Water quality monitoring in the Middle Rio Grande, New Mexico, USA, 2021-2025, Final Report

Over the past two decades, research in the Middle Rio Grande (MRG) has greatly advanced our understanding of water quality dynamics and ecosystem processes. A persistent gap, however, has been the lack of continuous data from sites south of Albuquerque, where habitat conditions for the Rio Grande Silvery Minnow (Hybognathus amarus; RGSM) are particularly important. To address this, we established and maintained water quality monitoring stations in each of the three southern sub-reaches of the MRG (Angostura, Isleta, and San Acacia). Our primary objectives were to characterize site- and reach-specific water quality, quantify exceedances of ecological thresholds relevant to RGSM, and describe patterns of longitudinal variation across the system. Results demonstrate that water quality is strongly shaped by hydrologic variability and spatial context. Storm-driven flows from ephemeral tributaries produce extremes in dissolved oxygen, turbidity, and specific conductance, with non-urban inputs delivering high sediment and salts, and urban runoff primarily depressing oxygen. Conversely, low-flow conditions drive thermal extremes and magnify the role of primary production. Longitudinally, storm-driven impacts attenuate downstream, while agricultural drains contribute cooler water that provides localized refugia, and leakage below diversion dams maintains low-temperature flows in incised reaches. Collectively, these findings underscore strong seasonal and spatial tradeoffs in habitat suitability for RGSM conservation.