New Mexico Geological Society Annual Spring Meeting — Abstracts

Urbanization of previously agricultural land decreases the utilization of acequia irrigation systems and alters how agrarian practices contribute to an ecosystem. Our current understanding of how urbanization influences acequia system utilization is limited, and existing data are sparse. This study quantified temporal land use/land cover (LULC) changes to a portion of the irrigable lands of the Acequia del Finado Francisco Martinez del Llano Quemado (Francisco Martinez Acequia) in Taos County, New Mexico. Spatiotemporal LULC analyses quantify changes in irrigable acreage over time and generate geospatial data which are visualized on maps then disseminated to stakeholders. Like most acequias in the Southwest, the Francisco Martinez Acequia Association struggles with development pressures and worsening drought, both of which make water resources less reliable and acequia flows less sustainable. As population has grown in the last quarter-century, the area has been parceled and developed, leaving behind a patchwork of residential lots interspersed with the remnants of agricultural land. To quantify the types and amount of land use change between 1969 and 2024, we conducted a comparative LULC analysis using GIS techniques. Map sections from the Rio Grande del Rancho Hydrographic Survey, published by the New Mexico Office of the State Engineer in 1969, were used as the historical dataset. We collected aerial imagery in April 2024 using a WingtraOne fixed-wing drone. We then digitized and orthorectified the historical maps, delineated land use classes based on Hydrographic Survey classifications, and quantified the total acreage of each class. For the modern imagery reference, we established parameters to define land use classifications, used visual inspection to delineate land use classes, and summed total acreages for each class. Total irrigated acreage for both historical and modern datasets were calculated and compared, determining a 44.03% reduction in irrigated land coverage since 1969. These results have implications for the integrity of the acequia irrigation system and the ecosystem services they provide.

The workflow developed for this study will be used as the foundation of a graduate thesis by the primary author. To gain deeper insight into the ecological relationship between acequias and the landscape, the planned research will entail a comprehensive LULC change analysis throughout all the irrigated lands associated with the Francisco Martinez Acequia. Vegetation surveys and soil sampling will be conducted in a randomly selected subsection of land parcels to provide supporting data for the comparison of ecological conditions between irrigated and non-irrigated areas. Flood irrigation practices maintain riparian- and pasture-associated vegetation by providing seasonal water to areas that otherwise have no consistent access to surface water. Based on prior data, we predict that areas that were once irrigated but no longer receive inputs because of land use change will likely have altered and/or diminished plant communities and modified soil characteristics. The vegetation and soils field data will be used to determine whether significant variation occurs between actively irrigated parcels and parcels where irrigation has ceased since 1969. Combined with the LULC analysis results, these data will allow us to generate a comprehensive picture of how modern land uses are affecting the functionality of the Francisco Martinez Acequia and the ecological conditions of acequia-associated lands.