Effect of riparian shade on stream water temperature: A collaboration among eleven primarily undergraduate institutions

Background/Question/Methods

Through the Ecological Research as Education Network (EREN), researchers from the United States and Canada have been developing collaborative research projects aimed at analyzing broad ecological patterns. The Riparian Buffers Affect Stream Temperature (RBAST) project is one of these activities. Temperature variation across ecosystems can be assessed at various spatial and temporal scales. These variations in spatiotemporal patterns can be found in terrestrial and aquatic systems and significantly influence ecosystem functions and structure. This project examines the effect of riparian shade on the temperature regime of streams (1^st to 3^rd order) at eleven locations across the United States and Canada. At each site, we paired a forested stream (>90% canopy cover) with an adjacent or nearby open stream (<10% canopy cover). To measure fine scale temporal variation, water temperatures were measured every 15 minutes using data loggers at the upper and lower ends of each reach from June through September 2011. Also air temperature, canopy cover, channel width and depth, light levels, and discharge were measured for each reach.  At five sites, we continuously monitored air temperature and PAR in each reach.

Results/Conclusions

Results varied among sites. Mean daily temperature differences between upstream and downstream ends of the reach were significantly greater in open streams at most sites indicating that the open reaches had a greater net heat flux than forested reaches at these locations.  Maximum temperature differences between upstream and downstream ends of the open reach averaged between 0.34 and 2.9^oC. The daily fluctuation in temperature was significantly greater in open streams due mainly to greater daily maximum temperatures (as much as 8.4°C). Extreme temperature fluctuations may act as pulsed disturbances on aquatic organisms. Stream temperature daily means and maxima were significantly correlated with air temperature among and within sites, highlighting the importance of this factor. Additional data at one of the open sites suggested groundwater inputs buffered diel temperature fluctuations. The significance of this study is twofold. First, it demonstrates that factors such as groundwater inputs and variability among microhabitats can overshadow the effect of canopy cover on stream temperature. Second, cross continental collaboration can improve our ability to understand the inherent variability among stream ecosystems. Organizations such as EREN, which facilitate these sorts of collaborations, are essential, especially for researchers/educators at primarily undergraduate institutions