Water Quality and Ecosystem Processing in the MRG

Abstract

Over the past two decades, discrete and continuous sampling efforts have provided a foundational understanding of the baseline conditions and drivers of variation in water quality and ecosystem processes in the northern reach of the Middle Rio Grande (MRG). In this portion of the river, high spatial variability results from changing discharge, turbidity, geomorphology, and benthic substrates, while temporal changes are associated with annual and interannual fluctuations in discharge and sediment transport. Additionally, water quality and ecosystem processes are susceptible to natural and anthropogenic disturbances including inputs from wildfire, urban and non-urban storms, and anthropogenic point sources. A significant limitation in our current understanding of water quality in the MRG is the absence of data from sites south of Albuquerque. In the southern sub-reach of the MRG, from the Isleta Diversion Dam to Elephant Butte Reservoir, numerous factors likely impact water quality, including water extraction for agricultural use, inflows from agricultural return drains, inputs from tributaries that drain highly erosive watersheds, and the effects of agricultural diversion dams. Collecting and analyzing water quality data from this sub-reach is of paramount importance as this section of river supports the largest remaining population of the endangered Rio Grande silvery minnow (RGSM). Beginning in April 2021, the NM ISC has supported three continuous water quality monitoring stations immediately upstream of Isleta Diversion Dam, on the Sevilleta National Wildlife Refuge, and at Escondida NM. The goals of this effort were to provide information about the southern portion of the MRG with respect to; 1) seasonal and interannual variation in baseline water quality, particularly as it pertains to habitat suitability for the RGSM, 2) the impacts of tributary inputs (the Rio Puerco and Rio Salado) and water diversion structures on water quality, and 3) the estimation of whole stream metabolism parameters in this portion of the MRG. This presentation will summarize the current understanding of water quality and ecosystem processes in the northern portion of the MRG and compare these findings with new data from the understudied southern portion of the river.