The influence of landscape characteristics on the spatial variability of river temperatures

Abstract

River temperature is well established as an important variable for aquatic denizens. Given its importance, researchers are attempting to disentangle complex interactions between landscapes and river temperatures. We investigated how landscape variables of geomorphology, geology, and vegetation can explain a large portion of the spatial variations amongst tributary temperatures in the large, Miramichi watershed, New Brunswick. We utilize thermal infrared imagery (TIR) to characterize river temperature and remote sensed data to delineate landscape variables. Partial Least Squares regression (PLS) models indicated that variability in river temperature was associated with landscape attributes, but these differed with physiography. For the Clearwater Brook and Burnthill Brook watersheds located on the Miramichi Highlands physiographic unit, solar radiation exposure, surficial geology deposit (comprising gravels, sands, and minor silt), geological contact zones, and maximum watershed slope were strongly and positively correlated with river temperature. We stipulate that the interaction of slope steepness and geologic contact zones can produce complex local and larger groundwater interactions influencing river temperatures in this physiographic region. In the lower elevation, and lower relief, Cains River watershed, located on the Maritime Plains physiographic unit, watershed elevation and wetlands were significant and positively correlated with river temperatures. Here the main stem was cooler in the downstream reaches, likely due to the semi-confined channel interaction with groundwater discharge originating from the surficial deposits and fractured underlying sandstone of the lowlands, and possibly hyporheic processes. These findings illustrate how physiography and geomorphology influence thermal processes in flowing waters at both the landscape and local scales, and the resultant implications for management and conservation efforts both in terms of land use and climate change.