Characterizing spatially variable water table depths in a disturbed Zoige peatland watershed

Abstract

Understanding spatial variability of water table depth (WTD) in larger peatland area is crucial for peat conservation. This study investigated spatial patterns of WTDs in a peatland watershed of about 0.151 km2, located in the Zoige basin of the Qinghai-Tibet Plateau, China. Using conventional dipwells, we measured WTDs on 5/17/2017, 5/20/2017, 5/23/2017, 7/17/2017, and 9/18/2017 at 114, 103, 105, 77, and 81 locations, as well as peat depths (H) and elevations at 119 and 831 locations over the watershed, respectively. Then, we performed hotspot analysis and Geographically Weighted Regression (GWR) modeling, showing (1) highly localized spatial patterns of WTDs, H, and S (slope gradient, calculated from elevations), and (2) the area that had statistically significant local coefficients for H ranged between 51 and 57% of the total watershed area, while that for S was only <11%. These complex spatial patterns of WTDs were further illustrated by our results of examining WTD changes in the lateral and longitudinal directions for two types of channels, deep gullies whose beds are deep and cut through the peat layer and shallow artificial ditches. The findings suggested that spatial and temporal changes of WTDs at the watershed scale may only be examined by collecting in situ samples, which may be achieved using an efficient sampling method provided in this study.