Low-tech process-based restoration (LTPBR) aims to restore physical, chemical, and biological processes in river and floodplain ecosystems and has been widely adopted, particularly in the Intermountain West. These projects often employ small structures designed to slow and spread flow across the landscape, reconnect floodplains, and thereby support chemical and biological processes. While LTPBR shows promise, scientifically rigorous monitoring is frequently limited by funding and time constraints.
Here, I explore whether paired air and stream temperature (PASTA) monitoring may serve as a suitable low-cost method for assessing whether LTPBR projects alter hydrology. PASTA uses paired air and stream temperatures, and particularly the difference between the two in both magnitude and lag, to infer the contribution of groundwater. If LTPBR projects are successful at reconnecting floodplains, then there should be an increase in shallow groundwater flow, which may be detectable though changes in the relationship between air and water temperatures.
This study was conducted in three streams treated with LTPBR in Northern New Mexico, USA on established sites deem effective by practitioners. This study uses paired upstream–downstream sampling from three treated reaches to test whether changes in groundwater connectivity can be detected through shifts in the relationship between air and water temperatures. Specifically, I evaluate differences in temperature magnitude and temporal lags between air and stream temperature both above and within reaches treated with LTPBR. I hypothesize that treated reaches will see greater lags between changes in air temperature and the subsequent changes in water temperature, due to an increase in shallow groundwater contributions. Further, I hypothesize that these changes will be largest in after high flows when water absorbed by the floodplain is reentering the stream channel. If these changes are detectible, then our results will suggest that the PASTA method could provide practitioners with a practical, cost-effective tool to evaluate whether restoration projects are influencing hydrological conditions.