CATASTROPHIC FOREST FIRE AND WATER QUALITY: THE LAS CONCHAS FIRE OF 2011

Forest diebacks from insect infestations and catastrophic forest fires have hit the forests of the southwestern United States hard in the past decade. The effects of these events on hydrology and water quality are important questions for water resource planning for the region. The Las Conchas fire in June and July of 2011 was the largest recorded fire in New Mexico history. A network of continuous monitoring water quality sensors in the Rio Grande and the Valles Caldera National Preserve has been deployed since 2006 with support from the New Mexico Experimental Program to Stimulate Competitive Research (EPSCoR), the US Army Corps of Engineers, USDA Valles Caldera Trust, US Geological Survey, US Forest Service and the US Fish and Wildlife Service and allows before and after conditions due to the Las Conchas fire to be accurately assessed. Monsoonal precipitation events beginning in late July of 2011 have mobilized ash, charcoal, and sediment from the burned sites into nearby tributaries. Water quality responses have included major dissolved oxygen sags, extremely high turbidity, pH declines, conductivity increases and large spikes in dissolved phosphate, nitrate, and total ammonia. Hypoxic and anoxic conditions have occurred during discharge pulses from burned catchments affected by the fire. Rates of primary production in the streams and rivers have been suppressed due to reduced light levels in the water. Food web effects have been documented including fish kills. Measurements immediately after the forest fire have documented seriously degraded water quality in regional streams and rivers. Dissolved oxygen sags with hypoxic and anoxic conditions propagated down the Rio Grande over distances of at least 100 km. The City of Albuquerque had to cease water diversions for municipal water supply during these periods of degraded water quality. This study demonstrates that interagency cooperation coupled with real-time sensors can provide tools for early trend detection, help identify monitoring gaps, and ensure timely data for science-based decision support across a range of issues related to water quality, freshwater ecosystems, and human health. Long-term effects on water quality and aquatic food webs will be assessed with continued deployment of continuous in situ sensors and biological surveys in the coming years.