BASELINE MONITORING AND USE OF NATURAL TRACERS IN GRAND CANYON SPRINGS

Springs and associated riparian environments provide critical habitats for both aquatic and terrestrial wildlife in the Grand Canyon region. The springs are fed by karst aquifer systems on the Colorado Plateau, but increasing pressure on groundwater resources from climate change, mining and other development activities pose major challenges to resource managers. Significant decreases in flow from the springs would likely be devastating to the ecosystems that currently thrive in those locations.

A robust monitoring and geochemical sampling program provides data for understanding the sustainability of spring-fed water supplies for local habitats. Continuous monitoring of temperature, conductivity and depth of key springs has taken place in multiple locations within Grand Canyon since 2012. The individual data sets shown the continuous and constant nature of the springs, as well as providing baseline data against which future variations can be compared, while combining data sets highlights the timing and response of springs to variations in river discharge. The monitoring data is vital to detect changes in spring discharge, and subsequent effects on the island ecosystems they support. Our ongoing geochemical studies of spring waters have identified the importance of tectonic activity in contributing CO₂ and dissolved salts to the regional aquifer systems from deep levels along faults providing important controls on water quality. They give an indication of the pathway the water has taken from source to discharge as well as indicating mixing of different water sources. At Fence fault in Grand Canyon, a series of springs discharge from either side of the river and geochemistry indicates that water from the south rim is moving in the fault plane below river level, mixing with water and discharging from the north rim. Current efforts are aimed at modeling the fluid circulation within the fault zone. Combining monitoring data and geochemistry provides a unique way to understand Grand Canyon springs. While the monitoring data can be used to investigate aspects of recharge, tying these variations to alterations in geochemistry can highlight temporal variations in individual springs and spatial variations between springs.