Monitoring Grand Canyon Springs as An Assessment of Water Resources Response to Climate Change and Groundwater Withdraw

Springs are one of the critical natural resources of Grand Canyon National Park. Spring discharge is a singular response to the hydrologic character of a large area and an indication of the status of the supplying aquifer systems. Climate change in concert with groundwater developments on the Coconino Plateau threaten the springs resources of Grand Canyon. Routine monitoring of springs was conducted at 3 gage sites and 12 ungaged sites along the South Rim for discharge and water quality parameters from 1994-2007. The Seasonal Kendall test for trend was conducted on monthly and quarterly discharge data for the gage sites and the results were compared against similar analyses of precipitation patterns in the study area. Stable isotope data from springs and precipitation were used to constrain the seasonal contribution of recharge water. Results showed statistically significant decreasing trends at Cottonwood Creek and Pumphouse Spring over the period of record. The rate of decrease based on quarterly medians (-0.0004cfs/yr and -0.0033cfs/yr, respectively) was high in comparison to the median discharge rates at these springs (0.008cfs and 0.10cfs, respectively), representing a 5.0% to 3.3% reduction in median discharge per year over the period of record. Two-component mixing models performed on oxygen isotope (d18O) values of seasonal precipitation and spring water indicated aquifers are recharged primarily by winter precipitation (67-78% of total). Trend analyses on precipitation over the monitoring period showed a significant decrease in winter snowfall amounts. This indicated that future climate changes affecting winter precipitation distribution or intensity would have a more significant impact than changes to summer precipitation on springs and their related ecosystems. The addition of increased groundwater withdraw by developments near Grand Canyon would quite likely exacerbate reductions in spring discharge. Recent studies have predicted both of these factors are likely to continue in the upcoming years.