## 2 Materials and Methods
### Model Inputs, Calibration, and Validation  
A DEM, land-use map, and soil map were the basic inputs to set up the SWAT model for the Athabasca Basin [19; 27] (Figure 4). A 90 m \(\times\) 90 m digital elevation model (DEM), a 1 km \(\times\) 1 km land-use map, and a 1:1 million-scale soil map [27] were used to build up the SWAT model of the Athabasca River Basin (Table 1). Daily precipitation, maximum and minimum temperatures [27; 40], relative humidity, solar radiation, and wind speed [41] were fed into the model. The watershed elevation was estimated at 207 m in the lower part of the Athabasca River Basin, whereas it is about 3669 m high in the mountainous part of the Athabasca River Basin (Figure 4). The soil input map was prepared and defined for the SWAT model. Climate data such as daily precipitation, maximum temperature, minimum temperature, relative humidity, and wind speed were used for the modified model input. The monitoring site located in the Athabasca River Basin was used to obtain the groundwater table, RECO, CO\({}_{2}\), and NEE at the Fluxnet Canada Research Network ([[https://daac.ornl.gov/cgi-bin/dsviewer.pl?ds_id](https://daac.ornl.gov/cgi-bin/dsviewer.pl?ds_id)]([https://daac.ornl.gov/cgi-bin/dsviewer.pl?ds_id](https://daac.ornl.gov/cgi-bin/dsviewer.pl?ds_id)) = 1335; accessed on 31 January 2019). The data were obtained from the Flux Canada Research Network (FCRN), which is an easily accessible database on the Ameriflux website ([[https://ameriflux.lbl.gov/data/download-data/](https://ameriflux.lbl.gov/data/download-data/)]([https://ameriflux.lbl.gov/data/download-data/](https://ameriflux.lbl.gov/data/download-data/)); accessed on 31 January 2019) with the necessary data policy ([[https://ameriflux.lbl.gov/data/data-policy/](https://ameriflux.lbl.gov/data/data-policy/)]([https://ameriflux.lbl.gov/data/data-policy/](https://ameriflux.lbl.gov/data/data-policy/)); accessed on 31 January 2019). The SWAT-CU was used for the model calibration, validation, and uncertainty analysis [42; 43]. The observed groundwater table, RECO, CO\({}_{2}\), and NEE data from 2006-2007 were used for calibration, and data from 2008-2009 were used for the validation processes. SWAT-CUP Sequential Uncertainty Fitting Version 2 (SUFI-2) was used for the sensitivity analysis [44]. The streamflow and the sediment load have been calibrated and validated,  
Figure 4: Model input: slope classification of Athabasca River Basin derived from DEM (**a**), and land-use/land-cover classification of Athabasca River Basin (**b**). Model input: soil maps of Athabasca River Basin (**c**). since sediment directly affects the transport amount of particular carbon and nitrogen. Because they are from the same river basin, the model coefficients related to streamflow and sediment transport can be used directly for the current study. Readers can refer to references for streamflow for the period (1983-2013) [27] and erosion and sediment transport for the period (1990-2006) [45]. Although the SWAT offers a wide range of parameters for sensitive analysis, we selected a limited number of parameters (Table 2) that are known to influence the snowmelt, soil temperature, and carbon cycle in the studied river basin. The program generated different parameter sets from the specified range of values using the Latin hypercube (LH) sampling technique, which were regressed against the selected objective function. To identify the total predictive uncertainty band of the simulated results, the SWAT-CUP was run several times, each one identifying a narrower parameter range for each parameter (Table 1), until reasonable goodness-of-fit statistic values were achieved.