Long-Term Discharge Records from United States and European Karst Springs: Data Limitations in Trend Analysis

A cross-site comparison of 49 springs from the United States and Europe with more than a 30-year record of spring discharge was conducted to look for response to climate change (temperature and precipitation). The dataset included both carbonate and non-carbonate springs across urban and rural settings, covering a wide range of discharge (0.001 to 25 m³/s) and discharge variability (45 to 6500% variability index) to encompass aquifers with a variety of hydrologic regimes and degrees of karstification. Relatively small changes in discharge trends (i.e., change in discharge over the long-term time record) and similar responses across the diverse spring dataset were observed, which suggested that groundwater storage buffers hydrologic stresses in these aquifers despite varying degrees of karstification. Although decreases in discharge were associated with an observed increase in air temperature, larger air temperature trends did not lead to larger discharge trends. Spring discharge trends over time could not be categorized by spring behavior as measured by mean discharge, variability in discharge, or rural vs. urban setting. The detection of trends was sensitive to the time period being considered, with selected time periods yielding different and sometimes opposite discharge trends, highlighting the importance of time period selection when making cross-site comparisons. This study benefited from cross-site comparison by finding similarities in spring discharge trends across varied karst regimes.