Morphology and drivers of channel incision in a wet meadow-fen system in the Sangre de Cristo Mountains of New Mexico
- Mangini, Seth A. [ Montana State University: Earth Sciences ]
- Dixon, Jean L. [ Montana State University: Earth Sciences ]
Wetlands in southern Rocky Mountain headwater valleys are critical reservoirs of biodiversity and sites for storing water, sediment, and carbon in an otherwise dry region. In these systems, the rapid downcutting of stream channels into incised arroyos can drain wetland areas and impair ecosystem function. Arroyo processes are widely studied in higher-order streams but remain understudied in montane headwater systems. We study Bonito Creek, a model headwater wetland system in northern New Mexico, to understand the causes, timing, and effects of incision on channel and wetland morphology. Using topographic surveys, historic photographs, and subsurface geophysical exploration, we find that Bonito Creek exhibits multiple discontinuous arroyos that incise approximately 65% of the 5.6 km long valley bottom and that the valley was primed to incise due to a stair-step longitudinal profile created by the deposition of alluvial fans from side drainages. Arroyos reached similar to 85-90% of their current extent by 1944 and have continued to expand headward at 0.06-3.0 m/yr. Incision likely began in the late 19th or early 20th century and was triggered by overgrazing and the removal of willows by livestock and elk. Historic photos show that willows were nearly eliminated from the valley by the 1920s. Incision has altered the creek's morphology from an anastomosing system with access to the entire valley floor at base flow to a meandering single-channel system set into arroyo bottoms. This change has lowered water tables and drained wetlands, processes likely to continue so long as overbrowsing inhibits the establishment of woody species.