-1 (0.6%) at Lake Fryxell to 3.8 mol photons m-2 day-1 (5.8%) at Lake Hoare. We attribute error to variability in terrain and sun position. Finally, a user interface was developed in order to estimate total daily surface photosynthetically active radiation for any location and date within the basin. T-sPAR improves upon existing toolboxes and models by allowing for the inclusion of a statistical treatment of light attenuation due to cloud cover. The T-sPAR toolbox could be used to inform biological sampling sites based on radiation distribution, which could collectively improve estimates of net primary productivity, in some cases by up to 25%.
Highlights
Solar radiation drives hydrological and biological systems
The optimized parameters accurately predict photosynthetically active radiation (PAR) flux values of > ∼1600 μmol photons m-2 s-1 during the summer solstice of the 2014–15 field season; these values are up to ∼250 μmol photons m-2 s-1 higher than best-fit mean locally estimated scatterplot smoothing (LOESS) curve values for all years included in this study
BOYM has the largest range in expected daily values (1262 μmol photons m-2 s-1) and receives the lowest total daily PAR (65.34 mol photons m2), only 7.39 mol photons m2 less than EXEM, which receives the highest total daily PAR
Summary
Solar radiation drives hydrological and biological systems. Visible light occupies a narrow waveband within short-wave radiation (SWR) between 400 and 700 nm, and it is referred to as photosynthetically active radiation (PAR) because photoautotrophs harness this energy for primary production (McCree 1981). Polar regions receive 24 h of sunlight during the summer and experience complete darkness during the winter, and annually receive significantly less solar energy than the equator. Current sampling of lake biology is restricted to a few locations per season due to lake ice cover and the availability of time and resources in the field. Present interpretations of these samples assume spatial homogeneity of biological processes across each lake (Hawes et al 2014, Obryk et al 2014)
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