New Mexico Geological Society Annual Spring Meeting — Abstracts

Government Springs is the complex perennial source of the lower Rio Bonito in central New Mexico with numerous ephemeral sources and a complex surface water – groundwater interface. Discharge from this karst spring is critical in maintaining downstream agricultural activities and communities.
We established 12 repeatable measurement sites for discharge, temperature, pH, specific conductivity, and turbidity. Data collected at a monthly interval provides a snapshot of surface water – groundwater interactions in the system. Results from this indicate that the spring is fed by two distinct sources: a more variable flow component with relatively high pH, low conductivity and temperature and another with more constant flow, more neutral pH, and higher temperature and conductivity. These two sources emerge in two distinct channels and combine partway through the spring run. These data suggest that the more stable discharge source is likely driven by discharge from the karst aquifer while the more variable source may be shallow flow through an overlying alluvial aquifer fed by the upstream ephemeral sections of Rio Bonito. Once these two upstream sources merge, there are surface water – groundwater interactions that vary in magnitude and direction, depending on flow conditions. While there are consistent losing and gaining reaches, there are a few reaches where these changes are dependent on flow level. Overall, during lower flow conditions, there is increased flow from upstream to downstream as more water emerges from the alluvium, with a 701% increase measured during lowest flow. During higher flow, the system shows a decrease of up to -26% indicating recharge to the shallow aquifer. For reaches that show increased flow in Rio Bonito, end-member mixing analysis, using specific conductance, suggests that this is likely a result of additional alluvial storage discharging to the river, rather than an additional karst source. These results suggest Government springs is an outlet for multiple groundwater systems, however there is likely only one primary outlet of the karst system. Additional flow is more likely driven by the overlying alluvial system with substantial surface water-groundwater interactions.