For many stream organisms, groundwater inputs provide important habitat and refuge from extreme temperature and flow fluctuations. Climatic changes will likely increase the frequency and magnitude of these extremes and have substantial effects on aquatic organisms. Consequently, the ecological and recreational value of groundwater inflows for aquatic organisms will likely increase. In the Ozark Highlands of Arkansas and Oklahoma, there are numerous streams with gaining and losing segments. This variation makes these streams well-suited for improving our understanding of groundwater and surface-water temperature relationships both spatially and temporally.
We conducted our study on Spavinaw Creek, an emblematic stream of the Ozark Highlands ecoregion. We chose nine 1-km reaches of Spavinaw Creek based on spatial variations in stream conditions and access to private lands. We quantified inflows and outflows of discharge using an incremental streamflow approach and also measured surface-water temperatures. We compared changes in stream discharge with average temperatures over approximately one month using linear regression analysis. Our study objective was to evaluate the relationships between groundwater flux and surface water temperature across a broad spatial extent.
Results/Conclusions
The average temperature in Spavinaw Creek increased from our upstream to downstream sites. As anticipated, discharge also increased downstream, with an overall gain of 1.6 m3/s. However, we found no relationships between groundwater flux and surface-water temperatures. We conclude that reach-level groundwater inputs do not have a significant effect on average stream temperature in Spavinaw Creek. They do, however, appear to stabilize diurnal water temperature variations within the reach. This suggests that streams with groundwater influence could provide aquatic organisms living in altered environments (i.e. deforestation limiting shading) with thermal refugia. In the future, we hope to investigate groundwater-surface-water interactions at a finer, channel unit scale, thereby accounting for previously uncontrolled variables via stream segment modeling. Data from this project will inform stocking projects in the Ozark Highlands ecoregion and further research into the relationships between groundwater and surface water temperature.