CAN SPRING CONTRIBUTING AREAS BE USED TO IDENTIFY INTERBASIN GROUNDWATER FLOW? THE ROLE OF INTERBASIN GROUNDWATER FLOW IN SPRINGFLOW GENERATION IN THE TUSAS MOUNTAINS OF NEW MEXICO

Agriculture in northern New Mexico depends on a system of community operated acequias, which divert water from nearby creeks into fields for irrigation. During dry summer months, baseflow in these creeks is sustained by groundwater. Therefore, understanding groundwater processes in these semi-arid watersheds is critical. Ongoing research is quantifying these processes in four adjacent watersheds (Canjilon, El Rito, Rio Vallecitos, and Rio Tusas) located in the Tusas Mountains of northern New Mexico. Recent research provides strong evidence for an interbasin groundwater flow (IGF) connection from the headwaters of Canjilon to the headwaters of El Rito. This IGF connection occurs through an east-dipping, poorly lithified conglomerate layer. This east-dipping conglomerate layer extends into all four watersheds suggesting that the IGF connection may be regional, supporting baseflow in adjacent watersheds. In El Rito, perennial springs are the primary contributor to streamflow. These springs have small upslope contributing areas. In contrast, adjacent watersheds have springs with large upslope contributing areas, yet are ephemeral and have low discharge. This disparity is due to the misleading term “contributing area”, which is defined by surface water divides. In cases where groundwater divides do not follow surface water divides, such as where IGF occurs in El Rito, there is an expanded source area that needs to be addressed. Should we instead use the term contributing volume, since the groundwater that discharges at a spring is sourced from a distribution of flowpaths representing a volume of the bedrock aquifer? Hypothesis: If a regional IGF connection exists, then we would expect to see discrepancies between upslope and estimated contributing areas. If this hypothesis is true, then solute loads from springs will be disproportional to the upslope contributing area. In this poster, we will use solute weathering mass-balances along with oxygen isotopes to estimate contributing volumes of springs. Elevated solute loads are observed at many perennial springs indicating that IGF is contributing additional solutes and discharge to these springs. This simple methodology may offer additional benefits in identifying IGF and quantifying the magnitude of the exchanges.