Effects of Riparian Patch Structure on Cumulative Network Thermal Regimes

To assess the cumulative impact of riparian patch structure on downstream thermal regime, this field experiment measured longitudinal temperature dynamics in streams that traversed adjacent forested and open riparian landscape patches in six different watersheds in Southeastern Pennsylvania, USA. Not surprisingly, open reaches attained temperatures high (> 26^oC) enough to present limitation for cold water fish species. The beneficial cooling effects of forested reaches are lost as soon as the canopy opens up, leading to an instant warming of the temperature regime. Overall temperature increases in open patches was strongly correlated with the length of stream traversing the open patch. Our results also highlighted the importance of other cooling landscape features, such as wetlands and groundwater seeps, in controlling the water temperature regime and tempering the warming effect of open riparian zones. The mosaic of riparian landscapes limits the connectivity between suitable cold water habitats when too few forested patches are present or if they are not evenly distributed trough the watershed. This study informs management recommendations of the riparian zone, especially in connection with cold water fish species management and restoration.