Spiking regional vis-NIR calibration models with local samples to predict soil organic carbon in two High Arctic polar deserts using a vis-NIR probe

Abstract

Guy, A. L., Siciliano, S. D. and Lamb, E. G. 2015. Spiking regional vis-NIR calibration models with local samples to predict soil organic carbon in two High Arctic polar deserts using a vis-NIR probe. Can. J. Soil Sci. 95: 237–249. In situ visible and near-infrared (vis-NIR) spectroscopy is a potential solution to the logistic constraints limiting the accuracy and spatial resolution of soil organic carbon (SOC) estimates for Arctic regions. The objective of our study was to develop a calibration model based on field-condition soils for in situ applications to predict SOC in High Arctic polar desert soils from vis-NIR spectra. Soils (n=240) for calibration models were collected from three regional Canadian Arctic sites in 2010 and two local target sites in 2013. Local and regional calibration models were developed using partial least squares regression (PLSR). We assessed whether spiking or spiking and extra-weighting, regional models with calibration samples from local sites improved prediction of the local sites. The local model yielded successful prediction of target sites (R2=0.91) whereas unspiked regional models had poor prediction accuracy (R2=0.07 to 0.36; n=4). Spiking regional models with as few as 12 local samples greatly improved the SOC prediction of target sites; the best spiked models had R2 between 0.69 and 0.86. Extra-weighting spiking subsets in regional models yielded limited improvements in prediction performance. These results suggest that regional vis-NIR calibration models can be successfully used to predict SOC in High Arctic polar desert soils. The in situ application of these calibration models using field-portable instruments in remote areas, relative to traditional laboratory methods, can achieve higher sample sizes and the ability to characterize the spatial variability of SOC.

Salix arctica changes root distribution and nutrient uptake in response to subsurface nutrients in High Arctic deserts

“…, Guy et al. ). Further, laboratory based and in situ models have been applied to successfully predict soil properties from spectra taken in situ (Viscarra Rossel et al.…”

“…This model was later updated using local samples per the methodology described in Guy et al. () and final models are summarized below. Briefly, models were developed separately for dolomite and granite parent materials by optimizing the regional Ellesmere Island ( n = 199) and local Dome ( n = 41) samples included in the calibration model to reduce error and model bias.…”

“…Spectral samples collected from dolomitic and granitic sites were reanalyzed separately for carbon using partial least squares regression (PLSR) models that were optimized to predict SOC at those sites as described in (Guy et al. ). As recommended by Guerrero et al.…”

“…(, ), we tested which samples from regional and local arctic sites to include in the models and whether weighting samples from our local field sites improved model predictions (Guy et al. ). The final model for granitic sites contained 89 regional arctic samples and 15 samples from the granitic site ( R 2 = 0.75, RMSE = 0.11% SOC).…”

Could Cryoturbic Diapirs Be Key for Understanding Ecological Feedbacks to Climate Change in High Arctic Polar Deserts?

“…Frost boils were randomly selected from each block using two perpendicular transects (17–50 m in length and 3–4 m in width); within each the center point and the orientations were chosen randomly. To assess if these were diapiric frost boils (i.e., Bhy horizon present), we quantified the SOC within each soil profile using a field‐portable visible and near‐infrared (vis‐NIR) reflectance spectrophotometer with a soil probe attachment (Guy et al, ). We classified frost boils as diapiric if there was an abrupt increase of at least 0.2 log % SOC in the subsurface—indicative of a diapiric Bhy horizon and nondiapiric in the absence of increasing SOC concentrations with depth (Muller et al, ).…”